面试学习总结

之前根据视频做的总结，备个份。

一、Volatile关键字

volatile是Java虚拟机提供的轻量级的同步机制。

三个特性：

1. 保证可见性

   线程修改了工作内存中的值并写回到主内存之后，主内存立刻通知所有线程。称为可见性。（结合JMM理解）

   代码演示可见性+原子性代码

   import java.util.concurrent.TimeUnit;
   
   /**
    * 1. 验证volatile可见性
    * 1.1 假如number=0，number变量之前没有添加volatile关键字，没有可见性。
    *
    * @author shiwenquan
    * @Create 2020-12-10 16:16
    * @description
    */
   public class VolatileDemo {
   
       public static void main(String[] args) {
           MyData myData = new MyData();
           new Thread(() -> {
               System.out.println(Thread.currentThread().getName() + "\t come in");
               //睡眠三秒
               try {TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {e.printStackTrace();}
               myData.addT060();
               System.out.println(Thread.currentThread().getName() + "\t update number value: " + myData.number);
           }, "AAA").start();
   
   
           // 第二个main线程
           while (myData.number == 0) {
               // main线程一直在这里等待循环，直到number不等于0
   
               // 如果不添加volatile关键字，会一直循环，因为此时没有可见性。
           }
           System.out.println(Thread.currentThread().getName() + "\t minssion is over, main is value" + myData.number);
   
       }
   
   }
   
   class MyData {
   
       volatile int number = 0;
       public void addT060() {
           this.number = 60;
       }
   }
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2. 不保证原子性

   volatile不保证原子性代码验证

   /**
    * 1. 验证volatile可见性
    *  1.1 假如number=0，number变量之前没有添加volatile关键字，没有可见性。
    *  1.2 添加了volatile，可以解决可见性问题。
    *
    * 2. 验证volatile不保证原子性
    *  2.1 原子性指的是什么意思？
    *      不可分割，完整性。要么同时成功要么同时失败。
    *  2.2 volatile不保证原子性案例。
    *
    * @author shiwenquan
    * @Create 2020-12-10 16:16
    * @description
    */
   public class VolatileDemo {
   
       public static void main(String[] args) {
           MyData myData = new MyData();
   
           for (int i = 0; i < 20; i++) {
               new Thread(() -> {
                   for (int j = 0; j < 1000; j++) {
                       myData.addPlusPlus();
                   }
               },String.valueOf(i)).start();
           }
   
           // 需要等待所有线程计算完成之后，计算最终结果。
           while (Thread.activeCount() > 2){
               Thread.yield();
           }
           System.out.println(Thread.currentThread().getName()+"\t number value: " + myData.number);
   
       }
   
   
   }
   
   class MyData {
   
       volatile int number = 0;
   
       // 此时number前面加了volatile
       public void addPlusPlus(){
           number++;
       }
   }
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3. 禁止指令重排（指令重排结合JMM的有序性查看）
   volatile实现禁止指令重排优化，从而避免多线程环境下程序出现乱序执行的现象。

JMM(Java内存模型)(Volatile补充)

是一种抽象概念并不真实存在，它描述是一组规则或规范，通过规范定义了程序中各个变量（包括实例字段，静态字段和构成数组对象的元素）的访问方式。

由于JVM运行程序的实体是线程，而每个线程创建时JVM都会为其创建一个工作内存（有些地方称为栈空间），工作内存是每个线程的私有数据区域，而Java内存模型中规定所有变量都存储在主内存，主内存是共享内存区域，所有线程都可访问，但线程对变量的操作（读取赋值等）必须在工作内存中进行，首先要将变量从主内存拷贝到自己的工作内存空间，然后对变量进行操作，操作完成后再将变量写回主内存。不能直接操作主内存中的变量，各个线程中的工作内存里存储着主内存中的变量副本拷贝，因此不同的线程间无法访问对方的工作内存，线程间的通信（传值）必须通过主内存来完成，其简要访问过程如下图：

JMM关于同步的规定：

1. 线程加锁前，必须把共享变量的值刷新回主内存
2. 线程加锁前，必须读取主内存的最新值到自己的工作内存
3. 加锁解锁是同一把锁

特性：

1. 可见性

2. 原子性

3. 有序性

   计算机在执行程序时，为了提高性能，编译器和处理器常常会对指令做重排。一般分为一下3种。

   | 源代码 | --> | 编译器优化的重排 | --> | 指令并行的重排 | --> | 内存系统的重排 | --> | 最终执行的指令 |

   单线程环境里确保程序最终执行结果和代码顺序执行结果一致。

   处理器在进行重排序时必须要考虑指令之间的数据依赖性。

   多线程环境中线程交替执行，由于编译器优化重排的存在，两个线程中使用的变量能否保证一致性是无法确定的，结果无法预测。

单例模式在多线程环境下出现的问题

问题实例代码，可以在getInstance()方法前加synchronized关键字来避免这个问题，但是synchronized直接加在方法上不推荐，效率会急剧降低。

/**
 * @author shiwenquan
 * @Create 2020-12-11 13:46
 * @description
 */
public class SingletonDemo {

    private static SingletonDemo instance = null;

    private SingletonDemo(){
        System.out.println(Thread.currentThread().getName() + "\t 构造方法。。");
    }

    public static SingletonDemo getInstance(){
        if (instance == null){
            instance = new SingletonDemo();
        }
        return instance;
    }

    public static void main(String[] args) {
        // 单线程
/*        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);
        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);
        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);*/

        // 多线程并发
        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                SingletonDemo.getInstance();
            },String.valueOf(i)).start();
        }
    }

}
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修正之后（DCL案例），为减少代码这里只贴getInstance()方法的代码：

DCL（双端检查）机制不一定安全，因为时有指令重排的存在，加入volatile可以禁止指令重排。

原因在于某一个线程执行到第一次检测，读取到的instance不为null时，instance的引用对象可能没有完成初始化。

instance = new SingletonDemo();可以分为3布完成（伪代码）

memory = allocate();//1.分配对象内存空间

instance(memory);//2.初始化对象

instance = memory;//3.设置instance指向刚分配的内存地址，此时instance!=null

2和3不存在数据依赖关系，而且无论重排前还是重排后程序的执行结果在单线程中没有改变，因此这种重排优化时允许的。

memory = allocate();//1.分配对象内存空间

instance = memory;//3.设置instance指向刚分配的内存地址，此时instance!=null，但是此时对象还没有初始化完成！

instance(memory);//2.初始化对象

但是指令重排只会保证串行语义执行的一致性（单线程），但并不会关心多线程间的语义一致性。

所以当一条线程访问instance不为null时，由于instance实例未必已经初始化完成，也就造成了线程安全问题。

    // DCL(Double Check Lock双端检锁机制)
    public static synchronized SingletonDemo getInstance(){
        if (instance == null){
            synchronized (SingletonDemo.class){
                if (instance == null){
                    instance = new SingletonDemo();
                }
            }
        }
        return instance;
    }
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这样修改之后绝大部分情况都不会出现线程安全问题，并不绝对，因为编译里和处理器有可能做指令重排，重排之后可能还会出现创建多个对象的问题。volatile可以禁止指令重排，于是可以在变量前面用volatile关键字修饰。

最后代码：

/**
 * @author shiwenquan
 * @Create 2020-12-11 13:46
 * @description
 */
public class SingletonDemo {

    private volatile static SingletonDemo instance = null;

    private SingletonDemo(){
        System.out.println(Thread.currentThread().getName() + "\t 构造方法。。");
    }

    // DCL(Double Check Lock双端检锁机制)
    public static synchronized SingletonDemo getInstance(){
        if (instance == null){
            synchronized (SingletonDemo.class){
                if (instance == null){
                    instance = new SingletonDemo();
                }
            }
        }
        return instance;
    }

    public static void main(String[] args) {
        // 单线程
/*        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);
        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);
        System.out.println(SingletonDemo.getInstance() == SingletonDemo.instance);*/

        // 多线程并发
        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                SingletonDemo.getInstance();
            },String.valueOf(i)).start();
        }
    }

}
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二、CAS

什么是CAS？

全称Compare-And-Swap并比较并交换，它是CPU并发原语。

它的功能是判断内存某个位置的值是否为预期值，如果是则更改为新的值，这个过程是原子的。

CAS并发原语体现在Java语言中就是sun.misc.Unsafe类中的各个方法。调用Unsafe类中的CAS方法，JVM会帮我们实现出CAS汇编指令。这是一种完全依赖于硬件的功能，通过它实现原子操作。再次强调，由于CAS是一种系统原语，原语属于操作系统用语范畴，是由若干条指令组成的，用于完成某个功能的一个过程，并且原语的执行必须是连续的，在执行过程中不允许被中断，也就是说CAS是一条CPU的原子指令，不会造成所谓的数据不一致问题。

compareAndSet()

如果当前值==期望值，则以原子方式将该值设置为给定的更新值

参数：

​ 期望值，更新值

返回值：

​ 如果成功返回true，错误返回false

示例代码：

    public static void main(String[] args) {

        AtomicInteger atomicInteger = new AtomicInteger(5);

        System.out.println(atomicInteger.compareAndSet(5, 2019)+ "\t  update : " + atomicInteger.get());
        System.out.println(atomicInteger.compareAndSet(5, 1024)+ "\t  update : " + atomicInteger.get());

    }
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Unsafe

1. Unsafe是CAS的核心类，由于Java方法无法直接访问底层系统，需要通过本地（native）方法来访问，Unsafe相当于一个后门，基于该类可以直接操作特定内存的数据。Unsafe类存在于sun.misc包中，其内部方法操作可以像C的指针一样直接操作内存，因为Java中CAS操作的执行依赖于Unsafe类的方法。

   注意：Unsafe类中的所有方法都是native修饰的，也就是说Unsafe类中的方法都是直接调用操作系统底层资源，执行相应任务。

2. 变量valueOffset，表示该变量值在内存中的偏移地址，因为Unsafe就是根据内存偏移地址来获取数据的。

       /**
        * Atomically increments by one the current value.
        *
        * @return the previous value
        */
       public final int getAndIncrement() {
           return unsafe.getAndAddInt(this, valueOffset, 1);
       }
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3. 变量value用volatile修饰，保证了多线程之间的内存可见性。

CAS缺点

1. 循环时间长开销大（do while）

2. 只能保证一个共享变量的原子操作

   当对一个共享变量执行操作时，可以使用CAS方式来保证原子操作，但是对多个共享变量操作时，循环CAS就无法保证操作的原子性，这个时候就需要锁来保证原子性。

3. ABA问题

   假如有两个线程，线程一从内存位置V中取出A，这时候另一个线程二也从内存中取出A，并且线程二进行了一些操作将值变成了B，然后线程二又将V位置的数据变成A，这时候线程一进行CAS操作发现内存中仍是A，然后线程一操作成功。

   尽管线程一的CAS操作成功，但是不代表这个过程就是没问题的。

4. 原子引用
   原子引用实例代码（无法避免ABA问题）：

   import java.util.concurrent.atomic.AtomicReference;
   
   class User {
       String userName;
       int age;
   
       public User(String userName, int age) {
           this.userName = userName;
           this.age = age;
       }
   
       public String getUserName() {
           return userName;
       }
   
       public void setUserName(String userName) {
           this.userName = userName;
       }
   
       public int getAge() {
           return age;
       }
   
       public void setAge(int age) {
           this.age = age;
       }
   
       @Override
       public String toString() {
           return "User{" +
                   "userName='" + userName + '\'' +
                   ", age=" + age +
                   '}';
       }
   }
   
   /**
    * @author shiwenquan
    * @Create 2020-12-14 9:28
    * @description
    */
   public class AtomicReferenceDemo {
       public static void main(String[] args) {
           User z3 = new User("z3", 22);
           User l4 = new User("l4", 23);
   
           AtomicReference<User> reference = new AtomicReference<>();
           reference.set(z3);
   
           boolean b = reference.compareAndSet(z3, l4);
           System.out.println(b + "\t " + reference.get().toString());
   
       }
   }
   
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三、集合类不安全之并发修改异常

集合类线程不安全之List

代码实例：

/**
 * 集合类不安全问题
 *      java.util.ConcurrentModificationException  异常
 * @author shiwenquan
 * @Create 2020-12-14 10:11
 * @description
 */
public class ContainerNotSageDemo {
    public static void main(String[] args) {
/*        List<String> list = new ArrayList<>();
        List<String> list = new Vector<>();
        List<String> list = Collections.synchronizedList(new ArrayList<>());*/
        List<String> list = new CopyOnWriteArrayList<>();
        list.add("1");

        for (int i = 0; i < 30; i++) {
            new Thread(()->{
                // java.util.ConcurrentModificationException  异常
                list.add(UUID.randomUUID().toString().substring(0,8));
                System.out.println(Thread.currentThread().getName()+list);
            },String.valueOf(i)).start();
        }

        /**
         * 1.故障现象
         *      java.util.ConcurrentModificationException
         *
         * 2.导致原因
         *      并发争抢修改导致，一个线程正在写，另一个线程来抢，导致数据不一致。
         *
         * 3.解决方案
         *      3.1 使用new Vector<>();
         *      3.2 使用Collections.synchronizedList(new ArrayList<>());
         *      3.3 使用new CopyOnWriteArrayList<>();
         *
         * 4.优化建议
         *      写时复制：CopyOnWrite容器即写时复制的容器。往一个容器添加元素的时候，不直接往当前容器Object[]添加，而是先将当前容器
         *      Object[]进行copy，复制出一个新的容器Object[] newElements，然后在新的容器Object[] newElements里添加元素，添加元素
         *      之后再将原容器的引用指向新的容器 setArray(newElements)。这样做的好处是可以对CopyOnWrite容器进行并发读，而不需要加锁，
         *      因为当前容器不会添加任何元素。所以CopyOnWrite容器也是一种读写分离的思想。读和写不同的容器。
         *      
         *     CopyOnWrite的add方法源码：
         *     Appends the specified element to the end of this list.
         *     @param e element to be appended to this list
         *     @return {@code true} (as specified by {@link Collection#add})
         *     
         *     public boolean add(E e) {
         *         final ReentrantLock lock = this.lock;
         *         lock.lock();
         *         try {
         *             Object[] elements = getArray();
         *             int len = elements.length;
         *             Object[] newElements = Arrays.copyOf(elements, len + 1);
         *             newElements[len] = e;
         *             setArray(newElements);
         *             return true;
         *         } finally {
         *             lock.unlock();
         *         }
         *     }
         */
    }
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集合类线程不安全之Set

实例代码：（错误和解决办法和List类似）

//        Set<String> set = new HashSet<>();
//        Set<String> set = Collections.synchronizedSet(new HashSet<>());
        Set<String> set = new CopyOnWriteArraySet<>();

        for (int i = 0; i < 30; i++) {
            new Thread(()->{
                // java.util.ConcurrentModificationException  异常
                set.add(UUID.randomUUID().toString().substring(0,8));
                System.out.println(Thread.currentThread().getName()+set);
            },String.valueOf(i)).start();
        }
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集合类线程不安全之Map

实例代码：（用ConcurrentHashMap解决）

//        Map<String,String> map = new HashMap<>();
//        Map<String,String> map = Collections.synchronizedMap(new HashMap<>());
        Map<String,String> map = new ConcurrentHashMap<>();

        for (int i = 0; i < 30; i++) {
            new Thread(()->{
                // java.util.ConcurrentModificationException  异常
                map.put(Thread.currentThread().getName(),UUID.randomUUID().toString().substring(0,8));
                System.out.println(Thread.currentThread().getName()+map);
            },String.valueOf(i)).start();
        }

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四、锁

公平锁和非公平锁

公平锁：指多个线程按照申请锁的顺序来获得锁。

非公平锁：指多个线程获取锁的顺序并不是按照申请锁的顺序，有可能后申请的线程比先申请的线程优先获取锁。在高并发的情况下，有可能会造成优先级反转或者饥饿现象。

可重入锁（递归锁）

指的是同一线程外层函数获得锁之后，内层递归函数仍能获取该锁的代码，在同一个线程在外层方法获取锁的时候，进入内层方法锁会自动获取锁。

也就说，线程可以进入任何一个它已经拥有的锁 所同步着的代码块。

ReentrantLock/Synchronized就是典型的可重入锁。

最大作用就是避免死锁。

可重入锁代码示例：

class Phone{
    public synchronized void sendSMS() throws Exception{
        System.out.println(Thread.currentThread().getId()+"\t   sendSMS方法。。");
        sendEmail();
    }
    public synchronized void sendEmail() throws Exception{
        System.out.println(Thread.currentThread().getId()+"\t   sendEmail方法。。");
    }
}


/**
 * @author shiwenquan
 * @Create 2020-12-14 14:50
 * @description
 */
public class ReenterLockDemo {

    public static void main(String[] args) {
        Phone phone = new Phone();
        
        for (int i = 0; i < 2; i++) {
            new Thread(()->{
                try {
                    phone.sendSMS();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            },String.valueOf(i)).start();
        }

        /**
         * 输出：
         * 11	   sendSMS方法。。
         * 11	   sendEmail方法。。
         * 12	   sendSMS方法。。
         * 12	   sendEmail方法。。
         */
    }

}
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独占锁（写锁）/共享锁（读锁）/互斥锁

独占：指该锁一次只能被一个线程所持有。ReentrantLock和Synchronized而言都是独占锁。

共享：指该锁可被多个线程所持有。对ReentrantReadWriteLock其读锁是共享锁，写锁是独占锁。读锁的共享锁可保证并发读是非常高效的，读写，写读，写写的过程是互斥的。

代码示例：

/**
 * 资源类
 */
class MyCache{

    private volatile Map<String, Object> map = new HashMap<>();
    private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();

    public void put(String key, Object value){
        rwLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 正在写入："+key);
            try {
                // 暂停线程一会
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            map.put(key,value);
            System.out.println(Thread.currentThread().getName()+"\t 写入完成。");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            rwLock.writeLock().unlock();
        }

    }

    public void get(String key){
        rwLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 正在读取。");
            try {
                // 暂停线程一会
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Object result = map.get(key);
            System.out.println(Thread.currentThread().getName()+"\t 读取完成："+result);
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            rwLock.readLock().unlock();
        }
    }

}

/**
 * 多线程同时读一个资源类没有任何问题，所以为了满足并发量，读取共享资源应该可以同时进行。
 * 但是如果有一个线程想去写共享资源，就不应该再有其他线程可以对该资源进行读或写。
 *
 * 小总结：
 *      读-读     能共存
 *      读-写     不能共存
 *      写-写     不能共存
 *
 *      写操作：原子+独占，中间整个过程必须是一个完整的统一体，中间不许被分割或者打断。
 *
 * @author shiwenquan
 * @Create 2020-12-14 15:43
 * @description
 */
public class ReadWriteLockDemo{
    public static void main(String[] args) {
        MyCache myCache = new MyCache();

        for (int i = 0; i < 5; i++) {
            final int tempInt = i;
            new Thread(()->{
                myCache.put(tempInt+"", tempInt+"");
            },String.valueOf(i)).start();
        }


        for (int i = 0; i < 5; i++) {
            final int tempInt = i;
            new Thread(()->{
                myCache.get(tempInt+"");
            },String.valueOf(i)).start();
        }
    }
}

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自旋锁

是指尝试获取锁的线程不会立即阻塞，而是采用循环的方式去尝试获取锁，这样的好处是减少线程上下文切换的消耗，缺点是循环会消耗CPU。

代码示例：

public class SpinLockDemo {

    AtomicReference<Thread> atomicReference = new AtomicReference<>();

    public void myLook(){
        Thread thread = Thread.currentThread();
        // 自旋
        while (!atomicReference.compareAndSet(null, thread)){

        }
        System.out.println(thread.getName()+"获得锁。。");
    }

    public void myUnLock(){
        Thread thread = Thread.currentThread();
        atomicReference.compareAndSet(thread, null);
        System.out.println(thread.getName()+"释放锁。。");

    }

    public static void main(String[] args) throws InterruptedException {
        SpinLockDemo demo = new SpinLockDemo();

        new Thread(()->{
            demo.myLook();
            try {
                TimeUnit.SECONDS.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            demo.myUnLock();
        },"t1").start();

        // 确保线程一先获得锁。
        TimeUnit.SECONDS.sleep(2);

        new Thread(()->{
            demo.myLook();
            demo.myUnLock();
        },"t2").start();

    }
}
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CountDownLath/CyclicBarrier/Semaphone

1. CountDownLath
   让一些线程阻塞直到另一些线程完成一系列操作后才被唤醒。
   主要有两个方法，当一个或者多个线程调用await方法时，调用线程会被阻塞。其它线程调用countDown方法会将计数器减 1（调用countDown方法的线程不会阻塞），当计数器的值变为零时，因调用await方法被阻塞的线程会被唤醒，继续执行。

   代码实例：

   public class CountDownLatchDemo {
       public static void main(String[] args) {
   
           CountDownLatch latch = new CountDownLatch(6);
   
           for (int i = 0; i < 6; i++) {
               new Thread(()->{
                   System.out.println(Thread.currentThread().getName()+"\t 结束。");
                   latch.countDown();
                   try {
                       TimeUnit.SECONDS.sleep(5);
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
                   System.out.println(Thread.currentThread().getName()+"\t 结束。。");
               },String.valueOf(i)).start();
           }
   
           try {
               latch.await();
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
           System.out.println(Thread.currentThread().getName()+"\t main结束。");
       }
   }
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   注意结果（当计数器变成零时，不管线程是否已经结束，被阻塞的线程会被立即唤醒）：

   0 结束。
   1 结束。
   2 结束。
   3 结束。
   4 结束。
   5 结束。
   main main结束。
   3 结束。。
   5 结束。。
   0 结束。。
   1 结束。。
   4 结束。。
   2 结束。。

2. CyclicBarrier
   CyclicBarrier的字面意思时可循环（Cyclic）使用的屏障（Barrier）。它要做的事情是让一组线程到达一个屏障（也可以叫同步点）时被阻塞，直到最后一个线程达到屏障时，屏障才会开门，所有被屏障拦截的线程才会继续干活，线程进入屏障通过CyclicBarrier的await()方法。

   public class CyclicBarrierDemo {
       public static void main(String[] args) {
           CyclicBarrier barrier = new CyclicBarrier(7, ()->{
               System.out.println("---------");
           });
   
   
           for (int i = 0; i < 7; i++) {
               final int tempInt = i;
               new Thread(()->{
                   System.out.println(Thread.currentThread().getName()+"\t 第" + tempInt + "个！");
                   try {
                       barrier.await();
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   } catch (BrokenBarrierException e) {
                       e.printStackTrace();
                   }
                   
                   try {
                       TimeUnit.SECONDS.sleep(5);
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
                   System.out.println(Thread.currentThread().getName()+"\t 结束。。");
               },String.valueOf(i)).start();
           }
       }
   }
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   注意结果（和CountDownLath差不多，不管线程是否已经结束，被阻塞的线程会被立即唤醒）：

   0 第0个！
   1 第1个！
   2 第2个！
   3 第3个！
   4 第4个！
   5 第5个！
   6 第6个！
   ---------
   0 结束。。
   6 结束。。
   5 结束。。
   1 结束。。
   2 结束。。
   4 结束。。
   3 结束。。

3. Semaphore
   Semaphore(信号灯)主要有两个目的，一个用于多个共享资源的互斥使用，另一个用于并发线程数的控制。
   代码示例：

   public class SemaphoreDemo {
       public static void main(String[] args) {
           // 模拟三个停车位
           Semaphore semaphore = new Semaphore(3);
           // 模拟六个汽车
           for (int i = 0; i < 6; i++) {
               new Thread(()->{
                   try {
                       semaphore.acquire();
                       System.out.println(Thread.currentThread().getName()+"\t 抢到车位。");
                       TimeUnit.SECONDS.sleep(3);
                       System.out.println(Thread.currentThread().getName()+"\t 离开车位。");
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }finally {
                       semaphore.release();
                   }
               },String.valueOf(i)).start();
           }
       }
   }
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五、队列

队列+阻塞队列（BlockintQueue）

阻塞队列：首先是一个队列，而一个阻塞队列在数据结构中所起的作用大致是，线程1往阻塞队列中添加元素，而线程2从阻塞队列中移除元素。

当阻塞队列是空时，从队列中获取元素的操作会被阻塞。

当队列是满的时候，往队列中添加元素的操作将会被阻塞。

有七种：

• ArrayBlockintQueue：由数组结构组成的有界阻塞队列。
• LinkedBlockingQueue：由链表结构组成的有界（但默认值为Integer.MAX_VALUE）阻塞队列。
• PriorityBlockingQueue：支持优先级排序的无界阻塞队列。
• DelayQueue：使用优先级队列实现的延迟误解阻塞队列。
• SynchronousQueue：不存储元素的阻塞队列，即单个元素队列。
• LinkedTransferQueue：由链表组成的无界阻塞队列。
• LinkedBlockingDeque：由链表结构组成的双向阻塞队列。

BlockingQueue核心方法：

抛出异常：

• 当阻塞队列满时，再往队列add插入元素会抛IllegalStateException：Queue full
• 当阻塞队列空时，再往队列remove移除元素会抛NoSuchElementException

特殊值：

• 插入方法，成功true失败false
• 移除方法，成功返回队列里的元素，队列里面没有就返回null

一直阻塞：

• 当阻塞队列满时，生产者线程继续往队列里put元素，队列会一直阻塞生产线程直到put数据or响应中断退出。
• 当阻塞队列空时，消费者试图从队列里take元素，队列会一直阻塞消费者线程直到队列可用。

超时退出：

• 当阻塞队列满时，队列会阻塞生产者线程一定时间，超过限时时间后生产者线程会退出。

用在哪里？

• 生产者消费者模式

1. 传统版代码示例：

   /**
    * 题目：一个初始值为零的变量，两个线程交替操作，一个加1一个减一，来五次
    *
    *      1. 线程   操作(方法)  资源类
    *      2. 判断   干活  通知
    *      3. 防止虚假唤醒机制
    *
    * @author shiwenquan
    * @Create 2020-12-16 14:34
    * @description
    */
   public class ProdConsumer_TraditionDemo {
   
       private static int i = 0;
   
       public static void main(String[] args) throws InterruptedException {
           ShareData data = new ShareData();
           new Thread(()->{
               for (int j = 0; j < 5; j++) {
                   data.decrement();
                   try {
                       TimeUnit.SECONDS.sleep(2);
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
               }
           },"AA").start();
           new Thread(()->{
               for (int j = 0; j < 5; j++) {
                   data.increment();
               }
           },"BB").start();
       }
   }
   
   
   class ShareData{
       private int number;
       private Lock lock = new ReentrantLock();
       private Condition condition = lock.newCondition();
   
       // 加
       public void increment() {
           lock.lock();
           try {
               // 1. 判断
               while (number != 0){
                   // 等待，不能生产
                   condition.await();
               }
               // 2.干活
               number++;
               System.out.println(Thread.currentThread().getName()+"\t "+number);
               // 3. 通知唤醒
               condition.signal();
           }catch (Exception e){
               e.printStackTrace();
           }finally {
               lock.unlock();
           }
       }
   
   
       // 减
       public void decrement() {
           lock.lock();
           try {
               // 1. 判断
               while (number == 0){
                   // 等待，不能生产
                   condition.await();
               }
               // 2.干活
               number--;
               System.out.println(Thread.currentThread().getName()+"\t "+number);
               // 3. 通知唤醒
               condition.signal();
           }catch (Exception e){
               e.printStackTrace();
           }finally {
               lock.unlock();
           }
       }
   
   }
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2. 阻塞队列版代码示例：

   /**
    * volatile/CAS/atomicInteger/blockQueue/线程交互/原子引用
    *
    * @author shiwenquan
    * @Create 2020-12-16 14:35
    * @description
    */
   public class ProdConsumer_BlockQueueDemo {
       public static void main(String[] args) {
           MyResource resource = new MyResource(new ArrayBlockingQueue<>(10));
   
           new Thread(()->{
               System.out.println(Thread.currentThread().getName()+"\t 生产线程启动！");
               try {
                   resource.myProd();
               } catch (Exception e) {
                   e.printStackTrace();
               }
           },"prod").start();
   
           new Thread(()->{
               System.out.println(Thread.currentThread().getName()+"\t 消费线程启动！");
               try {
   
                   try {
                       // 线程睡眠4秒钟
                       TimeUnit.SECONDS.sleep(4);
                   } catch (InterruptedException e) {e.printStackTrace();}
                   resource.myConsumer();
               } catch (Exception e) {
                   e.printStackTrace();
               }
           },"consumer").start();
   
           try {
               // 线程睡眠10秒钟
               TimeUnit.SECONDS.sleep(10);
           } catch (InterruptedException e) {e.printStackTrace();}
   
           System.out.println();
           System.out.println();
           System.out.println();
           System.out.println("10秒钟后，停止生产线程");
           resource.stop();
       }
   }
   
   
   class MyResource{
       /*
        默认开启，进行生产+消费
        */
       private volatile boolean FLAG = true;
       private AtomicInteger atomicInteger = new AtomicInteger();
   
       BlockingQueue<String> blockingQueue = null;
       public MyResource(BlockingQueue<String> blockingQueue) {
           System.out.println(blockingQueue.getClass().getName());
           this.blockingQueue = blockingQueue;
       }
   
       public void myProd() throws Exception{
           String data = null;
           boolean retValue;
           while (FLAG){
               data = String.valueOf(atomicInteger.incrementAndGet());
               retValue = blockingQueue.offer(data, 2L, TimeUnit.SECONDS);
               if (retValue){
                   System.out.println(Thread.currentThread().getName()+"\t 插入队列"+data+"成功！");
               }else{
                   System.out.println(Thread.currentThread().getName()+"\t 插入队列"+data+"失败！");
               }
   
               try {
                   // 线程睡眠1秒钟
                   TimeUnit.SECONDS.sleep(1);
               } catch (InterruptedException e) {e.printStackTrace();}
           }
   
           System.out.println(Thread.currentThread().getName()+"\t 线程停止，生产动作结束！");
       }
   
       public void myConsumer() throws Exception{
           String result = null;
           while (FLAG){
               result = blockingQueue.poll(4L,TimeUnit.SECONDS);
               if (null == result||result.equalsIgnoreCase("")){
                   FLAG = false;
                   System.out.println(Thread.currentThread().getName()+"\t 超过4秒没有消费，消费退出");
                   return;
               }
               System.out.println(Thread.currentThread().getName()+"\t 消费队列"+result+"成功！");
           }
       }
   
       public void stop(){
           this.FLAG = false;
       }
   
   }
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• 线程池
• 消息中间间

有什么好处？为什么用？为什么需要？

在多线程领域：所谓阻塞，在某些情况下会挂起线程（即阻塞），一旦条件满足，被挂起的线程又会自动被唤醒。

好处是我们u需要关心什么时候需要阻塞线程，什么时候需要唤醒线程，因为Blocking Queue都包办了。

在concurrent包发布以前，在多线程环境下，我们每个程序员都必须自己控制这些细节，尤其还要兼顾效率和线程安全，而这会给们的程序带来不小的复杂度。

六、Synchronized和Lock有什么区别？用新的lock有什么好处？

1. 原始结构

Synchronized是关键字属于JVM层面，编译之后Synchronized会有monitorenter和monitorexit

​ monitorenter（底层是通过monitor对象来完成，其实wait/notify等方法也依赖于monitor对象只有在同步方法块或方法中才能调wait/notify等方法）

​ monitorexit

lock是类，api层面的锁。
synchronized反编译之后会生成一个monitorenter和两个monitorexit，monitorenter用于上锁，monitorexit用于去掉锁，有两个是防止报异常之后锁不释放。

2. 使用方法

Synchronized 不需要用户手动释放锁，当Synchronized 代码执行完后系统会让线程释放对锁的占用
ReentrantLock 需要 用户主动释放锁，如果没有主动释放则可能会导致出现死锁问题。

3. 等待是否可中断

Synchronized 不可中断，除非抛出异常或者正常运行。
ReentrantLock 可中断。设置超时方法tryLock(long timeout, TimeUnit unit); lockInterruptibly()放入代码块中，调用interr()方法可中断。

4. 加锁是否公平

Synchronized 非公平锁
ReentrantLock 两种锁都可以，默认非公平锁，构造方法可以传入Boolean值

5. 锁绑定多个条件condition

Synchronized 没有
ReentrantLock 用来实现分组唤醒需要唤醒的县城们，可以精确唤醒，而不像Synchronized 要么随机唤醒要么全部唤醒

精确唤醒指定线程案例：

/**
 * 题目：多线程之间按顺序调用，实现A->B->C三个线程启动，要求如下
 * AA打印五次，BB打印十次，CC打印十五次
 * 紧接着
 * AA打印五次，BB打印十次，CC打印十五次
 * ......
 * 来十轮
 * 
 * @author shiwenquan
 * @Create 2020-12-16 15:20
 * @description
 */
public class SyncAndLockDemo {
    public static void main(String[] args) {
        ShareResource resource = new ShareResource();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                resource.print5();
            }
        },"AA").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                resource.print10();
            }
        },"BB").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                resource.print15();
            }
        },"CC").start();
    }
}


class ShareResource{
    private int num = 1;
    private Lock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();

    public void print5(){
        lock.lock();
        try {
            while (num != 1){
                condition1.await();
            }
            for (int i = 0; i < 5; i++) {
                System.out.println(Thread.currentThread().getName()+"\t "+i);
            }
            num = 2;
            condition2.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }

    public void print10(){
        lock.lock();
        try {
            while (num != 2){
                condition2.await();
            }
            for (int i = 0; i < 10; i++) {
                System.out.println(Thread.currentThread().getName()+"\t "+i);
            }
            num = 3;
            condition3.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }

    public void print15(){

        lock.lock();
        try {
            while (num != 3){
                try {
                    TimeUnit.SECONDS.sleep(4);} catch (InterruptedException e) {e.printStackTrace();}
                condition3.await();
            }
            for (int i = 0; i < 15; i++) {
                System.out.println(Thread.currentThread().getName()+"\t "+i);
            }
            num = 1;
            condition1.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }

        lock.lock();
        try {

        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }


    }
}
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七、线程池（ThreadPoolExecutor理解）

为什么用线程池，优势

线程池做的工作主要是控制运行的线程的数量，处理过程中将任务放入队列，然后在线程创建后启动这些任务，如果线程数量超过了最大数量的线程排队等候，等其他线程执行完毕，再从队列中取出任务执行。

特点：线程复用、控制最大并发数、管理线程。

• 降低资源消耗，通过重复利用已创建的线程降低线程创建和销毁造成的消耗。

• 提高响应速度，当任务到达时，任务可以不需要等到线程创建就能立即执行。

• 提高线程管理性，线程是稀缺资源，如果无限制创建，不仅会消耗系统资源，还会降低系统的稳定性，使用线程池可以进行统一分配调优和监控。

线程池如何使用

• 架构说明
  Java中线程池是通过Executor框架来实现，该框架中用到了Executor，Executors，ExecutorService，ThreadPoolExecutor这几个类。

• 编码实现

  • Executors.newScheduledThreadPool()

  • Executors.newWorkStealingpool(int) ----->java8新出

  • Executors.newFixedThreadPool(int) ----->执行长期的任务，性能好很多。

        /**
         * Creates a thread pool that reuses a fixed number of threads
         * operating off a shared unbounded queue.  At any point, at most
         * {@code nThreads} threads will be active processing tasks.
         * If additional tasks are submitted when all threads are active,
         * they will wait in the queue until a thread is available.
         * If any thread terminates due to a failure during execution
         * prior to shutdown, a new one will take its place if needed to
         * execute subsequent tasks.  The threads in the pool will exist
         * until it is explicitly {@link ExecutorService#shutdown shutdown}.
         *
         * @param nThreads the number of threads in the pool
         * @return the newly created thread pool
         * @throws IllegalArgumentException if {@code nThreads <= 0}
         */
        public static ExecutorService newFixedThreadPool(int nThreads) {
            return new ThreadPoolExecutor(nThreads, nThreads,
                                          0L, TimeUnit.MILLISECONDS,
                                          new LinkedBlockingQueue<Runnable>());
        }
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    特点：

  1. 创建一个固定长度的线程池，可控制线程最大并发数，超出的线程会在队列中等待。
  2. newFixedThreadPool创建线程池corePoolSize和maximumPoolSize值是相等的，它使用LinkedBlockingQueue。

  • Executors.newSingleThreadExecutor() ----->一个任务一个任务执行的场景

        /**
         * Creates an Executor that uses a single worker thread operating
         * off an unbounded queue. (Note however that if this single
         * thread terminates due to a failure during execution prior to
         * shutdown, a new one will take its place if needed to execute
         * subsequent tasks.)  Tasks are guaranteed to execute
         * sequentially, and no more than one task will be active at any
         * given time. Unlike the otherwise equivalent
         * {@code newFixedThreadPool(1)} the returned executor is
         * guaranteed not to be reconfigurable to use additional threads.
         *
         * @return the newly created single-threaded Executor
         */
        public static ExecutorService newSingleThreadExecutor() {
            return new FinalizableDelegatedExecutorService
                (new ThreadPoolExecutor(1, 1,
                                        0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>()));
        }
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    > 特点：
    >
    > 1. 创建只有一个线程的线程池，它只会用唯一的工作线程来执行任务，保证所有任务按照指定顺序执行。
    > 2. newSingleThreadExecutor将corePoolSize和maximumPoolSize值都是 1 ，它使用**LinkedBlockingQueue**。
  
  * Executors.newCachedTheadPool() ----->执行很多短期异步的小程序或者负责较轻的服务器。
  
    ```java
        /**
         * Creates a thread pool that creates new threads as needed, but
         * will reuse previously constructed threads when they are
         * available.  These pools will typically improve the performance
         * of programs that execute many short-lived asynchronous tasks.
         * Calls to {@code execute} will reuse previously constructed
         * threads if available. If no existing thread is available, a new
         * thread will be created and added to the pool. Threads that have
         * not been used for sixty seconds are terminated and removed from
         * the cache. Thus, a pool that remains idle for long enough will
         * not consume any resources. Note that pools with similar
         * properties but different details (for example, timeout parameters)
         * may be created using {@link ThreadPoolExecutor} constructors.
         *
         * @return the newly created thread pool
         */
        public static ExecutorService newCachedThreadPool() {
            return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                          60L, TimeUnit.SECONDS,
                                          new SynchronousQueue<Runnable>());
        }
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  特点：

  1. 创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。
  2. newCachedThreadPool将corePoolSize设置为0，maximumPoolSize设置为Integer.MAX_VALUE，使用的SynchronousQueue，也就是说来了任务就创建线程运行，当线程空闲超过60秒，就销毁线程。

• ThreadPoolExecutor

线程池的几个重要参数介绍

ThreadPoolExecutor七大参数介绍：

1. corePoolSize：线程池中常驻核心线程数
2. maximumPoolSize：线程池能够容纳同时执行的最大线程数，此值必须大于1.
3. keepAliveTime：多余的空闲线程存活时间。
   当前线程池数量超过corePoolSize时，当空闲时间达到keepAliveTime值时，多余空闲线程会被销毁直到只剩下corePoolSize个线程为止。
4. unit：keepAliveTime的单位。
5. workQueue：任务队列，被提交但尚未执行的任务。
6. threadFactory：表示生成线程池中工作线程的线程工厂，用于创建线程一般用默认的即可。
7. handler：拒绝策略，表示当队列满了并且工作线程大于等于线程池的最大线程数（maximumPoolSize）时如何来

线程池底层工作原理

1. 在创建线程池后，等待提交过来的任务请求。
2. 当调用execute()方法添加一个请求任务时，线程池会做如下判断：
   2.1 如果正在运行的线程数量小于corePoolSize，那么马上创建线程运行这个任务。
   2.2 如果正在运行的线程数量大于或者等于corePoolSize，那么将这个任务放入队列。
   2.3 如果这个时候队列满了且正在运行的线程数量还小于maximumPoolSize，那么还是要创建非核心线程立刻运行这个任务。
   2.4 如果队列满了且正在运行的线程数量大于或等于maximumPoolSize，那么线程池会启动饱和和拒绝策略来执行。
3. 当一个线程完成任务之后，他会从队列中取下一个任务来执行。
4. 当一个线程无事可做超过一定的时间（keepAliveTime）时，线程池会判断：
   如果当前运行的线程数大于corePoolSize，那么这个线程会停掉。
   所以线程池的所有任务完成后他最终会收缩到corePoolSize大小。

线程池拒绝策略：

JDK内置的拒绝策略：(均实现了RejectedExecutionHandler接口)

1. AbortPolicy（默认）：直接抛出RejectedExecutionException异常组织系统正常运行。
2. CallerRunsPolicy：“调用者运行”一种调节机制，该策略既不会抛弃任务，也不会抛出异常，而是将某些任务回退到调用者，从而降低新任务流量。
3. DiscardOldestPolicy：抛弃队列中等待最久的任务，然后把当前任务加入队列中尝试再次提交当前任务。
4. DiscardPolicy：直接丢弃任务，不予处理也不抛异常。如果允许任务丢失，这是最好的一种方案。

八、死锁编码以及定位分析

• 产生死锁的原因
  死锁是指两个或者两个以上的进程在执行过程中，因争夺资源而造成的一种相互等待现象，若无外力干涉那他们都将无法推进下去，如果系统资源充足，进程的资源请求都能够得到满足，死锁出现的可能性比较低，否则就会因争夺有限的资源而陷入死锁。

• 代码:

  /**
   * 死锁是指两个或者两个以上的进程在执行过程中，因争夺资源而造成的一种相互等待现象
   *
   * @author shiwenquan
   * @Create 2020-12-24 16:53
   * @description
   */
  public class DeadLockDemo {
      public static void main(String[] args) {
          String lockA = "lockA";
          String lockB = "lockB";
  
          new Thread(new HoldLockThread(lockA,lockB),"AAA").start();
          new Thread(new HoldLockThread(lockB,lockA),"BBB").start();
      }
  
  }
  
  
  class HoldLockThread implements Runnable{
  
      private String lockA;
      private String lockB;
  
      public HoldLockThread(String lockA, String lockB) {
          this.lockA = lockA;
          this.lockB = lockB;
      }
  
      @Override
      public void run() {
          synchronized (lockA){
              System.out.println(Thread.currentThread().getName()+"\t 自己持有" + lockA + "\t 尝试获得" + lockB);
              try {
                  // 线程睡眠2秒钟
                  TimeUnit.SECONDS.sleep(2);
              } catch (InterruptedException e) {e.printStackTrace();}
  
              synchronized (lockB){
                  System.out.println(Thread.currentThread().getName()+"\t 自己持有" + lockB + "\t 尝试获得" + lockA);
              }
          }
      }
  }
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• 解决：

  • jps命令定位进程号

    jps -l
    11488 org.jetbrains.idea.maven.server.RemoteMavenServer36
    16304 org.jetbrains.jps.cmdline.Launcher
    14452 org.study.guigu.DeadLockDemo
    12760
    13164 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
    15596 sun.tools.jps.Jps
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  • jstack查看具体进程号确定是否是死锁。

    jstack 14452
    2020-12-24 17:04:55
    Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.231-b11 mixed mode):
    
    "DestroyJavaVM" #13 prio=5 os_prio=0 tid=0x0000000002d32800 nid=0x19f8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "BBB" #12 prio=5 os_prio=0 tid=0x0000000018e81000 nid=0x4194 waiting for monitor entry [0x0000000019aff000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at org.study.guigu.HoldLockThread.run(DeadLockDemo.java:44)
            - waiting to lock <0x00000000d5dfd838> (a java.lang.String)
            - locked <0x00000000d5dfd870> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    "AAA" #11 prio=5 os_prio=0 tid=0x0000000018e7e000 nid=0x3f9c waiting for monitor entry [0x00000000199ff000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at org.study.guigu.HoldLockThread.run(DeadLockDemo.java:44)
            - waiting to lock <0x00000000d5dfd870> (a java.lang.String)
            - locked <0x00000000d5dfd838> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    "Service Thread" #10 daemon prio=9 os_prio=0 tid=0x0000000018dea000 nid=0x4354 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C1 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x0000000018d48800 nid=0x3644 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x0000000018d46000 nid=0x3108 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x0000000018d19000 nid=0x42d8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x0000000018d51800 nid=0x3f74 runnable [0x00000000193fe000]
       java.lang.Thread.State: RUNNABLE
            at java.net.SocketInputStream.socketRead0(Native Method)
            at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
            at java.net.SocketInputStream.read(SocketInputStream.java:171)
            at java.net.SocketInputStream.read(SocketInputStream.java:141)
            at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
            at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
            at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
            - locked <0x00000000d5d8ca88> (a java.io.InputStreamReader)
            at java.io.InputStreamReader.read(InputStreamReader.java:184)
            at java.io.BufferedReader.fill(BufferedReader.java:161)
            at java.io.BufferedReader.readLine(BufferedReader.java:324)
            - locked <0x00000000d5d8ca88> (a java.io.InputStreamReader)
            at java.io.BufferedReader.readLine(BufferedReader.java:389)
            at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64)
    
    "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x00000000179af000 nid=0x3e98 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x0000000018d08800 nid=0x4108 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000002e2b800 nid=0x416c in Object.wait() [0x0000000018cff000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x00000000d5c08ed8> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
            - locked <0x00000000d5c08ed8> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
            at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)
    
    "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x000000001798a000 nid=0x244 in Object.wait() [0x0000000018bff000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x00000000d5c06c00> (a java.lang.ref.Reference$Lock)
            at java.lang.Object.wait(Object.java:502)
            at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
            - locked <0x00000000d5c06c00> (a java.lang.ref.Reference$Lock)
            at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
    
    "VM Thread" os_prio=2 tid=0x0000000017968000 nid=0x4310 runnable
    
    "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002d48800 nid=0x3654 runnable
    
    "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002d4a000 nid=0x608 runnable
    
    "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002d4b800 nid=0xdec runnable
    
    "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002d4e000 nid=0x2568 runnable
    
    "VM Periodic Task Thread" os_prio=2 tid=0x0000000018df0000 nid=0x42d4 waiting on condition
    
    JNI global references: 12
    
    
    Found one Java-level deadlock:
    =============================
    "BBB":
      waiting to lock monitor 0x0000000002e28768 (object 0x00000000d5dfd838, a java.lang.String),
      which is held by "AAA"
    "AAA":
      waiting to lock monitor 0x0000000002e2aff8 (object 0x00000000d5dfd870, a java.lang.String),
      which is held by "BBB"
    
    Java stack information for the threads listed above:
    ===================================================
    "BBB":
            at org.study.guigu.HoldLockThread.run(DeadLockDemo.java:44)
            - waiting to lock <0x00000000d5dfd838> (a java.lang.String)
            - locked <0x00000000d5dfd870> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    "AAA":
            at org.study.guigu.HoldLockThread.run(DeadLockDemo.java:44)
            - waiting to lock <0x00000000d5dfd870> (a java.lang.String)
            - locked <0x00000000d5dfd838> (a java.lang.String)
            at java.lang.Thread.run(Thread.java:748)
    
    Found 1 deadlock.
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九、JVM+GC

GC作用在方法区和堆中。

常见垃圾回收算法：

• 引用计数，JVM一般不采用这种方式。
• 复制，
• 标记清除，
• 标记清理，

JVM如何确定垃圾？是否知道GC Roots

什么是垃圾：内存中已经不再使用的的空间就是垃圾。

可以作为GC Roots的对象：

• 虚拟机栈（栈帧中的局部变量区，也叫做局部变量表）中引用的对象。
• 方法区中的类静态属性引用的对象。
• 方法区中常量引用的对象。
• 本地方法栈中JNI（Native方法）引用的对象。

JVM参数

• X参数

  • -Xint------解释执行
  • -Xcomp------第一次使用就编译成本地代码
  • -Xmixed------混合模式

• XX参数

  • Boolean类型

    • -XX：+或者 -某个属性

    • +表示开启

    • -表示关闭

      Case：

      1. 是否打印GC收集细节

         E:\workspace\study-guigu>jps -l
         1520 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
         15144 org.study.guigu.GCRootsDemo
         15020 sun.tools.jps.Jps
         508 org.jetbrains.jps.cmdline.Launcher
         8316
         
         E:\workspace\study-guigu>jinfo -flag PrintGCDetails 15144
         -XX:-PrintGCDetails
         1
         2
         3
         4
         5
         6
         7
         8
         9

      2. 是否使用串行垃圾回收器

         E:\workspace\study-guigu>jps -l
         1520 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
         240 org.jetbrains.jps.cmdline.Launcher
         8580 sun.tools.jps.Jps
         15048 org.study.guigu.GCRootsDemo
         8316
         
         E:\workspace\study-guigu>jinfo -flag UseSerialGC 15048
         -XX:-UseSerialGC
         
         1
         2
         3
         4
         5
         6
         7
         8
         9
         10

  • kv设置类型

    • -XX：属性key=属性值value

      Case：

      1. -XX:MetaspaceSize=128M

         E:\workspace\study-guigu>jps -l
         1520 org.jetbrains.kotlin.daemon.KotlinCompileDaemon
         240 org.jetbrains.jps.cmdline.Launcher
         15048 org.study.guigu.GCRootsDemo
         1260 sun.tools.jps.Jps
         8316
         
         E:\workspace\study-guigu>jinfo -flag MetaspaceSize 15048
         -XX:MetaspaceSize=21807104
         1
         2
         3
         4
         5
         6
         7
         8
         9

      2. -XX:MaxTenuringThreshold=15

         E:\workspace\study-guigu>jinfo -flag MaxTenuringThreshold 15048
         -XX:MaxTenuringThreshold=15
         1
         2

  • jinfo举例，如何查看当前运行程序的配置

    E:\workspace\study-guigu>jinfo -flags 15048
    Attaching to process ID 15048, please wait...
    Debugger attached successfully.
    Server compiler detected.
    JVM version is 25.231-b11
    Non-default VM flags: -XX:CICompilerCount=3 -XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2126512128 -XX:MaxNewSize=708837376 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=44
    564480 -XX:OldSize=89653248 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParalle
    lGC
    Command line:  -javaagent:D:\IntellijIDEA\IntelliJ IDEA 2019.2.4\lib\idea_rt.jar=55753:D:\IntellijIDEA\IntelliJ IDEA 2019.2.4\bin -Dfile.encoding=UTF-8
    1
    2
    3
    4
    5
    6
    7
    8
    9

  • 两个经典参数：-Xms和-Xmx

    -Xms等价于-XX:InitialHeapSize

    -Xmx等价于-XX:MaxHeapSize

JVM默认值

命令：java -XX:+PrintFlagsInitial

E:\workspace\study-guigu>java -XX:+PrintFlagsInitial
[Global flags]
     intx ActiveProcessorCount                      = -1                                  {product}
    uintx AdaptiveSizeDecrementScaleFactor          = 4                                   {product}
    uintx AdaptiveSizeMajorGCDecayTimeScale         = 10                                  {product}
    uintx AdaptiveSizePausePolicy                   = 0                                   {product}
    uintx AdaptiveSizePolicyCollectionCostMargin    = 50                                  {product}
    uintx AdaptiveSizePolicyInitializingSteps       = 20                                  {product}
    uintx AdaptiveSizePolicyOutputInterval          = 0                                   {product}
    uintx AdaptiveSizePolicyWeight                  = 10                                  {product}
    uintx AdaptiveSizeThroughPutPolicy              = 0                                   {product}
    uintx AdaptiveTimeWeight                        = 25                                  {product}
     bool AdjustConcurrency                         = false                               {product}
     bool AggressiveHeap                            = false                               {product}
     bool AggressiveOpts                            = false                               {product}
     intx AliasLevel                                = 3                                   {C2 product}
     bool AlignVector                               = true                                {C2 product}
     intx AllocateInstancePrefetchLines             = 1                                   {product}
     intx AllocatePrefetchDistance                  = -1                                  {product}
     intx AllocatePrefetchInstr                     = 0                                   {product}
     intx AllocatePrefetchLines                     = 3                                   {product}
     intx AllocatePrefetchStepSize                  = 16                                  {product}
     intx AllocatePrefetchStyle                     = 1                                   {product}
     bool AllowJNIEnvProxy                          = false                               {product}
     bool AllowNonVirtualCalls                      = false                               {product}
     bool AllowParallelDefineClass                  = false                               {product}
     bool AllowUserSignalHandlers                   = false                               {product}
     bool AlwaysActAsServerClassMachine             = false                               {product}
     bool AlwaysCompileLoopMethods                  = false                               {product}
     bool AlwaysLockClassLoader                     = false                               {product}
     bool AlwaysPreTouch                            = false                               {product}
     bool AlwaysRestoreFPU                          = false                               {product}
     bool AlwaysTenure                              = false                               {product}
     bool AssertOnSuspendWaitFailure                = false                               {product}
     bool AssumeMP                                  = false                               {product}
     intx AutoBoxCacheMax                           = 128                                 {C2 product}
    uintx AutoGCSelectPauseMillis                   = 5000                                {product}
     intx BCEATraceLevel                            = 0                                   {product}
     intx BackEdgeThreshold                         = 100000                              {pd product}
     bool BackgroundCompilation                     = true                                {pd product}
    uintx BaseFootPrintEstimate                     = 268435456                           {product}
     intx BiasedLockingBulkRebiasThreshold          = 20                                  {product}
     intx BiasedLockingBulkRevokeThreshold          = 40                                  {product}
     intx BiasedLockingDecayTime                    = 25000                               {product}
     intx BiasedLockingStartupDelay                 = 4000                                {product}
     bool BindGCTaskThreadsToCPUs                   = false                               {product}
     bool BlockLayoutByFrequency                    = true                                {C2 product}
     intx BlockLayoutMinDiamondPercentage           = 20                                  {C2 product}
     bool BlockLayoutRotateLoops                    = true                                {C2 product}
     bool BranchOnRegister                          = false                               {C2 product}
     bool BytecodeVerificationLocal                 = false                               {product}
     bool BytecodeVerificationRemote                = true                                {product}
     bool C1OptimizeVirtualCallProfiling            = true                                {C1 product}
     bool C1ProfileBranches                         = true                                {C1 product}
     bool C1ProfileCalls                            = true                                {C1 product}
     bool C1ProfileCheckcasts                       = true                                {C1 product}
     bool C1ProfileInlinedCalls                     = true                                {C1 product}
     bool C1ProfileVirtualCalls                     = true                                {C1 product}
     bool C1UpdateMethodData                        = true                                {C1 product}
     intx CICompilerCount                           = 2                                   {product}
     bool CICompilerCountPerCPU                     = false                               {product}
     bool CITime                                    = false                               {product}
     bool CMSAbortSemantics                         = false                               {product}
    uintx CMSAbortablePrecleanMinWorkPerIteration   = 100                                 {product}
     intx CMSAbortablePrecleanWaitMillis            = 100                                 {manageable}
    uintx CMSBitMapYieldQuantum                     = 10485760                            {product}
    uintx CMSBootstrapOccupancy                     = 50                                  {product}
     bool CMSClassUnloadingEnabled                  = true                                {product}
    uintx CMSClassUnloadingMaxInterval              = 0                                   {product}
     bool CMSCleanOnEnter                           = true                                {product}
     bool CMSCompactWhenClearAllSoftRefs            = true                                {product}
    uintx CMSConcMarkMultiple                       = 32                                  {product}
     bool CMSConcurrentMTEnabled                    = true                                {product}
    uintx CMSCoordinatorYieldSleepCount             = 10                                  {product}
     bool CMSDumpAtPromotionFailure                 = false                               {product}
     bool CMSEdenChunksRecordAlways                 = true                                {product}
    uintx CMSExpAvgFactor                           = 50                                  {product}
     bool CMSExtrapolateSweep                       = false                               {product}
    uintx CMSFullGCsBeforeCompaction                = 0                                   {product}
    uintx CMSIncrementalDutyCycle                   = 10                                  {product}
    uintx CMSIncrementalDutyCycleMin                = 0                                   {product}
     bool CMSIncrementalMode                        = false                               {product}
    uintx CMSIncrementalOffset                      = 0                                   {product}
     bool CMSIncrementalPacing                      = true                                {product}
    uintx CMSIncrementalSafetyFactor                = 10                                  {product}
    uintx CMSIndexedFreeListReplenish               = 4                                   {product}
     intx CMSInitiatingOccupancyFraction            = -1                                  {product}
    uintx CMSIsTooFullPercentage                    = 98                                  {product}
   double CMSLargeCoalSurplusPercent                = 0.950000                            {product}
   double CMSLargeSplitSurplusPercent               = 1.000000                            {product}
     bool CMSLoopWarn                               = false                               {product}
    uintx CMSMaxAbortablePrecleanLoops              = 0                                   {product}
     intx CMSMaxAbortablePrecleanTime               = 5000                                {product}
    uintx CMSOldPLABMax                             = 1024                                {product}
    uintx CMSOldPLABMin                             = 16                                  {product}
    uintx CMSOldPLABNumRefills                      = 4                                   {product}
    uintx CMSOldPLABReactivityFactor                = 2                                   {product}
     bool CMSOldPLABResizeQuicker                   = false                               {product}
    uintx CMSOldPLABToleranceFactor                 = 4                                   {product}
     bool CMSPLABRecordAlways                       = true                                {product}
    uintx CMSParPromoteBlocksToClaim                = 16                                  {product}
     bool CMSParallelInitialMarkEnabled             = true                                {product}
     bool CMSParallelRemarkEnabled                  = true                                {product}
     bool CMSParallelSurvivorRemarkEnabled          = true                                {product}
    uintx CMSPrecleanDenominator                    = 3                                   {product}
    uintx CMSPrecleanIter                           = 3                                   {product}
    uintx CMSPrecleanNumerator                      = 2                                   {product}
     bool CMSPrecleanRefLists1                      = true                                {product}
     bool CMSPrecleanRefLists2                      = false                               {product}
     bool CMSPrecleanSurvivors1                     = false                               {product}
     bool CMSPrecleanSurvivors2                     = true                                {product}
    uintx CMSPrecleanThreshold                      = 1000                                {product}
     bool CMSPrecleaningEnabled                     = true                                {product}
     bool CMSPrintChunksInDump                      = false                               {product}
     bool CMSPrintEdenSurvivorChunks                = false                               {product}
     bool CMSPrintObjectsInDump                     = false                               {product}
    uintx CMSRemarkVerifyVariant                    = 1                                   {product}
     bool CMSReplenishIntermediate                  = true                                {product}
    uintx CMSRescanMultiple                         = 32                                  {product}
    uintx CMSSamplingGrain                          = 16384                               {product}
     bool CMSScavengeBeforeRemark                   = false                               {product}
    uintx CMSScheduleRemarkEdenPenetration          = 50                                  {product}
    uintx CMSScheduleRemarkEdenSizeThreshold        = 2097152                             {product}
    uintx CMSScheduleRemarkSamplingRatio            = 5                                   {product}
   double CMSSmallCoalSurplusPercent                = 1.050000                            {product}
   double CMSSmallSplitSurplusPercent               = 1.100000                            {product}
     bool CMSSplitIndexedFreeListBlocks             = true                                {product}
     intx CMSTriggerInterval                        = -1                                  {manageable}
    uintx CMSTriggerRatio                           = 80                                  {product}
     intx CMSWaitDuration                           = 2000                                {manageable}
    uintx CMSWorkQueueDrainThreshold                = 10                                  {product}
     bool CMSYield                                  = true                                {product}
    uintx CMSYieldSleepCount                        = 0                                   {product}
    uintx CMSYoungGenPerWorker                      = 67108864                            {pd product}
    uintx CMS_FLSPadding                            = 1                                   {product}
    uintx CMS_FLSWeight                             = 75                                  {product}
    uintx CMS_SweepPadding                          = 1                                   {product}
    uintx CMS_SweepTimerThresholdMillis             = 10                                  {product}
    uintx CMS_SweepWeight                           = 75                                  {product}
     bool CheckEndorsedAndExtDirs                   = false                               {product}
     bool CheckJNICalls                             = false                               {product}
     bool ClassUnloading                            = true                                {product}
     bool ClassUnloadingWithConcurrentMark          = true                                {product}
     intx ClearFPUAtPark                            = 0                                   {product}
     bool ClipInlining                              = true                                {product}
    uintx CodeCacheExpansionSize                    = 65536                               {pd product}
    uintx CodeCacheMinimumFreeSpace                 = 512000                              {product}
     bool CollectGen0First                          = false                               {product}
     bool CompactFields                             = true                                {product}
     intx CompilationPolicyChoice                   = 0                                   {product}
ccstrlist CompileCommand                            =                                     {product}
    ccstr CompileCommandFile                        =                                     {product}
ccstrlist CompileOnly                               =                                     {product}
     intx CompileThreshold                          = 10000                               {pd product}
     bool CompilerThreadHintNoPreempt               = true                                {product}
     intx CompilerThreadPriority                    = -1                                  {product}
     intx CompilerThreadStackSize                   = 0                                   {pd product}
    uintx CompressedClassSpaceSize                  = 1073741824                          {product}
    uintx ConcGCThreads                             = 0                                   {product}
     intx ConditionalMoveLimit                      = 3                                   {C2 pd product}
     intx ContendedPaddingWidth                     = 128                                 {product}
     bool ConvertSleepToYield                       = true                                {pd product}
     bool ConvertYieldToSleep                       = false                               {product}
     bool CrashOnOutOfMemoryError                   = false                               {product}
     bool CreateMinidumpOnCrash                     = false                               {product}
     bool CriticalJNINatives                        = true                                {product}
     bool DTraceAllocProbes                         = false                               {product}
     bool DTraceMethodProbes                        = false                               {product}
     bool DTraceMonitorProbes                       = false                               {product}
     bool Debugging                                 = false                               {product}
    uintx DefaultMaxRAMFraction                     = 4                                   {product}
     intx DefaultThreadPriority                     = -1                                  {product}
     intx DeferPollingPageLoopCount                 = -1                                  {product}
     intx DeferThrSuspendLoopCount                  = 4000                                {product}
     bool DeoptimizeRandom                          = false                               {product}
     bool DisableAttachMechanism                    = false                               {product}
     bool DisableExplicitGC                         = false                               {product}
     bool DisplayVMOutputToStderr                   = false                               {product}
     bool DisplayVMOutputToStdout                   = false                               {product}
     bool DoEscapeAnalysis                          = true                                {C2 product}
     bool DontCompileHugeMethods                    = true                                {product}
     bool DontYieldALot                             = false                               {pd product}
    ccstr DumpLoadedClassList                       =                                     {product}
     bool DumpReplayDataOnError                     = true                                {product}
     bool DumpSharedSpaces                          = false                               {product}
     bool EagerXrunInit                             = false                               {product}
     intx EliminateAllocationArraySizeLimit         = 64                                  {C2 product}
     bool EliminateAllocations                      = true                                {C2 product}
     bool EliminateAutoBox                          = true                                {C2 product}
     bool EliminateLocks                            = true                                {C2 product}
     bool EliminateNestedLocks                      = true                                {C2 product}
     intx EmitSync                                  = 0                                   {product}
     bool EnableContended                           = true                                {product}
     bool EnableResourceManagementTLABCache         = true                                {product}
     bool EnableSharedLookupCache                   = true                                {product}
     bool EnableTracing                             = false                               {product}
    uintx ErgoHeapSizeLimit                         = 0                                   {product}
    ccstr ErrorFile                                 =                                     {product}
    ccstr ErrorReportServer                         =                                     {product}
   double EscapeAnalysisTimeout                     = 20.000000                           {C2 product}
     bool EstimateArgEscape                         = true                                {product}
     bool ExitOnOutOfMemoryError                    = false                               {product}
     bool ExplicitGCInvokesConcurrent               = false                               {product}
     bool ExplicitGCInvokesConcurrentAndUnloadsClasses  = false                               {product}
     bool ExtendedDTraceProbes                      = false                               {product}
    ccstr ExtraSharedClassListFile                  =                                     {product}
     bool FLSAlwaysCoalesceLarge                    = false                               {product}
    uintx FLSCoalescePolicy                         = 2                                   {product}
   double FLSLargestBlockCoalesceProximity          = 0.990000                            {product}
     bool FailOverToOldVerifier                     = true                                {product}
     bool FastTLABRefill                            = true                                {product}
     intx FenceInstruction                          = 0                                   {ARCH product}
     intx FieldsAllocationStyle                     = 1                                   {product}
     bool FilterSpuriousWakeups                     = true                                {product}
    ccstr FlightRecorderOptions                     =                                     {product}
     bool ForceNUMA                                 = false                               {product}
     bool ForceTimeHighResolution                   = false                               {product}
     intx FreqInlineSize                            = 325                                 {pd product}
   double G1ConcMarkStepDurationMillis              = 10.000000                           {product}
    uintx G1ConcRSHotCardLimit                      = 4                                   {product}
    uintx G1ConcRSLogCacheSize                      = 10                                  {product}
     intx G1ConcRefinementGreenZone                 = 0                                   {product}
     intx G1ConcRefinementRedZone                   = 0                                   {product}
     intx G1ConcRefinementServiceIntervalMillis     = 300                                 {product}
    uintx G1ConcRefinementThreads                   = 0                                   {product}
     intx G1ConcRefinementThresholdStep             = 0                                   {product}
     intx G1ConcRefinementYellowZone                = 0                                   {product}
    uintx G1ConfidencePercent                       = 50                                  {product}
    uintx G1HeapRegionSize                          = 0                                   {product}
    uintx G1HeapWastePercent                        = 5                                   {product}
    uintx G1MixedGCCountTarget                      = 8                                   {product}
     intx G1RSetRegionEntries                       = 0                                   {product}
    uintx G1RSetScanBlockSize                       = 64                                  {product}
     intx G1RSetSparseRegionEntries                 = 0                                   {product}
     intx G1RSetUpdatingPauseTimePercent            = 10                                  {product}
     intx G1RefProcDrainInterval                    = 10                                  {product}
    uintx G1ReservePercent                          = 10                                  {product}
    uintx G1SATBBufferEnqueueingThresholdPercent    = 60                                  {product}
     intx G1SATBBufferSize                          = 1024                                {product}
     intx G1UpdateBufferSize                        = 256                                 {product}
     bool G1UseAdaptiveConcRefinement               = true                                {product}
    uintx GCDrainStackTargetSize                    = 64                                  {product}
    uintx GCHeapFreeLimit                           = 2                                   {product}
    uintx GCLockerEdenExpansionPercent              = 5                                   {product}
     bool GCLockerInvokesConcurrent                 = false                               {product}
    uintx GCLogFileSize                             = 8192                                {product}
    uintx GCPauseIntervalMillis                     = 0                                   {product}
    uintx GCTaskTimeStampEntries                    = 200                                 {product}
    uintx GCTimeLimit                               = 98                                  {product}
    uintx GCTimeRatio                               = 99                                  {product}
    uintx HeapBaseMinAddress                        = 2147483648                          {pd product}
     bool HeapDumpAfterFullGC                       = false                               {manageable}
     bool HeapDumpBeforeFullGC                      = false                               {manageable}
     bool HeapDumpOnOutOfMemoryError                = false                               {manageable}
    ccstr HeapDumpPath                              =                                     {manageable}
    uintx HeapFirstMaximumCompactionCount           = 3                                   {product}
    uintx HeapMaximumCompactionInterval             = 20                                  {product}
    uintx HeapSizePerGCThread                       = 87241520                            {product}
     bool IgnoreEmptyClassPaths                     = false                               {product}
     bool IgnoreUnrecognizedVMOptions               = false                               {product}
    uintx IncreaseFirstTierCompileThresholdAt       = 50                                  {product}
     bool IncrementalInline                         = true                                {C2 product}
    uintx InitialBootClassLoaderMetaspaceSize       = 4194304                             {product}
    uintx InitialCodeCacheSize                      = 2555904                             {pd product}
    uintx InitialHeapSize                           = 0                                   {product}
    uintx InitialRAMFraction                        = 64                                  {product}
   double InitialRAMPercentage                      = 1.562500                            {product}
    uintx InitialSurvivorRatio                      = 8                                   {product}
    uintx InitialTenuringThreshold                  = 7                                   {product}
    uintx InitiatingHeapOccupancyPercent            = 45                                  {product}
     bool Inline                                    = true                                {product}
    ccstr InlineDataFile                            =                                     {product}
     intx InlineSmallCode                           = 1000                                {pd product}
     bool InlineSynchronizedMethods                 = true                                {C1 product}
     bool InsertMemBarAfterArraycopy                = true                                {C2 product}
     intx InteriorEntryAlignment                    = 16                                  {C2 pd product}
     intx InterpreterProfilePercentage              = 33                                  {product}
     bool JNIDetachReleasesMonitors                 = true                                {product}
     bool JavaMonitorsInStackTrace                  = true                                {product}
     intx JavaPriority10_To_OSPriority              = -1                                  {product}
     intx JavaPriority1_To_OSPriority               = -1                                  {product}
     intx JavaPriority2_To_OSPriority               = -1                                  {product}
     intx JavaPriority3_To_OSPriority               = -1                                  {product}
     intx JavaPriority4_To_OSPriority               = -1                                  {product}
     intx JavaPriority5_To_OSPriority               = -1                                  {product}
     intx JavaPriority6_To_OSPriority               = -1                                  {product}
     intx JavaPriority7_To_OSPriority               = -1                                  {product}
     intx JavaPriority8_To_OSPriority               = -1                                  {product}
     intx JavaPriority9_To_OSPriority               = -1                                  {product}
     bool LIRFillDelaySlots                         = false                               {C1 pd product}
    uintx LargePageHeapSizeThreshold                = 134217728                           {product}
    uintx LargePageSizeInBytes                      = 0                                   {product}
     bool LazyBootClassLoader                       = true                                {product}
     intx LiveNodeCountInliningCutoff               = 40000                               {C2 product}
     bool LogCommercialFeatures                     = false                               {product}
     intx LoopMaxUnroll                             = 16                                  {C2 product}
     intx LoopOptsCount                             = 43                                  {C2 product}
     intx LoopUnrollLimit                           = 60                                  {C2 pd product}
     intx LoopUnrollMin                             = 4                                   {C2 product}
     bool LoopUnswitching                           = true                                {C2 product}
     bool ManagementServer                          = false                               {product}
    uintx MarkStackSize                             = 4194304                             {product}
    uintx MarkStackSizeMax                          = 536870912                           {product}
    uintx MarkSweepAlwaysCompactCount               = 4                                   {product}
    uintx MarkSweepDeadRatio                        = 5                                   {product}
     intx MaxBCEAEstimateLevel                      = 5                                   {product}
     intx MaxBCEAEstimateSize                       = 150                                 {product}
    uintx MaxDirectMemorySize                       = 0                                   {product}
     bool MaxFDLimit                                = true                                {product}
    uintx MaxGCMinorPauseMillis                     = 4294967295                          {product}
    uintx MaxGCPauseMillis                          = 4294967295                          {product}
    uintx MaxHeapFreeRatio                          = 70                                  {manageable}
    uintx MaxHeapSize                               = 130862280                           {product}
     intx MaxInlineLevel                            = 9                                   {product}
     intx MaxInlineSize                             = 35                                  {product}
     intx MaxJNILocalCapacity                       = 65536                               {product}
     intx MaxJavaStackTraceDepth                    = 1024                                {product}
     intx MaxJumpTableSize                          = 65000                               {C2 product}
     intx MaxJumpTableSparseness                    = 5                                   {C2 product}
     intx MaxLabelRootDepth                         = 1100                                {C2 product}
     intx MaxLoopPad                                = 15                                  {C2 product}
    uintx MaxMetaspaceExpansion                     = 5452592                             {product}
    uintx MaxMetaspaceFreeRatio                     = 70                                  {product}
    uintx MaxMetaspaceSize                          = 4294967295                          {product}
    uintx MaxNewSize                                = 4294967295                          {product}
     intx MaxNodeLimit                              = 80000                               {C2 product}
 uint64_t MaxRAM                                    = 0                                   {pd product}
    uintx MaxRAMFraction                            = 4                                   {product}
   double MaxRAMPercentage                          = 25.000000                           {product}
     intx MaxRecursiveInlineLevel                   = 1                                   {product}
    uintx MaxTenuringThreshold                      = 15                                  {product}
     intx MaxTrivialSize                            = 6                                   {product}
     intx MaxVectorSize                             = 32                                  {C2 product}
    uintx MetaspaceSize                             = 21810376                            {pd product}
     bool MethodFlushing                            = true                                {product}
    uintx MinHeapDeltaBytes                         = 170392                              {product}
    uintx MinHeapFreeRatio                          = 40                                  {manageable}
     intx MinInliningThreshold                      = 250                                 {product}
     intx MinJumpTableSize                          = 10                                  {C2 pd product}
    uintx MinMetaspaceExpansion                     = 340784                              {product}
    uintx MinMetaspaceFreeRatio                     = 40                                  {product}
    uintx MinRAMFraction                            = 2                                   {product}
   double MinRAMPercentage                          = 50.000000                           {product}
    uintx MinSurvivorRatio                          = 3                                   {product}
    uintx MinTLABSize                               = 2048                                {product}
     intx MonitorBound                              = 0                                   {product}
     bool MonitorInUseLists                         = false                               {product}
     intx MultiArrayExpandLimit                     = 6                                   {C2 product}
     bool MustCallLoadClassInternal                 = false                               {product}
    uintx NUMAChunkResizeWeight                     = 20                                  {product}
    uintx NUMAInterleaveGranularity                 = 2097152                             {product}
    uintx NUMAPageScanRate                          = 256                                 {product}
    uintx NUMASpaceResizeRate                       = 1073741824                          {product}
     bool NUMAStats                                 = false                               {product}
    ccstr NativeMemoryTracking                      = off                                 {product}
     bool NeedsDeoptSuspend                         = false                               {pd product}
     bool NeverActAsServerClassMachine              = false                               {pd product}
     bool NeverTenure                               = false                               {product}
    uintx NewRatio                                  = 2                                   {product}
    uintx NewSize                                   = 1363144                             {product}
    uintx NewSizeThreadIncrease                     = 5320                                {pd product}
     intx NmethodSweepActivity                      = 10                                  {product}
     intx NmethodSweepCheckInterval                 = 5                                   {product}
     intx NmethodSweepFraction                      = 16                                  {product}
     intx NodeLimitFudgeFactor                      = 2000                                {C2 product}
    uintx NumberOfGCLogFiles                        = 0                                   {product}
     intx NumberOfLoopInstrToAlign                  = 4                                   {C2 product}
     intx ObjectAlignmentInBytes                    = 8                                   {lp64_product}
    uintx OldPLABSize                               = 1024                                {product}
    uintx OldPLABWeight                             = 50                                  {product}
    uintx OldSize                                   = 5452592                             {product}
     bool OmitStackTraceInFastThrow                 = true                                {product}
ccstrlist OnError                                   =                                     {product}
ccstrlist OnOutOfMemoryError                        =                                     {product}
     intx OnStackReplacePercentage                  = 140                                 {pd product}
     bool OptimizeFill                              = true                                {C2 product}
     bool OptimizePtrCompare                        = true                                {C2 product}
     bool OptimizeStringConcat                      = true                                {C2 product}
     bool OptoBundling                              = false                               {C2 pd product}
     intx OptoLoopAlignment                         = 16                                  {pd product}
     bool OptoScheduling                            = false                               {C2 pd product}
    uintx PLABWeight                                = 75                                  {product}
     bool PSChunkLargeArrays                        = true                                {product}
     intx ParGCArrayScanChunk                       = 50                                  {product}
    uintx ParGCDesiredObjsFromOverflowList          = 20                                  {product}
     bool ParGCTrimOverflow                         = true                                {product}
     bool ParGCUseLocalOverflow                     = false                               {product}
    uintx ParallelGCBufferWastePct                  = 10                                  {product}
    uintx ParallelGCThreads                         = 0                                   {product}
     bool ParallelGCVerbose                         = false                               {product}
    uintx ParallelOldDeadWoodLimiterMean            = 50                                  {product}
    uintx ParallelOldDeadWoodLimiterStdDev          = 80                                  {product}
     bool ParallelRefProcBalancingEnabled           = true                                {product}
     bool ParallelRefProcEnabled                    = false                               {product}
     bool PartialPeelAtUnsignedTests                = true                                {C2 product}
     bool PartialPeelLoop                           = true                                {C2 product}
     intx PartialPeelNewPhiDelta                    = 0                                   {C2 product}
    uintx PausePadding                              = 1                                   {product}
     intx PerBytecodeRecompilationCutoff            = 200                                 {product}
     intx PerBytecodeTrapLimit                      = 4                                   {product}
     intx PerMethodRecompilationCutoff              = 400                                 {product}
     intx PerMethodTrapLimit                        = 100                                 {product}
     bool PerfAllowAtExitRegistration               = false                               {product}
     bool PerfBypassFileSystemCheck                 = false                               {product}
     intx PerfDataMemorySize                        = 32768                               {product}
     intx PerfDataSamplingInterval                  = 50                                  {product}
    ccstr PerfDataSaveFile                          =                                     {product}
     bool PerfDataSaveToFile                        = false                               {product}
     bool PerfDisableSharedMem                      = false                               {product}
     intx PerfMaxStringConstLength                  = 1024                                {product}
     intx PreInflateSpin                            = 10                                  {pd product}
     bool PreferInterpreterNativeStubs              = false                               {pd product}
     intx PrefetchCopyIntervalInBytes               = -1                                  {product}
     intx PrefetchFieldsAhead                       = -1                                  {product}
     intx PrefetchScanIntervalInBytes               = -1                                  {product}
     bool PreserveAllAnnotations                    = false                               {product}
     bool PreserveFramePointer                      = false                               {pd product}
    uintx PretenureSizeThreshold                    = 0                                   {product}
     bool PrintAdaptiveSizePolicy                   = false                               {product}
     bool PrintCMSInitiationStatistics              = false                               {product}
     intx PrintCMSStatistics                        = 0                                   {product}
     bool PrintClassHistogram                       = false                               {manageable}
     bool PrintClassHistogramAfterFullGC            = false                               {manageable}
     bool PrintClassHistogramBeforeFullGC           = false                               {manageable}
     bool PrintCodeCache                            = false                               {product}
     bool PrintCodeCacheOnCompilation               = false                               {product}
     bool PrintCommandLineFlags                     = false                               {product}
     bool PrintCompilation                          = false                               {product}
     bool PrintConcurrentLocks                      = false                               {manageable}
     intx PrintFLSCensus                            = 0                                   {product}
     intx PrintFLSStatistics                        = 0                                   {product}
     bool PrintFlagsFinal                           = false                               {product}
     bool PrintFlagsInitial                         = false                               {product}
     bool PrintGC                                   = false                               {manageable}
     bool PrintGCApplicationConcurrentTime          = false                               {product}
     bool PrintGCApplicationStoppedTime             = false                               {product}
     bool PrintGCCause                              = true                                {product}
     bool PrintGCDateStamps                         = false                               {manageable}
     bool PrintGCDetails                            = false                               {manageable}
     bool PrintGCID                                 = false                               {manageable}
     bool PrintGCTaskTimeStamps                     = false                               {product}
     bool PrintGCTimeStamps                         = false                               {manageable}
     bool PrintHeapAtGC                             = false                               {product rw}
     bool PrintHeapAtGCExtended                     = false                               {product rw}
     bool PrintHeapAtSIGBREAK                       = true                                {product}
     bool PrintJNIGCStalls                          = false                               {product}
     bool PrintJNIResolving                         = false                               {product}
     bool PrintOldPLAB                              = false                               {product}
     bool PrintOopAddress                           = false                               {product}
     bool PrintPLAB                                 = false                               {product}
     bool PrintParallelOldGCPhaseTimes              = false                               {product}
     bool PrintPromotionFailure                     = false                               {product}
     bool PrintReferenceGC                          = false                               {product}
     bool PrintSafepointStatistics                  = false                               {product}
     intx PrintSafepointStatisticsCount             = 300                                 {product}
     intx PrintSafepointStatisticsTimeout           = -1                                  {product}
     bool PrintSharedArchiveAndExit                 = false                               {product}
     bool PrintSharedDictionary                     = false                               {product}
     bool PrintSharedSpaces                         = false                               {product}
     bool PrintStringDeduplicationStatistics        = false                               {product}
     bool PrintStringTableStatistics                = false                               {product}
     bool PrintTLAB                                 = false                               {product}
     bool PrintTenuringDistribution                 = false                               {product}
     bool PrintTieredEvents                         = false                               {product}
     bool PrintVMOptions                            = false                               {product}
     bool PrintVMQWaitTime                          = false                               {product}
     bool PrintWarnings                             = true                                {product}
    uintx ProcessDistributionStride                 = 4                                   {product}
     bool ProfileInterpreter                        = true                                {pd product}
     bool ProfileIntervals                          = false                               {product}
     intx ProfileIntervalsTicks                     = 100                                 {product}
     intx ProfileMaturityPercentage                 = 20                                  {product}
     bool ProfileVM                                 = false                               {product}
     bool ProfilerPrintByteCodeStatistics           = false                               {product}
     bool ProfilerRecordPC                          = false                               {product}
    uintx PromotedPadding                           = 3                                   {product}
    uintx QueuedAllocationWarningCount              = 0                                   {product}
    uintx RTMRetryCount                             = 5                                   {ARCH product}
     bool RangeCheckElimination                     = true                                {product}
     intx ReadPrefetchInstr                         = 0                                   {ARCH product}
     bool ReassociateInvariants                     = true                                {C2 product}
     bool ReduceBulkZeroing                         = true                                {C2 product}
     bool ReduceFieldZeroing                        = true                                {C2 product}
     bool ReduceInitialCardMarks                    = true                                {C2 product}
     bool ReduceSignalUsage                         = false                               {product}
     intx RefDiscoveryPolicy                        = 0                                   {product}
     bool ReflectionWrapResolutionErrors            = true                                {product}
     bool RegisterFinalizersAtInit                  = true                                {product}
     bool RelaxAccessControlCheck                   = false                               {product}
    ccstr ReplayDataFile                            =                                     {product}
     bool RequireSharedSpaces                       = false                               {product}
    uintx ReservedCodeCacheSize                     = 50331648                            {pd product}
     bool ResizeOldPLAB                             = true                                {product}
     bool ResizePLAB                                = true                                {product}
     bool ResizeTLAB                                = true                                {pd product}
     bool RestoreMXCSROnJNICalls                    = false                               {product}
     bool RestrictContended                         = true                                {product}
     bool RewriteBytecodes                          = true                                {pd product}
     bool RewriteFrequentPairs                      = true                                {pd product}
     intx SafepointPollOffset                       = 256                                 {C1 pd product}
     intx SafepointSpinBeforeYield                  = 2000                                {product}
     bool SafepointTimeout                          = false                               {product}
     intx SafepointTimeoutDelay                     = 10000                               {product}
     bool ScavengeBeforeFullGC                      = true                                {product}
     intx SelfDestructTimer                         = 0                                   {product}
    uintx SharedBaseAddress                         = 0                                   {product}
    ccstr SharedClassListFile                       =                                     {product}
    uintx SharedMiscCodeSize                        = 122880                              {product}
    uintx SharedMiscDataSize                        = 4194304                             {product}
    uintx SharedReadOnlySize                        = 16777216                            {product}
    uintx SharedReadWriteSize                       = 16777216                            {product}
     bool ShowMessageBoxOnError                     = false                               {product}
     intx SoftRefLRUPolicyMSPerMB                   = 1000                                {product}
     bool SpecialEncodeISOArray                     = true                                {C2 product}
     bool SplitIfBlocks                             = true                                {C2 product}
     intx StackRedPages                             = 1                                   {pd product}
     intx StackShadowPages                          = 6                                   {pd product}
     bool StackTraceInThrowable                     = true                                {product}
     intx StackYellowPages                          = 3                                   {pd product}
     bool StartAttachListener                       = false                               {product}
     intx StarvationMonitorInterval                 = 200                                 {product}
     bool StressLdcRewrite                          = false                               {product}
    uintx StringDeduplicationAgeThreshold           = 3                                   {product}
    uintx StringTableSize                           = 60013                               {product}
     bool SuppressFatalErrorMessage                 = false                               {product}
    uintx SurvivorPadding                           = 3                                   {product}
    uintx SurvivorRatio                             = 8                                   {product}
     intx SuspendRetryCount                         = 50                                  {product}
     intx SuspendRetryDelay                         = 5                                   {product}
     intx SyncFlags                                 = 0                                   {product}
    ccstr SyncKnobs                                 =                                     {product}
     intx SyncVerbose                               = 0                                   {product}
    uintx TLABAllocationWeight                      = 35                                  {product}
    uintx TLABRefillWasteFraction                   = 64                                  {product}
    uintx TLABSize                                  = 0                                   {product}
     bool TLABStats                                 = true                                {product}
    uintx TLABWasteIncrement                        = 4                                   {product}
    uintx TLABWasteTargetPercent                    = 1                                   {product}
    uintx TargetPLABWastePct                        = 10                                  {product}
    uintx TargetSurvivorRatio                       = 50                                  {product}
    uintx TenuredGenerationSizeIncrement            = 20                                  {product}
    uintx TenuredGenerationSizeSupplement           = 80                                  {product}
    uintx TenuredGenerationSizeSupplementDecay      = 2                                   {product}
     intx ThreadPriorityPolicy                      = 0                                   {product}
     bool ThreadPriorityVerbose                     = false                               {product}
    uintx ThreadSafetyMargin                        = 52428800                            {product}
     intx ThreadStackSize                           = 0                                   {pd product}
    uintx ThresholdTolerance                        = 10                                  {product}
     intx Tier0BackedgeNotifyFreqLog                = 10                                  {product}
     intx Tier0InvokeNotifyFreqLog                  = 7                                   {product}
     intx Tier0ProfilingStartPercentage             = 200                                 {product}
     intx Tier23InlineeNotifyFreqLog                = 20                                  {product}
     intx Tier2BackEdgeThreshold                    = 0                                   {product}
     intx Tier2BackedgeNotifyFreqLog                = 14                                  {product}
     intx Tier2CompileThreshold                     = 0                                   {product}
     intx Tier2InvokeNotifyFreqLog                  = 11                                  {product}
     intx Tier3BackEdgeThreshold                    = 60000                               {product}
     intx Tier3BackedgeNotifyFreqLog                = 13                                  {product}
     intx Tier3CompileThreshold                     = 2000                                {product}
     intx Tier3DelayOff                             = 2                                   {product}
     intx Tier3DelayOn                              = 5                                   {product}
     intx Tier3InvocationThreshold                  = 200                                 {product}
     intx Tier3InvokeNotifyFreqLog                  = 10                                  {product}
     intx Tier3LoadFeedback                         = 5                                   {product}
     intx Tier3MinInvocationThreshold               = 100                                 {product}
     intx Tier4BackEdgeThreshold                    = 40000                               {product}
     intx Tier4CompileThreshold                     = 15000                               {product}
     intx Tier4InvocationThreshold                  = 5000                                {product}
     intx Tier4LoadFeedback                         = 3                                   {product}
     intx Tier4MinInvocationThreshold               = 600                                 {product}
     bool TieredCompilation                         = true                                {pd product}
     intx TieredCompileTaskTimeout                  = 50                                  {product}
     intx TieredRateUpdateMaxTime                   = 25                                  {product}
     intx TieredRateUpdateMinTime                   = 1                                   {product}
     intx TieredStopAtLevel                         = 4                                   {product}
     bool TimeLinearScan                            = false                               {C1 product}
     bool TraceBiasedLocking                        = false                               {product}
     bool TraceClassLoading                         = false                               {product rw}
     bool TraceClassLoadingPreorder                 = false                               {product}
     bool TraceClassPaths                           = false                               {product}
     bool TraceClassResolution                      = false                               {product}
     bool TraceClassUnloading                       = false                               {product rw}
     bool TraceDynamicGCThreads                     = false                               {product}
     bool TraceGen0Time                             = false                               {product}
     bool TraceGen1Time                             = false                               {product}
    ccstr TraceJVMTI                                =                                     {product}
     bool TraceLoaderConstraints                    = false                               {product rw}
     bool TraceMetadataHumongousAllocation          = false                               {product}
     bool TraceMonitorInflation                     = false                               {product}
     bool TraceParallelOldGCTasks                   = false                               {product}
     intx TraceRedefineClasses                      = 0                                   {product}
     bool TraceSafepointCleanupTime                 = false                               {product}
     bool TraceSharedLookupCache                    = false                               {product}
     bool TraceSuspendWaitFailures                  = false                               {product}
     intx TrackedInitializationLimit                = 50                                  {C2 product}
     bool TransmitErrorReport                       = false                               {product}
     bool TrapBasedNullChecks                       = false                               {pd product}
     bool TrapBasedRangeChecks                      = false                               {C2 pd product}
     intx TypeProfileArgsLimit                      = 2                                   {product}
    uintx TypeProfileLevel                          = 111                                 {pd product}
     intx TypeProfileMajorReceiverPercent           = 90                                  {C2 product}
     intx TypeProfileParmsLimit                     = 2                                   {product}
     intx TypeProfileWidth                          = 2                                   {product}
     intx UnguardOnExecutionViolation               = 0                                   {product}
     bool UnlinkSymbolsALot                         = false                               {product}
     bool Use486InstrsOnly                          = false                               {ARCH product}
     bool UseAES                                    = false                               {product}
     bool UseAESIntrinsics                          = false                               {product}
     intx UseAVX                                    = 99                                  {ARCH product}
     bool UseAdaptiveGCBoundary                     = false                               {product}
     bool UseAdaptiveGenerationSizePolicyAtMajorCollection  = true                                {product}
     bool UseAdaptiveGenerationSizePolicyAtMinorCollection  = true                                {product}
     bool UseAdaptiveNUMAChunkSizing                = true                                {product}
     bool UseAdaptiveSizeDecayMajorGCCost           = true                                {product}
     bool UseAdaptiveSizePolicy                     = true                                {product}
     bool UseAdaptiveSizePolicyFootprintGoal        = true                                {product}
     bool UseAdaptiveSizePolicyWithSystemGC         = false                               {product}
     bool UseAddressNop                             = false                               {ARCH product}
     bool UseAltSigs                                = false                               {product}
     bool UseAutoGCSelectPolicy                     = false                               {product}
     bool UseBMI1Instructions                       = false                               {ARCH product}
     bool UseBMI2Instructions                       = false                               {ARCH product}
     bool UseBiasedLocking                          = true                                {product}
     bool UseBimorphicInlining                      = true                                {C2 product}
     bool UseBoundThreads                           = true                                {product}
     bool UseCLMUL                                  = false                               {ARCH product}
     bool UseCMSBestFit                             = true                                {product}
     bool UseCMSCollectionPassing                   = true                                {product}
     bool UseCMSCompactAtFullCollection             = true                                {product}
     bool UseCMSInitiatingOccupancyOnly             = false                               {product}
     bool UseCRC32Intrinsics                        = false                               {product}
     bool UseCodeCacheFlushing                      = true                                {product}
     bool UseCompiler                               = true                                {product}
     bool UseCompilerSafepoints                     = true                                {product}
     bool UseCompressedClassPointers                = false                               {lp64_product}
     bool UseCompressedOops                         = false                               {lp64_product}
     bool UseConcMarkSweepGC                        = false                               {product}
     bool UseCondCardMark                           = false                               {C2 product}
     bool UseCountLeadingZerosInstruction           = false                               {ARCH product}
     bool UseCountTrailingZerosInstruction          = false                               {ARCH product}
     bool UseCountedLoopSafepoints                  = false                               {C2 product}
     bool UseCounterDecay                           = true                                {product}
     bool UseDivMod                                 = true                                {C2 product}
     bool UseDynamicNumberOfGCThreads               = false                               {product}
     bool UseFPUForSpilling                         = false                               {C2 product}
     bool UseFastAccessorMethods                    = true                                {product}
     bool UseFastEmptyMethods                       = true                                {product}
     bool UseFastJNIAccessors                       = true                                {product}
     bool UseFastStosb                              = false                               {ARCH product}
     bool UseG1GC                                   = false                               {product}
     bool UseGCLogFileRotation                      = false                               {product}
     bool UseGCOverheadLimit                        = true                                {product}
     bool UseGCTaskAffinity                         = false                               {product}
     bool UseGHASHIntrinsics                        = false                               {product}
     bool UseHeavyMonitors                          = false                               {product}
     bool UseInlineCaches                           = true                                {product}
     bool UseInterpreter                            = true                                {product}
     bool UseJumpTables                             = true                                {C2 product}
     bool UseLWPSynchronization                     = true                                {product}
     bool UseLargePages                             = false                               {pd product}
     bool UseLargePagesInMetaspace                  = false                               {product}
     bool UseLargePagesIndividualAllocation        := false                               {pd product}
     bool UseLockedTracing                          = false                               {product}
     bool UseLoopCounter                            = true                                {product}
     bool UseLoopInvariantCodeMotion                = true                                {C1 product}
     bool UseLoopPredicate                          = true                                {C2 product}
     bool UseMathExactIntrinsics                    = true                                {C2 product}
     bool UseMaximumCompactionOnSystemGC            = true                                {product}
     bool UseMembar                                 = false                               {pd product}
     bool UseMontgomeryMultiplyIntrinsic            = false                               {C2 product}
     bool UseMontgomerySquareIntrinsic              = false                               {C2 product}
     bool UseMulAddIntrinsic                        = false                               {C2 product}
     bool UseMultiplyToLenIntrinsic                 = false                               {C2 product}
     bool UseNUMA                                   = false                               {product}
     bool UseNUMAInterleaving                       = false                               {product}
     bool UseNewLongLShift                          = false                               {ARCH product}
     bool UseOSErrorReporting                       = false                               {pd product}
     bool UseOldInlining                            = true                                {C2 product}
     bool UseOnStackReplacement                     = true                                {pd product}
     bool UseOnlyInlinedBimorphic                   = true                                {C2 product}
     bool UseOptoBiasInlining                       = true                                {C2 product}
     bool UsePSAdaptiveSurvivorSizePolicy           = true                                {product}
     bool UseParNewGC                               = false                               {product}
     bool UseParallelGC                             = false                               {product}
     bool UseParallelOldGC                          = false                               {product}
     bool UsePerfData                               = true                                {product}
     bool UsePopCountInstruction                    = false                               {product}
     bool UseRDPCForConstantTableBase               = false                               {C2 product}
     bool UseRTMDeopt                               = false                               {ARCH product}
     bool UseRTMLocking                             = false                               {ARCH product}
     bool UseSHA                                    = false                               {product}
     bool UseSHA1Intrinsics                         = false                               {product}
     bool UseSHA256Intrinsics                       = false                               {product}
     bool UseSHA512Intrinsics                       = false                               {product}
     intx UseSSE                                    = 99                                  {product}
     bool UseSSE42Intrinsics                        = false                               {product}
     bool UseSerialGC                               = false                               {product}
     bool UseSharedSpaces                           = true                                {product}
     bool UseSignalChaining                         = true                                {product}
     bool UseSquareToLenIntrinsic                   = false                               {C2 product}
     bool UseStoreImmI16                            = true                                {ARCH product}
     bool UseStringDeduplication                    = false                               {product}
     bool UseSuperWord                              = true                                {C2 product}
     bool UseTLAB                                   = true                                {pd product}
     bool UseThreadPriorities                       = true                                {pd product}
     bool UseTypeProfile                            = true                                {product}
     bool UseTypeSpeculation                        = true                                {C2 product}
     bool UseUTCFileTimestamp                       = true                                {product}
     bool UseUnalignedLoadStores                    = false                               {ARCH product}
     bool UseVMInterruptibleIO                      = false                               {product}
     bool UseXMMForArrayCopy                        = false                               {product}
     bool UseXmmI2D                                 = false                               {ARCH product}
     bool UseXmmI2F                                 = false                               {ARCH product}
     bool UseXmmLoadAndClearUpper                   = true                                {ARCH product}
     bool UseXmmRegToRegMoveAll                     = false                               {ARCH product}
     bool VMThreadHintNoPreempt                     = false                               {product}
     intx VMThreadPriority                          = -1                                  {product}
     intx VMThreadStackSize                         = 0                                   {pd product}
     intx ValueMapInitialSize                       = 11                                  {C1 product}
     intx ValueMapMaxLoopSize                       = 8                                   {C1 product}
     intx ValueSearchLimit                          = 1000                                {C2 product}
     bool VerifyMergedCPBytecodes                   = true                                {product}
     bool VerifySharedSpaces                        = false                               {product}
     intx WorkAroundNPTLTimedWaitHang               = 1                                   {product}
    uintx YoungGenerationSizeIncrement              = 20                                  {product}
    uintx YoungGenerationSizeSupplement             = 80                                  {product}
    uintx YoungGenerationSizeSupplementDecay        = 8                                   {product}
    uintx YoungPLABSize                             = 4096                                {product}
     bool ZeroTLAB                                  = false                               {product}
     intx hashCode                                  = 5                                   {product}

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JVM改过以后的值

命令：java -XX:+PrintFlagsFinal

E:\workspace\study-guigu> java -XX:+PrintFlagsFinal -version
[Global flags]
     intx ActiveProcessorCount                      = -1                                  {product}
    uintx AdaptiveSizeDecrementScaleFactor          = 4                                   {product}
    uintx AdaptiveSizeMajorGCDecayTimeScale         = 10                                  {product}
    uintx AdaptiveSizePausePolicy                   = 0                                   {product}
    uintx AdaptiveSizePolicyCollectionCostMargin    = 50                                  {product}
    uintx AdaptiveSizePolicyInitializingSteps       = 20                                  {product}
    uintx AdaptiveSizePolicyOutputInterval          = 0                                   {product}
    uintx AdaptiveSizePolicyWeight                  = 10                                  {product}
    uintx AdaptiveSizeThroughPutPolicy              = 0                                   {product}
    uintx AdaptiveTimeWeight                        = 25                                  {product}
     bool AdjustConcurrency                         = false                               {product}
     bool AggressiveHeap                            = false                               {product}
     bool AggressiveOpts                            = false                               {product}
     intx AliasLevel                                = 3                                   {C2 product}
     bool AlignVector                               = false                               {C2 product}
     intx AllocateInstancePrefetchLines             = 1                                   {product}
     intx AllocatePrefetchDistance                  = 192                                 {product}
     intx AllocatePrefetchInstr                     = 3                                   {product}
     intx AllocatePrefetchLines                     = 4                                   {product}
     intx AllocatePrefetchStepSize                  = 64                                  {product}
     intx AllocatePrefetchStyle                     = 1                                   {product}
     bool AllowJNIEnvProxy                          = false                               {product}
     bool AllowNonVirtualCalls                      = false                               {product}
     bool AllowParallelDefineClass                  = false                               {product}
     bool AllowUserSignalHandlers                   = false                               {product}
     bool AlwaysActAsServerClassMachine             = false                               {product}
     bool AlwaysCompileLoopMethods                  = false                               {product}
     bool AlwaysLockClassLoader                     = false                               {product}
     bool AlwaysPreTouch                            = false                               {product}
     bool AlwaysRestoreFPU                          = false                               {product}
     bool AlwaysTenure                              = false                               {product}
     bool AssertOnSuspendWaitFailure                = false                               {product}
     bool AssumeMP                                  = false                               {product}
     intx AutoBoxCacheMax                           = 128                                 {C2 product}
    uintx AutoGCSelectPauseMillis                   = 5000                                {product}
     intx BCEATraceLevel                            = 0                                   {product}
     intx BackEdgeThreshold                         = 100000                              {pd product}
     bool BackgroundCompilation                     = true                                {pd product}
    uintx BaseFootPrintEstimate                     = 268435456                           {product}
     intx BiasedLockingBulkRebiasThreshold          = 20                                  {product}
     intx BiasedLockingBulkRevokeThreshold          = 40                                  {product}
     intx BiasedLockingDecayTime                    = 25000                               {product}
     intx BiasedLockingStartupDelay                 = 4000                                {product}
     bool BindGCTaskThreadsToCPUs                   = false                               {product}
     bool BlockLayoutByFrequency                    = true                                {C2 product}
     intx BlockLayoutMinDiamondPercentage           = 20                                  {C2 product}
     bool BlockLayoutRotateLoops                    = true                                {C2 product}
     bool BranchOnRegister                          = false                               {C2 product}
     bool BytecodeVerificationLocal                 = false                               {product}
     bool BytecodeVerificationRemote                = true                                {product}
     bool C1OptimizeVirtualCallProfiling            = true                                {C1 product}
     bool C1ProfileBranches                         = true                                {C1 product}
     bool C1ProfileCalls                            = true                                {C1 product}
     bool C1ProfileCheckcasts                       = true                                {C1 product}
     bool C1ProfileInlinedCalls                     = true                                {C1 product}
     bool C1ProfileVirtualCalls                     = true                                {C1 product}
     bool C1UpdateMethodData                        = true                                {C1 product}
     intx CICompilerCount                          := 3                                   {product}
     bool CICompilerCountPerCPU                     = true                                {product}
     bool CITime                                    = false                               {product}
     bool CMSAbortSemantics                         = false                               {product}
    uintx CMSAbortablePrecleanMinWorkPerIteration   = 100                                 {product}
     intx CMSAbortablePrecleanWaitMillis            = 100                                 {manageable}
    uintx CMSBitMapYieldQuantum                     = 10485760                            {product}
    uintx CMSBootstrapOccupancy                     = 50                                  {product}
     bool CMSClassUnloadingEnabled                  = true                                {product}
    uintx CMSClassUnloadingMaxInterval              = 0                                   {product}
     bool CMSCleanOnEnter                           = true                                {product}
     bool CMSCompactWhenClearAllSoftRefs            = true                                {product}
    uintx CMSConcMarkMultiple                       = 32                                  {product}
     bool CMSConcurrentMTEnabled                    = true                                {product}
    uintx CMSCoordinatorYieldSleepCount             = 10                                  {product}
     bool CMSDumpAtPromotionFailure                 = false                               {product}
     bool CMSEdenChunksRecordAlways                 = true                                {product}
    uintx CMSExpAvgFactor                           = 50                                  {product}
     bool CMSExtrapolateSweep                       = false                               {product}
    uintx CMSFullGCsBeforeCompaction                = 0                                   {product}
    uintx CMSIncrementalDutyCycle                   = 10                                  {product}
    uintx CMSIncrementalDutyCycleMin                = 0                                   {product}
     bool CMSIncrementalMode                        = false                               {product}
    uintx CMSIncrementalOffset                      = 0                                   {product}
     bool CMSIncrementalPacing                      = true                                {product}
    uintx CMSIncrementalSafetyFactor                = 10                                  {product}
    uintx CMSIndexedFreeListReplenish               = 4                                   {product}
     intx CMSInitiatingOccupancyFraction            = -1                                  {product}
    uintx CMSIsTooFullPercentage                    = 98                                  {product}
   double CMSLargeCoalSurplusPercent                = 0.950000                            {product}
   double CMSLargeSplitSurplusPercent               = 1.000000                            {product}
     bool CMSLoopWarn                               = false                               {product}
    uintx CMSMaxAbortablePrecleanLoops              = 0                                   {product}
     intx CMSMaxAbortablePrecleanTime               = 5000                                {product}
    uintx CMSOldPLABMax                             = 1024                                {product}
    uintx CMSOldPLABMin                             = 16                                  {product}
    uintx CMSOldPLABNumRefills                      = 4                                   {product}
    uintx CMSOldPLABReactivityFactor                = 2                                   {product}
     bool CMSOldPLABResizeQuicker                   = false                               {product}
    uintx CMSOldPLABToleranceFactor                 = 4                                   {product}
     bool CMSPLABRecordAlways                       = true                                {product}
    uintx CMSParPromoteBlocksToClaim                = 16                                  {product}
     bool CMSParallelInitialMarkEnabled             = true                                {product}
     bool CMSParallelRemarkEnabled                  = true                                {product}
     bool CMSParallelSurvivorRemarkEnabled          = true                                {product}
    uintx CMSPrecleanDenominator                    = 3                                   {product}
    uintx CMSPrecleanIter                           = 3                                   {product}
    uintx CMSPrecleanNumerator                      = 2                                   {product}
     bool CMSPrecleanRefLists1                      = true                                {product}
     bool CMSPrecleanRefLists2                      = false                               {product}
     bool CMSPrecleanSurvivors1                     = false                               {product}
     bool CMSPrecleanSurvivors2                     = true                                {product}
    uintx CMSPrecleanThreshold                      = 1000                                {product}
     bool CMSPrecleaningEnabled                     = true                                {product}
     bool CMSPrintChunksInDump                      = false                               {product}
     bool CMSPrintEdenSurvivorChunks                = false                               {product}
     bool CMSPrintObjectsInDump                     = false                               {product}
    uintx CMSRemarkVerifyVariant                    = 1                                   {product}
     bool CMSReplenishIntermediate                  = true                                {product}
    uintx CMSRescanMultiple                         = 32                                  {product}
    uintx CMSSamplingGrain                          = 16384                               {product}
     bool CMSScavengeBeforeRemark                   = false                               {product}
    uintx CMSScheduleRemarkEdenPenetration          = 50                                  {product}
    uintx CMSScheduleRemarkEdenSizeThreshold        = 2097152                             {product}
    uintx CMSScheduleRemarkSamplingRatio            = 5                                   {product}
   double CMSSmallCoalSurplusPercent                = 1.050000                            {product}
   double CMSSmallSplitSurplusPercent               = 1.100000                            {product}
     bool CMSSplitIndexedFreeListBlocks             = true                                {product}
     intx CMSTriggerInterval                        = -1                                  {manageable}
    uintx CMSTriggerRatio                           = 80                                  {product}
     intx CMSWaitDuration                           = 2000                                {manageable}
    uintx CMSWorkQueueDrainThreshold                = 10                                  {product}
     bool CMSYield                                  = true                                {product}
    uintx CMSYieldSleepCount                        = 0                                   {product}
    uintx CMSYoungGenPerWorker                      = 67108864                            {pd product}
    uintx CMS_FLSPadding                            = 1                                   {product}
    uintx CMS_FLSWeight                             = 75                                  {product}
    uintx CMS_SweepPadding                          = 1                                   {product}
    uintx CMS_SweepTimerThresholdMillis             = 10                                  {product}
    uintx CMS_SweepWeight                           = 75                                  {product}
     bool CheckEndorsedAndExtDirs                   = false                               {product}
     bool CheckJNICalls                             = false                               {product}
     bool ClassUnloading                            = true                                {product}
     bool ClassUnloadingWithConcurrentMark          = true                                {product}
     intx ClearFPUAtPark                            = 0                                   {product}
     bool ClipInlining                              = true                                {product}
    uintx CodeCacheExpansionSize                    = 65536                               {pd product}
    uintx CodeCacheMinimumFreeSpace                 = 512000                              {product}
     bool CollectGen0First                          = false                               {product}
     bool CompactFields                             = true                                {product}
     intx CompilationPolicyChoice                   = 3                                   {product}
ccstrlist CompileCommand                            =                                     {product}
    ccstr CompileCommandFile                        =                                     {product}
ccstrlist CompileOnly                               =                                     {product}
     intx CompileThreshold                          = 10000                               {pd product}
     bool CompilerThreadHintNoPreempt               = true                                {product}
     intx CompilerThreadPriority                    = -1                                  {product}
     intx CompilerThreadStackSize                   = 0                                   {pd product}
    uintx CompressedClassSpaceSize                  = 1073741824                          {product}
    uintx ConcGCThreads                             = 0                                   {product}
     intx ConditionalMoveLimit                      = 3                                   {C2 pd product}
     intx ContendedPaddingWidth                     = 128                                 {product}
     bool ConvertSleepToYield                       = true                                {pd product}
     bool ConvertYieldToSleep                       = false                               {product}
     bool CrashOnOutOfMemoryError                   = false                               {product}
     bool CreateMinidumpOnCrash                     = false                               {product}
     bool CriticalJNINatives                        = true                                {product}
     bool DTraceAllocProbes                         = false                               {product}
     bool DTraceMethodProbes                        = false                               {product}
     bool DTraceMonitorProbes                       = false                               {product}
     bool Debugging                                 = false                               {product}
    uintx DefaultMaxRAMFraction                     = 4                                   {product}
     intx DefaultThreadPriority                     = -1                                  {product}
     intx DeferPollingPageLoopCount                 = -1                                  {product}
     intx DeferThrSuspendLoopCount                  = 4000                                {product}
     bool DeoptimizeRandom                          = false                               {product}
     bool DisableAttachMechanism                    = false                               {product}
     bool DisableExplicitGC                         = false                               {product}
     bool DisplayVMOutputToStderr                   = false                               {product}
     bool DisplayVMOutputToStdout                   = false                               {product}
     bool DoEscapeAnalysis                          = true                                {C2 product}
     bool DontCompileHugeMethods                    = true                                {product}
     bool DontYieldALot                             = false                               {pd product}
    ccstr DumpLoadedClassList                       =                                     {product}
     bool DumpReplayDataOnError                     = true                                {product}
     bool DumpSharedSpaces                          = false                               {product}
     bool EagerXrunInit                             = false                               {product}
     intx EliminateAllocationArraySizeLimit         = 64                                  {C2 product}
     bool EliminateAllocations                      = true                                {C2 product}
     bool EliminateAutoBox                          = true                                {C2 product}
     bool EliminateLocks                            = true                                {C2 product}
     bool EliminateNestedLocks                      = true                                {C2 product}
     intx EmitSync                                  = 0                                   {product}
     bool EnableContended                           = true                                {product}
     bool EnableResourceManagementTLABCache         = true                                {product}
     bool EnableSharedLookupCache                   = true                                {product}
     bool EnableTracing                             = false                               {product}
    uintx ErgoHeapSizeLimit                         = 0                                   {product}
    ccstr ErrorFile                                 =                                     {product}
    ccstr ErrorReportServer                         =                                     {product}
   double EscapeAnalysisTimeout                     = 20.000000                           {C2 product}
     bool EstimateArgEscape                         = true                                {product}
     bool ExitOnOutOfMemoryError                    = false                               {product}
     bool ExplicitGCInvokesConcurrent               = false                               {product}
     bool ExplicitGCInvokesConcurrentAndUnloadsClasses  = false                               {product}
     bool ExtendedDTraceProbes                      = false                               {product}
    ccstr ExtraSharedClassListFile                  =                                     {product}
     bool FLSAlwaysCoalesceLarge                    = false                               {product}
    uintx FLSCoalescePolicy                         = 2                                   {product}
   double FLSLargestBlockCoalesceProximity          = 0.990000                            {product}
     bool FailOverToOldVerifier                     = true                                {product}
     bool FastTLABRefill                            = true                                {product}
     intx FenceInstruction                          = 0                                   {ARCH product}
     intx FieldsAllocationStyle                     = 1                                   {product}
     bool FilterSpuriousWakeups                     = true                                {product}
    ccstr FlightRecorderOptions                     =                                     {product}
     bool ForceNUMA                                 = false                               {product}
     bool ForceTimeHighResolution                   = false                               {product}
     intx FreqInlineSize                            = 325                                 {pd product}
   double G1ConcMarkStepDurationMillis              = 10.000000                           {product}
    uintx G1ConcRSHotCardLimit                      = 4                                   {product}
    uintx G1ConcRSLogCacheSize                      = 10                                  {product}
     intx G1ConcRefinementGreenZone                 = 0                                   {product}
     intx G1ConcRefinementRedZone                   = 0                                   {product}
     intx G1ConcRefinementServiceIntervalMillis     = 300                                 {product}
    uintx G1ConcRefinementThreads                   = 0                                   {product}
     intx G1ConcRefinementThresholdStep             = 0                                   {product}
     intx G1ConcRefinementYellowZone                = 0                                   {product}
    uintx G1ConfidencePercent                       = 50                                  {product}
    uintx G1HeapRegionSize                          = 0                                   {product}
    uintx G1HeapWastePercent                        = 5                                   {product}
    uintx G1MixedGCCountTarget                      = 8                                   {product}
     intx G1RSetRegionEntries                       = 0                                   {product}
    uintx G1RSetScanBlockSize                       = 64                                  {product}
     intx G1RSetSparseRegionEntries                 = 0                                   {product}
     intx G1RSetUpdatingPauseTimePercent            = 10                                  {product}
     intx G1RefProcDrainInterval                    = 10                                  {product}
    uintx G1ReservePercent                          = 10                                  {product}
    uintx G1SATBBufferEnqueueingThresholdPercent    = 60                                  {product}
     intx G1SATBBufferSize                          = 1024                                {product}
     intx G1UpdateBufferSize                        = 256                                 {product}
     bool G1UseAdaptiveConcRefinement               = true                                {product}
    uintx GCDrainStackTargetSize                    = 64                                  {product}
    uintx GCHeapFreeLimit                           = 2                                   {product}
    uintx GCLockerEdenExpansionPercent              = 5                                   {product}
     bool GCLockerInvokesConcurrent                 = false                               {product}
    uintx GCLogFileSize                             = 8192                                {product}
    uintx GCPauseIntervalMillis                     = 0                                   {product}
    uintx GCTaskTimeStampEntries                    = 200                                 {product}
    uintx GCTimeLimit                               = 98                                  {product}
    uintx GCTimeRatio                               = 99                                  {product}
    uintx HeapBaseMinAddress                        = 2147483648                          {pd product}
     bool HeapDumpAfterFullGC                       = false                               {manageable}
     bool HeapDumpBeforeFullGC                      = false                               {manageable}
     bool HeapDumpOnOutOfMemoryError                = false                               {manageable}
    ccstr HeapDumpPath                              =                                     {manageable}
    uintx HeapFirstMaximumCompactionCount           = 3                                   {product}
    uintx HeapMaximumCompactionInterval             = 20                                  {product}
    uintx HeapSizePerGCThread                       = 87241520                            {product}
     bool IgnoreEmptyClassPaths                     = false                               {product}
     bool IgnoreUnrecognizedVMOptions               = false                               {product}
    uintx IncreaseFirstTierCompileThresholdAt       = 50                                  {product}
     bool IncrementalInline                         = true                                {C2 product}
    uintx InitialBootClassLoaderMetaspaceSize       = 4194304                             {product}
    uintx InitialCodeCacheSize                      = 2555904                             {pd product}
    uintx InitialHeapSize                          := 134217728                           {product}
    uintx InitialRAMFraction                        = 64                                  {product}
   double InitialRAMPercentage                      = 1.562500                            {product}
    uintx InitialSurvivorRatio                      = 8                                   {product}
    uintx InitialTenuringThreshold                  = 7                                   {product}
    uintx InitiatingHeapOccupancyPercent            = 45                                  {product}
     bool Inline                                    = true                                {product}
    ccstr InlineDataFile                            =                                     {product}
     intx InlineSmallCode                           = 2000                                {pd product}
     bool InlineSynchronizedMethods                 = true                                {C1 product}
     bool InsertMemBarAfterArraycopy                = true                                {C2 product}
     intx InteriorEntryAlignment                    = 16                                  {C2 pd product}
     intx InterpreterProfilePercentage              = 33                                  {product}
     bool JNIDetachReleasesMonitors                 = true                                {product}
     bool JavaMonitorsInStackTrace                  = true                                {product}
     intx JavaPriority10_To_OSPriority              = -1                                  {product}
     intx JavaPriority1_To_OSPriority               = -1                                  {product}
     intx JavaPriority2_To_OSPriority               = -1                                  {product}
     intx JavaPriority3_To_OSPriority               = -1                                  {product}
     intx JavaPriority4_To_OSPriority               = -1                                  {product}
     intx JavaPriority5_To_OSPriority               = -1                                  {product}
     intx JavaPriority6_To_OSPriority               = -1                                  {product}
     intx JavaPriority7_To_OSPriority               = -1                                  {product}
     intx JavaPriority8_To_OSPriority               = -1                                  {product}
     intx JavaPriority9_To_OSPriority               = -1                                  {product}
     bool LIRFillDelaySlots                         = false                               {C1 pd product}
    uintx LargePageHeapSizeThreshold                = 134217728                           {product}
    uintx LargePageSizeInBytes                      = 0                                   {product}
     bool LazyBootClassLoader                       = true                                {product}
     intx LiveNodeCountInliningCutoff               = 40000                               {C2 product}
     bool LogCommercialFeatures                     = false                               {product}
     intx LoopMaxUnroll                             = 16                                  {C2 product}
     intx LoopOptsCount                             = 43                                  {C2 product}
     intx LoopUnrollLimit                           = 60                                  {C2 pd product}
     intx LoopUnrollMin                             = 4                                   {C2 product}
     bool LoopUnswitching                           = true                                {C2 product}
     bool ManagementServer                          = false                               {product}
    uintx MarkStackSize                             = 4194304                             {product}
    uintx MarkStackSizeMax                          = 536870912                           {product}
    uintx MarkSweepAlwaysCompactCount               = 4                                   {product}
    uintx MarkSweepDeadRatio                        = 1                                   {product}
     intx MaxBCEAEstimateLevel                      = 5                                   {product}
     intx MaxBCEAEstimateSize                       = 150                                 {product}
    uintx MaxDirectMemorySize                       = 0                                   {product}
     bool MaxFDLimit                                = true                                {product}
    uintx MaxGCMinorPauseMillis                     = 4294967295                          {product}
    uintx MaxGCPauseMillis                          = 4294967295                          {product}
    uintx MaxHeapFreeRatio                          = 100                                 {manageable}
    uintx MaxHeapSize                              := 2126512128                          {product}
     intx MaxInlineLevel                            = 9                                   {product}
     intx MaxInlineSize                             = 35                                  {product}
     intx MaxJNILocalCapacity                       = 65536                               {product}
     intx MaxJavaStackTraceDepth                    = 1024                                {product}
     intx MaxJumpTableSize                          = 65000                               {C2 product}
     intx MaxJumpTableSparseness                    = 5                                   {C2 product}
     intx MaxLabelRootDepth                         = 1100                                {C2 product}
     intx MaxLoopPad                                = 11                                  {C2 product}
    uintx MaxMetaspaceExpansion                     = 5451776                             {product}
    uintx MaxMetaspaceFreeRatio                     = 70                                  {product}
    uintx MaxMetaspaceSize                          = 4294901760                          {product}
    uintx MaxNewSize                               := 708837376                           {product}
     intx MaxNodeLimit                              = 75000                               {C2 product}
 uint64_t MaxRAM                                    = 0                                   {pd product}
    uintx MaxRAMFraction                            = 4                                   {product}
   double MaxRAMPercentage                          = 25.000000                           {product}
     intx MaxRecursiveInlineLevel                   = 1                                   {product}
    uintx MaxTenuringThreshold                      = 15                                  {product}
     intx MaxTrivialSize                            = 6                                   {product}
     intx MaxVectorSize                             = 32                                  {C2 product}
    uintx MetaspaceSize                             = 21807104                            {pd product}
     bool MethodFlushing                            = true                                {product}
    uintx MinHeapDeltaBytes                        := 524288                              {product}
    uintx MinHeapFreeRatio                          = 0                                   {manageable}
     intx MinInliningThreshold                      = 250                                 {product}
     intx MinJumpTableSize                          = 10                                  {C2 pd product}
    uintx MinMetaspaceExpansion                     = 339968                              {product}
    uintx MinMetaspaceFreeRatio                     = 40                                  {product}
    uintx MinRAMFraction                            = 2                                   {product}
   double MinRAMPercentage                          = 50.000000                           {product}
    uintx MinSurvivorRatio                          = 3                                   {product}
    uintx MinTLABSize                               = 2048                                {product}
     intx MonitorBound                              = 0                                   {product}
     bool MonitorInUseLists                         = false                               {product}
     intx MultiArrayExpandLimit                     = 6                                   {C2 product}
     bool MustCallLoadClassInternal                 = false                               {product}
    uintx NUMAChunkResizeWeight                     = 20                                  {product}
    uintx NUMAInterleaveGranularity                 = 2097152                             {product}
    uintx NUMAPageScanRate                          = 256                                 {product}
    uintx NUMASpaceResizeRate                       = 1073741824                          {product}
     bool NUMAStats                                 = false                               {product}
    ccstr NativeMemoryTracking                      = off                                 {product}
     bool NeedsDeoptSuspend                         = false                               {pd product}
     bool NeverActAsServerClassMachine              = false                               {pd product}
     bool NeverTenure                               = false                               {product}
    uintx NewRatio                                  = 2                                   {product}
    uintx NewSize                                  := 44564480                            {product}
    uintx NewSizeThreadIncrease                     = 5320                                {pd product}
     intx NmethodSweepActivity                      = 10                                  {product}
     intx NmethodSweepCheckInterval                 = 5                                   {product}
     intx NmethodSweepFraction                      = 16                                  {product}
     intx NodeLimitFudgeFactor                      = 2000                                {C2 product}
    uintx NumberOfGCLogFiles                        = 0                                   {product}
     intx NumberOfLoopInstrToAlign                  = 4                                   {C2 product}
     intx ObjectAlignmentInBytes                    = 8                                   {lp64_product}
    uintx OldPLABSize                               = 1024                                {product}
    uintx OldPLABWeight                             = 50                                  {product}
    uintx OldSize                                  := 89653248                            {product}
     bool OmitStackTraceInFastThrow                 = true                                {product}
ccstrlist OnError                                   =                                     {product}
ccstrlist OnOutOfMemoryError                        =                                     {product}
     intx OnStackReplacePercentage                  = 140                                 {pd product}
     bool OptimizeFill                              = true                                {C2 product}
     bool OptimizePtrCompare                        = true                                {C2 product}
     bool OptimizeStringConcat                      = true                                {C2 product}
     bool OptoBundling                              = false                               {C2 pd product}
     intx OptoLoopAlignment                         = 16                                  {pd product}
     bool OptoScheduling                            = false                               {C2 pd product}
    uintx PLABWeight                                = 75                                  {product}
     bool PSChunkLargeArrays                        = true                                {product}
     intx ParGCArrayScanChunk                       = 50                                  {product}
    uintx ParGCDesiredObjsFromOverflowList          = 20                                  {product}
     bool ParGCTrimOverflow                         = true                                {product}
     bool ParGCUseLocalOverflow                     = false                               {product}
    uintx ParallelGCBufferWastePct                  = 10                                  {product}
    uintx ParallelGCThreads                         = 4                                   {product}
     bool ParallelGCVerbose                         = false                               {product}
    uintx ParallelOldDeadWoodLimiterMean            = 50                                  {product}
    uintx ParallelOldDeadWoodLimiterStdDev          = 80                                  {product}
     bool ParallelRefProcBalancingEnabled           = true                                {product}
     bool ParallelRefProcEnabled                    = false                               {product}
     bool PartialPeelAtUnsignedTests                = true                                {C2 product}
     bool PartialPeelLoop                           = true                                {C2 product}
     intx PartialPeelNewPhiDelta                    = 0                                   {C2 product}
    uintx PausePadding                              = 1                                   {product}
     intx PerBytecodeRecompilationCutoff            = 200                                 {product}
     intx PerBytecodeTrapLimit                      = 4                                   {product}
     intx PerMethodRecompilationCutoff              = 400                                 {product}
     intx PerMethodTrapLimit                        = 100                                 {product}
     bool PerfAllowAtExitRegistration               = false                               {product}
     bool PerfBypassFileSystemCheck                 = false                               {product}
     intx PerfDataMemorySize                        = 32768                               {product}
     intx PerfDataSamplingInterval                  = 50                                  {product}
    ccstr PerfDataSaveFile                          =                                     {product}
     bool PerfDataSaveToFile                        = false                               {product}
     bool PerfDisableSharedMem                      = false                               {product}
     intx PerfMaxStringConstLength                  = 1024                                {product}
     intx PreInflateSpin                            = 10                                  {pd product}
     bool PreferInterpreterNativeStubs              = false                               {pd product}
     intx PrefetchCopyIntervalInBytes               = 576                                 {product}
     intx PrefetchFieldsAhead                       = 1                                   {product}
     intx PrefetchScanIntervalInBytes               = 576                                 {product}
     bool PreserveAllAnnotations                    = false                               {product}
     bool PreserveFramePointer                      = false                               {pd product}
    uintx PretenureSizeThreshold                    = 0                                   {product}
     bool PrintAdaptiveSizePolicy                   = false                               {product}
     bool PrintCMSInitiationStatistics              = false                               {product}
     intx PrintCMSStatistics                        = 0                                   {product}
     bool PrintClassHistogram                       = false                               {manageable}
     bool PrintClassHistogramAfterFullGC            = false                               {manageable}
     bool PrintClassHistogramBeforeFullGC           = false                               {manageable}
     bool PrintCodeCache                            = false                               {product}
     bool PrintCodeCacheOnCompilation               = false                               {product}
     bool PrintCommandLineFlags                     = false                               {product}
     bool PrintCompilation                          = false                               {product}
     bool PrintConcurrentLocks                      = false                               {manageable}
     intx PrintFLSCensus                            = 0                                   {product}
     intx PrintFLSStatistics                        = 0                                   {product}
     bool PrintFlagsFinal                          := true                                {product}
     bool PrintFlagsInitial                         = false                               {product}
     bool PrintGC                                   = false                               {manageable}
     bool PrintGCApplicationConcurrentTime          = false                               {product}
     bool PrintGCApplicationStoppedTime             = false                               {product}
     bool PrintGCCause                              = true                                {product}
     bool PrintGCDateStamps                         = false                               {manageable}
     bool PrintGCDetails                            = false                               {manageable}
     bool PrintGCID                                 = false                               {manageable}
     bool PrintGCTaskTimeStamps                     = false                               {product}
     bool PrintGCTimeStamps                         = false                               {manageable}
     bool PrintHeapAtGC                             = false                               {product rw}
     bool PrintHeapAtGCExtended                     = false                               {product rw}
     bool PrintHeapAtSIGBREAK                       = true                                {product}
     bool PrintJNIGCStalls                          = false                               {product}
     bool PrintJNIResolving                         = false                               {product}
     bool PrintOldPLAB                              = false                               {product}
     bool PrintOopAddress                           = false                               {product}
     bool PrintPLAB                                 = false                               {product}
     bool PrintParallelOldGCPhaseTimes              = false                               {product}
     bool PrintPromotionFailure                     = false                               {product}
     bool PrintReferenceGC                          = false                               {product}
     bool PrintSafepointStatistics                  = false                               {product}
     intx PrintSafepointStatisticsCount             = 300                                 {product}
     intx PrintSafepointStatisticsTimeout           = -1                                  {product}
     bool PrintSharedArchiveAndExit                 = false                               {product}
     bool PrintSharedDictionary                     = false                               {product}
     bool PrintSharedSpaces                         = false                               {product}
     bool PrintStringDeduplicationStatistics        = false                               {product}
     bool PrintStringTableStatistics                = false                               {product}
     bool PrintTLAB                                 = false                               {product}
     bool PrintTenuringDistribution                 = false                               {product}
     bool PrintTieredEvents                         = false                               {product}
     bool PrintVMOptions                            = false                               {product}
     bool PrintVMQWaitTime                          = false                               {product}
     bool PrintWarnings                             = true                                {product}
    uintx ProcessDistributionStride                 = 4                                   {product}
     bool ProfileInterpreter                        = true                                {pd product}
     bool ProfileIntervals                          = false                               {product}
     intx ProfileIntervalsTicks                     = 100                                 {product}
     intx ProfileMaturityPercentage                 = 20                                  {product}
     bool ProfileVM                                 = false                               {product}
     bool ProfilerPrintByteCodeStatistics           = false                               {product}
     bool ProfilerRecordPC                          = false                               {product}
    uintx PromotedPadding                           = 3                                   {product}
    uintx QueuedAllocationWarningCount              = 0                                   {product}
    uintx RTMRetryCount                             = 5                                   {ARCH product}
     bool RangeCheckElimination                     = true                                {product}
     intx ReadPrefetchInstr                         = 0                                   {ARCH product}
     bool ReassociateInvariants                     = true                                {C2 product}
     bool ReduceBulkZeroing                         = true                                {C2 product}
     bool ReduceFieldZeroing                        = true                                {C2 product}
     bool ReduceInitialCardMarks                    = true                                {C2 product}
     bool ReduceSignalUsage                         = false                               {product}
     intx RefDiscoveryPolicy                        = 0                                   {product}
     bool ReflectionWrapResolutionErrors            = true                                {product}
     bool RegisterFinalizersAtInit                  = true                                {product}
     bool RelaxAccessControlCheck                   = false                               {product}
    ccstr ReplayDataFile                            =                                     {product}
     bool RequireSharedSpaces                       = false                               {product}
    uintx ReservedCodeCacheSize                     = 251658240                           {pd product}
     bool ResizeOldPLAB                             = true                                {product}
     bool ResizePLAB                                = true                                {product}
     bool ResizeTLAB                                = true                                {pd product}
     bool RestoreMXCSROnJNICalls                    = false                               {product}
     bool RestrictContended                         = true                                {product}
     bool RewriteBytecodes                          = true                                {pd product}
     bool RewriteFrequentPairs                      = true                                {pd product}
     intx SafepointPollOffset                       = 256                                 {C1 pd product}
     intx SafepointSpinBeforeYield                  = 2000                                {product}
     bool SafepointTimeout                          = false                               {product}
     intx SafepointTimeoutDelay                     = 10000                               {product}
     bool ScavengeBeforeFullGC                      = true                                {product}
     intx SelfDestructTimer                         = 0                                   {product}
    uintx SharedBaseAddress                         = 0                                   {product}
    ccstr SharedClassListFile                       =                                     {product}
    uintx SharedMiscCodeSize                        = 122880                              {product}
    uintx SharedMiscDataSize                        = 4194304                             {product}
    uintx SharedReadOnlySize                        = 16777216                            {product}
    uintx SharedReadWriteSize                       = 16777216                            {product}
     bool ShowMessageBoxOnError                     = false                               {product}
     intx SoftRefLRUPolicyMSPerMB                   = 1000                                {product}
     bool SpecialEncodeISOArray                     = true                                {C2 product}
     bool SplitIfBlocks                             = true                                {C2 product}
     intx StackRedPages                             = 1                                   {pd product}
     intx StackShadowPages                          = 6                                   {pd product}
     bool StackTraceInThrowable                     = true                                {product}
     intx StackYellowPages                          = 3                                   {pd product}
     bool StartAttachListener                       = false                               {product}
     intx StarvationMonitorInterval                 = 200                                 {product}
     bool StressLdcRewrite                          = false                               {product}
    uintx StringDeduplicationAgeThreshold           = 3                                   {product}
    uintx StringTableSize                           = 60013                               {product}
     bool SuppressFatalErrorMessage                 = false                               {product}
    uintx SurvivorPadding                           = 3                                   {product}
    uintx SurvivorRatio                             = 8                                   {product}
     intx SuspendRetryCount                         = 50                                  {product}
     intx SuspendRetryDelay                         = 5                                   {product}
     intx SyncFlags                                 = 0                                   {product}
    ccstr SyncKnobs                                 =                                     {product}
     intx SyncVerbose                               = 0                                   {product}
    uintx TLABAllocationWeight                      = 35                                  {product}
    uintx TLABRefillWasteFraction                   = 64                                  {product}
    uintx TLABSize                                  = 0                                   {product}
     bool TLABStats                                 = true                                {product}
    uintx TLABWasteIncrement                        = 4                                   {product}
    uintx TLABWasteTargetPercent                    = 1                                   {product}
    uintx TargetPLABWastePct                        = 10                                  {product}
    uintx TargetSurvivorRatio                       = 50                                  {product}
    uintx TenuredGenerationSizeIncrement            = 20                                  {product}
    uintx TenuredGenerationSizeSupplement           = 80                                  {product}
    uintx TenuredGenerationSizeSupplementDecay      = 2                                   {product}
     intx ThreadPriorityPolicy                      = 0                                   {product}
     bool ThreadPriorityVerbose                     = false                               {product}
    uintx ThreadSafetyMargin                        = 52428800                            {product}
     intx ThreadStackSize                           = 0                                   {pd product}
    uintx ThresholdTolerance                        = 10                                  {product}
     intx Tier0BackedgeNotifyFreqLog                = 10                                  {product}
     intx Tier0InvokeNotifyFreqLog                  = 7                                   {product}
     intx Tier0ProfilingStartPercentage             = 200                                 {product}
     intx Tier23InlineeNotifyFreqLog                = 20                                  {product}
     intx Tier2BackEdgeThreshold                    = 0                                   {product}
     intx Tier2BackedgeNotifyFreqLog                = 14                                  {product}
     intx Tier2CompileThreshold                     = 0                                   {product}
     intx Tier2InvokeNotifyFreqLog                  = 11                                  {product}
     intx Tier3BackEdgeThreshold                    = 60000                               {product}
     intx Tier3BackedgeNotifyFreqLog                = 13                                  {product}
     intx Tier3CompileThreshold                     = 2000                                {product}
     intx Tier3DelayOff                             = 2                                   {product}
     intx Tier3DelayOn                              = 5                                   {product}
     intx Tier3InvocationThreshold                  = 200                                 {product}
     intx Tier3InvokeNotifyFreqLog                  = 10                                  {product}
     intx Tier3LoadFeedback                         = 5                                   {product}
     intx Tier3MinInvocationThreshold               = 100                                 {product}
     intx Tier4BackEdgeThreshold                    = 40000                               {product}
     intx Tier4CompileThreshold                     = 15000                               {product}
     intx Tier4InvocationThreshold                  = 5000                                {product}
     intx Tier4LoadFeedback                         = 3                                   {product}
     intx Tier4MinInvocationThreshold               = 600                                 {product}
     bool TieredCompilation                         = true                                {pd product}
     intx TieredCompileTaskTimeout                  = 50                                  {product}
     intx TieredRateUpdateMaxTime                   = 25                                  {product}
     intx TieredRateUpdateMinTime                   = 1                                   {product}
     intx TieredStopAtLevel                         = 4                                   {product}
     bool TimeLinearScan                            = false                               {C1 product}
     bool TraceBiasedLocking                        = false                               {product}
     bool TraceClassLoading                         = false                               {product rw}
     bool TraceClassLoadingPreorder                 = false                               {product}
     bool TraceClassPaths                           = false                               {product}
     bool TraceClassResolution                      = false                               {product}
     bool TraceClassUnloading                       = false                               {product rw}
     bool TraceDynamicGCThreads                     = false                               {product}
     bool TraceGen0Time                             = false                               {product}
     bool TraceGen1Time                             = false                               {product}
    ccstr TraceJVMTI                                =                                     {product}
     bool TraceLoaderConstraints                    = false                               {product rw}
     bool TraceMetadataHumongousAllocation          = false                               {product}
     bool TraceMonitorInflation                     = false                               {product}
     bool TraceParallelOldGCTasks                   = false                               {product}
     intx TraceRedefineClasses                      = 0                                   {product}
     bool TraceSafepointCleanupTime                 = false                               {product}
     bool TraceSharedLookupCache                    = false                               {product}
     bool TraceSuspendWaitFailures                  = false                               {product}
     intx TrackedInitializationLimit                = 50                                  {C2 product}
     bool TransmitErrorReport                       = false                               {product}
     bool TrapBasedNullChecks                       = false                               {pd product}
     bool TrapBasedRangeChecks                      = false                               {C2 pd product}
     intx TypeProfileArgsLimit                      = 2                                   {product}
    uintx TypeProfileLevel                          = 111                                 {pd product}
     intx TypeProfileMajorReceiverPercent           = 90                                  {C2 product}
     intx TypeProfileParmsLimit                     = 2                                   {product}
     intx TypeProfileWidth                          = 2                                   {product}
     intx UnguardOnExecutionViolation               = 0                                   {product}
     bool UnlinkSymbolsALot                         = false                               {product}
     bool Use486InstrsOnly                          = false                               {ARCH product}
     bool UseAES                                    = true                                {product}
     bool UseAESIntrinsics                          = true                                {product}
     intx UseAVX                                    = 2                                   {ARCH product}
     bool UseAdaptiveGCBoundary                     = false                               {product}
     bool UseAdaptiveGenerationSizePolicyAtMajorCollection  = true                                {product}
     bool UseAdaptiveGenerationSizePolicyAtMinorCollection  = true                                {product}
     bool UseAdaptiveNUMAChunkSizing                = true                                {product}
     bool UseAdaptiveSizeDecayMajorGCCost           = true                                {product}
     bool UseAdaptiveSizePolicy                     = true                                {product}
     bool UseAdaptiveSizePolicyFootprintGoal        = true                                {product}
     bool UseAdaptiveSizePolicyWithSystemGC         = false                               {product}
     bool UseAddressNop                             = true                                {ARCH product}
     bool UseAltSigs                                = false                               {product}
     bool UseAutoGCSelectPolicy                     = false                               {product}
     bool UseBMI1Instructions                       = true                                {ARCH product}
     bool UseBMI2Instructions                       = true                                {ARCH product}
     bool UseBiasedLocking                          = true                                {product}
     bool UseBimorphicInlining                      = true                                {C2 product}
     bool UseBoundThreads                           = true                                {product}
     bool UseCLMUL                                  = true                                {ARCH product}
     bool UseCMSBestFit                             = true                                {product}
     bool UseCMSCollectionPassing                   = true                                {product}
     bool UseCMSCompactAtFullCollection             = true                                {product}
     bool UseCMSInitiatingOccupancyOnly             = false                               {product}
     bool UseCRC32Intrinsics                        = true                                {product}
     bool UseCodeCacheFlushing                      = true                                {product}
     bool UseCompiler                               = true                                {product}
     bool UseCompilerSafepoints                     = true                                {product}
     bool UseCompressedClassPointers               := true                                {lp64_product}
     bool UseCompressedOops                        := true                                {lp64_product}
     bool UseConcMarkSweepGC                        = false                               {product}
     bool UseCondCardMark                           = false                               {C2 product}
     bool UseCountLeadingZerosInstruction           = true                                {ARCH product}
     bool UseCountTrailingZerosInstruction          = true                                {ARCH product}
     bool UseCountedLoopSafepoints                  = false                               {C2 product}
     bool UseCounterDecay                           = true                                {product}
     bool UseDivMod                                 = true                                {C2 product}
     bool UseDynamicNumberOfGCThreads               = false                               {product}
     bool UseFPUForSpilling                         = true                                {C2 product}
     bool UseFastAccessorMethods                    = false                               {product}
     bool UseFastEmptyMethods                       = false                               {product}
     bool UseFastJNIAccessors                       = true                                {product}
     bool UseFastStosb                              = true                                {ARCH product}
     bool UseG1GC                                   = false                               {product}
     bool UseGCLogFileRotation                      = false                               {product}
     bool UseGCOverheadLimit                        = true                                {product}
     bool UseGCTaskAffinity                         = false                               {product}
     bool UseGHASHIntrinsics                        = true                                {product}
     bool UseHeavyMonitors                          = false                               {product}
     bool UseInlineCaches                           = true                                {product}
     bool UseInterpreter                            = true                                {product}
     bool UseJumpTables                             = true                                {C2 product}
     bool UseLWPSynchronization                     = true                                {product}
     bool UseLargePages                             = false                               {pd product}
     bool UseLargePagesInMetaspace                  = false                               {product}
     bool UseLargePagesIndividualAllocation        := false                               {pd product}
     bool UseLockedTracing                          = false                               {product}
     bool UseLoopCounter                            = true                                {product}
     bool UseLoopInvariantCodeMotion                = true                                {C1 product}
     bool UseLoopPredicate                          = true                                {C2 product}
     bool UseMathExactIntrinsics                    = true                                {C2 product}
     bool UseMaximumCompactionOnSystemGC            = true                                {product}
     bool UseMembar                                 = false                               {pd product}
     bool UseMontgomeryMultiplyIntrinsic            = true                                {C2 product}
     bool UseMontgomerySquareIntrinsic              = true                                {C2 product}
     bool UseMulAddIntrinsic                        = true                                {C2 product}
     bool UseMultiplyToLenIntrinsic                 = true                                {C2 product}
     bool UseNUMA                                   = false                               {product}
     bool UseNUMAInterleaving                       = false                               {product}
     bool UseNewLongLShift                          = false                               {ARCH product}
     bool UseOSErrorReporting                       = false                               {pd product}
     bool UseOldInlining                            = true                                {C2 product}
     bool UseOnStackReplacement                     = true                                {pd product}
     bool UseOnlyInlinedBimorphic                   = true                                {C2 product}
     bool UseOptoBiasInlining                       = true                                {C2 product}
     bool UsePSAdaptiveSurvivorSizePolicy           = true                                {product}
     bool UseParNewGC                               = false                               {product}
     bool UseParallelGC                            := true                                {product}
     bool UseParallelOldGC                          = true                                {product}
     bool UsePerfData                               = true                                {product}
     bool UsePopCountInstruction                    = true                                {product}
     bool UseRDPCForConstantTableBase               = false                               {C2 product}
     bool UseRTMDeopt                               = false                               {ARCH product}
     bool UseRTMLocking                             = false                               {ARCH product}
     bool UseSHA                                    = false                               {product}
     bool UseSHA1Intrinsics                         = false                               {product}
     bool UseSHA256Intrinsics                       = false                               {product}
     bool UseSHA512Intrinsics                       = false                               {product}
     intx UseSSE                                    = 4                                   {product}
     bool UseSSE42Intrinsics                        = true                                {product}
     bool UseSerialGC                               = false                               {product}
     bool UseSharedSpaces                           = false                               {product}
     bool UseSignalChaining                         = true                                {product}
     bool UseSquareToLenIntrinsic                   = true                                {C2 product}
     bool UseStoreImmI16                            = false                               {ARCH product}
     bool UseStringDeduplication                    = false                               {product}
     bool UseSuperWord                              = true                                {C2 product}
     bool UseTLAB                                   = true                                {pd product}
     bool UseThreadPriorities                       = true                                {pd product}
     bool UseTypeProfile                            = true                                {product}
     bool UseTypeSpeculation                        = true                                {C2 product}
     bool UseUTCFileTimestamp                       = true                                {product}
     bool UseUnalignedLoadStores                    = true                                {ARCH product}
     bool UseVMInterruptibleIO                      = false                               {product}
     bool UseXMMForArrayCopy                        = true                                {product}
     bool UseXmmI2D                                 = false                               {ARCH product}
     bool UseXmmI2F                                 = false                               {ARCH product}
     bool UseXmmLoadAndClearUpper                   = true                                {ARCH product}
     bool UseXmmRegToRegMoveAll                     = true                                {ARCH product}
     bool VMThreadHintNoPreempt                     = false                               {product}
     intx VMThreadPriority                          = -1                                  {product}
     intx VMThreadStackSize                         = 0                                   {pd product}
     intx ValueMapInitialSize                       = 11                                  {C1 product}
     intx ValueMapMaxLoopSize                       = 8                                   {C1 product}
     intx ValueSearchLimit                          = 1000                                {C2 product}
     bool VerifyMergedCPBytecodes                   = true                                {product}
     bool VerifySharedSpaces                        = false                               {product}
     intx WorkAroundNPTLTimedWaitHang               = 1                                   {product}
    uintx YoungGenerationSizeIncrement              = 20                                  {product}
    uintx YoungGenerationSizeSupplement             = 80                                  {product}
    uintx YoungGenerationSizeSupplementDecay        = 8                                   {product}
    uintx YoungPLABSize                             = 4096                                {product}
     bool ZeroTLAB                                  = false                               {product}
     intx hashCode                                  = 5                                   {product}
java version "1.8.0_231"
Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.231-b11, mixed mode)
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-XX:+PrintCommandLineFlags -version 可以查看垃圾回收器

E:\workspace\study-guigu>java -XX:+PrintCommandLineFlags -version
-XX:InitialHeapSize=132899584 -XX:MaxHeapSize=2126393344 -XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAl
location -XX:+UseParallelGC
java version "1.8.0_231"
Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.231-b11, mixed mode)

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JVM常用参数

-Xms：初始化大小内存，默认为物理内存1/64。（等价于-XX:InitialHeapSize）

-Xmx：最大分配内存，默认为物理内存1/4。（等价于-XX:MaxHeapSize）

-Xss：设置单个线程栈的大小，一般默认为512k~1024k。（等价于-XX:ThreadStackSize）

-Xmn：设置年轻代大小

-XX:MetaspaceSize：元空间的本质和永久代类似，都是对JVM规范中方法区的实现。不过元空间于永久代之间最大的区别在于：**元空间并不在虚拟机中，而是使用本地内存。**因此默认情况下，元空间的大小仅受本地内存限制。

-Xms128m -Xmx4096m -Xss1024k -XX:MetaspaceSize=512m -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseSerialGC