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//产生一个随机数
ThreadLocalRandom.current().nextInt(100)
java8 实际测试效果:
线程数量 | 线程内循环生产次数 | random耗时(毫秒) | ThreadLocalRandom耗时(毫秒) |
---|---|---|---|
1 | 1w | 6 | 11 |
10 | 1w | 16 | 15 |
10 | 10w | 101 | 65 |
50 | 1w | 56 | 54 |
50 | 10w | 509 | 115 |
100 | 1w | 105 | 80 |
100 | 10w | 1115 | 131 |
import java.util.Random; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.ThreadLocalRandom; public class ThreadLocalRandomTask { private static Random random = ThreadLocalRandom.current(); public static void main(String[] args) { ExecutorService taskPool = Executors.newCachedThreadPool(); for(int n = 1; n < 10; n++) { taskPool.submit(() -> System.out.println(random.nextInt())); } taskPool.shutdown(); } }
基于jdk 1.8。
ThreadLocalRandom extends Random,使用方法大致相同。
package java.util.concurrent; import java.io.ObjectStreamField; import java.util.Random; import java.util.Spliterator; import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.atomic.AtomicLong; import java.util.function.DoubleConsumer; import java.util.function.IntConsumer; import java.util.function.LongConsumer; import java.util.stream.DoubleStream; import java.util.stream.IntStream; import java.util.stream.LongStream; import java.util.stream.StreamSupport; import sun.misc.VM; /** * ThreadLocalRandom的实例在密码上是不安全的,安全敏感的程序应该使用 * java.security中的SecureRandom * @since 1.7 * @author Doug Lea */ public class ThreadLocalRandom extends Random { /* * 使用一个静态实例来访问Thread中的threadLocalRandomSeed值 = seed值。 */ /** 生成每个线程的初始化/探测字段 */ private static final AtomicInteger probeGenerator = new AtomicInteger(); /** * The next seed for default constructors. */ private static final AtomicLong seeder = new AtomicLong(initialSeed()); //初始化一个种子,值是固定的 private static long initialSeed() { String sec = VM.getSavedProperty("java.util.secureRandomSeed"); if (Boolean.parseBoolean(sec)) { byte[] seedBytes = java.security.SecureRandom.getSeed(8); long s = (long)(seedBytes[0]) & 0xffL; for (int i = 1; i < 8; ++i) s = (s << 8) | ((long)(seedBytes[i]) & 0xffL); return s; } return (mix64(System.currentTimeMillis()) ^ mix64(System.nanoTime())); } /** * The seed increment */ private static final long GAMMA = 0x9e3779b97f4a7c15L; /** * The increment for generating probe values */ private static final int PROBE_INCREMENT = 0x9e3779b9; /** * The increment of seeder per new instance */ private static final long SEEDER_INCREMENT = 0xbb67ae8584caa73bL; // Constants from SplittableRandom private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53) private static final float FLOAT_UNIT = 0x1.0p-24f; // 1.0f / (1 << 24) /** Rarely-used holder for the second of a pair of Gaussians */ private static final ThreadLocal<Double> nextLocalGaussian = new ThreadLocal<Double>(); private static long mix64(long z) { z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; return z ^ (z >>> 33); } private static int mix32(long z) { z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; return (int)(((z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L) >>> 32); } /** * Field used only during singleton initialization. * True when constructor completes. */ boolean initialized; /** Constructor used only for static singleton */ private ThreadLocalRandom() { initialized = true; // false during super() call } /** The common ThreadLocalRandom */ static final ThreadLocalRandom instance = new ThreadLocalRandom(); /** * 初始化,主要是获取当前线程并设置当前线程对应的seed和probe探针值 * 每次获取后,(跨Thread)seed值都会变化(加上了增量SEEDER_INCREMENT) */ static final void localInit() { int p = probeGenerator.addAndGet(PROBE_INCREMENT); int probe = (p == 0) ? 1 : p; // skip 0 long seed = mix64(seeder.getAndAdd(SEEDER_INCREMENT)); Thread t = Thread.currentThread(); UNSAFE.putLong(t, SEED, seed); UNSAFE.putInt(t, PROBE, probe); } /** * 如果获取值 = 0,则初始化,否则直接使用静态实例 */ public static ThreadLocalRandom current() { if (UNSAFE.getInt(Thread.currentThread(), PROBE) == 0) localInit(); return instance; } /** * 无效操作 */ public void setSeed(long seed) { // only allow call from super() constructor if (initialized) throw new UnsupportedOperationException(); } //生成当前线程对应的下一个seed,并保存到对应Thread,种子加上固定的 //增量值 GAMMA final long nextSeed() { Thread t; long r; // read and update per-thread seed UNSAFE.putLong(t = Thread.currentThread(), SEED, r = UNSAFE.getLong(t, SEED) + GAMMA); return r; } // We must define this, but never use it. protected int next(int bits) { return (int)(mix64(nextSeed()) >>> (64 - bits)); } // IllegalArgumentException messages static final String BadBound = "bound must be positive"; static final String BadRange = "bound must be greater than origin"; static final String BadSize = "size must be non-negative"; /** * The form of nextLong used by LongStream Spliterators. If * origin is greater than bound, acts as unbounded form of * nextLong, else as bounded form. * 如果 origin >= bound 则不使用值大小限定。 * //ps: 如果是2的n此幂,则取差值利用位运算获取比差值小,然后算出随机数r * * @param origin the least value, unless greater than bound * @param bound the upper bound (exclusive), must not equal origin * @return a pseudorandom value */ final long internalNextLong(long origin, long bound) { long r = mix64(nextSeed()); if (origin < bound) { long n = bound - origin, m = n - 1; if ((n & m) == 0L) // power of two r = (r & m) + origin; else if (n > 0L) { // reject over-represented candidates //确保非负数,产生随机数每次变小相加直到符合条件 for (long u = r >>> 1; // ensure nonnegative u + m - (r = u % n) < 0L; // rejection check u = mix64(nextSeed()) >>> 1) // retry ; r += origin; } else { //r不再范围内,则重新生成 //ps://bound为正,origin为负,可能导致超过Long最大值,这时随机生成范围内的值 while (r < origin || r >= bound) r = mix64(nextSeed()); } } return r; } final int internalNextInt(int origin, int bound) { int r = mix32(nextSeed()); if (origin < bound) { int n = bound - origin, m = n - 1; if ((n & m) == 0) r = (r & m) + origin; else if (n > 0) { for (int u = r >>> 1; u + m - (r = u % n) < 0; u = mix32(nextSeed()) >>> 1) ; r += origin; } else { while (r < origin || r >= bound) r = mix32(nextSeed()); } } return r; } /** * double 内部使用的nextLong() */ final double internalNextDouble(double origin, double bound) { double r = (nextLong() >>> 11) * DOUBLE_UNIT; if (origin < bound) { r = r * (bound - origin) + origin; if (r >= bound) // correct for rounding r = Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1); } return r; } public int nextInt() { return mix32(nextSeed()); } public int nextInt(int bound) { if (bound <= 0) throw new IllegalArgumentException(BadBound); int r = mix32(nextSeed()); int m = bound - 1; if ((bound & m) == 0) // power of two r &= m; else { // reject over-represented candidates for (int u = r >>> 1; u + m - (r = u % bound) < 0; u = mix32(nextSeed()) >>> 1) ; } return r; } public int nextInt(int origin, int bound) { if (origin >= bound) throw new IllegalArgumentException(BadRange); return internalNextInt(origin, bound); } public long nextLong() { return mix64(nextSeed()); } public long nextLong(long bound) { if (bound <= 0) throw new IllegalArgumentException(BadBound); long r = mix64(nextSeed()); long m = bound - 1; if ((bound & m) == 0L) // power of two r &= m; else { // reject over-represented candidates for (long u = r >>> 1; u + m - (r = u % bound) < 0L; u = mix64(nextSeed()) >>> 1) ; } return r; } public long nextLong(long origin, long bound) { if (origin >= bound) throw new IllegalArgumentException(BadRange); return internalNextLong(origin, bound); } public double nextDouble() { return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT; } public double nextDouble(double bound) { if (!(bound > 0.0)) throw new IllegalArgumentException(BadBound); double result = (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT * bound; return (result < bound) ? result : // correct for rounding Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1); } public double nextDouble(double origin, double bound) { if (!(origin < bound)) throw new IllegalArgumentException(BadRange); return internalNextDouble(origin, bound); } //ps: //正数或者0 = false,负数 = true, //恰好默认数值因为符号位的原因,负数比正数多一个数,所以正好平衡。 public boolean nextBoolean() { return mix32(nextSeed()) < 0; } public float nextFloat() { return (mix32(nextSeed()) >>> 8) * FLOAT_UNIT; } public double nextGaussian() { // Use nextLocalGaussian instead of nextGaussian field Double d = nextLocalGaussian.get(); if (d != null) { nextLocalGaussian.set(null); return d.doubleValue(); } double v1, v2, s; do { v1 = 2 * nextDouble() - 1; // between -1 and 1 v2 = 2 * nextDouble() - 1; // between -1 and 1 s = v1 * v1 + v2 * v2; } while (s >= 1 || s == 0); double multiplier = StrictMath.sqrt(-2 * StrictMath.log(s)/s); nextLocalGaussian.set(new Double(v2 * multiplier)); return v1 * multiplier; } // stream methods, coded in a way intended to better isolate for // maintenance purposes the small differences across forms. /** * 从intStream中拆出int数据以得到IntStream(限定了streamSize) * @since 1.8 */ public IntStream ints(long streamSize) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); return StreamSupport.intStream (new RandomIntsSpliterator (0L, streamSize, Integer.MAX_VALUE, 0), false); } public IntStream ints() { return StreamSupport.intStream (new RandomIntsSpliterator (0L, Long.MAX_VALUE, Integer.MAX_VALUE, 0), false); } public IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); if (randomNumberOrigin >= randomNumberBound) throw new IllegalArgumentException(BadRange); return StreamSupport.intStream (new RandomIntsSpliterator (0L, streamSize, randomNumberOrigin, randomNumberBound), false); } public IntStream ints(int randomNumberOrigin, int randomNumberBound) { if (randomNumberOrigin >= randomNumberBound) throw new IllegalArgumentException(BadRange); return StreamSupport.intStream (new RandomIntsSpliterator (0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound), false); } public LongStream longs(long streamSize) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); return StreamSupport.longStream (new RandomLongsSpliterator (0L, streamSize, Long.MAX_VALUE, 0L), false); } public LongStream longs() { return StreamSupport.longStream (new RandomLongsSpliterator (0L, Long.MAX_VALUE, Long.MAX_VALUE, 0L), false); } public LongStream longs(long streamSize, long randomNumberOrigin, long randomNumberBound) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); if (randomNumberOrigin >= randomNumberBound) throw new IllegalArgumentException(BadRange); return StreamSupport.longStream (new RandomLongsSpliterator (0L, streamSize, randomNumberOrigin, randomNumberBound), false); } public LongStream longs(long randomNumberOrigin, long randomNumberBound) { if (randomNumberOrigin >= randomNumberBound) throw new IllegalArgumentException(BadRange); return StreamSupport.longStream (new RandomLongsSpliterator (0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound), false); } public DoubleStream doubles(long streamSize) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); return StreamSupport.doubleStream (new RandomDoublesSpliterator (0L, streamSize, Double.MAX_VALUE, 0.0), false); } public DoubleStream doubles() { return StreamSupport.doubleStream (new RandomDoublesSpliterator (0L, Long.MAX_VALUE, Double.MAX_VALUE, 0.0), false); } public DoubleStream doubles(long streamSize, double randomNumberOrigin, double randomNumberBound) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); if (!(randomNumberOrigin < randomNumberBound)) throw new IllegalArgumentException(BadRange); return StreamSupport.doubleStream (new RandomDoublesSpliterator (0L, streamSize, randomNumberOrigin, randomNumberBound), false); } public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) { if (!(randomNumberOrigin < randomNumberBound)) throw new IllegalArgumentException(BadRange); return StreamSupport.doubleStream (new RandomDoublesSpliterator (0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound), false); } /** * 用于int流的Spliterator。我们将四个int版本多路复用到一个类中, * 方法是将一个小于原点的绑定视为无界,并将“infinite”视为等同于 * Long.MAX_VALUE。对于分割,它使用标准的二除法。这个类的长版本 * 和双版本除了类型之外是相同的。 * ps://等学习stream再深入了解,这里当成一个支持类即可 */ static final class RandomIntsSpliterator implements Spliterator.OfInt { long index; final long fence; final int origin; final int bound; RandomIntsSpliterator(long index, long fence, int origin, int bound) { this.index = index; this.fence = fence; this.origin = origin; this.bound = bound; } public RandomIntsSpliterator trySplit() { long i = index, m = (i + fence) >>> 1; return (m <= i) ? null : new RandomIntsSpliterator(i, index = m, origin, bound); } public long estimateSize() { return fence - index; } public int characteristics() { return (Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL | Spliterator.IMMUTABLE); } public boolean tryAdvance(IntConsumer consumer) { if (consumer == null) throw new NullPointerException(); long i = index, f = fence; if (i < f) { consumer.accept(ThreadLocalRandom.current().internalNextInt(origin, bound)); index = i + 1; return true; } return false; } public void forEachRemaining(IntConsumer consumer) { if (consumer == null) throw new NullPointerException(); long i = index, f = fence; if (i < f) { index = f; int o = origin, b = bound; ThreadLocalRandom rng = ThreadLocalRandom.current(); do { consumer.accept(rng.internalNextInt(o, b)); } while (++i < f); } } } /** * Spliterator for long streams. */ static final class RandomLongsSpliterator implements Spliterator.OfLong { long index; final long fence; final long origin; final long bound; RandomLongsSpliterator(long index, long fence, long origin, long bound) { this.index = index; this.fence = fence; this.origin = origin; this.bound = bound; } public RandomLongsSpliterator trySplit() { long i = index, m = (i + fence) >>> 1; return (m <= i) ? null : new RandomLongsSpliterator(i, index = m, origin, bound); } public long estimateSize() { return fence - index; } public int characteristics() { return (Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL | Spliterator.IMMUTABLE); } public boolean tryAdvance(LongConsumer consumer) { if (consumer == null) throw new NullPointerException(); long i = index, f = fence; if (i < f) { consumer.accept(ThreadLocalRandom.current().internalNextLong(origin, bound)); index = i + 1; return true; } return false; } public void forEachRemaining(LongConsumer consumer) { if (consumer == null) throw new NullPointerException(); long i = index, f = fence; if (i < f) { index = f; long o = origin, b = bound; ThreadLocalRandom rng = ThreadLocalRandom.current(); do { consumer.accept(rng.internalNextLong(o, b)); } while (++i < f); } } } /** * Spliterator for double streams. */ static final class RandomDoublesSpliterator implements Spliterator.OfDouble { long index; final long fence; final double origin; final double bound; RandomDoublesSpliterator(long index, long fence, double origin, double bound) { this.index = index; this.fence = fence; this.origin = origin; this.bound = bound; } public RandomDoublesSpliterator trySplit() { long i = index, m = (i + fence) >>> 1; return (m <= i) ? null : new RandomDoublesSpliterator(i, index = m, origin, bound); } public long estimateSize() { return fence - index; } public int characteristics() { return (Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL | Spliterator.IMMUTABLE); } public boolean tryAdvance(DoubleConsumer consumer) { if (consumer == null) throw new NullPointerException(); long i = index, f = fence; if (i < f) { consumer.accept(ThreadLocalRandom.current().internalNextDouble(origin, bound)); index = i + 1; return true; } return false; } public void forEachRemaining(DoubleConsumer consumer) { if (consumer == null) throw new NullPointerException(); long i = index, f = fence; if (i < f) { index = f; double o = origin, b = bound; ThreadLocalRandom rng = ThreadLocalRandom.current(); do { consumer.accept(rng.internalNextDouble(o, b)); } while (++i < f); } } } /** * 探针是保存在当前线程中的,调用ThreadLocalRandom.current()初始化 */ static final int getProbe() { return UNSAFE.getInt(Thread.currentThread(), PROBE); } /** * 伪随机生成新探针值 */ static final int advanceProbe(int probe) { probe ^= probe << 13; // xorshift probe ^= probe >>> 17; probe ^= probe << 5; UNSAFE.putInt(Thread.currentThread(), PROBE, probe); return probe; } /** * Returns the pseudo-randomly initialized or updated secondary seed. */ static final int nextSecondarySeed() { int r; Thread t = Thread.currentThread(); if ((r = UNSAFE.getInt(t, SECONDARY)) != 0) { r ^= r << 13; // xorshift r ^= r >>> 17; r ^= r << 5; } else { localInit(); if ((r = (int)UNSAFE.getLong(t, SEED)) == 0) r = 1; // avoid zero } UNSAFE.putInt(t, SECONDARY, r); return r; } // Serialization support private static final long serialVersionUID = -5851777807851030925L; /** * @serialField rnd long * seed for random computations * @serialField initialized boolean * always true */ private static final ObjectStreamField[] serialPersistentFields = { new ObjectStreamField("rnd", long.class), new ObjectStreamField("initialized", boolean.class), }; private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { java.io.ObjectOutputStream.PutField fields = s.putFields(); fields.put("rnd", UNSAFE.getLong(Thread.currentThread(), SEED)); fields.put("initialized", true); s.writeFields(); } private Object readResolve() { return current(); } // Unsafe mechanics private static final sun.misc.Unsafe UNSAFE; private static final long SEED; private static final long PROBE; private static final long SECONDARY; static { try { UNSAFE = sun.misc.Unsafe.getUnsafe(); Class<?> tk = Thread.class; SEED = UNSAFE.objectFieldOffset (tk.getDeclaredField("threadLocalRandomSeed")); PROBE = UNSAFE.objectFieldOffset (tk.getDeclaredField("threadLocalRandomProbe")); SECONDARY = UNSAFE.objectFieldOffset (tk.getDeclaredField("threadLocalRandomSecondarySeed")); } catch (Exception e) { throw new Error(e); } } }
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