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多个客户端,通过watch一个键-值,然后开启事务
如果在开启事务的期间,watch的值没有被其他客户端修改过,则执行成功
如果在开启事务的期间,watch的值被其他客户端修改了,则执行失败
set name erick
set age 10
watch name age # 监控对应的属性
multi
set address shanxi
set year 2022
exec
满足分布式系统或集群模式下,多进程可见并互斥的锁
多线程可见
互斥
高可用
高并发
安全
基础版本
获取锁:
SETNX key value
释放锁
redis.del(LOCK_NAME)
SET lock value EX 10 NX
package com.erick;
import redis.clients.jedis.Jedis;
public class Test {
private static String LOCK_NAME = "LOCK";
/*可以将value替换为Thread的名字*/
private static String LOCK_VALUE = "ERICK";
private static int EXPIRE_SECS = 5;
public static void main(String[] args) {
thirdLock();
}
/*假如执行完业务后,redis还没来的及释放锁,redis就挂了*/
private static void firstLock() {
Jedis redis = getRedis();
/*获取锁,单线程保证一定只有一个线程来执行*/
Long result = redis.setnx(LOCK_NAME, LOCK_VALUE);
if (result == 1) {
executeBusiness();
/*释放锁*/
redis.del(LOCK_NAME);
} else {
/*等待*/
}
}
/*假如在上锁和设置过期时间内,redis挂了,锁依然无法释放
* 因此在设置时候,必须要将加锁和设置过期时间,做成原子性的*/
private static void secondLock() {
Jedis redis = getRedis();
Long result = redis.setnx(LOCK_NAME, LOCK_VALUE);
/*加锁的时候,加上过期时间*/
redis.setex(LOCK_NAME, EXPIRE_SECS, "");
if (result == 1) {
executeBusiness();
/*释放锁*/
redis.del(LOCK_NAME);
} else {
/*等待*/
}
}
private static void thirdLock() {
Jedis redis = getRedis();
/*是一条原子指令*/
String result = redis.set(LOCK_NAME, LOCK_VALUE, "NX", "EX", EXPIRE_SECS);
if ("OK".equalsIgnoreCase(result)) {
executeBusiness();
/*释放锁*/
//redis.del(LOCK_NAME);
} else {
/*等待*/
}
}
private static void executeBusiness() {
System.out.println("执行业务");
}
private static Jedis getRedis() {
Jedis jedis = new Jedis("60.205.229.31", 6380);
return jedis;
}
}
上面的分布式锁存在的问题
最简单的方法:将超时时间设置的长一些,远大于业务执行的时间,但是会带来性能问题
解决方法:
锁的key-value:
package com.erick.redis;
import redis.clients.jedis.Jedis;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
public class Test02 {
public static void main(String[] args) {
new Thread(() -> businessWithLock()).start();
new Thread(() -> businessWithLock()).start();
}
private static void businessWithLock() {
Jedis redis = getRedis();
String lockName = "LOCK_BUSINESS";
/*锁的值,用threadId和uuid来表示,避免了多个线程*/
String lockValue = Thread.currentThread().getId() + UUID.randomUUID().toString();
String result = redis.set(lockName, lockValue, "NX", "EX", 5);
if ("OK".equalsIgnoreCase(result)) {
executeBusiness();
} else {
return;
}
/*删除的逻辑
* 1. 将当前的key的值拿过来与自己之前存的来比较
* 2. 如果相同,则删除,如果不同,则什么都不要做*/
String presentLockValue = redis.get(lockName);
if (lockValue.equals(presentLockValue)) {
System.out.println("删除锁");
redis.del(lockName);
} else {
System.out.println("业务执行完了,但是当前锁已经不是自己的,所以不用删除");
}
}
/*耗时业务*/
private static void executeBusiness() {
try {
System.out.println("doing business");
TimeUnit.SECONDS.sleep(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private static Jedis getRedis() {
Jedis jedis = new Jedis("60.205.229.31", 6380);
return jedis;
}
}
Redis提供了Lua脚本功能,在一个脚本中编写多条Redis命令,确保多条命令的原子性
set: 表示redis的命令
KEYS[1]: redis的key值个数
ARGV[1]: redis的value的值个数
1: 具体包含几个值
age: 实际传递的key值
20: 实际传递的value值
EVAL “return redis.call(‘set’,KEYS[1],ARGV[1])” 1 age 20
-- 获取锁中的线程标示,动态传递参数
local keyName = redis.call('get',KEYS[1])
-- 比较线程标示与锁中的是否一直
if (ARGV[1] == keyName) then
-- 释放锁
redis.call('del',KEYS[1])
return 1
-- 如果不一致,则返回结果为0
else
return 0
end
private static boolean deleteLockIfMy(Jedis redis, String lockKey, String lockValue) {
/*用lua脚本来保证*/
String luaScript = "-- 获取锁中的线程标示,动态传递参数
" +
"local keyName = redis.call('get',KEYS[1])
" +
"
" +
"-- 比较线程标示与锁中的是否一直
" +
"if (keyName == ARGV[1]) then
" +
" -- 释放锁
" +
" redis.call('del',KEYS[1])
" +
" return 1
" +
" -- 如果不一致,则返回结果为0
" +
"else
" +
" return 0
" +
"end";
/*加载脚本*/
String script = redis.scriptLoad(luaScript);
/*向脚本中传递参数*/
Object delResult = redis.evalsha(script, Arrays.asList(lockKey), Arrays.asList(lockValue));
/*上面的结果是Long类型*/
if (delResult.equals(1L)) {
return true;
} else {
return false;
}
}
一个用来进行分布式锁的工具类
org.redisson redisson 3.16.8package com.erick.redis;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;
import java.util.concurrent.TimeUnit;
public class Test03 {
public static void main(String[] args) {
new Thread(() -> lockWithBusiness()).start();
new Thread(() -> lockWithBusiness()).start();
}
private static void lockWithBusiness() {
RedissonClient redissonClient = redissonClient();
/*获取对应的key的锁*/
String lockKey = "COMMERCE-BUSINESS";
RLock lock = redissonClient.getLock(lockKey);
try {
// 内部包含重试时间
/*参数一: 最长等待时间
* 参数二:锁超时释放时间
* 参数三:时间单位*/
boolean hasLok = lock.tryLock();
if (hasLok) {
business();
} else {
System.out.println("暂时没有获取到锁");
}
} finally {
/*第二个锁释放的时候,会报 删除异常
* IllegalMonitorStateException*/
lock.unlock();
}
}
/*等待超时的锁*/
private static void lockWithBusinessWithTime() {
RedissonClient redissonClient = redissonClient();
/*获取对应的key的锁*/
String lockKey = "COMMERCE-BUSINESS";
RLock lock = redissonClient.getLock(lockKey);
try {
// 内部包含重试时间
/*参数一: 最长等待时间
* 参数二:锁超时释放时间
* 参数三:时间单位*/
boolean hasLok = lock.tryLock(6, 20, TimeUnit.SECONDS);
if (hasLok) {
business();
} else {
System.out.println("暂时没有获取到锁");
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
// 最长等待时间获取不到,删除的时候依然会报错
lock.unlock();
}
}
private static void business() {
System.out.println("执行业务");
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
/*Redis的配置类*/
private static RedissonClient redissonClient() {
Config config = new Config();
config.useSingleServer().setAddress("redis://60.205.229.31:6380");
return Redisson.create(config);
}
}
解决方案:设立多个redis作为主节点
只有每个都获取成功的时候,才会去执行
package com.erick.redis;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;
import java.util.concurrent.TimeUnit;
public class Test04 {
public static void main(String[] args) {
businessWithLock();
}
private static void businessWithLock() {
String lockKey = "BUSINESS";
RedissonClient firstClient = redissonClient01();
RedissonClient secondClient = redissonClient02();
RedissonClient thirdClient = redissonClient03();
RLock firstLock = firstClient.getLock(lockKey);
RLock secondLock = secondClient.getLock(lockKey);
RLock thirdLock = thirdClient.getLock(lockKey);
/*获取到多把锁*/
RLock multiLock = firstClient.getMultiLock(firstLock, secondLock, thirdLock);
boolean hasLock = multiLock.tryLock();
try{
if (hasLock) {
business();
} else {
System.out.println("未获取到锁,业务没有执行");
}
}finally {
multiLock.unlock();
}
}
private static void business() {
System.out.println("执行业务");
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
/*Redis的配置类*/
private static RedissonClient redissonClient01() {
Config config = new Config();
config.useSingleServer().setAddress("redis://60.205.229.31:6379");
return Redisson.create(config);
}
private static RedissonClient redissonClient02() {
Config config = new Config();
config.useSingleServer().setAddress("redis://60.205.229.31:6380");
return Redisson.create(config);
}
private static RedissonClient redissonClient03() {
Config config = new Config();
config.useSingleServer().setAddress("redis://60.205.229.31:6381");
return Redisson.create(config);
}
}
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