基于Redis的分布式锁 - IT评测·应用市场-qidao123.com技术社区

SET mykey myvalue NX EX 10

复制代码

redisTemplate.opsForValue().setIfAbsent(key,"uid",10,TimeUnit.SECONDS);
//底层是execute直接执行,也可以保证操作的原子性
return (Boolean)this.execute((connection) -> {
return connection.set(rawKey, rawValue, expiration, SetOption.ifAbsent());
}, true);

复制代码

RLock rLock = redissonClient.getLock(name);
try {
/**
* waitTime 获取锁的最长等待时间
* leaseTime 持有锁的时间
* unit 单位
* */
//TODO 开启看门狗lease -1 自我理解看门狗的功能就是在超时后任务没有执行完成就续期,
// 如果没有看门狗并且设置了leaseTime 就是当前锁的失效时间了
Boolean bo = rLock.tryLock(5,-1,TimeUnit.MINUTES);
if (!bo){
System.out.println("没有拿到锁,遗憾离场:"+name);
continue;
}else {
System.out.println("拿到了锁,并开始耗时:"+name);
Thread.sleep(600);
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
if (rLock.isHeldByCurrentThread()){
rLock.unlock();
System.out.println("释放了锁:"+name);
} else {
System.out.println("遗憾离场,并来到了finally:"+name);
}
}

复制代码

//底层逻辑开一个监听线程看执行完毕删除锁,未执行完毕就加过期时间
Long ttl = this.tryAcquire(leaseTime, unit, threadId);
//判断是否开启了看门狗机制
private RFuture<Boolean> tryAcquireOnceAsync(long leaseTime, TimeUnit unit, final long threadId) {
if (leaseTime != -1L) {
return this.tryLockInnerAsync(leaseTime, unit, threadId,
RedisCommands.EVAL_NULL_BOOLEAN);
} else {
//延期时间默认30毫秒 this.lockWatchdogTimeout = 30000L;
RFuture<Boolean> ttlRemainingFuture = this.tryLockInnerAsync(this.commandExecutor.
getConnectionManager().getCfg().getLockWatchdogTimeout(),
TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_NULL_BOOLEAN);
//监听这个线程时间
ttlRemainingFuture.addListener(new FutureListener<Boolean>() {
public void operationComplete(Future<Boolean> future) throws Exception {
if (future.isSuccess()) {
Boolean ttlRemaining = (Boolean)future.getNow();
if (ttlRemaining) {
RedissonLock.this.scheduleExpirationRenewal(threadId);
}
}
}
});
return ttlRemainingFuture;
}
}
//线程的具体监听方法锁不存在了就取消监听
private void scheduleExpirationRenewal(final long threadId) {
if (!expirationRenewalMap.containsKey(this.getEntryName())) {
Timeout task = this.commandExecutor.getConnectionManager().newTimeout(new TimerTask() {
public void run(Timeout timeout) throws Exception {
RFuture<Boolean> future = RedissonLock.this.commandExecutor.evalWriteAsync(RedissonLock.this.getName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN, "if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then redis.call('pexpire', KEYS[1], ARGV[1]); return 1; end; return 0;", Collections.singletonList(RedissonLock.this.getName()), new Object[]{RedissonLock.this.internalLockLeaseTime, RedissonLock.this.getLockName(threadId)});
future.addListener(new FutureListener<Boolean>() {
public void operationComplete(Future<Boolean> future) throws Exception {
RedissonLock.expirationRenewalMap.remove(RedissonLock.this.getEntryName());
if (!future.isSuccess()) {
RedissonLock.log.error("Can't update lock " + RedissonLock.this.getName() + " expiration", future.cause());
} else {
if ((Boolean)future.getNow()) {
RedissonLock.this.scheduleExpirationRenewal(threadId);
}
}
}
});
}
}, this.internalLockLeaseTime / 3L, TimeUnit.MILLISECONDS);
if (expirationRenewalMap.putIfAbsent(this.getEntryName(), task) != null) {
task.cancel();
}
}
}

复制代码

RLock lock1 = redissonInstance1.getLock("lock1");
RLock lock2 = redissonInstance2.getLock("lock2");
RLock lock3 = redissonInstance3.getLock("lock3");
RedissonRedLock lock = new RedissonRedLock(lock1, lock2, lock3);
// 同时加锁：lock1 lock2 lock3
// 红锁在大部分节点上加锁成功就算成功。
lock.lock();
...
lock.unlock();

复制代码

RReadWriteLock readWriteLock = redissonClient.getReadWriteLock(mobile);
readWriteLock.readLock();
readWriteLock.writeLock();

复制代码