Redisson可重入锁解锁逻辑详细讲解

来源：jb51　　时间：2023/2/13 8:43:50　　对本文有异议

主动释放

我们查看org.redisson.RedissonLock#unlock()方法：

public void unlock() {
        try {
            get(unlockAsync(Thread.currentThread().getId()));
        } catch (RedisException e) {
            if (e.getCause() instanceof IllegalMonitorStateException) {
                throw (IllegalMonitorStateException) e.getCause();
            } else {
                throw e;
            }
        }
//        Future<Void> future = unlockAsync();
//        future.awaitUninterruptibly();
//        if (future.isSuccess()) {
//            return;
//        }
//        if (future.cause() instanceof IllegalMonitorStateException) {
//            throw (IllegalMonitorStateException)future.cause();
//        }
//        throw commandExecutor.convertException(future);
    }

同样采用异步的方式释放锁，unlockAsync()：

public RFuture<Void> unlockAsync(long threadId) {
    // 异步方式释放锁
    RFuture<Boolean> future = unlockInnerAsync(threadId);
    CompletionStage<Void> f = future.handle((opStatus, e) -> {
        // 取消看门狗定时任务
        cancelExpirationRenewal(threadId);
        if (e != null) {
            throw new CompletionException(e);
        }
        if (opStatus == null) {
            IllegalMonitorStateException cause = new IllegalMonitorStateException("attempt to unlock lock, not locked by current thread by node id: "
                    + id + " thread-id: " + threadId);
            throw new CompletionException(cause);
        }
        return null;
    });
    return new CompletableFutureWrapper<>(f);
}

可以看到，首先调用unlockInnerAsync()方法释放锁，在释放锁之后，执行cancelExpirationRenewal(threadId)取消看门狗自动续期的定时任务。

释放锁核心逻辑：

protected RFuture<Boolean> unlockInnerAsync(long threadId) {
    /**
     * Redisson解锁：通过LUA脚本释放锁，保证多个命令之间的原子性
     */
    return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
            "if (redis.call('hexists', KEYS[1], ARGV[3]) == 0) then " +
                    "return nil;" +
                    "end; " +
                    "local counter = redis.call('hincrby', KEYS[1], ARGV[3], -1); " +
                    "if (counter > 0) then " +
                    "redis.call('pexpire', KEYS[1], ARGV[2]); " +
                    "return 0; " +
                    "else " +
                    "redis.call('del', KEYS[1]); " +
                    "redis.call('publish', KEYS[2], ARGV[1]); " +
                    "return 1; " +
                    "end; " +
                    "return nil;",
            Arrays.asList(getRawName(), getChannelName()), LockPubSub.UNLOCK_MESSAGE, internalLockLeaseTime, getLockName(threadId));
}