redis分布式锁：Redisson（看门狗的底层代码实现）

1、由此rlock.lock()进入源码

public class GrabRedisRedissonServiceImpl implements GrabService {

	@Autowired
	RedissonClient redissonClient;
	
	@Autowired
	OrderService orderService;
	
    @Override
    public ResponseResult grabOrder(int orderId , int driverId){
        //生成key
    	String lock = "order_"+(orderId+"");
    	
    	RLock rlock = redissonClient.getLock(lock.intern());
    	
    	
    	try {
    		// 此代码默认 设置key 超时时间30秒，过10秒，再延时
            //由此rlock.lock()进入源码
    		rlock.lock();
			System.out.println("司机:"+driverId+" 执行抢单逻辑");
			
            boolean b = orderService.grab(orderId, driverId);
            if(b) {
            	System.out.println("司机:"+driverId+" 抢单成功");
            }else {
            	System.out.println("司机:"+driverId+" 抢单失败");
            }
            
        } finally {
        	rlock.unlock();
        }
        return null;
    }
}

2、rt.jar包JUC（java->util->concurrent）目录下->locks的Lock接口类

 3、Lock接口类的实现类RedissonLock接口的重写lock() 方法

（步骤3->7均是在RedissonLock接口中的方法实现的）

                //由此方法进入
            lockInterruptibly();

@Override
    public void lock() {
        try {
            //由此方法进入
            lockInterruptibly();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }

4、        //由此进入方法
        Long ttl = tryAcquire(leaseTime, unit, threadId);

@Override
    public void lockInterruptibly(long leaseTime, TimeUnit unit) throws InterruptedException {
        long threadId = Thread.currentThread().getId();

        //由此进入方法
        Long ttl = tryAcquire(leaseTime, unit, threadId);

        // lock acquired
        if (ttl == null) {
            return;
        }

        RFuture future = subscribe(threadId);
        commandExecutor.syncSubscription(future);

        try {
            while (true) {
                ttl = tryAcquire(leaseTime, unit, threadId);
                // lock acquired
                if (ttl == null) {
                    break;
                }

                // waiting for message
                if (ttl >= 0) {
                    getEntry(threadId).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);
                } else {
                    getEntry(threadId).getLatch().acquire();
                }
            }
        } finally {
            unsubscribe(future, threadId);
        }
//        get(lockAsync(leaseTime, unit));
    }

5、//由此进入方法    tryAcquireAsync(leaseTime, unit, threadId)

private Long tryAcquire(long leaseTime, TimeUnit unit, long threadId) {
        
        //由此进入方法    tryAcquireAsync(leaseTime, unit, threadId)

        return get(tryAcquireAsync(leaseTime, unit, threadId));
    }

6、//由此进入方法

tryLockInnerAsync(LOCK_EXPIRATION_INTERVAL_SECONDS, TimeUnit.SECONDS, threadId, RedisCommands.EVAL_LONG);

private  RFuture tryAcquireAsync(long leaseTime, TimeUnit unit, final long threadId) {
        if (leaseTime != -1) {
            return tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
        }

        //由此进入方法 tryLockInnerAsync(LOCK_EXPIRATION_INTERVAL_SECONDS, TimeUnit.SECONDS, threadId, RedisCommands.EVAL_LONG);

        RFuture ttlRemainingFuture = tryLockInnerAsync(LOCK_EXPIRATION_INTERVAL_SECONDS, TimeUnit.SECONDS, threadId, RedisCommands.EVAL_LONG);
        ttlRemainingFuture.addListener(new FutureListener() {
            @Override
            public void operationComplete(Future future) throws Exception {
                if (!future.isSuccess()) {
                    return;
                }

                Long ttlRemaining = future.getNow();
                // lock acquired
                if (ttlRemaining == null) {
                    scheduleExpirationRenewal(threadId);
                }
            }
        });
        return ttlRemainingFuture;
    }

7、//找到关键信息：

最终是通过lua脚本实现，redis中的key默认为30s过期，每10秒查询一下key，并自动续期到30s，以此来实现看门狗自动续期的！

 RFuture tryLockInnerAsync(long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand command) {
        internalLockLeaseTime = unit.toMillis(leaseTime);


        //找到关键信息：最终是通过lua脚本实现，redis中的key默认为30s过期，每10秒查询一下key，并自动续期到30s，以此来实现看门狗自动续期的！

        return commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, command,
                  "if (redis.call('exists', KEYS[1]) == 0) then " +
                      "redis.call('hset', KEYS[1], ARGV[2], 1); " +
                      "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                      "return nil; " +
                  "end; " +
                  "if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +
                      "redis.call('hincrby', KEYS[1], ARGV[2], 1); " +
                      "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                      "return nil; " +
                  "end; " +
                  "return redis.call('pttl', KEYS[1]);",
                    Collections.