RedissonLock-tryLock-续期
redisson版本3.16.6
1.什么是看门狗
Redisson提供的分布式锁是支持锁自动续期的，也就是说，如果线程仍旧没有执行完，那么redisson会自动给redis中的目标key延长超时时间，这在Redisson中称之为 Watch Dog 机制。默认情况下，看门狗的检查锁的超时时间是30秒钟，也可以通过修改Config.lockWatchdogTimeout来另行指定。
2.什么情况会续期
什么情况会续期，总结一句话：不传入leaseTime（锁自动释放时间），使用默认值-1；
tryLock可传入参数有三个
lockName需要锁住的内容关键字
waitTime 获取锁最大等待时间，没有传-1
leaseTime锁自动释放时间，没有传-1
boolean tryLock 重载了三个方法，分别如下：
boolean tryLock(String lockName);boolean tryLock(String lockName, long waitTime) throws InterruptedException;boolean tryLock(String lockName, long waitTime, long leaseTime) throws InterruptedException;从实现上看，使用才传参，不用，千万别主动写入-1，会对入参有校验。可以实现续期的情况只能使用前两个构造器，不能使用主动传入leaseTime的构造器。为什么这么说呢，源码如下：
方法都会调用tryLock获取锁，tryLock方法中调用tryAcquire方法
public boolean tryLock(long waitTime, long leaseTime, TimeUnit unit) throws InterruptedException {long time = unit.toMillis(waitTime);long current = System.currentTimeMillis();long threadId = Thread.currentThread().getId();Long ttl = tryAcquire(waitTime, leaseTime, unit, threadId);// lock acquiredif (ttl == null) {return true;}....省略tryAcquire方法会调用tryAcquireAsync，源码如下：
private <T> RFuture<Long> tryAcquireAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId) {RFuture<Long> ttlRemainingFuture;if (leaseTime != -1) {ttlRemainingFuture = tryLockInnerAsync(waitTime, leaseTime, unit, threadId, RedisCommands.EVAL_LONG);} else {ttlRemainingFuture = tryLockInnerAsync(waitTime, internalLockLeaseTime,TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);}ttlRemainingFuture.onComplete((ttlRemaining, e) -> {if (e != null) {return;}// lock acquiredif (ttlRemaining == null) {if (leaseTime != -1) {internalLockLeaseTime = unit.toMillis(leaseTime);} else {scheduleExpirationRenewal(threadId);}}});return ttlRemainingFuture;
}从源码上看，只有当leaseTime为-1时scheduleExpirationRenewal这个方法才会生效，这个方法会进行续期。
3.续期源码分析
启一个task任务进行锁的自动续期
scheduleExpirationRenewal()->renewExpiration()
private void renewExpiration() {ExpirationEntry ee = EXPIRATION_RENEWAL_MAP.get(getEntryName());if (ee == null) {return;}// 启一个定时任务Timeout task = commandExecutor.getConnectionManager().newTimeout(new TimerTask() {@Overridepublic void run(Timeout timeout) throws Exception {ExpirationEntry ent = EXPIRATION_RENEWAL_MAP.get(getEntryName());if (ent == null) {return;}Long threadId = ent.getFirstThreadId();if (threadId == null) {return;}// 核心续期代码，执行lua脚本RFuture<Boolean> future = renewExpirationAsync(threadId);future.onComplete((res, e) -> {if (e != null) {log.error("Can't update lock " + getRawName() + " expiration", e);EXPIRATION_RENEWAL_MAP.remove(getEntryName());return;}if (res) {// renewExpirationAsync执行成功，进行递归调用，调用自己，就可以实现不停的续期// 第一次执行这个函数，设置task任务，10s后执行task任务，刷新有效期，又重新设置一个task任务，10s后执行renewExpiration();} else {cancelExpirationRenewal(null);}});}// 定时任务是lockWatchdogTimeout的1/3时间去执行，就是每10s执行一次,renewExpirationAsync进行续期}, internalLockLeaseTime / 3, TimeUnit.MILLISECONDS);ee.setTimeout(task);
}