之前说的如果使用setnx做分布式锁的时候，会有锁续期的问题，也就是说如果锁过期时间10s，而业务处理花了30s，而redisson就可以处理恰好处理这类锁续期的问题；

而这类自动续期的机制就是所谓的看门狗机制

总的来说就是默认锁过期时间是30s，而自动续期机制在源码当中就是开启了定时任务，定时间隔是看门狗时间的三分之一，也就是10s，所以就是在业务没有处理完的情况下锁默认每隔10s续期到30s；

下面主要看看源码当中是怎么定义的；

看门狗源码分析

源码：RedissonLock.class

private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException {
    long threadId = Thread.currentThread().getId();
    Long ttl = this.tryAcquire(leaseTime, unit, threadId);
    if (ttl != null) {
        RFuture<RedissonLockEntry> future = this.subscribe(threadId);
        if (interruptibly) {
            this.commandExecutor.syncSubscriptionInterrupted(future);
        } else {
            this.commandExecutor.syncSubscription(future);
        }

        try {
            while(true) {
                ttl = this.tryAcquire(leaseTime, unit, threadId);
                if (ttl == null) {
                    return;
                }

                if (ttl >= 0L) {
                    try {
                        ((RedissonLockEntry)future.getNow()).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);
                    } catch (InterruptedException var13) {
                        if (interruptibly) {
                            throw var13;
                        }

                        ((RedissonLockEntry)future.getNow()).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);
                    }
                } else if (interruptibly) {
                    ((RedissonLockEntry)future.getNow()).getLatch().acquire();
                } else {
                    ((RedissonLockEntry)future.getNow()).getLatch().acquireUninterruptibly();
                }
            }
        } finally {
            this.unsubscribe(future, threadId);
        }
    }
}

private Long tryAcquire(long leaseTime, TimeUnit unit, long threadId) {
    return (Long)this.get(this.tryAcquireAsync(leaseTime, unit, threadId));
}

private RFuture<Boolean> tryAcquireOnceAsync(long leaseTime, TimeUnit unit, long threadId) {
    if (leaseTime != -1L) {
        return this.tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_NULL_BOOLEAN);
    } else {
        //此处获取锁的看门狗的时间getLockWatchdogTimeout()
        RFuture<Boolean> ttlRemainingFuture = this.tryLockInnerAsync(this.commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_NULL_BOOLEAN);
        ttlRemainingFuture.onComplete((ttlRemaining, e) -> {
            if (e == null) {
                if (ttlRemaining) {
                    this.scheduleExpirationRenewal(threadId);
                }

            }
        });
        return ttlRemainingFuture;
    }
}

private <T> RFuture<Long> tryAcquireAsync(long leaseTime, TimeUnit unit, long threadId) {
    if (leaseTime != -1L) {
        return this.tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
    } else {
        RFuture<Long> ttlRemainingFuture = this.tryLockInnerAsync(this.commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);
        ttlRemainingFuture.onComplete((ttlRemaining, e) -> {
            if (e == null) {
                if (ttlRemaining == null) {
                    this.scheduleExpirationRenewal(threadId);
                }

            }
        });
        return ttlRemainingFuture;
    }
}

得到看门狗的超时时间

this.lockWatchdogTimeout = 30000L;//配置看门狗的超时时间为30s

private long lockWatchdogTimeout;
public long getLockWatchdogTimeout() {
    return this.lockWatchdogTimeout;
}
public Config() {
    this.transportMode = TransportMode.NIO;
    this.lockWatchdogTimeout = 30000L;//配置看门狗的超时时间为30s
    this.keepPubSubOrder = true;
    this.decodeInExecutor = false;
    this.useScriptCache = false;
    this.minCleanUpDelay = 5;
    this.maxCleanUpDelay = 1800;
    this.cleanUpKeysAmount = 100;
    this.nettyHook = new DefaultNettyHook();
    this.useThreadClassLoader = true;
    this.addressResolverGroupFactory = new DnsAddressResolverGroupFactory();
}

占锁

private <T> RFuture<Long> tryAcquireAsync(long leaseTime, TimeUnit unit, long threadId) {
    if (leaseTime != -1L) {
        return this.tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
    } else {
        //异步编排，去占锁
        RFuture<Long> ttlRemainingFuture = this.tryLockInnerAsync(this.commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);
        //占锁成功
        ttlRemainingFuture.onComplete((ttlRemaining, e) -> {
            if (e == null) {
                if (ttlRemaining == null) {
                    this.scheduleExpirationRenewal(threadId);
                }

            }
        });
        return ttlRemainingFuture;
    }
}

private void scheduleExpirationRenewal(long threadId) {
    RedissonLock.ExpirationEntry entry = new RedissonLock.ExpirationEntry();
    RedissonLock.ExpirationEntry oldEntry = (RedissonLock.ExpirationEntry)EXPIRATION_RENEWAL_MAP.putIfAbsent(this.getEntryName(), entry);
    if (oldEntry != null) {
        oldEntry.addThreadId(threadId);
    } else {
        entry.addThreadId(threadId);
        //重新设置过期时间
        this.renewExpiration();
    }
}

重新设置过期时间,续期

开启定时任务new TimerTask()来自动续期；间隔是this.internalLockLeaseTime / 3L，也就是10s；

private void renewExpiration() {
    RedissonLock.ExpirationEntry ee = (RedissonLock.ExpirationEntry)EXPIRATION_RENEWAL_MAP.get(this.getEntryName());
    if (ee != null) {
        Timeout task = this.commandExecutor.getConnectionManager().newTimeout(new TimerTask() {
            public void run(Timeout timeout) throws Exception {
                RedissonLock.ExpirationEntry ent = (RedissonLock.ExpirationEntry)RedissonLock.EXPIRATION_RENEWAL_MAP.get(RedissonLock.this.getEntryName());
                if (ent != null) {
                    Long threadId = ent.getFirstThreadId();
                    if (threadId != null) {
                        RFuture<Boolean> future = RedissonLock.this.renewExpirationAsync(threadId);
                        future.onComplete((res, e) -> {
                            if (e != null) {
                                RedissonLock.log.error("Can't update lock " + RedissonLock.this.getName() + " expiration", e);
                            } else {
                                if (res) {
                                    RedissonLock.this.renewExpiration();
                                }

                            }
                        });
                    }
                }
            }
        }, this.internalLockLeaseTime / 3L, TimeUnit.MILLISECONDS);
        ee.setTimeout(task);
    }
}