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
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
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
ttlRemainingFuture.onComplete((ttlRemaining, e) -> {
if (e == null) {
if (ttlRemaining) {
this.scheduleExpirationRenewal(threadId);
}
}
});
return ttlRemainingFuture;
}
}
private
if (leaseTime != -1L) {
return this.tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
} else {
RFuture
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
if (leaseTime != -1L) {
return this.tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
} else {
//异步编排，去占锁
RFuture
//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
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);
}
}