追踪一下redission加锁的实现源码，并详细介绍核心加锁代码lua脚本的执行原理和过程。
1.获取锁
这里是我们自己实现，调用redission的方法，获取锁，然后加锁。lock.lock(expireTime, timeUnit)是关键，我们追进去。
/**
* 获取锁，如果没有主动调用unlock解锁，expireTime后会自动释放
* @param lockKey
* @param expireTime 如果没有调用unlock解锁，expireTime 后自动释放
* @param timeUnit 时间单位
* @return
*/
public RLock lock(String lockKey,Integer expireTime,TimeUnit timeUnit){
RLock lock = redisson.getLock(lockKey);
lock.lock(expireTime, timeUnit);
logger.info("【Redisson lock】success to acquire lock for [ " lockKey " ],expire time:" expireTime timeUnit);
return lock;
}进入 lock.lock(expireTime, timeUnit);
/**
* Acquires the lock.
*
* <p>If the lock is not available then the current thread becomes
* disabled for thread scheduling purposes and lies dormant until the
* lock has been acquired.
*
* If the lock is acquired, it is held until <code>unlock</code> is invoked,
* or until leaseTime milliseconds have passed
* since the lock was granted - whichever comes first.
*
* @param leaseTime the maximum time to hold the lock after granting it,
* before automatically releasing it if it hasn't already been released by invoking <code>unlock</code>.
* If leaseTime is -1, hold the lock until explicitly unlocked.
* @param unit the time unit of the {@code leaseTime} argument
*
*/
void lock(long leaseTime, TimeUnit unit);进入实现方法
代码语言：javascript复制 @Override
public void lock(long leaseTime, TimeUnit unit) {
try {
lockInterruptibly(leaseTime, unit);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}进入 lockInterruptibly(leaseTime, unit);
@Override
public void lockInterruptibly(long leaseTime, TimeUnit unit) throws InterruptedException {
long threadId = Thread.currentThread().getId();
Long ttl = tryAcquire(leaseTime, unit, threadId);
// lock acquired
if (ttl == null) {
return;
}
RFuture<RedissonLockEntry> 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));
}进入Long ttl = tryAcquire(leaseTime, unit, threadId);
private Long tryAcquire(long leaseTime, TimeUnit unit, long threadId) {
return get(tryAcquireAsync(leaseTime, unit, threadId));
}进入
代码语言：javascript复制 private <T> RFuture<Long> tryAcquireAsync(long leaseTime, TimeUnit unit, final long threadId) {
if (leaseTime != -1) {
return tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
}
RFuture<Long> ttlRemainingFuture = tryLockInnerAsync(commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);
ttlRemainingFuture.addListener(new FutureListener<Long>() {
@Override
public void operationComplete(Future<Long> future) throws Exception {
if (!future.isSuccess()) {
return;
}
Long ttlRemaining = future.getNow();
// lock acquired
if (ttlRemaining == null) {
scheduleExpirationRenewal(threadId);
}
}
});
return ttlRemainingFuture;
}进入核心tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG)
这里是加锁的核心方法：
代码语言：javascript复制 <T> RFuture<T> tryLockInnerAsync(long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
//时间转化为毫秒值
internalLockLeaseTime = unit.toMillis(leaseTime);
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.<Object>singletonList(getName()), internalLockLeaseTime, getLockName(threadId));
}这里最终的是执行了一段具有原子性的lua脚本，由CommandAsynExecutor执行； 这个锁最终持久化到redis时，使用的是hash类型的key field value; 这里注意下最后一行几个参数的对应关系： getName()), internalLockLeaseTime, getLockName(threadId) 分别是key[1],ARGV[1],ARGV[2];
- getName()是逻辑锁名称，例如：我们发起锁的一方传递的锁名称 productId1672822；
- internalLockLeaseTime是毫秒单位的锁过期时间；
- getLockName则是锁对应的线程级别的名称，因为支持相同线程可重入，不同线程不可重入，所以这里的锁的生成方式是：UUID ":"threadId
Lua脚本中的执行分为以下三步：
- 1:exists检查redis中是否存在锁名称；如果不存在，则获取成功；同时把逻辑锁名称KEYS[1]，线程级别的锁名称[ARGV[2]，value=1,设置到redis。并设置逻辑锁名称的过期时间ARGV[2]，返回；
- 2:如果检查到存在KEYS[1],[ARGV[2],则说明获取成功，此时会自增对应的value值，记录重入次数；并更新锁的过期时间
- 3：key不存，直接返回key的剩余过期时间（-2）
