这是常规Redisson使用代码
@Autowired
Redisson redisson;
@Test
public void Redisson入门Demo() {
String lockKey = "自定义一个key(一般是用户Id锁自己的操作)";
RLock redissonLock = redisson.getLock(lockKey);
boolean doLockRes = redissonLock.tryLock();
if (doLockRes) {
try {
// TODO 执行业务操作
} finally {
if (doLockRes) {
redissonLock.unlock();
}
}
} else {
System.out.println("加锁失败!");
}
}
idea查看trylock方法 其是一个接口,我们去找具体实现RedisonLock类的发现其调用
@Override
public boolean tryLock() {
return get(tryLockAsync());
}
<T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
"if (redis.call('exists', KEYS[1]) == 0) then " +
"redis.call('hincrby', 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.singletonList(getRawName()), unit.toMillis(leaseTime), getLockName(threadId));
}
原码讲解:
整体讲解
上述就是lua的加锁脚本。再去看看释放锁的源码(也再RedisonLock类中):
protected RFuture<Boolean> unlockInnerAsync(long threadId) {
return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
"if (redis.call('hexists', KEYS[1], ARGV[3]) == 0) then " +
"return nil;" +
"end; " +
"local counter = redis.call('hincrby', KEYS[1], ARGV[3], -1); " +
"if (counter > 0) then " +
"redis.call('pexpire', KEYS[1], ARGV[2]); " +
"return 0; " +
"else " +
"redis.call('del', KEYS[1]); " +
"redis.call('publish', KEYS[2], ARGV[1]); " +
"return 1; " +
"end; " +
"return nil;",
Arrays.asList(getRawName(), getChannelName()), LockPubSub.UNLOCK_MESSAGE, internalLockLeaseTime, getLockName(threadId));
}
大致原理太多太复杂了,不搞了!
Redis主从在切换时,会导致数据不一致。如果在切换异常期间就会导致解锁失败等情况。
Redisson解决办法时MuiltLock。就是向所有节点加锁,当所有节点锁加成功后,才算加锁成功!避免了数据不一致性!
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