序
本文主要研究一下redisson的分布式锁
maven
<dependency>
<groupId>org.redisson</groupId>
<artifactId>redisson</artifactId>
<version>3.8.1</version>
</dependency>实例
@Test
public void testDistributedLock(){
Config config = new Config();
// config.setTransportMode(TransportMode.EPOLL);
config.useSingleServer()
.setAddress("redis://192.168.99.100:6379");
RedissonClient redisson = Redisson.create(config);
IntStream.rangeClosed(1,5)
.parallel()
.forEach(i -> {
executeLock(redisson);
});
executeLock(redisson);
}
public void executeLock(RedissonClient redisson){
RLock lock = redisson.getLock("myLock");
boolean locked = false;
try{
LOGGER.info("try lock");
locked = lock.tryLock();
// locked = lock.tryLock(1,2,TimeUnit.MINUTES);
LOGGER.info("get lock result:{}",locked);
if(locked){
TimeUnit.HOURS.sleep(1);
LOGGER.info("get lock and finish");
}
}catch (Exception e){
e.printStackTrace();
}finally {
LOGGER.info("enter unlock");
if(locked){
lock.unlock();
}
}
}源码解析
RedissonLock.tryLock
redisson-3.8.1-sources.jar!/org/redisson/RedissonLock.java
@Override
public boolean tryLock() {
return get(tryLockAsync());
}
@Override
public RFuture<Boolean> tryLockAsync() {
return tryLockAsync(Thread.currentThread().getId());
}
@Override
public RFuture<Boolean> tryLockAsync(long threadId) {
return tryAcquireOnceAsync(-1, null, threadId);
}
private RFuture<Boolean> tryAcquireOnceAsync(long leaseTime, TimeUnit unit, final long threadId) {
if (leaseTime != -1) {
return tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_NULL_BOOLEAN);
}
RFuture<Boolean> ttlRemainingFuture = tryLockInnerAsync(commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_NULL_BOOLEAN);
ttlRemainingFuture.addListener(new FutureListener<Boolean>() {
@Override
public void operationComplete(Future<Boolean> future) throws Exception {
if (!future.isSuccess()) {
return;
}
Boolean ttlRemaining = future.getNow();
// lock acquired
if (ttlRemaining) {
scheduleExpirationRenewal(threadId);
}
}
});
return ttlRemainingFuture;
}
<T> RFuture<T> tryLockInnerAsync(long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
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));
}
protected String getLockName(long threadId) {
return id + ":" + threadId;
}
private void scheduleExpirationRenewal(final long threadId) {
if (expirationRenewalMap.containsKey(getEntryName())) {
return;
}
Timeout task = commandExecutor.getConnectionManager().newTimeout(new TimerTask() {
@Override
public void run(Timeout timeout) throws Exception {
RFuture<Boolean> future = renewExpirationAsync(threadId);
future.addListener(new FutureListener<Boolean>() {
@Override
public void operationComplete(Future<Boolean> future) throws Exception {
expirationRenewalMap.remove(getEntryName());
if (!future.isSuccess()) {
log.error("Can't update lock " + getName() + " expiration", future.cause());
return;
}
if (future.getNow()) {
// reschedule itself
scheduleExpirationRenewal(threadId);
}
}
});
}
}, internalLockLeaseTime / 3, TimeUnit.MILLISECONDS);
if (expirationRenewalMap.putIfAbsent(getEntryName(), new ExpirationEntry(threadId, task)) != null) {
task.cancel();
}
}
protected RFuture<Boolean> renewExpirationAsync(long threadId) {
return commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
"if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +
"redis.call('pexpire', KEYS[1], ARGV[1]); " +
"return 1; " +
"end; " +
"return 0;",
Collections.<Object>singletonList(getName()),
internalLockLeaseTime, getLockName(threadId));
}
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;
}- 这里leaseTime没有设置的话，默认是-1，使用的是commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout()，默认为30秒
- tryLockInnerAsync使用的是一段lua脚本，该脚本有3个参数，第一个参数为KEYS数组，后面几个参数为ARGV数组的元素
- 这里key的值为调用方指定的这个redissonLock的名称，两个变量，第一个为leaseTime，第二个为锁的名称，使用redissonLock的id+线程id
- lua脚本第一个方法判断redissonLock的hashmap是否存在，如果不存在则创建，该hashmap有一个entry的key为锁名称，valude为1，之后设置该hashmap失效时间为leaseTime
- lua脚本第二个方法是在redissonLock的hashmap存在的情况下，将该锁名的value增1，同时设置失效时间为leaseTime
- 最后返回该redissonLock名称的key的ttl
- 执行成功之后判断ttl是否还有值，有的话则调用scheduleExpirationRenewal，防止lock未执行完就失效
- scheduleExpirationRenewal是注册一个延时任务，在internalLockLeaseTime / 3的时候触发，执行的方法是renewExpirationAsync，将该锁失效时间重置回internalLockLeaseTime
- scheduleExpirationRenewal里头给scheduleExpirationRenewal任务增加listener，如果设置成功之后还会再次递归调用scheduleExpirationRenewal重新注册延时任务
- tryAcquireAsync(long leaseTime, TimeUnit unit, final long threadId)方法是指定自动解锁时间时调用的方法，它与tryAcquireOnceAsync的区别在于，它对ttl的方回值采用long值来判断，如果是null，才执行延长失效时间的定时任务，而tryAcquireOnceAsync方法采用的是BooleanNullReplayConvertor，只要返回不是null，则返回true
RedissonLock.unlock
redisson-3.8.1-sources.jar!/org/redisson/RedissonLock.java
@Override
public void unlock() {
try {
get(unlockAsync(Thread.currentThread().getId()));
} catch (RedisException e) {
if (e.getCause() instanceof IllegalMonitorStateException) {
throw (IllegalMonitorStateException)e.getCause();
} else {
throw e;
}
}
// Future<Void> future = unlockAsync();
// future.awaitUninterruptibly();
// if (future.isSuccess()) {
// return;
// }
// if (future.cause() instanceof IllegalMonitorStateException) {
// throw (IllegalMonitorStateException)future.cause();
// }
// throw commandExecutor.convertException(future);
}
@Override
public RFuture<Void> unlockAsync(final long threadId) {
final RPromise<Void> result = new RedissonPromise<Void>();
RFuture<Boolean> future = unlockInnerAsync(threadId);
future.addListener(new FutureListener<Boolean>() {
@Override
public void operationComplete(Future<Boolean> future) throws Exception {
if (!future.isSuccess()) {
cancelExpirationRenewal(threadId);
result.tryFailure(future.cause());
return;
}
Boolean opStatus = future.getNow();
if (opStatus == null) {
IllegalMonitorStateException cause = new IllegalMonitorStateException("attempt to unlock lock, not locked by current thread by node id: "
+ id + " thread-id: " + threadId);
result.tryFailure(cause);
return;
}
if (opStatus) {
cancelExpirationRenewal(null);
}
result.trySuccess(null);
}
});
return result;
}
protected RFuture<Boolean> unlockInnerAsync(long threadId) {
return commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
"if (redis.call('exists', KEYS[1]) == 0) then " +
"redis.call('publish', KEYS[2], ARGV[1]); " +
"return 1; " +
"end;" +
"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.<Object>asList(getName(), getChannelName()), LockPubSub.unlockMessage, internalLockLeaseTime, getLockName(threadId));
}
String getChannelName() {
return prefixName("redisson_lock__channel", getName());
}
void cancelExpirationRenewal(Long threadId) {
ExpirationEntry task = expirationRenewalMap.get(getEntryName());
if (task != null && (threadId == null || task.getThreadId() == threadId)) {
expirationRenewalMap.remove(getEntryName());
task.getTimeout().cancel();
}
}- unlockInnerAsync通过lua脚本来释放锁，该lua使用两个key，一个是redissonLock名称，一个是channelName
- 该lua使用的变量有三个，一个是pubSub的unlockMessage，默认为0，一个是internalLockLeaseTime，默认为commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout()，一个是锁名称
- 如果该redissonLock不存在，则直接发布unlock消息返回1；如果该锁不存在则返回nil；
- 如果该锁存在则将其计数-1，如果counter大于0，则重置下失效时间，返回0；如果counter不大于0，则删除该redissonLock锁，发布unlockMessage，返回1；如果上面条件都没有命中返回nil
- unlockAsync里头对unlockInnerAsync注册了FutureListener，主要是调用cancelExpirationRenewal，取消掉scheduleExpirationRenewal任务
LockPubSub
redisson-3.8.1-sources.jar!/org/redisson/pubsub/LockPubSub.java
public class LockPubSub extends PublishSubscribe<RedissonLockEntry> {
public static final Long unlockMessage = 0L;
@Override
protected RedissonLockEntry createEntry(RPromise<RedissonLockEntry> newPromise) {
return new RedissonLockEntry(newPromise);
}
@Override
protected void onMessage(RedissonLockEntry value, Long message) {
if (message.equals(unlockMessage)) {
Runnable runnableToExecute = value.getListeners().poll();
if (runnableToExecute != null) {
runnableToExecute.run();
}
value.getLatch().release();
}
}
}- 接收到unlockMessage的时候，会调用RedissonLockEntry的listener，然后触发latch的release
- tryAcquireOnceAsync这个方法默认没有创建LockPubSub，而且没有指定自动解锁时间，则定时任务会一直延长失效时间，这个可能存在锁一直没释放的风险
小结
加锁有如下注意事项：
- 加锁需要设置超时时间，防止出现死锁
- 加锁以及设置超时时间的时候，需要保证两个操作的原子性，因而最好使用lua脚本或者使用支持NX以及EX的set方法
- 加锁的时候需要把加锁的调用方信息，比如线程id给记录下来，这个在解锁的时候需要使用
- 对于加锁时长不确定的任务，为防止任务未执行完导致超时被释放，需要对尚未运行完的任务延长失效时间
解锁有如下注意事项：
- 解锁一系列操作(
判断key是否存在，存在的话删除key等)需要保证原子性，因而最好使用lua脚本 - 解锁需要判断调用方是否与加锁时记录的是否一致，防止锁被误删
- 如果有延续失效时间的延时任务，在解锁的时候，需要终止掉该任务
