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
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