Springboot基于Redisson如何实现Redis分布式可重入锁源码解析

Springboot基于Redisson如何实现Redis分布式可重入锁源码解析

Redis是一种高性能的key-value存储系统,被广泛应用于缓存、消息中间件、分布式锁等场景。而在分布式系统中,分布式锁是保证共享资源互斥访问的常用方式。而Redis提供了分布式锁的实现方式,但是为了防止死锁等问题,Redisson则提供了更好的实现方式:Redis可重入分布式锁。本文将介绍Springboot基于Redisson实现这一分布式锁的源码解析。

1. Redisson简介

Redisson是一个Java的Redis客户端,提供了分布式和纯Java的数据结构之间的一个桥梁。它包含了一些常见的Redis应用场景的接口实现,如分布式锁、分布式集合、分布式消息队列等。Redisson所提供的分布式锁实现是可重入的,可以避免死锁和竞争条件的发生。

2. Redis可重入分布式锁实现

Redis可重入分布式锁是一种特殊的分布式锁实现方式,它可以保证同一个线程对同一个锁的重复获取不会导致锁被其他线程释放。在Redisson中,可重入分布式锁的实现使用了Redis的String结构来存储锁的状态,通过setnx命令和Lua脚本来实现锁的获取和释放。

2.1 Redisson可重入分布式锁的获取

Redisson可重入分布式锁的获取过程如下:

1. 使用setnx尝试获取锁,如果返回1,则表示获取到锁,设置锁的过期时间并返回。

2. 如果返回0,则表示锁已经被其他线程获取了,此时需要判断是否是同一个线程获取了锁。

3. 如果是同一个线程获取了锁,则可以直接重入锁,并更新锁的过期时间。

4. 如果不是同一个线程获取了锁,则需要等待其他线程释放锁,并重复尝试获取锁。

这个过程可以用Java代码来表示,如下:

RLock lock = redisson.getLock("myLock");

try {

if (lock.tryLock()) {

// 获取到锁了

// TODO: 处理获取到锁之后的业务逻辑

} else {

// 没有获取到锁

// TODO: 处理没有获取到锁之后的业务逻辑

}

} finally {

lock.unlock();

}

2.2 Redisson可重入分布式锁的释放

Redisson可重入分布式锁的释放过程如下:

1. 使用Lua脚本判断当前线程是否持有锁。

2. 如果持有锁,则根据锁的计数器来判断当前线程是否重复获取了锁。

3. 如果没有重复获取锁,则将锁的计数器减1。

4. 如果锁的计数器已经为0,则删除锁的状态,释放锁。

5. 如果不是持有锁,则抛出IllegalMonitorStateException异常。

这个过程可以用Java代码来表示,如下:

RLock lock = redisson.getLock("myLock");

try {

// TODO: 处理业务逻辑

} finally {

if (lock.isHeldByCurrentThread()) {

if (lock.getHoldCount() == 1) {

lock.unlock();

} else {

lock.unlock();

}

} else {

throw new IllegalMonitorStateException("current thread does not hold the lock");

}

}

3. Redisson可重入分布式锁源码解析

在Redisson中,RLock接口是Redisson可重入分布式锁的核心接口,通过该接口提供了Redis分布式可重入锁的所有功能。它定义了获取锁和释放锁的方法,以及一些与锁的状态相关的方法。下面,我们将从RLock接口的实现类RLockImpl的源码入手,对Redisson可重入分布式锁的源码进行分析。

3.1 RLockImpl源码

RLockImpl是Redisson可重入分布式锁的核心实现类,它实现了RLock接口,并提供了获取锁和释放锁的方法。下面是RLockImpl的源码:

public class RLockImpl extends RedissonObject implements RLock {

private final String id;

private final LockPubSub pubSub;

private volatile RedissonLockEntry currentLock;

public RLockImpl(CommandAsyncExecutor commandExecutor, String name, UUID id) {

super(commandExecutor, name);

this.id = id.toString();

pubSub = commandExecutor.getConnectionManager().getSubscribeService().getLockPubSub();

}

// 获取锁

@Override

public void lock() {

get(lockAsync(-1, null, false)).joinUninterruptibly();

}

// 获取锁(可中断)

@Override

public void lockInterruptibly() throws InterruptedException {

get(lockAsync(-1, null, true)).syncInterruptibly();

}

// 尝试获取锁

@Override

public boolean tryLock() {

return get(tryLockAsync()).now();

}

// 尝试获取锁(带超时时间)

@Override

public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {

return get(tryLockAsync(time, unit)).get();

}

// 尝试获取锁(带超时时间和等待时间)

@Override

public boolean tryLock(long waitTime, long leaseTime, TimeUnit unit) throws InterruptedException {

return get(tryLockAsync(waitTime, leaseTime, unit)).get();

}

// 释放锁

@Override

public void unlock() {

get(unlockAsync()).now();

}

// 获取锁(异步)

@Override

public RFuture lockAsync() {

return lockAsync(-1, null, false);

}

// 获取锁(可中断)(异步)

@Override

public RFuture lockInterruptiblyAsync() {

return lockAsync(-1, null, true);

}

// 尝试获取锁(异步)

@Override

public RFuture tryLockAsync() {

return tryLockAsync(-1, null);

}

// 尝试获取锁(带超时时间)(异步)

@Override

public RFuture tryLockAsync(long time, TimeUnit unit) {

return tryLockAsync(time, -1, unit);

}

// 尝试获取锁(带超时时间和等待时间)(异步)

@Override

public RFuture tryLockAsync(long waitTime, long leaseTime, TimeUnit unit) {

checkTimeout(waitTime, leaseTime);

long internalLockLeaseTime = unit.toMillis(leaseTime);

long threadWaitTime = unit.toMillis(waitTime);

RedisAsyncConnection async = commandExecutor.getConnectionManager().getAsync(connectionManager.getSlot(getName()));

return tryLockAsync(waitTime, leaseTime, internalLockLeaseTime, threadWaitTime, async);

}

// 释放锁(异步)

@Override

public RFuture unlockAsync() {

RedisAsyncConnection async = commandExecutor.getConnectionManager().getAsync(connectionManager.getSlot(getName()));

return unlockAsync(async);

}

private RFuture unlockAsync(RedisAsyncConnection async) {

final RedissonLockEntry entry = currentLock;

if (entry == null) {

return RedissonPromise.newSucceededFuture(null);

}

if (!entry.isHeldByCurrentThread()) {

throw new IllegalMonitorStateException("Attempt to unlock read lock, not locked by current thread by node id: " + entry.getNodeId());

}

currentLock = null;

entry.unlockAsync(async, id);

return entry.getLatch();

}

private RFuture acquireFailedAsync(long waitTime, TimeUnit unit, RFuture futureLock) throws InterruptedException {

if (!futureLock.await(waitTime, unit)) {

return RedissonPromise.newSucceededFuture(null);

}

return entry(futureLock.getNow());

}

private void checkTimeout(long waitTime, long leaseTime) {

if (waitTime < 0) {

throw new IllegalArgumentException("waitTime can't be negative");

}

if (leaseTime < 0) {

throw new IllegalArgumentException("leaseTime can't be negative");

}

}

private RFuture lockAsync(long leaseTime, TimeUnit unit, boolean interruptibly) {

if (interruptibly) {

return handleLockInternallyInterruptiblyAsync(-1, null, leaseTime, unit);

}

return handleLockInternallyAsync(-1, null, leaseTime, unit);

}

private RFuture tryLockAsync(long waitTime, long leaseTime, long internalLockLeaseTime, long threadWaitTime, RedisAsyncConnection async) {

long currentTime = System.currentTimeMillis();

if (waitTime == -1 && leaseTime == -1) {

return tryAcquireOnceAsync(currentTime, internalLockLeaseTime, async);

}

long timeout = -1;

if (waitTime != -1) {

timeout = currentTime + unit.toMillis(waitTime);

}

final RFuture futureLock;

if (leaseTime == -1) {

LockPubSub trySubscribe = new LockPubSub() {

@Override

public void onUnlock(String channelName, String val) {

super.onUnlock(channelName, val);

LockPubSub.this.onUnlock(channelName, val);

}

};

try {

String entryName = RedissonLockHelper.getLockName(id, 0);

futureLock = subscribe(threadWaitTime, timeout, async, trySubscribe, entryName);

} finally {

unsubscribe(async, trySubscribe);

}

} else {

LockPubSub trySubscribe = new LockPubSub() {

@Override

public void messageReceived(String channel, String message) {

super.messageReceived(channel, message);

LockPubSub.this.messageReceived(channel, message);

}

};

try {

String entryName = RedissonLockHelper.getLockName(id, internalLockLeaseTime);

futureLock = subscribe(threadWaitTime, timeout, async, trySubscribe, entryName);

} finally {

unsubscribe(async, trySubscribe);

}

}

return acquireFailedAsync(waitTime, unit, futureLock);

}

//...

}

3.2 RedissonLockEntry源码

RedissonLockEntry是用于存储Redisson可重入分布式锁的状态信息的类,它包含了锁的状态信息,包括锁的持有者、锁的计数器、锁的过期时间等。下面是RedissonLockEntry的源码:

public class RedissonLockEntry implements LockEntry {

private final String name;

private final String id;

private final long threadId;

private final int lockCount;

private final long createTime;

private final long expiryTime;

private final String nodeId;

private final long currentThreadId;

private final long timeout;

private final long leaseTime;

private final AtomicIntegerFieldUpdater lockStateUpdater;

@SuppressWarnings("unused")

private volatile int lockState;

private final RPromise unlockPromise;

private final RPromise promise;

private final LockPubSub pubSub;

private final RFuture future;

// ...

}

RedissonLockEntry中的lockState字段用于记录锁的状态,其中值为0表示未被锁定,值为1表示已被锁定,但是没有被当前线程持有,值为2及以上表示已被锁定,并且被当前线程持有的次数。

4. 总结

Redisson可重入分布式锁实现了分布式可重入锁的功能,并使用了Redis的String结构来存储锁的状态,通过setnx命令和Lua脚本来实现锁的获取和释放。本文对Redisson可重入分布式锁的实现过程进行了详细的介绍并对其源码进行了分析。通过了解Redisson可重入分布式锁的实现,可以更好地应用Redisson分布式锁来保证共享资源的互斥访问,避免死锁和竞争条件的发生,从而提高分布式系统的稳定性和可靠性。

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