聊聊redisson的RLock的unlock

序

本文主要研究一下redisson的RLock的unlock

RLock

org/redisson/api/RLock.java

/**
 * Redis based implementation of {@link java.util.concurrent.locks.Lock}
 * Implements re-entrant lock.
 *
 * @author Nikita Koksharov
 *
 */
public interface RLock extends Lock, RLockAsync {

    /**
     * Returns name of object
     *
     * @return name - name of object
     */
    String getName();
    
    /**
     * Acquires the lock with defined <code>leaseTime</code>.
     * Waits if necessary until lock became available.
     *
     * Lock will be released automatically after defined <code>leaseTime</code> interval.
     *
     * @param leaseTime the maximum time to hold the lock after it's acquisition,
     *        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
     * @throws InterruptedException - if the thread is interrupted
     */
    void lockInterruptibly(long leaseTime, TimeUnit unit) throws InterruptedException;

    /**
     * Tries to acquire the lock with defined <code>leaseTime</code>.
     * Waits up to defined <code>waitTime</code> if necessary until the lock became available.
     *
     * Lock will be released automatically after defined <code>leaseTime</code> interval.
     *
     * @param waitTime the maximum time to acquire the lock
     * @param leaseTime lease time
     * @param unit time unit
     * @return <code>true</code> if lock is successfully acquired,
     *          otherwise <code>false</code> if lock is already set.
     * @throws InterruptedException - if the thread is interrupted
     */
    boolean tryLock(long waitTime, long leaseTime, TimeUnit unit) throws InterruptedException;

    /**
     * Acquires the lock with defined <code>leaseTime</code>.
     * Waits if necessary until lock became available.
     *
     * Lock will be released automatically after defined <code>leaseTime</code> interval.
     *
     * @param leaseTime the maximum time to hold the lock after it's acquisition,
     *        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
     *
     */
    void lock(long leaseTime, TimeUnit unit);

    /**
     * Unlocks the lock independently of its state
     *
     * @return <code>true</code> if lock existed and now unlocked
     *          otherwise <code>false</code>
     */
    boolean forceUnlock();

    /**
     * Checks if the lock locked by any thread
     *
     * @return <code>true</code> if locked otherwise <code>false</code>
     */
    boolean isLocked();

    /**
     * Checks if the lock is held by thread with defined <code>threadId</code>
     *
     * @param threadId Thread ID of locking thread
     * @return <code>true</code> if held by thread with given id
     *          otherwise <code>false</code>
     */
    boolean isHeldByThread(long threadId);

    /**
     * Checks if this lock is held by the current thread
     *
     * @return <code>true</code> if held by current thread
     * otherwise <code>false</code>
     */
    boolean isHeldByCurrentThread();

    /**
     * Number of holds on this lock by the current thread
     *
     * @return holds or <code>0</code> if this lock is not held by current thread
     */
    int getHoldCount();

    /**
     * Remaining time to live of the lock
     *
     * @return time in milliseconds
     *          -2 if the lock does not exist.
     *          -1 if the lock exists but has no associated expire.
     */
    long remainTimeToLive();
    
}

RLock接口继承了JDK的java.util.concurrent.locks.Lock接口，同时还扩展提供了isLocked、isHeldByThread、isHeldByCurrentThread等方法

RedissonLock

org/redisson/RedissonLock.java

public class RedissonLock extends RedissonBaseLock {

    //......

    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);
    }

    //......
}    

RedissonLock继承了RedissonBaseLock，其unlock方法调用的是父类的unlockAsync，传递的参数为Thread.currentThread().getId()

unlockAsync

org/redisson/RedissonBaseLock.java

public abstract class RedissonBaseLock extends RedissonExpirable implements RLock {

    //......

    @Override
    public RFuture<Void> unlockAsync() {
        long threadId = Thread.currentThread().getId();
        return unlockAsync(threadId);
    }

    @Override
    public RFuture<Void> unlockAsync(long threadId) {
        RPromise<Void> result = new RedissonPromise<>();
        RFuture<Boolean> future = unlockInnerAsync(threadId);

        future.onComplete((opStatus, e) -> {
            cancelExpirationRenewal(threadId);

            if (e != null) {
                result.tryFailure(e);
                return;
            }

            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;
            }

            result.trySuccess(null);
        });

        return result;
    }

    //......
}

unlockAsync执行的是unlockInnerAsync，参数为当前thread的id，再其完成之后触发cancelExpirationRenewal

unlockInnerAsync

org/redisson/RedissonLock.java

    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));
    }

RedissonLock提供了unlockInnerAsync方法，执行的是一段lua脚本：

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

先判断当前hash结构指定getLockName(threadId)的元素是否存在，不存在直接返回nil；接着对该线程的count减1，之后判断，若大于0则使用pexpire执行过期返回0；否则执行del命令，然后publish发送LockPubSub.UNLOCK_MESSAGE通知，返回1

isLocked

org/redisson/RedissonBaseLock.java

public abstract class RedissonBaseLock extends RedissonExpirable implements RLock {

    //......

    @Override
    public boolean isLocked() {
        return isExists();
    }

    //......
}

isLocked方法是执行父类的isExists方法

    @Override
    public boolean isExists() {
        return get(isExistsAsync());
    }

    @Override
    public RFuture<Boolean> isExistsAsync() {
        return commandExecutor.readAsync(getRawName(), StringCodec.INSTANCE, RedisCommands.EXISTS, getRawName());
    }

通过exists命令来判断，参数为getRawName

isHeldByCurrentThread

org/redisson/RedissonBaseLock.java

    @Override
    public boolean isHeldByCurrentThread() {
        return isHeldByThread(Thread.currentThread().getId());
    }

    @Override
    public boolean isHeldByThread(long threadId) {
        RFuture<Boolean> future = commandExecutor.writeAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.HEXISTS, getRawName(), getLockName(threadId));
        return get(future);
    }

isHeldByCurrentThread调用的是isHeldByThread方法，传递的是Thread.currentThread().getId()；isHeldByThread执行的是hexist命令，参数是getRawName()及getLockName(threadId)

小结

redisson的RLock接口继承了JDK的java.util.concurrent.locks.Lock接口，同时还扩展提供了isLocked、isHeldByThread、isHeldByCurrentThread等方法。

• 其中unlock的时候先判断当前hash结构指定getLockName(threadId)的元素是否存在，不存在直接返回nil；接着对该线程的count减1，之后判断，若大于0则使用pexpire执行过期返回0；否则执行del命令，然后publish发送LockPubSub.UNLOCK_MESSAGE通知，返回1；
• isLocked通过exists命令来判断，参数为getRawName()
• isHeldByThread执行的是hexist命令，参数是getRawName()及getLockName(threadId)

doc

• locks-and-synchronizers