java - 为什么我会收到 IllegalMonitorStateException？

Question

当我尝试解锁一个对象时，我收到以下异常。

Exception in thread "Thread-1" java.lang.IllegalMonitorStateException
    at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(Unknown Source)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(Unknown Source)
    at java.util.concurrent.locks.ReentrantLock.unlock(Unknown Source)
    at Pipe.unlock(Pipe.java:21)
    at Station.doWork(Station.java:81)
    at Station.run(Station.java:66)
    at java.lang.Thread.run(Unknown Source)

Pipe.unlock 所做的一切如下:

public void unlock(){
   accessLock.unlock();
}

其中 accessLock 是 ReentrantLock

你知道问题出在哪里吗？

编辑:

这是Station中的run方法

if(Pipes[inConnection].accessLock.tryLock()){
    System.out.println("Station "+ StationNumber+": granted access to pipe "+inConnection+".");

//This is just a way for me to keep track if both pipes have been granted
            if(connected<0)
                connected=inConnection;
            else
                connected+=inConnection;
}


if(Pipes[outConnection].accessLock.tryLock()){
            System.out.println("Station "+ StationNumber+": granted access to pipe "+outConnection+".");

    //This is just a way for me to keep track if both pipes have been granted
    if(connected<0)
        connected=outConnection;
    else
        connected+=outConnection;   
}


        doWork();

虽然这是 doWork 方法:

private void doWork() {
    if(connected==inConnection+outConnection){
        System.out.println("Station "+StationNumber+": successfully flows "+inConnection+".");
        System.out.println("Station "+StationNumber+": successfully flows "+outConnection+".");

        Pipes[inConnection].unlock();
        System.out.println("Station "+StationNumber+": released access to pipe "+inConnection+".");

        Pipes[outConnection].unlock();
        System.out.println("Station "+StationNumber+": released access to pipe "+outConnection+".");

        try {
            Thread.sleep(rand.nextInt(200));
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        WorkLoad--;
    }else if(connected >=0 ){
        Pipes[connected].unlock();
        System.out.println("Station "+StationNumber+": released access to pipe "+connected);

    }

    connected=-1;
}

Answer 1

我知道这个问题已经有一年多了，但我遇到了同样的问题，结果证明解决方案不是另一个以某种方式持有锁的线程，而是一个非常简单的错误和 ReentrantLock 的内部细节。如果我们看一下 tryRelease 的实现:

protected final boolean tryRelease(int releases) {
  int c = getState() - releases;
  if (Thread.currentThread() != getExclusiveOwnerThread())
     throw new IllegalMonitorStateException();
  ..
  if (c == 0) {
    ..
    setExclusiveOwnerThread(null);
  }
  ..
}

如果发布计数降为零，则exclusiveOwnerThread 设置为空。如果您之后再次尝试释放锁，您就不再是exclusiveOwnerThread，因为您的线程不太可能为空。所以一个简单的 .unlock() 太多会导致这个(在这种情况下相当困惑)异常。