java - 在 Reentrantlock 上使用 lockInterruptibly 时如何避免 IllegalMonitorStateException

Question

我想用 ReentrantLock 替换 syncronized block 以支持中断等待锁。为此，我使用了 lockInterruptibly() 方法和惯用的 try/finally block :

private ReentrantLock lock = new ReentrantLock();

try
{
  lock.lockInterruptably();
}
catch( InterruptedException e )
{
  Thread.currentThread.interrupt();
}
finally
{
  lock.unlock();
}

问题是 finally 当然也会在 InterruptedException 发生时发生。这会导致 IllegalMonitorStateException，因为当前线程未持有锁。

这个简单的程序证明了这一点:

public class LockTest
{
public static void main( String[] args )
{
    System.out.println("START");

    Thread interruptThread = new Thread( new MyRunnable( Thread.currentThread() ) );
    interruptThread.start();
    ReentrantLock lock = new ReentrantLock();

    Thread takeLockThread = new Thread( new TakeLockRunnable( lock ) );
    takeLockThread.start();

    try
    {
        Thread.sleep( 500 );
        System.out.println("Trying to take lock on thread " + Thread.currentThread().getName());
        lock.lockInterruptibly();
    }
    catch (InterruptedException e)
    {
        e.printStackTrace();
    }
    finally {
        lock.unlock();
    }

    System.out.println( "DONE");
}

private static class MyRunnable implements Runnable
{
    private Thread m_thread;

    private MyRunnable( Thread thread)
    {
        m_thread = thread;
    }

    @Override
    public void run()
    {
        try
        {
            Thread.sleep( 1000 );
        }
        catch (InterruptedException e)
        {
            // ignore
        }
        System.out.println( "Interrupting thread " + m_thread.getName() );
        m_thread.interrupt();
    }
}

private static class TakeLockRunnable implements Runnable
{
    private ReentrantLock m_lock;

    public TakeLockRunnable( ReentrantLock lock )
    {
        m_lock = lock;
    }

    @Override
    public void run()
    {
        try
        {
            System.out.println("Taking lock on thread " + Thread.currentThread().getName());
            m_lock.lock();
            Thread.sleep( 20000 );
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        finally {
            m_lock.unlock();
        }
    }
}
}

它打印这个输出:

STARTTaking lock on thread Thread-1Trying to take lock on thread mainjava.lang.InterruptedException    at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireInterruptibly(AbstractQueuedSynchronizer.java:877)    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(AbstractQueuedSynchronizer.java:1201)    at java.util.concurrent.locks.ReentrantLock.lockInterruptibly(ReentrantLock.java:312)    at LockTest.main(LockTest.java:25)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)    at java.lang.reflect.Method.invoke(Method.java:597)    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)Exception in thread "main" java.lang.IllegalMonitorStateException    at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:127)    at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1239)    at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:431)    at LockTest.main(LockTest.java:32)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)    at java.lang.reflect.Method.invoke(Method.java:597)    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)Interrupting thread main

知道避免这种情况的最佳方法是什么吗？

Answer 1

lockInterruptibly() 调用应该在 finally block 的外部。请注意，这总是尝试使用 Lock API(无论您使用 lock() 还是 lockInterruptibly())，因为您 除非您已获得锁，否则不想进行“解锁”工作。

try {
  lock.lockInterruptibly();
  try {
    // do locked work here
  } finally {
    lock.unlock();
  }
} catch( InterruptedException e ) {
  Thread.currentThread.interrupt();
}