Question

我想用syncronized替换ReentrantLock块以支持等待锁定的中断。为此，我使用lockInterruptibly()方法和惯用的try / finally块：

private ReentrantLock lock = new ReentrantLock();

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

问题是当InterruptedException发生时，最终的当然也会发生。这导致IllegalMonitorStateException，因为当前线程不保持锁定。

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();
        }
    }
}
}

打印此输出：

START
Taking lock on thread Thread-1
Trying to take lock on thread main
java.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

有什么最好的方法可以避免这个？

Answer 1

lockInterruptibly()调用应该在外面 finally块。请注意，这总是尝试使用Lock API（无论您使用lock()还是lockInterruptibly()），因为不想要“解锁” “除非你获得锁定，否则就会工作。

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

Answer 2

只需使用boolean-flag就可以解决这个问题：

private ReentrantLock lock = new ReentrantLock();

boolean lockAcquired = false;

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

在Reentrantlock上使用lockInterruptibly时如何避免IllegalMonitorStateException

2 个答案: