线路监听器事件丢失

Question

我尝试使用Java剪辑对象播放信号。我开始剪辑，然后等待STOP事件被触发，直到我继续线程。我观察到，如果我退出调用线程（可能发生在我的应用程序中），则声音不会播放或仅播放第一部分。

但是，大多数情况下，这种方法很好，但是，大约每隔50次，START和STOP事件都不会被触发，导致当前线程永远等待。

现在的问题是，我做了一些错误的同步，使我失去了事件？

private static volatile boolean isPlaying = false; 
private static final Object waitObject = new Object(); 

public static void playClip(...) 

... 

    Clip clip = (Clip) AudioSystem.getLine(...); 

    clip.addLineListener(new LineListener() { 
     public void update(LineEvent event) { 
      if (event.getType() == LineEvent.Type.STOP) { 
       event.getLine().close(); 
       synchronized (waitObject) { 
        isPlaying = false;       
        waitObject.notifyAll(); 
       } 
      } 
     } 
    }); 


    // start playing clip 
    synchronized (waitObject) { 
     isPlaying = true; 
    } 
    clip.start(); 

    // keep Thread running otherwise the audio output is stopped when caller thread exits 
    try { 
     while (isPlaying) { 
      synchronized (waitObject) { 
       waitObject.wait();      
      } 
     } 
    } catch (InterruptedException e) {   
     e.printStackTrace(); 
    } 
} 

下面是使用新版本 CountDownLatch：

private static volatile CountDownLatch playingFinished = new CountDownLatch(1); 

public static void playClip(...) 

... 
    Clip clip = (Clip) AudioSystem.getLine(...); 
    clip.open(audioInputStream); 

    // use line listener to take care of synchronous call 
    clip.addLineListener(new LineListener() { 
     public void update(LineEvent event) { 
      if (event.getType() == LineEvent.Type.STOP) { 
       event.getLine().close(); 
       playingFinished.countDown(); 
      } 
     } 
    }); 

    clip.start(); 

    try { 
     playingFinished.await(); 
    } catch (InterruptedException e) { 
     e.printStackTrace(); 
    } 

    playingFinished = new CountDownLatch(1); 

我不包括调试，但是他们表示线程在playingFinished.await();挂起，因为停止事件没有被解雇，并永远不会调用playingFinished.countDown();。

Answer 1

帮你自己一个忙，并重写代码，以使用CountDownLatch而不是低级的等待通知API。你的问题可能会自行消失。

public void playClip() throws Exception { 
    final CountDownLatch playingFinished = new CountDownLatch(1); 
    final Clip clip = (Clip) AudioSystem.getLine(...); 
    clip.open(...); 
    clip.addLineListener(new LineListener() { 
    public void update(LineEvent event) { 
     if (event.getType() == LineEvent.Type.STOP) { 
     event.getLine().close(); 
     playingFinished.countDown(); 
     } 
    } 
    }); 
    clip.start(); 
    try { 
    playingFinished.await(); 
    } catch (InterruptedException e) { 
    Thread.currentThread().interrupt(); 
    } 
}