并发编程陷阱系列 (二)InterruptException无处不在

当一个方法抛出 InterruptedException 时，它是在告诉您，如果执行该方法的线程被中断，它将尝试停止它正在做的事情而提前返回，并通过抛出 InterruptedException 表明它提前返回。

一旦你catch了中断异常，默认你就会处理它，所以JVM会清除中断状态，以防止方法退出后上层调用代码再处理一次异常。如果你只是简单地catch住，并不打算处理，那么就需要恢复被清除的中断位，让上层知晓，所以需要调用interrupt()

切忌生吞InterruptedException 异常，正确的做法：

1、将异常传递给调用方。

public class TaskQueue {
    private static final int MAX_TASKS = 1000;

    private BlockingQueue<Task> queue 
        = new LinkedBlockingQueue<Task>(MAX_TASKS);

    public void putTask(Task r) throws InterruptedException { 
        queue.put(r);
    }

    public Task getTask() throws InterruptedException { 
        return queue.take();
    }
}

 2、在重新抛出 InterruptedException 之前执行特定于任务的清理工作。

 

public class PlayerMatcher {
    private PlayerSource players;

    public PlayerMatcher(PlayerSource players) { 
        this.players = players; 
    }

    public void matchPlayers() throws InterruptedException { 
        try {
             Player playerOne, playerTwo;
             while (true) {
                 playerOne = playerTwo = null;
                 // Wait for two players to arrive and start a new game
                 playerOne = players.waitForPlayer(); // could throw IE
                 playerTwo = players.waitForPlayer(); // could throw IE
                 startNewGame(playerOne, playerTwo);
             }
         }
         catch (InterruptedException e) {  
             // If we got one player and were interrupted, put that player back
             if (playerOne != null)
                 players.addFirst(playerOne);
             // Then propagate the exception
             throw e;
         }
    }
}

 3、捕捉 InterruptedException 后恢复中断状态

例如当由 Runnable 定义的任务调用一个可中断的方法时，就是如此。在这种情况下，不能重新抛出 InterruptedException，但是您也不想什么都不做。当一个阻塞方法检测到中断并抛出 InterruptedException 时，它清除中断状态。如果捕捉到 InterruptedException 但是不能重新抛出它，那么应该保留中断发生的证据，以便调用栈中更高层的代码能知道中断，并对中断作出响应。该任务可以通过调用 interrupt() 以 “重新中断” 当前线程来完成。

public class TaskRunner implements Runnable {
    private BlockingQueue<Task> queue;

    public TaskRunner(BlockingQueue<Task> queue) { 
        this.queue = queue; 
    }

    public void run() { 
        try {
             while (true) {
                 Task task = queue.take(10, TimeUnit.SECONDS);
                 task.execute();
             }
         }
         catch (InterruptedException e) { 
             // Restore the interrupted status
             Thread.currentThread().interrupt();
         }
    }
}

参考： http://www.ibm.com/developerworks/cn/java/j-jtp05236.html