Question

此代码挂起。我理解我将Future.get（）称为未执行的未来，但我希望在future.get（）方法上看到CancellationExcetpion或InterruptedException或其他一些异常。我错了吗？

public class ExecutorTest {
    static ExecutorService executorService = Executors.newFixedThreadPool(1);
    public static void main(String[] args) throws Exception {
        List<Future> futures = new ArrayList<Future>();
        for (int i = 0; i < 10; i++) {
            Future<Object> future = executorService.submit(new Callable<Object>() {
                @Override
                public Object call() throws Exception {
                    System.out.println("Start task");
                    try {
                        Thread.sleep(3000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("Finish task");
                    return "anything";
                }
            });
            futures.add(future);
        }

        new Thread() {
            @Override
            public void run() {
                try {
                    Thread.sleep(10000);
                    System.out.println("Shutdown Now");
                    executorService.shutdownNow();
                } catch (InterruptedException e) {
                    System.out.println("Interrupted Exception during shutdown");
                }
            }
        }.start();

        for(Future f : futures) {
            System.out.println("-------------------------");
            System.out.println("before sleep");
            Thread.sleep(3000);
            System.out.println("after sleep...");
            try {
                f.get();
            } catch (Exception ex) {
                System.out.println("exception during future.get");
            }
            System.out.println("after get!");
        }

    }
}

这是我的输出

Start task
-------------------------
before sleep
after sleep...
Finish task
after get!
-------------------------
Start task
before sleep
after sleep...
Finish task
Start task
after get!
-------------------------
before sleep
after sleep...
Finish task
Start task
after get!
-------------------------
before sleep
Shutdown Now
Finish task
java.lang.InterruptedException: sleep interrupted
    at java.lang.Thread.sleep(Native Method)
    at ru.pp.ExecutorTest$1.call(ExecutorTest.java:28)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)
after sleep...
after get!
-------------------------
before sleep
after sleep...

Java 8，Intellij

如果我更换

System.out.println("Start task");
try {
    Thread.sleep(3000);
} catch (InterruptedException e) {
    e.printStackTrace();
}

用这个

System.out.println("Start task");
Thread.sleep(3000);

然后它不会挂起

我很沮丧......

Answer 1

当您调用shutdownNow时，ExecutorService会删除所有已安排但尚未运行的任务，并将其作为List<Runnable>返回给您。这些任务具有相应的Future，您已经引用了它。由于这些任务永远不会运行，因此它们永远不会产生结果，即。永远不会完成因此，这些任务的Future#get()将永远不会返回。

如果您愿意，可以使用

返回运行这些任务

executorService.shutdownNow().forEach(r -> r.run());

您将看到所有Future#get()次来电回复。

如果您知道任务已完成/取消，您应该只调用Future#get()。或者，暂停一下。

Answer 2

当Thread_1调用 FutureTask＃get 时，将调用 Thread_1 #wait 。现在继续Thread_1应该由某人通知。仅当FutureTask终止时（在 FutureTask＃set ， FutureTask #setException 或 FutureTask＃cancelning ）上才会调用通知。但就我而言，由于shutdownNow（FutureTask处于NEW状态），FutureTask从未启动过。因此它从未被终止，并且从未调用过 Thread_1＃notify 。为了解决这个问题，我没有从 #shutdownNow 开始期货，也没有为他们调用 FutureTask＃get 。

PS：老实说FutureTask使用sun.misc.Unsafe＃park #unpark方法而不是wait and notify。

当Callback捕获InterruptedException时，Future.get挂起

2 个答案: