java - ExecutorService.awaitTermination() 永远不会超时

Question

我正在尝试实现一个函数，其中可调用对象在规定时间内完成或操作超时。我曾希望 ExecutorService.awaitTermination() 能够执行此操作，但惊讶地发现它没有执行此操作。代码如下。运行永远不会完成。

public class Counter implements Callable<Void> {

    public static void main(String[] args) throws InterruptedException {
        final Map<String, Counter> map = new HashMap<>();
        map.put("", new Counter());
        final Map<String, Future<Void>> result = executeTasksInParallel(map);
        final Future<Void> voidFuture = result.get("");
        try {
            voidFuture.get();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public Void call() throws Exception {
        for (long i = 0L; i < Long.MAX_VALUE; i++);
        return null;
    }

    public static <K, V> Map<K, Future<V>> executeTasksInParallel(final Map<K, ? extends Callable<V>> callablesById) throws InterruptedException {
        final Map<K, Future<V>> resultFuturesById = new HashMap<>();
        final ExecutorService executorService = Executors.newFixedThreadPool(callablesById.size());
        for (final Map.Entry<K, ? extends Callable<V>> callableByIdEntry : callablesById.entrySet()) {
            final K id = callableByIdEntry.getKey();
            final Callable<V> callable = callableByIdEntry.getValue();
            final Future<V> resultFuture = executorService.submit(callable);
            resultFuturesById.put(id, resultFuture);
        }
        executorService.shutdown();
        executorService.awaitTermination(5L, TimeUnit.SECONDS);
        return resultFuturesById;
    }
}

我在这里遗漏了什么吗？谢谢!

更新:

我尝试用下面的内容替换 try block 内容以避免 Future.get() 阻塞，但这也没有帮助

if (voidFuture.isDone()) {
   voidFuture.get();
}

Answer 1

1. 使用shutdownNow()正如 Joe C 所指定的...
2. ...但只有当你的代码在 call() 中时它才会起作用。允许它这样做，例如通过检查当前线程是否被中断。参见例如this question及其详细答案。有时，如果循环调用(直接或间接)通过抛出 InterruptedException 正确处理中断请求的方法，您可能会在循环中没有这种“协作”行为。 (例如 Thread.sleep(...) 、 Object.wait(...) 、 Future.get(...) 、实现 InterruptibleChannel 的 channel 上的阻塞操作等)。 编辑: ...如果 InterruptedException抛出的内容不会被抑制。
3. 是的，只需调用 get()如果 future isDone() (因为它位于主线程上，不受您的 executorService 管理)。

最终的代码是

public class Counter implements Callable<Void> {

    public static void main(String[] args) throws InterruptedException {
        final Map<String, Counter> map = new HashMap<>();
        map.put("", new Counter());
        final Map<String, Future<Void>> result = executeTasksInParallel(map);
        final Future<Void> voidFuture = result.get("");
        try {
            if (voidFuture.isDone()) {
                voidFuture.get();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public Void call() throws Exception {
        for (long i = 0L; i < Long.MAX_VALUE; i++) {
            if (Thread.currentThread().isInterrupted()) {
                Thread.currentThread().interrupt(); // restore interrupted flag
                return null;
            }
            /* or e.g. throw an exception */
        }
        return null;
    }

    public static <K, V> Map<K, Future<V>> executeTasksInParallel(
            final Map<K, ? extends Callable<V>> callablesById)
            throws InterruptedException {
        final Map<K, Future<V>> resultFuturesById = new HashMap<>();
        final ExecutorService executorService =
            Executors.newFixedThreadPool(callablesById.size());
        for (final Map.Entry<K, ? extends Callable<V>> callableByIdEntry : callablesById
            .entrySet()) {
            final K id = callableByIdEntry.getKey();
            final Callable<V> callable = callableByIdEntry.getValue();
            final Future<V> resultFuture = executorService.submit(callable);
            resultFuturesById.put(id, resultFuture);
        }
        executorService.shutdown();
        executorService.awaitTermination(5L, TimeUnit.SECONDS);
        executorService.shutdownNow();
        return resultFuturesById;
    }
}