如何关闭 ExecutorService？

Question

每当我拨打shutdownNow() 或shutdown() 时，它都不会关闭。我读过一些帖子，上面说不能保证关闭 - 有人可以为我提供一个好的方法吗？

Answer 1

最好的方法是我们在 javadoc 中实际拥有的：

以下方法分两个阶段关闭ExecutorService， 首先调用shutdown 拒绝传入的任务，然后调用 shutdownNow，如有必要，取消任何挥之不去的任务：

void shutdownAndAwaitTermination(ExecutorService pool) {
    pool.shutdown(); // Disable new tasks from being submitted
    try {
        // Wait a while for existing tasks to terminate
        if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
            pool.shutdownNow(); // Cancel currently executing tasks
            // Wait a while for tasks to respond to being cancelled
            if (!pool.awaitTermination(60, TimeUnit.SECONDS))
                System.err.println("Pool did not terminate");
        }
    } catch (InterruptedException ie) {
        // (Re-)Cancel if current thread also interrupted
        pool.shutdownNow();
        // Preserve interrupt status
        Thread.currentThread().interrupt();
    }
}

Answer 2

典型的模式是：

executorService.shutdownNow();
executorService.awaitTermination();

当调用shutdownNow 时，执行程序（通常）会尝试中断它管理的线程。要使关闭优雅，您需要在线程中捕获中断的异常或检查中断状态。如果您不这样做，您的线程将永远运行，您的执行程序将永远无法关闭。这是因为 Java 中线程的中断是一个协作过程（即，当要求停止时，中断代码必须做某事，而不是中断代码）。

例如，以下代码打印Exiting normally...。但是如果你注释掉if (Thread.currentThread().isInterrupted()) break;这一行，它将打印Still waiting...，因为执行器中的线程仍在运行。

public static void main(String args[]) throws InterruptedException {
    ExecutorService executor = Executors.newFixedThreadPool(1);
    executor.submit(new Runnable() {

        @Override
        public void run() {
            while (true) {
                if (Thread.currentThread().isInterrupted()) break;
            }
        }
    });

    executor.shutdownNow();
    if (!executor.awaitTermination(100, TimeUnit.MICROSECONDS)) {
        System.out.println("Still waiting...");
        System.exit(0);
    }
    System.out.println("Exiting normally...");
}

或者，它可以用InterruptedException 写成这样：

public static void main(String args[]) throws InterruptedException {
    ExecutorService executor = Executors.newFixedThreadPool(1);
    executor.submit(new Runnable() {

        @Override
        public void run() {
            try {
                while (true) {Thread.sleep(10);}
            } catch (InterruptedException e) {
                //ok let's get out of here
            }
        }
    });

    executor.shutdownNow();
    if (!executor.awaitTermination(100, TimeUnit.MICROSECONDS)) {
        System.out.println("Still waiting...");
        System.exit(0);
    }
    System.out.println("Exiting normally...");
}