Question

我正在尝试实现生产者 - 消费者模式，我希望能够阻止消费者。到目前为止我写道：

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;

public class Test {

    public static void main(final String[] args) throws InterruptedException {
        final BlockingQueue<String> messages = new LinkedBlockingQueue<>(100);
        final ExecutorService producer = Executors.newSingleThreadExecutor();
        final Consumer consumer = new Consumer(messages);

        producer.execute(new Runnable() {

            @Override
            public void run() {
                for (int i = 0;; i++) {
                    try {
                        messages.put("Message " + i);
                        Thread.sleep(500);
                    } catch (final InterruptedException e) {
                        Thread.currentThread().interrupt();
                    }
                }
            }

        });

        consumer.start();

        consumer.stop();
        consumer.start();
    }

    private static class Consumer {

        private final ExecutorService consumer = Executors.newSingleThreadExecutor();
        private final BlockingQueue<String> messages;

        public Consumer(final BlockingQueue<String> m) {
            messages = m;
        }

        public void start() {
            consumer.execute(new Runnable() {

                @Override
                public void run() {
                    while (!Thread.currentThread().isInterrupted()) {
                        try {
                            System.out.println(messages.take());
                        } catch (final InterruptedException e) {
                            Thread.currentThread().interrupt();
                            break;
                        }
                    }
                }

            });
        }

        public void stop() {
            consumer.shutdownNow();
        }

    }

}

但这总是给我上面的例外。控制台输出是：

Exception in thread "main" java.util.concurrent.RejectedExecutionException: Task Test$Consumer$1@31602bbc rejected from java.util.concurrent.ThreadPoolExecutor@20d75cf7[Terminated, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 1]
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
    at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
    at java.util.concurrent.Executors$DelegatedExecutorService.execute(Executors.java:628)
    at Test$Consumer.start(Test.java:46)
    at Test.main(Test.java:31)

为什么我无法重启＆＃34;遗嘱执行人或我如何实现这一目标？

提前致谢！

Answer 1

Documentation说

启动以前提交的任务的有序关闭已执行，但不会接受任何新任务

因此，除非修改JDK代码，否则无法重启。

Answer 2

这是因为当您的班级Consumer尝试consumer.execute(new Runnable() {时，其执行人已被关闭。为什么？因为在行consumer.start();之后，您的程序会立即终止：您不会等到任务执行完毕。

你应该修改你的代码：

使用submit方法，而不是execute：producer.submit(new Runnable() {...}
从execute()方法Future<?>对象接收： Future f = producer.submit(new Runnable() { ... }
等到该对象终止：

consumer.start();

f.get();

更新根据有关的更新代码，我们应该讨论两个新行：

    consumer.start();

    consumer.stop();
    consumer.start();

你应该知道，在执行者被停止一次后，你将无法在其中执行新任务。这就解释了为什么你在最后一行consumer.start();收到此例外。

启动先前关闭的ExecutorService时获取RejectedExecutionException

2 个答案: