如何避免每个线程创建不同的池？

Question

在我的程序中，我有一个名为“Vehicle”的类，它从 Thread 扩展而来，问题是在某个时候我需要这些 Threads 来创建一个任务（可运行），并且我希望所有这些任务都由同一个管理线程池，问题在于，如果我从包含此池的不同类调用方法，则每个其他线程都在创建不同的池。 我怎样才能避免这种情况？ 提前致谢。

public class Station {
    Arrivals arrivals;
    Vehicle k;
    ListPumps lp;

    ExecutorService executor = Executors.newFixedThreadPool(3);
    public synchronized void startWork(Pump p) {

        Runnable w = new Work(p);
        executor.execute(w);

        executor.shutdown();
        while (!executor.isTerminated()) {
    }
        System.out.println("Finished all threads");
     }
}

Answer 1

您的代码已经使用了一个线程池。但是，如果您的类可能有多个实例，并且您希望它们都共享同一个线程池，则将其分配为静态变量。

虽然我现在也会将关闭代码提取到它自己的方法中。也不要轮询 isTerminated，使用 awaitTermination。

类似于以下内容：

public class Station {

    private Arrivals arrivals;
    private Vehicle k;
    private ListPumps lp;

    private static ExecutorService executor = Executors.newFixedThreadPool(3);

    public void startWork(Pump p) {
        Runnable w = new Work(p);
        executor.execute(w);
    }

    public static synchronized void shutdown() {
        executor.shutdown();
        if(executor.awaitTermination(60, TimeUnit.SECONDS))
            System.out.println("Finished all threads");
        else
            System.out.println("Executor shutdown timed out");
    }
}

Answer 2

两种选择：

1. 您可以将ExecutorService 对象声明为静态，或者：
2. 创建Station 类为singleton

我推荐阅读这篇文章： should ExecutorService be static and global

public class Station {

    private Arrivals arrivals;
    private Vehicle k;
    private ListPumps lp;

    // Bill Pugh Singleton Implementation
    private static class ExecutorServiceHelper {

        // volatile keyword to avoid CPU caching EXECUTOR object
        // famous volatile illutration http://tutorials.jenkov.com/images/java-concurrency/java-volatile-2.png
        private static volatile ExecutorService EXECUTOR = Executors
                .newFixedThreadPool(3);;

    }

    public ExecutorService getInstance() {
        return ExecutorServiceHelper.EXECUTOR;
    }

    // implementation of executor framework is threadsafe, so you don't need 
    // to use synchronized keyword on methods calling executors methods
    // here is the discussion https://stackoverflow.com/questions/1702386/is-threadpoolexecutor-thread-safe#answer-7596354
    public void submitWork(Pump p) {
        Runnable w = new Work(p);
        getInstance().execute(w);
    }

    public void shutdown() {
        getInstance().shutdown();
        if(getInstance().awaitTermination(60, TimeUnit.SECONDS))
            System.out.println("Finished all threads");
        else
            System.out.println("Executor shutdown timed out");
    }


}