Java 中的 Executor 和 Daemon

Executor and Daemon in Java

提问by Ittai

I have a MyThread object which I instantiate when my app is loaded through the server, I mark it as a Daemon thread and then call start()on it. The thread is meant to sit and wait for information from a queue as long as the application is active. My problem/question is this: Currently MyThread is extending Thread because I mark it as Daemon and I read about how it's more prefferable to implement Runnable and to use Executors. So what I wanted to ask is if MyThread will implement Runnable instead of extending Thread (and of course will be renamed) and I'll use newSingleThreadScheduledExecutor()how, what or maybe where, do I mark something as Daemon. I hope I haven't made a mess of terms, please excuse me if I have as some parts of the multithreading environment are very new to me.

我有一个 MyThread 对象，当我的应用程序通过服务器加载时，我会实例化它，我将它标记为守护线程，然后调用start()它。只要应用程序处于活动状态，该线程就会坐下来等待来自队列的信息。我的问题/问题是：目前 MyThread 正在扩展 Thread，因为我将其标记为 Daemon，并且我阅读了有关实现 Runnable 和使用 Executors 的更多信息。所以我想问的是，MyThread 是否会实现 Runnable 而不是扩展 Thread（当然会被重命名），我将使用newSingleThreadScheduledExecutor()如何、什么或可能在哪里将某些东西标记为 Daemon。我希望我没有把术语弄得一团糟，请原谅我，因为多线程环境的某些部分对我来说很陌生。

Thanks Ittai

谢谢一泰

Update: The module I'm referring to in my app is a web-app which has a few threads actually of this sort and what they do have in common is that they all in the ServletContextas a member for various reasons. Currently I extend Threadto WebThreadwhich has the ServletContextas a memebr and all subclasses can utilize this. If I switch over to the Runnable paradigm with the Executor and ThreadFactory than basically I need to have an ugly hybrid of WebRunnablewhich implements Runnableand has the ServletContextas a public member and have my ThreadFactoryimplement newThread(WebRunnable arg0)in addition to newThread(Runnable arg0). I'm not sure what's best. Thanks

更新：我在我的应用程序中所指的模块是一个网络应用程序，它实际上有一些此类线程，它们的共同点是ServletContext出于各种原因，它们都作为成员加入。目前我扩展Thread到WebThread具有ServletContext作为 memebr 的所有子类都可以使用它。如果我切换到与执行人及的ThreadFactory了Runnable范式比基本上我需要有一个丑陋的混合动力车WebRunnable，它实现Runnable并具有ServletContext作为公共成员，并且对我的ThreadFactory落实newThread(WebRunnable arg0)除了newThread(Runnable arg0)。我不确定什么是最好的。谢谢

回答by Stu Thompson

Check out the JavaDoc for newSingleThreadScheduledExecutor(ThreadFactory threadFactory)

查看 JavaDoc newSingleThreadScheduledExecutor(ThreadFactory threadFactory)

It would be implemented something like this:

它将被实现如下：

public class MyClass { 
    private DaemonThreadFactory dtf = new DaemonThreadFactory();
    private ScheduledExecutorService executor = 
                                 Executors.newSingleThreadScheduledExecutor(dtf);
    // ....class stuff.....
    // ....Instance the runnable.....
    // ....submit() to executor....
}

class DaemonThreadFactory implements ThreadFactory {
    public Thread newThread(Runnable r) {
        Thread thread = new Thread(r);
        thread.setDaemon(true);
        return thread;
    }
}

回答by Brian Agnew

If you're using a scheduled executor, you can provide a ThreadFactory. This is used to create new Threads, and you can modify these (e.g. make them daemon) as you require.

如果您使用的是预定的执行程序，则可以提供ThreadFactory。这用于创建新线程，您可以根据需要修改它们（例如，使它们成为守护进程）。

EDIT: To answer your update, your ThreadFactoryjust needs to implement newThread(Runnable r)since your WebRunnableis aRunnable. So no real extra work.

编辑：要回答您的更新，您ThreadFactory只需要实施，newThread(Runnable r)因为您WebRunnable是Runnable. 所以没有真正的额外工作。

回答by Johan Sj?berg

Just to complement with another possible solution for completeness. It may not be as nice though.

只是为了补充另一个可能的完整性解决方案。不过可能没那么好。

final Executor executor = Executors.newSingleThreadExecutor();
Runtime.getRuntime().addShutdownHook(new Thread() {

    @Override
    public void run() {
        executor.shutdownNow();
    }
});