在主线程上从辅助线程运行代码？ [英] Running code on the main thread from a secondary thread?

问题描述

这是一个一般的Java问题，而不是一个Android首先！

This is a general Java question and not an Android one first off!

我想知道如何在主线程上运行代码，从上下文的次级螺纹。例如：

I'd like to know how to run code on the main thread, from the context of a secondary thread. For example:

new Thread(new Runnable() {
        public void run() {
            //work out pi to 1,000 DP (takes a while!)

            //print the result on the main thread
        }
    }).start();

这样的事情 - 我意识到我的例子有点不好，因为在Java中你不需要要在主线程中打印出一些东西，而且Swing也有一个事件队列 - 但是在一般情况下，你可能需要在后台线程的上下文中在主线程上运行一个Runnable。

That sort of thing - I realise my example is a little poor since in Java you don't need to be in the main thread to print something out, and that Swing has an event queue also - but the generic situation where you might need to run say a Runnable on the main thread while in the context of a background thread.

编辑：为了比较，这里我将如何在Objective-C中执行：

For comparison - here's how I'd do it in Objective-C:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0UL), ^{
    //do background thread stuff

    dispatch_async(dispatch_get_main_queue(), ^{
        //update UI
    });
});

提前感谢！

推荐答案

没有通用的方式只是发送一些代码到另一个正在运行的线程，说嘿，你，这样做。您需要将主线程置于一个具有接收工作并等待工作的机制的状态。

There is no universal way to just send some code to another running thread and say "Hey, you, do this." You would need to put the main thread into a state where it has a mechanism for receiving work and is waiting for work to do.

这里有一个简单的示例，主线程等待从其他线程接收工作，并在它到达时运行它。显然你想添加一个方法来实际结束程序等等...

Here's a simple example of setting up the main thread to wait to receive work from other threads and run it as it arrives. Obviously you would want to add a way to actually end the program and so forth...!

public static final BlockingQueue<Runnable> queue = new LinkedBlockingQueue<Runnable>();

public static void main(String[] args) throws Exception {
    new Thread(new Runnable(){
        @Override
        public void run() {
            final int result;
            result = 2+3;
            queue.add(new Runnable(){
                @Override
                public void run() {
                    System.out.println(result);
                }
            });
        }
    }).start();

    while(true) {
        queue.take().run();
    }
}

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