确保CompletableFuture回调中的代码在之后执行

问题描述

说我有这个

public void foo(){
     CompletableFuture.delayedExecutor(1, TimeUnit.MILLISECONDS).execute(() -> {
         doSomethingA();
      });
      doSomethingB();
}

是否可以保证doSomethingB（）;将始终在doSomethingA（）;之前运行？ 线程抢占告诉我，有可能（虽然不太可能）首先运行doSomethingA（）？

Is there any guarantee that doSomethingB(); will always run before doSomethingA();? Something tells me with thread pre-emption, it's possible, although unlikely, that doSomethingA() could be run first?

推荐答案

否，不能保证在具有多个处理器的计算机上，doSomethingB（）将始终在doSomethingA（）之前执行 。虽然很可能会在99.999999999％的时间发生。

No, there is no guarantee, when on a machine which has multiple processors, that doSomethingB() would always execute before doSomethingA(). Though it will likely happen 99.999999999% of the time.

在您的某些评论中，我注意到对事件循环的引用。在Java中，没有像Node和Javascript这样的事件循环本机概念。如果您有4个线程，四个处理器，并且提交了四个任务，则所有四个任务将并行运行。

I noticed in some of your comments a reference to an "Event Loop". In Java there is no native concept of an Event Loop like there is in, say, Node and Javascript. If you have 4 threads, with four processors, and you submit four tasks, all four tasks will run in parallel.

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