java – 为什么CompletableFuture的thenAccept()没有在主线程上运行

我在CompletableFuture的supplyAsync()中处理长时间运行的操作,并将结果输入thenAccept().在某些时候,然后接受()执行主线程但有时它在工作线程上运行.但是我想在主线程上运行thenAccept()操作.这是示例代码.

private void test() {

    ExecutorService executorService = Executors.newSingleThreadExecutor();

    CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {
        System.out.println("supplyAsync | I am running on : " + Thread.currentThread().getName());
        return "Hello world";
    }, executorService);

    CompletableFuture<Void> cf3 = cf1.thenAccept(s -> {
        System.out.print("thenAccept | I am running on : " + Thread.currentThread().getName());
        System.out.println(" | answer : " + s);
    });

    cf3.thenRun(() -> {
        System.out.println("thenRun | I am running on : " + Thread.currentThread().getName());
        System.out.println();
    });

}

public static void main(String[] args) {

    App app = new App();
    for(int i = 0; i < 3; i++){
        app.test();
    }
}

结果是:

supplyAsync | I am running on : pool-1-thread-1
thenAccept | I am running on : main | answer : Hello world
thenRun | I am running on : main

supplyAsync | I am running on : pool-2-thread-1
thenAccept | I am running on : main | answer : Hello world
thenRun | I am running on : main

supplyAsync | I am running on : pool-3-thread-1
thenAccept | I am running on : pool-3-thread-1 | answer : Hello world
thenRun | I am running on : pool-3-thread-1

我怎样才能解决这个问题 ?

最佳答案 看一下
CompletableFuture的JavaDoc.有趣的部分是关于CompletionStage策略的部分.

在那里,您会发现使用非异步方法会产生一种或者一种情况.如果您随后查看实现,您将最终进入Java Runtime的非公共部分.有一些UNSAFE处理意味着可能会发生某种竞争条件.

我建议使用thenAcceptAsync()和thenRunAsync()变体,并将executorService变量传递给两个调用.

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