java - 如何使用 runAsync 等待完整的 future 完全完成？

Question

此测试失败:

package com.stackoverflow.demo;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ForkJoinPool;

import org.junit.Assert;
import org.junit.Test;

public class AsyncTest {

    @Test
    public void test1() {
        Assert.assertTrue("please run this test in a machine with 2 or more cores", ForkJoinPool.getCommonPoolParallelism() > 1);

        CompletableFuture<String> cf = CompletableFuture.completedFuture("ok");
        ConcurrentLinkedQueue<String> out = new ConcurrentLinkedQueue<>();

        cf.thenRunAsync(() -> {
            out.add("one");
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            out.add("two");
        }, ForkJoinPool.commonPool());

        cf.join();

        Assert.assertEquals(2, out.size());
    }

}

我很惊讶，因为我预料到了 cf.join()考虑所有附加任务。我确信文档中的某个地方说 join只等待初始任务，但不知何故我错过了。

如何获得我想要的行为:等待 CompletableFuture 及其所有附加子任务完成？

Answer 1

校对我的帖子时修复了它:

public class AsyncTest {

    @Test
    public void test1() {
        Assert.assertTrue("please run this test in a machine with 2 or more cores", ForkJoinPool.getCommonPoolParallelism() > 1);

        CompletableFuture<String> cf = CompletableFuture.completedFuture("ok");
        ConcurrentLinkedQueue<String> out = new ConcurrentLinkedQueue<>();

        CompletableFuture<Void> cf2 = cf.thenRunAsync(() -> {
            out.add("one");
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            out.add("two");
        }, ForkJoinPool.commonPool());

        cf2.join();

        Assert.assertEquals(2, out.size());
    }

}