CompletableFuture的执行线程

默认使用的线程池

不传executor时默认使用ForkJoinPool.commonPool()

IntStream.range(0, 15).parallel().forEach(i -> {
            System.out.println(Thread.currentThread());
        });

输出

Thread[ForkJoinPool.commonPool-worker-1,5,main]
Thread[main,5,main]
Thread[ForkJoinPool.commonPool-worker-1,5,main]
Thread[ForkJoinPool.commonPool-worker-3,5,main]
Thread[ForkJoinPool.commonPool-worker-2,5,main]
Thread[ForkJoinPool.commonPool-worker-3,5,main]
Thread[ForkJoinPool.commonPool-worker-1,5,main]
Thread[main,5,main]
Thread[ForkJoinPool.commonPool-worker-1,5,main]
Thread[ForkJoinPool.commonPool-worker-3,5,main]
Thread[ForkJoinPool.commonPool-worker-2,5,main]
Thread[ForkJoinPool.commonPool-worker-3,5,main]
Thread[ForkJoinPool.commonPool-worker-1,5,main]
Thread[main,5,main]
Thread[ForkJoinPool.commonPool-worker-2,5,main]

• commonPool

This pool is statically constructed; its run state is unaffected by attempts to shutdown() or shutdownNow(). However this pool and any ongoing processing are automatically terminated upon program System.exit(int). Any program that relies on asynchronous task processing to complete before program termination should invoke commonPool().awaitQuiescence, before exit.

thenRun测试实例1

不设定executor

    @Test
    public void testRunOnCommonPool() throws InterruptedException {

        CompletionStage futurePrice = CompletableFuture.runAsync(() -> {
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("test1:1 - runAsync(runnable), job thread: " + Thread.currentThread());
            //Thread[ForkJoinPool.commonPool-worker-1,5,main]
                }
        );

        System.out.println("test1:flag1");

        futurePrice.thenRun(() -> {
            System.out.println("test1:2 - thenRun(runnable)), action thread: " + Thread.currentThread());
            //Thread[ForkJoinPool.commonPool-worker-1,5,main]
        });

        System.out.println("test1:flag2");

        futurePrice.thenRunAsync(() -> {
            System.out.println("test1:3 - thenRunAsync(runnable), action thread: " + Thread.currentThread());
            //Thread[ForkJoinPool.commonPool-worker-1,5,main]
        });

        TimeUnit.SECONDS.sleep(100);

    }

输出

test1:flag1
test1:flag2
test1:1 - runAsync(runnable), job thread: Thread[ForkJoinPool.commonPool-worker-1,5,main]
test1:2 - thenRun(runnable)), action thread: Thread[ForkJoinPool.commonPool-worker-1,5,main]
test1:3 - thenRunAsync(runnable), action thread: Thread[ForkJoinPool.commonPool-worker-1,5,main]

设定executor

    @Test
    public void testRunOnExecutors() throws InterruptedException {
        CompletionStage futurePrice = CompletableFuture.runAsync(() -> {
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("test2:1 - runAsync(runnable, executor), job thread: " + Thread.currentThread());
            //Thread[pool-1-thread-1,5,main]
        }, executor);

        System.out.println("test2:flag1");

        futurePrice.thenRunAsync(() -> {
            System.out.println("test2:2 - thenRunAsync(runnable), action thread: " + Thread.currentThread());
            //Thread[pool-1-thread-1,5,main]
        });

        System.out.println("test2:flag2");

        futurePrice.thenRun(() -> {
            System.out.println("test2:3 - thenRun(runnable), action thread: " + Thread.currentThread());
            //Thread[pool-1-thread-2,5,main]
        });

        futurePrice.thenRunAsync(() -> {
            System.out.println("test2:4 - thenRunAsync(runnable, executor), action thread: " + Thread.currentThread());
            //Thread[ForkJoinPool.commonPool-worker-1,5,main]
        }, executor);

        TimeUnit.SECONDS.sleep(100);
    }

输出

test2:flag1
test2:flag2
test2:1 - runAsync(runnable, executor), job thread: Thread[pool-1-thread-1,5,main]
test2:3 - thenRun(runnable), action thread: Thread[pool-1-thread-1,5,main]
test2:4 - thenRunAsync(runnable, executor), action thread: Thread[pool-1-thread-2,5,main]
test2:2 - thenRunAsync(runnable), action thread: Thread[ForkJoinPool.commonPool-worker-1,5,main]

thenRun测试实例2

没有sleep

@Test
    public void testThenRun(){
        CompletableFuture f1 = CompletableFuture.supplyAsync(() -> {
            System.out.println("f1 thread:"+Thread.currentThread().getName());
            return "zero";
        }, executor);
        f1.thenRun(new Runnable() {
            @Override
            public void run() {
                System.out.println("then run thread:"+Thread.currentThread().getName());
                System.out.println("finished");
            }
        });
        TimeUnit.SECONDS.sleep(10);
    }

• 使用executor的输出

f1 thread:pool-1-thread-1
then run thread:main
finished

• 不使用executor的输出

f1 thread:ForkJoinPool.commonPool-worker-1
then run thread:main
finished

加上sleep

CompletableFuture f1 = CompletableFuture.supplyAsync(() -> {
            System.out.println("f1 thread:"+Thread.currentThread().getName());
            try {
                TimeUnit.SECONDS.sleep(2);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return "zero";
        }, executor);
        f1.thenRun(new Runnable() {
            @Override
            public void run() {
                System.out.println("then run thread:"+Thread.currentThread().getName());
                System.out.println("finished");
            }
        });
        TimeUnit.SECONDS.sleep(10);

• 使用executor的输出

f1 thread:pool-1-thread-1
then run thread:pool-1-thread-1
finished

• 不使用executor的输出

f1 thread:ForkJoinPool.commonPool-worker-1
then run thread:ForkJoinPool.commonPool-worker-1
finished

小结

不带 async 的 thenRun() 方法仍然是一个异步方法，可能是使用main线程，commonPool的线程或者是executor的线程。

doc

• ForkJoinPool.commonPool
• 理解 CompletableFuture 的任务与回调函数的线程
• 哪个线程执行 CompletableFuture’s tasks 和 callbacks?