Question

我是Java线程的新手，我正在尝试学习completableFuture API的工作方式。当我运行下面的代码时，我得到线程名称输出，如下所示。 SupplyAsync和ThenApplyAsync似乎正在使用同一线程，即ForkJoinPool.commonPool-worker-1。我的理解是，如果我使用ThenApplyAsync，那么ThenApplyAsync将使用与SupplyAsync不同的线程。你能告诉我这是怎么回事吗？谢谢！

代码：

      override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
            self.bottomConstraint.isActive = false
            self.topConstraint.isActive = true
    self.view.layoutIfNeeded()
}

输出：

public static void main(String[] args) throws InterruptedException, ExecutionException {
        System.out.println("Current Thread : " + Thread.currentThread().getName());

        CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
            System.out.println("Current Thread (SupplyAsync) : " + Thread.currentThread().getName());
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException ex) {
                throw new IllegalStateException(ex);
            }
            return "Result";
        }).thenApplyAsync(result -> {
            System.out.println("Current Thread (ThenApplyAsync) : " + Thread.currentThread().getName());
            return result.toUpperCase();
        });

        System.out.println("CompletableFuture Result : " + future.get());
    }

Answer 1

您错误地认为thenApplyAsync将使用与上一个完成阶段不同的线程。

<U> CompletableFuture<U> thenApplyAsync(Function<? super T,? extends U> fn)

Returns a new CompletionStage that, when this stage completes normally, is executed using this stage's default asynchronous execution facility, with this stage's result as the argument to the supplied function.

它使用与上一个阶段相同的executionFacility，即ForkJoinPool.commonPool()。但是除此之外，不能保证它在池中的哪个线程上运行。

具有CompletableFuture的TheApplyAsync使用与SupplyAsync线程相同的线程

1 个答案: