Java。 按完成顺序连接线程，并在每次连接后运行一个钩子

Question

I want to be able to join each thread at once it finished its job. In the code example below main thread will wait as long as each thread will run by their order in the list and only then next thread will be joined.

    List<Thread> threads = new ArrayList<>();

    threads.add(new Thread(new Worker(), "T1"));
    threads.add(new Thread(new Worker(), "T2"));
    threads.add(new Thread(new Worker(), "T3"));

    threads.forEach(Thread::start);

    threads.forEach(thread -> {
        try {
            thread.join();
            someHook();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    });

Answer 1

You should use a CompletableFuture

    ExecutorService e = Executors.newFixedThreadPool(3);
    ExecutorService single = Executors.newSingleThreadExecutor();
    List<CompletableFuture<?>> futures = new ArrayList<>();
    futures.add(CompletableFuture.runAsync(new Worker(), e).thenRunAsync(this::someHook, single));
    futures.add(CompletableFuture.runAsync(new Worker(), e).thenRunAsync(this::someHook, single));
    futures.add(CompletableFuture.runAsync(new Worker(), e).thenRunAsync(this::someHook, single));

    futures.forEach(f -> f.get()); // try-catch left out for brevity

In this case you will run 3 tasks async and have a single thread force each hook to be done sequentially.