如何使用 executor.execute 和 future.get() 结束任务（使线程超时）（通过上升中断）而不阻塞主线程

Question

I tried using future inside executor service, it works without blocking the main thread. However this ends up creating double the amount of threads which is not desirable. in the code below i was able to use future.get() without blocking but i have to create double the amount of threads

 for (int i : array) {
                executor.execute(() -> {
                    Future f = new FutureTask(() -> {
                        Goring goring = new Goring();
    
                        goring.goring(i);
    
                    }, null);
                    Thread thread = new Thread((Runnable) f);
                    thread.start();
    
                    try {
                        f.get(1, TimeUnit.NANOSECONDS);
                    } catch (InterruptedException | ExecutionException | TimeoutException|RuntimeException e) {
                        // TODO Auto-generated catch block
                        // System.out.println(e.getMessage());
                        e.printStackTrace();
                        f.cancel(true);
                    }
    
                });
            }
            
    
        executor.shutdown();
    
        }

Answer 1

Normally I would recommend using ExecutorService.invokeAll , which allows the submission of any number of tasks with a timeout and which will cancel any tasks which haven't completed when that timeout expires.

But you have stated in a comment that you want to be able to submit tasks in smaller parallelized groups, for example having no more than three running concurrently at a time.

You can create a thread pool with a limited amount of parallelism:

ExecutorService executor = Executors.newFixedThreadPool(3);

The challenge here is that you want the timeout to start when the task starts, not when the task is submitted. Since a submitted task has no way to access its own Future, I would use a SynchronousQueue to wait for that Future to be passsed from the submitting thread:

ScheduledExecutorService cancelScheduler =
    Executors.newSingleThreadScheduledExecutor();

for (int i : array) {
    SynchronousQueue<Runnable> cancelQueue = new SynchronousQueue<>();

    Future<?> task = executor.submit(() -> {
        Runnable canceler = cancelQueue.take();
        cancelScheduler.schedule(canceler, 5, TimeUnit.SECONDS);

        Goring goring = new Goring();
        goring.goring(i);

        return null;
    });

    cancelQueue.put(() -> task.cancel(true));
}

executor.shutdown();
cancelScheduler.shutdown();

As the name implies, Executors.newSingleThreadScheduledExecutor() uses just one thread for all scheduling, which is perfectly suitable for your purposes, since the scheduled tasks only call Future.cancel, which takes a negligible amount of time.

The reason for having return null; in the task is that returning a value from the lambda makes it a Callable rather than a Runnable. (Runnable's run method has a return type of void , so the presence of a returned value tells the compiler this lambda cannot possibly represent a Runnable.) This means its signature implicitly has throws Exception in it, so there is no need to catch the InterruptedException that might be thrown by cancelQueue.take() .