java thread pool task timeout issue

Question

I have a thread pool:

ThreadPoolExecutor pool = new ThreadPoolExecutor(cores, 50, 30L, TimeUnit.SECONDS, new ArrayBlockingQueue<>(3000));

And then I run:

try {
    pool.execute(() -> 
{
  //Very very long task, fetching from an external URL
});
}catch(Exception e){
    e.printStackTrace();
}

I never get an exception, and this code waits for minutes. What should I do to make it cancel in 30 secs?

Answer 1

According to the documentation the 3th parameter, keepAlive, does not specify the await time for a specific task in the thread pool, but time till idle threads should be released from the pool.

  * @param keepAliveTime when the number of threads is greater than * the core, this is the maximum time that excess idle threads * will wait for new tasks before terminating. 

For your desired behavior you should wrap your task in a FutureTask , then submit the future task to thread pool. On the future task you can call get(timeout, timeunit)

FutureTask<T> task = new FutureTask<T>(c);
pool.execute(task);
return task.get(timeout, timeUnit);

Answer 2

What you're specifying to be 30 seconds is the keepAliveTime of the idle threads of your executor. This is the duration in which excess threads that are not currently processing tasks will be kept alive. Here excess threads is defined as threads created in addition to the one thread per core that your ThreadPoolExecutor will keep alive, depending on the corePoolSize that you've specified.

In order to submit a task with a timeout, you can just submit the task in your ThreadPoolExecutor , take the returned Future and use its timing out get(long timeout, TimeUnit unit) method:

Future<Result> future = pool.execute(yourTask);
Result result = future.get(30, TimeUnit.SECONDS);

You can also take a look at this related question: ExecutorService that interrupts tasks after a timeout