ThreadPoolExecutor : Pull out hanged tasks

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I have implemented ThreadPoolExecutor to invoke a task. And It seems tasks got hanged on I/O because of the core/queue size misconfiguration. I want to pull the hanging thread out so that the other threads in my queue starts executing.

Is there any way to list the threads inside a threadpoolexecutor and pull out the hanging thread?

threadpoolexecutor threadpool java
1 Answers

You have control over the used executor, you could use the ThreadPoolExecutor's beforeExecute and afterExecute methods to keep track of running tasks and use that to create a getActiveTasks method.

import java.util.Set;
import java.util.concurrent.*;


public class ActiveTasksThreadPool extends ThreadPoolExecutor {

private final ConcurrentHashMap<Runnable, Boolean> activeTasks = new ConcurrentHashMap<>();

public ActiveTasksThreadPool(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
    super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}

@Override
protected void beforeExecute(Thread t, Runnable r) {

    activeTasks.put(r, Boolean.TRUE);
    super.beforeExecute(t, r);
}

@Override
protected void afterExecute(Runnable r, Throwable t) {

    super.afterExecute(r, t);
    activeTasks.remove(r);
}

public Set<Runnable> getActiveTasks() {
    // the returned set will not throw a ConcurrentModificationException.
    return activeTasks.keySet();
}

In order to set a timeout on thread tasks with Future:

 ActiveTasksThreadPool executor = new ActiveTasksThreadPool(maxTasks, maxTasks, 10, TimeUnit.SECONDS, new SynchronousQueue<Runnable>());Executors.newFixedThreadPool(2);

      List<Future<Integer>> resultList = new ArrayList<>();

      Random random = new Random();

      for (int i=0; i<4; i++)
      {
          Integer number = random.nextInt(10);
          FactorialCalculator calculator  = new FactorialCalculator(number);
          Future<Integer> result = executor.submit(calculator);
          result .get(100, TimeUnit.MILLISECONDS); // here is a timeout of 100 milisecond
      }
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