Unable to get CallableThread in RejectionHandler

Question

I have thread pool, which will take Callable worker thread with a RejectionHandler. I need to get this Callable task in RejectionHandler

Answer 1

In your code

workers[i] = new CallableWorkerThread(random.nextInt(100));
FutureTask<Integer> task = new FutureTask<Integer>(workers[i]);
executor.submit(task);

you create a FutureTask which wraps the CallableWorkerThread instance but then you are using submit which accepts an arbitrary Runnable and returns a FutureTask which wraps the Runnable.

In other words, you are wrapping your FutureTask in another FutureTask. There are two ways to solve this

1. Use

   workers[i] = new CallableWorkerThread(random.nextInt(100));
   executor.submit(workers[i]);
   

   to let the ExecutorService wrap your Callable inside a FutureTask.

2. Use

   workers[i] = new CallableWorkerThread(random.nextInt(100));
   executor.execute(new FutureTask<Integer>(workers[i]));
   

   to wrap the Callable manually and enqueue it as Runnable without further wrapping (note the use of execute rather than submit)

Since you want to enable retrieval of the original Callable, the second option is for you, as it gives you full control over the FutureTask instance:

static class MyFutureTask<T> extends FutureTask<T> {
    final Callable<T> theCallable;

    public MyFutureTask(Callable<T> callable) {
        super(callable);
        theCallable=callable;
    }
}

submitting code:

    for (int i=0; i< workers.length; i++){
        workers[i] = new CallableWorkerThread(random.nextInt(100));
        executor.execute(new MyFutureTask<Integer>(workers[i]));
    }

RejectedExecutionHandler:

class RejectionHandlerImpl implements RejectedExecutionHandler{
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        if(r instanceof MyFutureTask) {
            MyFutureTask<?> myFutureTask = (MyFutureTask)r;
            Callable<?> c=myFutureTask.theCallable;
            System.out.println(c);
        }
        else System.out.println(r);
    }
}