ThreadPoolExecutor Block When Queue Is Full?

Question

I am trying to execute lots of tasks using a ThreadPoolExecutor. Below is a hypothetical example:

def workQueue = new ArrayBlockingQueue(3, f         


        

Answer 1

I solved this problem using a custom RejectedExecutionHandler, which simply blocks the calling thread for a little while and then tries to submit the task again:

public class BlockWhenQueueFull implements RejectedExecutionHandler {

    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {

        // The pool is full. Wait, then try again.
        try {
            long waitMs = 250;
            Thread.sleep(waitMs);
        } catch (InterruptedException interruptedException) {}

        executor.execute(r);
    }
}

This class can just be used in the thread-pool executor as a RejectedExecutionHandler like any other. In this example:

executorPool = new def threadPoolExecutor = new ThreadPoolExecutor(3, 3, 1L, TimeUnit.HOURS, workQueue, new BlockWhenQueueFull())

The only downside I see is that the calling thread might get locked slightly longer than strictly necessary (up to 250ms). For many short-running tasks, perhaps decrease the wait-time to 10ms or so. Moreover, since this executor is effectively being called recursively, very long waits for a thread to become available (hours) might result in a stack overflow.

Nevertheless, I personally like this method. It's compact, easy to understand, and works well. Am I missing anything important?