ExecutorService, standard way to avoid to task queue getting too full

user_236370 0
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I am using ExecutorService for ease of concurrent multithreaded program. Take following code:

while(xxx) {
    ExecutorService exService = Executors.newFixedThreadPool(NUMBER_THREADS);
    ...  
    Future<..> ... = exService.submit(..);
    ...
}

In my case the problem is that submit() is not blocking if all NUMBER_THREADS are occupied. The consequence is that the Task queue is getting flooded by many tasks. The consequence of this is, that shutting down the execution service with ExecutorService.shutdown() takes ages (ExecutorService.isTerminated() will be false for long time). Reason is that the task queue is still quite full.

For now my workaround is to work with semaphores to disallow to have to many entries inside the task queue of ExecutorService:

...
Semaphore semaphore=new Semaphore(NUMBER_THREADS);

while(xxx) {
    ExecutorService exService = Executors.newFixedThreadPool(NUMBER_THREADS); 
    ...
    semaphore.aquire();  
    // internally the task calls a finish callback, which invokes semaphore.release()
    // -> now another task is added to queue
    Future<..> ... = exService.submit(..); 
    ...
}

I am sure there is a better more encapsulated solution?

concurrency java
6 Answers

You can call ThreadPoolExecutor.getQueue().size() to find out the size of the waiting queue. You can take an action if the queue is too long. I suggest running the task in the current thread if the queue is too long to slow down the producer (if that is appropriate).

user_576950

You're better off creating the ThreadPoolExecutor yourself (which is what Executors.newXXX() does anyway).

In the constructor, you can pass in a BlockingQueue for the Executor to use as its task queue. If you pass in a size constrained BlockingQueue (like LinkedBlockingQueue), it should achieve the effect you want.

ExecutorService exService = new ThreadPoolExecutor(NUMBER_THREADS, NUMBER_THREADS, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>(workQueueSize));
Kevin_266200

I know this is too old but might be useful for other developers. So submitting one of the solution.

As you asked for better encapsulated solution. It is done by extending ThreadPoolExecutor and overriding submit method.

BoundedThreadpoolExecutor implemented using Semaphore. Java executor service throws RejectedExecutionException when the task queue becomes full. Using unbounded queue may result in out of memory error. This can be avoided by controlling the number of tasks being submitted using executor service. This can be done by using semaphore or by implementing RejectedExecutionHandler.

user_89878980
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