Java Thread Pool with a Bounded Queue

Question

I'm using java.util.concurrent's Executors class to create a fixed thread pool for running request handlers for a web server:

static ExecutorService  newFixedThreadPool(int nThreads)  

and the description is:

Creates a thread pool that reuses a fixed set of threads operating off a shared unbounded queue.

However, I am looking for thread pool implementation which will do the exact same thing, except with a bounded queue. Is there such an implementation? Or do I need to implement my own wrapper for the fixed thread pool?

Answer 1

What you want to do is new your own ExecutorService, probably using ThreadPoolExecutor. ThreadPoolExecutor has a constructor which takes a BlockingQueue and to get a bounded queue you use for example ArrayBlockingQueue properly constructed for bounding. You can also include a RejectedExecutionHandler in order to determine what to do when your queue is full, or hang on to a reference to the blocking queue and use the offer methods.

Here's a mini example:

BlockingQueue<Runnable> linkedBlockingDeque = new LinkedBlockingDeque<Runnable>(     100); ExecutorService executorService = new ThreadPoolExecutor(1, 10, 30,     TimeUnit.SECONDS, linkedBlockingDeque,     new ThreadPoolExecutor.CallerRunsPolicy()); 

Answer 2

I've solved this with a Semaphore which I use to throttle tasks being submitted to the ExecutorService.

Eg:

int threadCount = 10; ExecutorService consumerPool = Executors.newFixedThreadPool(threadCount);  // set the permit count greater than thread count so that we  // build up a limited buffer of waiting consumers Semaphore semaphore = new Semaphore(threadCount * 100);   for (int i = 0; i < 1000000; ++i) {     semaphore.acquire(); // this might block waiting for a permit      Runnable consumer = () -> {        try {           doSomeWork(i);        } finally {           semaphore.release(); // release a permit         }     };     consumerPool.submit(consumer); }