500 Worker Threads, what kind of thread pool?

Question

I am wondering if this is the best way to do this. I have about 500 threads that run indefinitely, but Thread.sleep for a minute when done one cycle of processing.

   ExecutorService es = Executors.newFixedThreadPool(list.size()+1);
   for (int i = 0; i < list.size(); i++) {
      es.execute(coreAppVector.elementAt(i)); //coreAppVector is a vector of extends thread objects
   }

The code that is executing is really simple and basically just this

class aThread extends Thread {
   public void run(){
      while(true){
         Thread.sleep(ONE_MINUTE);
         //Lots of computation every minute
      }
   }
}

I do need a separate threads for each running task, so changing the architecture isn't an option. I tried making my threadPool size equal to Runtime.getRuntime().availableProcessors() which attempted to run all 500 threads, but only let 8 (4xhyperthreading) of them execute. The other threads wouldn't surrender and let other threads have their turn. I tried putting in a wait() and notify(), but still no luck. If anyone has a simple example or some tips, I would be grateful!

Well, the design is arguably flawed. The threads implement Genetic-Programming or GP, a type of learning algorithm. Each thread analyzes advanced trends makes predictions. If the thread ever completes, the learning is lost. That said, I was hoping that sleep() would allow me to share some of the resources while one thread isn't "learning"

So the actual requirements are

how can I schedule tasks that maintain state and run every 2 minutes, but control how many execute at one time.

Answer 1

If your threads are not terminating, this is the fault of the code within the thread, not the thread pool. For more detailed help you will need to post the code that is being executed.

Also, why do you put each Thread to sleep when it is done; wouldn't it be better just to let it complete?

Additionally, I think you are misusing the thread pool by having a number of threads equal to the number of tasks you wish to execute. The point of a thread pool is to put a constraint on the number of resources used; this approach is no better than not using a thread pool at all.

Finally, you don't need to pass instances of Thread to your ExecutorService, just instances of Runnable. ExecutorService maintains its own pool of threads which loop indefinitely, pulling work off of an internal queue (the work being the Runnables you submit).

Answer 2

Why not used a ScheduledExecutorService to schedule each task to run once per minute, instead of leaving all these threads idle for a full minute?

ScheduledExecutorService workers = 
  Executors.newScheduledThreadPool(Runtime.getRuntime().availableProcessors());
for (Runnable task : list) { 
  workers.scheduleWithFixedDelay(task, 0, 1, TimeUnit.MINUTES);
}

What do you mean by, "changing the architecture isn't an option"? If you mean that you can't modify your task at all (specifically, the tasks have to loop, instead of running once, and the call to Thread.sleep() can't be removed), then "good performance isn't an option," either.