多线程，计算正在运行的线程数

Question

I'm building an RL ai for checkers (so ill be running a lot of different games), and each thread will run a game separately on its own. Im trying to limit the amount of running threads. So if the amount of running threads is less than a certain amount ( threadAmount ): then create a new thread and run a new game, else: don't do anything and wait.

for (int i = 0; i < population.size(); i++) {
    int runningThreads = 0;
    for (int j = i; j < population.size(); j++) if (population.get(j).gameOver == false) runningThreads++; //for each running thread, add 1 to runningThreads
    if (runningThreads < threadAmount){ //threadAmount == max # of threads
      population.get(i).gameOver = false;
      Thread newThread = new Thread(population.get(i));
      newThread.start();
      println("\tnew thread started | "+runningThreads);
      delay(100);
    }
    else{
      i--; //retry this 
    }
  }

The problem is that it just creates all the threads willy nilly, the println shows "new thread started | 0" 25 times and the runningThreads var doesn't seem to increase in the for loop at all, and just stays at 0. Unsure what to do :/, but I know this is Processing and that its not thread safe so im ready to pull some fancy smancy stuff to get it done.

Answer 1

If I understood correctly, these are your requirements:

• Run each game in a separate Thread .
• Never allow more than n games (or Thread s) to run at the same time.
• If the maximum number of games are currently running, wait until one or more finish then run the new game.

The last bullet point is not entirely clear. It could mean the game should be queued for execution or it could mean the scheduling Thread should block until "space" becomes available.

In the first case (queuing) this can be easily solved by using an ExecutorService configured to have no more than n threads. Any tasks submitted while all threads are busy will be queued until a thread becomes available.

ExecutorService executor = Executors.newFixedThreadPool(threadAmount);
for (Runnable r : population) {
    executor.execute(r);
}
executor.shutdown(); // If you won't be using it later

This also has the added benefit of reusing Thread instances rather than creating a new Thread for each game.

Answer 2

As I said in the comments, here is a code sample but its in c#, i have no java code currently. But it should work similarly

List<Task> lTask = new List<Task>();

Worker w = new Worker(msg);
Task t = new Task(() => w.DoWork());
            t.Start();
            lTask.Add(t);`.

I keeping added tasks to the global list. ANd in a timer, I periodically check if anyone of the task (aka thread) expires,

foreach(Task t in lTask)
                {
                    if (!t.Status.Equals(TaskStatus.Running))
                    {
                        // This thread is running... do whatever you do
                    }

                }

Thats my way to work with muti threads, and keep log of their life.