Question

When I create ExecutorService with below code in JAVA,can someone explain how the ExecutorService works ?

ExecutorService executor = Executors.newFixedThreadPool(400);

    for (int i = 0; i < 500; i++) {
        Runnable worker = new MyRunnable(10000000L + i);
        executor.execute(worker);
    }

I believe that there will be a single Queue of work and my for loop will add 500 Runnable tasks to this queue. Now the ExecutorService has been created with a Thread Pool of 400 threads.

So of those 500 tasks in the queue, the 400 threads in the ExecutorService will execute this 400 tasks at a time, and the remaining as slots are freed up?

Am I correct in my understanding ?

Answer 1

JavaDoc newFixedThreadPool

Creates a thread pool that reuses a fixed number of threads operating
off a shared unbounded queue. At any point, at most nThreads threads
will be active processing tasks. If additional tasks are submitted
when all threads are active, they will wait in the queue until a
thread is available. If any thread terminates due to a failure during
execution prior to shutdown, a new one will take its place if needed
to execute subsequent tasks. The threads in the pool will exist until
it is explicitly shutdown.