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Among all my tasks, I have some that must be processed serially (they can never run concurrently and they must be processed in order).
I achieved that creating a separated thread pool with a single thread for each group of tasks that must be executed serially. It works but I don't have the resources for that. I don't control the number of groups, so I might end up with a ridiculous number of threads running simultaneously.
Is there any way I can accomplish that with a single thread pool? Is there a thread pool with multiple blocking queues where I could ensure serial execution for each queue?
Just emphasizing what I've said in my second paragraph: I've solved this with a single threaded thread pool for each group of tasks that must be executed serially. I can't go on with this solution, though. There are way too many groups and I can't have all these threads.
I've found this related question, but since it is not very recent, I still created mine. All I'm doing is trying to avoid reinventing the wheel, but it seems I don't have a choice.
Does Java have an indexable multi-queue thread pool?
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A thread pool manages a set of anonymous threads that perform work on request. The threads do not terminate right away. When one of the threads completes a task, the thread becomes idle, ready to be dispatched to another task.
A thread pool helps mitigate the issue of performance by reducing the number of threads needed and managing their lifecycle. Essentially, threads are kept in the thread pool until they're needed, after which they execute the task and return the pool to be reused later.
ThreadPool will create maximum of 10 threads to process 10 requests at a time. After process completion of any single Thread, ThreadPool will internally allocate the 11th request to this Thread and will keep on doing the same to all the remaining requests.
In computer programming, a thread pool is a software design pattern for achieving concurrency of execution in a computer program. Often also called a replicated workers or worker-crew model, a thread pool maintains multiple threads waiting for tasks to be allocated for concurrent execution by the supervising program.
Akka, as suggested by @SotiriosDelimanolis and @AlexeiKaigorodov seems promising, as well as @Dodd10x second answer, which certainly solves the problem. The only downside is that I'd have to code my own polling strategy to make sure my tasks are eventually added to the executor (like the infinite loop in his example).
On the other hand, the Striped Executor Service suggested by @OldCurmudgeon exactly matches my problem and works out of the box simply as a custom ExecutorService.
This magical thread pool would ensure that all Runnables with the same stripeClass would be executed in the order they were submitted, but StripedRunners with different stripedClasses could still execute independently. He wanted to use a relatively small thread pool to service a large number of Java NIO clients, but in such a way that the runnables would still be executed in-order.
There is even a comment about using a single threaded thread pool for each group (stripe), as it was suggested here:
Several suggestions were made, such as having a SingleThreadExecutor for each stripeClass. However, that would not satisfy the requirement that we could share the threads between connections.
I see this as the best solution for its simplicity and ease of use.
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