Question

I need to make a program with a limited amount of threads (currently using newFixedThreadPool) but I have the problem that all threads get created from start, filling up memory at alarming rate.

I wish to prevent this. Threads should only be created shortly before they are executed.

e.g.: I call the program and instruct it to use 2 threads in the pool. The program should create & launch the first 2 Threads immediately (obviously), create the next 2 to wait for the previous 2, and at that point wait until one or both of the first 2 ended executing.

I thought about extending executor or FixedThreadPool or such. However I have no clue on how to start there and doubt it is the best solution. Easiest would have my main Thread sleeping on intervals, which is not really good either…

Thanks in advance!

Answer 1

Looking at the details in your post…

I call the program and instruct it to use 2 threads in the pool. The program should create & launch the first 2 Threads immediately (obviously), create the next 2 to wait for the previous 2, and at that point wait until one or both of the first 2 ended executing.

Your problem is much more about synchronizing tasks execution than in fact pooling threads. From what you say here, you want to have 2 threads executing any number of tasks; if you don’t want to have 100 jobs running at the same time, don’t create a 100 threads pool…

I would suggest either using a BlockingQueue to control your Runnables, or create a 2 threads pool using a ThreadPoolExecutor, and feed it all your tasks. It will execute them when threads are available.

Does that make sense with what you try to achieve here?