What determines the number of threads a Java ForkJoinPool creates?

Question

As far as I had understood ForkJoinPool, that pool creates a fixed number of threads (default: number of cores) and will never create more threads (unless the a

Answer 1

strict, full-strict, and terminally-strict have to do with processing a directed acyclic graph (DAG). You can google those terms to get a full understanding of them. That is the type of processing the framework was designed to process. Look at the code in the API for Recursive..., the framework relies on your compute() code to do other compute() links and then do a join(). Each Task does a single join() just like processing a DAG.

You are not doing DAG processing. You are forking many new Tasks and waiting (join()) on each. Have a read in the source code. It's horrendously complex but you may be able to figure it out. The framework does not do proper Task Management. Where is it going to put the waiting Task when it does a join()? There is no suspended queue, that would require a monitor thread to constantly look at the queue to see what is finished. This is why the framework uses "continuation threads". When one task does join() the framework is assuming it is waiting for a single lower Task to finish. When many join() methods are present the thread cannot continue so a helper or continuation thread needs to exist.

As noted above, you need a scatter-gather type fork-join process. There you can fork as many Tasks