Question

I had set up my thread pool like this:

ThreadPool.SetMaxThreads(10000, 10000);
ThreadPool.SetMinThreads(20, 20);

However, my app started hanging under heavy load. This seemed to be because worker tasks were not executing: I had used ThreadPool.QueueUserWorkItem to run some tasks which in turn used the same method to queue further work. This is obviously dangerous with a limited thread pool (a deadlock situation), but I am using a thread pool not to limit maximum threads but to reduce thread creation overhead.

I can see the potential trap there, but I believed that setting a maximum of 10000 threads on the pool would mean that if an item was queued, all threads were busy, and there weren’t 10000 threads in the pool, a new one would be created and the task processed there.

However, I changed to this:

ThreadPool.SetMaxThreads(10000, 10000);
ThreadPool.SetMinThreads(200, 200);

..and the app started working. If that made it start working, am I missing something about how/when the thread pool expands from minimum toward maximum size?

Answer 1

Whenever you use the thread pool, you are at the mercy of its “thread injection and retirement algorithm”.

The algorithm is not properly documented ( that I know of ) and not configurable.

If you’re using Tasks, you can write your own Task Scheduler