ThreadPool SetMinThreads - the impact of setting it

Question

I am trying to understand the impact of setting ThreadPool.SetMinthreads. I have multiple virtual applications running in one Azure App Service. My understanding is

Answer 1

The MinThreads governs how many worker threads will be spawned without a delay.

Whenever you do something that requires a thread from the thread pool (whether worker or IOCP pool), the system will first see if there is a free thread.

If not, it looks to see how many threads are currently spawned. If that number is less than MinThreads, it immediately spawns a new thread. Otherwise it waits a short time, usually around 300-500ms, though that is system dependent. If there is still no free thread, it will then spawn a new thread.

Of course, this all is still limited by MaxThreads.

All that said, IIS is very good at figuring out a sensible number based on your machine and in most cases you are best to leave it alone; if you are just worried about serving requests then I wouldn't touch it personally. If, on the other hand, you are spawning a lot of background tasks yourself then it may be sensible. I'd strongly encourage you to measure it before you actually make changes.

Though... Setting MinThreads to 100 is rarely harmful, especially as the system will only start the number of threads it actually needs anyway