Should .NET thread-pool create the minimum amount of worker threads at start-up?

Question

Given an ASMX service application hosted on Windows server 2008r2, IIS 7.5, integrated pool, .net 4.0 CLR, 64-bit. It is almost asynchronous and widely use TPL library.

Is it correct to assume that .NET thread-pool minimum worker threads configured to be N forces N worker threads creation at start-up?

I'm expecting this behavior but it does not happen or happens intermittently.

Here are details on configuration: Machine.config section has its attribute 'minWorkerThreads' set to 100, in order to init thread-pool with minimum 100*CPUcount (let's say 400 for 4 core desktop) worker threads.

Just after service application start ThreadPool. GetMinThreads (out minWorkerThreadsCount, out minIoThreadsCount) shows as expected that minWorkerThreadsCount is 400 .

Despite this fact Debug 'Threads' window shows only 60 threads the same as Task manager. It seems like thread-pool falls back to the default behavior, but minWorkerThreadsCount is still 400.

Any ideas of what can trigger such behavior or decrease the number of threads at run-time? Allegedly this issue appears when application was build in .NET 4.5 run-time targeting .NET 4.0.

I would appreciate any input.

Answer 1

No. It will grow quickly up to that number rather than start with that many threads.

See part of ThreadPool.SetMinThreads I highligted:

Sets the minimum number of threads the thread pool creates on demand, as new requests are made , before switching to an algorithm for managing thread creation and destruction.