Thread Pool vs Thread Spawning

Question

Can someone list some comparison points between Thread Spawning vs Thread Pooling, which one is better? Please consider the .NET framework as a reference implementation tha

Answer 1

Assuming C# and Windows 7 and up...

When you create a thread using new Thread(), you create a managed thread that becomes backed by a native OS thread when you call Start – a one to one relationship. It is important to know only one thread runs on a CPU core at any given time.

An easier way is to call ThreadPool.QueueUserWorkItem (i.e. background thread), which in essence does the same thing, except those background threads aren’t forever tied to a single native thread. The .NET scheduler will simulate multitasking between managed threads on a single native thread. With say 4 cores, you’ll have 4 native threads each running multiple managed threads, determined by .NET. This offers lighter-weight multitasking since switching between managed threads happens within the .NET VM not in the kernel. There is some overhead associated with crossing from user mode to kernel mode, and the .NET scheduler minimizes such crossing.

It may be important to note that heavy multitasking might benefit from pure native OS threads in a well-designed multithreading framework. However, the performance benefits aren’t that much.

With using the ThreadPool, just make sure the minimum worker thread count is high enough or ThreadPool.QueueUserWorkItem will be slower than new Thread(). In a benchmark test looping 512 times calling new Thread() left ThreadPool.QueueUserWorkItem in the dust with default minimums. However, first setting the minimum worker thread count to 512, in this test, made new Thread() and ThreadPool.QueueUserWorkItem perform similarly.

A side effective of setting a high worker thread count is that new Task() (or Task.Factory.StartNew) also performed similarly as new Thread() and ThreadPool.QueueUserWorkItem.