How does a Handle relate to a thread?

Question

How exactly does a Handle relate to a thread? I am writing a service that accepts an HTTP request and calls a method before returning a response. I have written a test client that sends out 10,000 HTTP requests (using a semaphore to make sure that only 1000 request are made at a time).

If i call the method (the method processed before returning a response) through the ThreadPool, or through a generic Action<T>.BeginInvoke, the service's handles will go way up and stay there until all the request have finished, but the thread count of the service stays pretty much dead.

However, if I synchronously call the method before returning the response, the thread count goes up, but the handle count will will go through extreme peaks and valleys.

This is C# on a windows machine (Server 2008)

Answer 1

You can think of a handle as an abstraction of a pointer. There are lots of things in Windows that use handles (when you open a file at the API level, you get a handle to the file, when you create a window, the window has a handle, a thread has a handle, etc). So, Your handle count probably has to do with operations that are occuring on your threads. If you have more threads running, more stuff is going on at the same time, so you will see more handles open.

Answer 2

Your description is too vague to give a good diagnostic. But the ThreadPool was designed to carefully throttle the number of active threads. It will avoid running more threads than you have CPU cores. Only when a thread gets "stuck" will it schedule an extra thread. That explains why you see the number of threads not increase wildly. And, indirectly, why the handle count stays stable because the machine is doing less work.