A Custom Thread Pool Implementation Using C#

• Download source code - 4.26 KB

Introduction

The .NET Framework BCL contains a very nice implementation of a thread pool (the System.Threading.ThreadPool class).

But, this class is not suitable for the following scenarios:

1. Long-running operations. Usually, for long-running operations, it is recommended to use the Thread class.
2. ThreadPool is per process. It means that a situation when there is no available thread in the ThreadPool can happen pretty often. What if you have a very important and emergent work item and do not want to take such a risk? But pretty often, especially when you have an application with a number of app domains (like IIS or SQL server), you can run out of threads in the thread pool...
3. ThreadPool does not support IAsyncResult. BeginInvoke methods of all delegates internally pass control to ThreadPool, but ThreadPool itself does not support IAsyncResult.

Generally, there are number of strict recommendations about when you should use ThreadPool and when you should use the Thread class directly or MulticastDelegate.BeginInvoke. The main problem of System.Threading.ThreadPool is that it is per process. So, if you have a set of very important tasks to do, and also have a set of third-party assemblies that you host in the application, there is always a probability that your important tasks will be delayed. In the case of the CustomThreadPool, you have a separate threadpool for each application domain.

You can have as many CustomThreadPools as application domains.

This is just the initial version of CustomThreadPool, and I plan to extend it in future. Maybe, instead of WaitHandles, I will use Monitor.Wait and Monitor.Pulse to achieve better flexibility (and probably performance).

Using the Code

The CustomThreadPool has three methods: QueueUserWorkItem, QueueUserWorkItemResult<tresult>, and RetreiveUserWorkItemResult.

A sample of how to use these methods is provided below:

public static class Program
{
      //main entry point
      public static void Main()
      {
         //schedule of
         CustomThreadPool.QueueUserWorkItem(DoSomething);
         CustomThreadPool.QueueUserWorkItemResultt<int>(MyLongRunningFunc, 
                          MyLongRunningFuncFinished);
      }

      //my long-running task
      private static void DoSomething()
      {
          Console.WriteLine("Hello, world!");
      }

      //my long-running function
      private static int MyLongRunningFunc()
      {
          return 888;
      }

      //CustomThreadPool supports IAsyncResult
      private static void MyLongRunningFuncFinished(IAsyncResult result)
      {
         Console.WriteLine(CustomThreadPool.RetreiveUserWorkItemResult<int>(result)); 
      }
}

Points of Interest

I've learned a lot about multithreading, especially about volatile fields and IAsyncResult implementation.

History

• 20 Nov, 2008 -- Initial Posting
• 10 Mar, 2009 -- Added dispose functionality to CustomThreadPool. Class changed from static to "instanceable" to support creation of multiple instances within the same App Domain.