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A Custom Thread Pool Implementation Using C#

, 10 Mar 2009 CPOL
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This article describes a custom thread pool implementation using the .NET Framework and C# 3.0.


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

      //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)

Points of Interest

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


  • 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.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Vitaliy Liptchinsky
Technical Lead bwin Interactive Entertainment AG
Austria Austria
The views expressed in my articles are mine and do not necessarily reflect the views of my employer.

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Comments and Discussions

QuestionI found this very useful, with one little change. Pin
wookie2u@gmail.com2-Oct-12 21:16
memberwookie2u@gmail.com2-Oct-12 21:16 
GeneralDisposeImpl() is not working for big number of transactions Pin
Houssam Hamdan17-Jun-10 2:44
memberHoussam Hamdan17-Jun-10 2:44 
GeneralRe: DisposeImpl() is not working for big number of transactions Pin
Vitaliy Liptchinsky17-Jun-10 3:24
memberVitaliy Liptchinsky17-Jun-10 3:24 
QuestionArguments? Pin
Houssam Hamdan11-May-10 2:50
memberHoussam Hamdan11-May-10 2:50 
AnswerRe: Arguments? Pin
Vitaliy Liptchinsky11-May-10 3:18
memberVitaliy Liptchinsky11-May-10 3:18 
GeneralRe: Arguments? Pin
Houssam Hamdan11-May-10 4:02
memberHoussam Hamdan11-May-10 4:02 
Questioncan i use it in a WCF service Pin
ATM@CodeProject23-Dec-09 18:46
memberATM@CodeProject23-Dec-09 18:46 
AnswerRe: can i use it in a WCF service Pin
Vitaliy Liptchinsky24-Dec-09 1:50
memberVitaliy Liptchinsky24-Dec-09 1:50 
QuestionDemo program bug? Pin
MrRoger7-May-09 9:48
memberMrRoger7-May-09 9:48 
Generalv2 Pin
andreas___________11-Mar-09 22:14
memberandreas___________11-Mar-09 22:14 
GeneralRe: v2 Pin
Vitaliy Liptchinsky11-Mar-09 22:53
memberVitaliy Liptchinsky11-Mar-09 22:53 
Generalprogram hangs on exit [modified] Pin
andreaslanghoff4-Mar-09 5:16
memberandreaslanghoff4-Mar-09 5:16 
GeneralRe: program hangs on exit Pin
Vitaliy Liptchinsky5-Mar-09 0:05
memberVitaliy Liptchinsky5-Mar-09 0:05 
GeneralRe: program hangs on exit Pin
andreas___________5-Mar-09 3:22
memberandreas___________5-Mar-09 3:22 
GeneralRe: program hangs on exit Pin
Vitaliy Liptchinsky5-Mar-09 4:49
memberVitaliy Liptchinsky5-Mar-09 4:49 
GeneralRe: program hangs on exit Pin
Vitaliy Liptchinsky10-Mar-09 22:00
memberVitaliy Liptchinsky10-Mar-09 22:00 
GeneralRe: program hangs on exit Pin
Houssam Hamdan16-Jun-10 22:32
memberHoussam Hamdan16-Jun-10 22:32 

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