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Posted 4 May 2009

Simple Worker Thread Class

, 5 May 2009
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A simple worker thread class with Join and post thread message


Many times we need to create worker threads and generally we want to wait in the main thread till all worker threads finish their execution, something similar to pthread’s pthread_join call. We want some notification on the completion of worker thread; check the status of the worker thread if it is still executing in thread function or finished, etc. Also sometimes we want to keep the worker thread alive even on completion of thread function so that we can resubmit a different job (typically in a thread pool). All these things can be done with event objects by managing their state to signalled non signaled, etc. It is difficult to manage such code using different event objects. I consolidated all this commonly used worker thread functionality in a basic implementation of WorkerThread class.

WorkerThread Class

WorkerThread is a basic implementation for worker thread with PostThreadMessage, Join, RegisterOnCompleteRoutine and thread execution status. It can be enhanced further for many other features but I want to keep the idea simple. Here my main focus is just to show how to use a PostThreadMessage for worker threads.

Using the Code

Using WorkerThread class in your existing application is very simple. You just need to add WorkerThread.cpp in your project and include WorkerThread.h where you want to use this class.

Add variables of WorkerThread class wherever you want to create a worker thread. Create a worker thread using Start() with an optional auto quit parameter (default is true) and to end the thread, use End() method. If auto quit parameter is true, there is no need to call End() method of WorkerThread class. Join() method will simply cause calling thread to wait till work thread finishes its execution. GetStatus() will let you know the current thread status (NotCreated, Created, Started, Restarted, Complete). ReExecute() method can be used only for non auto quit threads (created with false parameter in constructor) with different or same data (this can be further enhanced to avoid overwriting the data). RegisterOnCompleteRoutine() method can be used to register an optional routine that will be called on completion of thread function.

Below is the sample code to show the usage of the WorkerThread class:

#include "stdafx.h"
#include "WorkerThread.h"

#define MAXCOUNT 5

DWORD WINAPI ThreadProc(void *param)
    int i = (int)param;
    // your code
    return 0;

DWORD WINAPI OnComplete(void *param)
    int i = (int)param;

    printf("OnComplete data = %d\n", i);

    return 0;

int _tmain(int argc, _TCHAR* argv[])
    // Create few worker threads with autoQuit false
    WorkerThread workerThread[MAXCOUNT] = {false, false, false, false, false};

    // Register an optional completion routine
    workerThread[2].RegisterOnCompleteRoutine(OnComplete, (void *)1234);

    // Start all of them
    for (int i = 0; i < MAXCOUNT; ++i) {
        if (workerThread[i].Start(ThreadProc, (void *)i)) {
            printf("Started %d\n", i);

    for (int i = 0; i < MAXCOUNT; ++i) {
        if (workerThread[i].ReExecute((void *)i)) {
            printf("Restarted %d\n", i);


    for (int i = 0; i < MAXCOUNT; ++i) {

    // main thread will wait here, till all others finish.
    for (int i = 0; i < MAXCOUNT; ++i) {

    return 0;

Points of Interest

Note the dummy PeekMessage() call in starting of ThreadProc(), just for force creation of a message queue for our worker thread.


  • 5th May, 2009: Initial revision


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


About the Author

Manish K. Agarwal
Software Developer (Senior) Oracle
India India
Working with Oracle. Using C/C++, VC++, MFC, STL, C#, Java etc. on various platform like Windows, Unix, Macintosh etc. from last 13+ years to convert various type of requirements into running software components. My core expertise is multithreaded desktop product and large scale enterprises software development.

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Comments and Discussions

SuggestionRead more on PostThreadMessage Pin
Manish K. Agarwal26-Jun-13 23:07
memberManish K. Agarwal26-Jun-13 23:07 
QuestionMy vote 5 Pin
Shlabh Sharma27-Sep-11 2:19
memberShlabh Sharma27-Sep-11 2:19 
GeneralMy vote of 1 Pin
Mike O'Neill12-May-09 8:01
memberMike O'Neill12-May-09 8:01 
The class jumbles together two distinctly different communication/sysnchronization paradigms: messages and events. If a thread has a message queue that it's servicing, use messaging for inter-thread communication and for synchronization. There is no point in complicating matters by trying to use both.

The class also uses the highly unreliable PostThreadMessage. Per MSDN documentation of this function, if the thread hosts any visible windows, PostThreadMessage is practically guaranteed to lose messages. It might be OK to use PostThreadMessage if the thread is a pure worker-style thread, but the article doesn't warn against use of the thread to host a window.
GeneralRe: My vote of 1 Pin
Manish K. Agarwal12-May-09 18:17
memberManish K. Agarwal12-May-09 18:17 
GeneralMy vote of 1 Pin
Rick York6-May-09 6:46
memberRick York6-May-09 6:46 
GeneralRe: My vote of 1 Pin
Manish K. Agarwal7-May-09 18:50
memberManish K. Agarwal7-May-09 18:50 
GeneralRe: My vote of 1 Pin
geoyar12-May-09 11:51
membergeoyar12-May-09 11:51 
GeneralMy vote of 1 Pin
Johann Gerell5-May-09 20:57
memberJohann Gerell5-May-09 20:57 
GeneralRe: My vote of 1 Pin
vampyr5-May-09 21:39
membervampyr5-May-09 21:39 
GeneralRe: My vote of 1 Pin
Manish K. Agarwal5-May-09 23:52
memberManish K. Agarwal5-May-09 23:52 

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