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A programming model to use a thread pool

, 30 Sep 2000
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A class to manage the thread pool
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    On many occasions we need to utilize mutiple threads to boost the system performance. The logic for each thread is almost the same, but we need to manage these threads. If the system is busy, we create more threads, otherwise we kill some thread to avoid the extra overhead.

    I have done a couple of projects involving the multiple-thread management. At last I decided to write a class to wrap this machenism. This class can dynamically allocate threads and assign jobs to these worker threads. You derive your own classes and you do not need to know the underlying machanism to handle the mutiple threading and synchronization between these threads. However, you need to make your worker classes thread safe since your objects may be assigned to different threads each time.

    The another thing I want to demonstrate is the using the feature of IOCompletion Port. I found that it is amazing easy and useful, especially when used as a way to transfer data between threads.


    To use the thread pool class you need to derive your worker class from IWorker and your job class from IJobDesc. The processing logic must be embedded within the member function IWorker::ProcessJob(IJobDesc* pJob). After you are finished, you can declare a thread pool like this:

    CThreadPool pool;
    pool.Start(6, 10);
    //do some other jobs here

    The Start function has two parameters. The first argument is the minimum number of the worker threads this thread pool object should spawn. The second argument indicates the maximum number of worker thread within this thread pool. If the thread pool is very busy working on the assigned jobs it will automatically spawn more worker threads. On the other hand, when the thread pool is idle some threads will be removed from the pool. Fine-tune these two parameters to get the best performance.

    To assign jobs to the thread pool for processing, simply call the function

    pool.ProcessJob(pJob, pWorker);

    You must make sure that your derived worker class is thread-safe since a worker instance may be on multiple threads simultaneously. You have no control as to whether the process is on the same thread as the last time or not.


    If the processing takes a very long time, when you call Stop(), the processing may not finished immediately. The Stop() function will wait for a maximum of 2 minutes and then return. This function has an optional argument. If this argument is set to true, the function will terminate these worker threads anyway. If this argument is set to false, these worker threads will not get terminated harshly and still live. Under this situation, you have to take care that the worker object may not exist after calling Stop() and you will get an access violation error if you attempt to access them.

    The job object must be generated on the heap using new operator. After the process ends it will automatically deleted by the framework.


    This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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    About the Author

    Sherwood Hu

    United States United States
    No Biography provided

    Comments and Discussions

    GeneralA question about CCriticalSection PinmemberSeanQA28-Oct-08 21:26 
    GeneralWhen the menber function "Stop" is used twice and more PinmemberSeanQA28-Oct-08 21:24 
    GeneralComment on design... PinmemberNigel de Costa5-Sep-06 0:02 
    GeneralRe: Comment on design... Pinmemberalexquisi28-Mar-07 0:01 
    Generalhave memory leaks! Pinmemberpcbirdwang3-Aug-05 15:43 
    GeneralATL Server provides its own thread pool class PinmemberAlexander Gräf6-May-04 5:10 
    GeneralRemoveThreads bug PinmemberLAT26-Jul-03 10:44 
    GeneralRe: RemoveThreads bug PinmemberLAT27-Jul-03 1:54 
    GeneralRe: RemoveThreads bug PinmemberWREY27-Jun-04 7:46 
    GeneralLinker could not find "pthreadVC.lib" PinmemberWREY30-Aug-02 0:12 
    GeneralBug fixed! PinmemberXSimon25-Aug-02 17:27 
    GeneralOther considerations PinmemberBill Wilson21-Nov-01 12:48 
    I have created some similar code. I did not use IOCompletionPort, however. I do use WaitForSingleObject and SetEvent to control the threads in the pool. Also my code is not as generic as yours.

    I did do something you might want to consider. My pool manager recognizes a maximum number of threads, but it is read from the registry on each request. This allows it to be set dynamically, the pool will resize itself accordingly. A second parameter is used as a throttle. While threads are already existing, if the CPU load is greate than a (read parameter from registry) value, the thread will be assigned, but not started until the CPU usage drops below the threshold. Each time a job finshes, my worker class determines whether the thread is still needed (if more than some percentage of threads are not busy or if we exceed the maximum).

    In any case thanks for the article I found some interesting ideas in it. I wish I'd seen it BEFORE I completed my project!Laugh | :laugh:

    GeneralRe: Other considerations PinmemberBill Wilson6-Dec-01 6:46 
    GeneralRe: Other considerations PinmemberBill Wilson6-Dec-01 7:05 
    GeneralThis is more like a hack than a clean solution Pinmemberzoly29-Jan-01 9:19 
    GeneralIOCP on Win16 based OSes PinsussJim Murphy4-Oct-00 5:42 
    GeneralRe: IOCP on Win16 based OSes Pinmemberconnex22-Apr-01 6:03 
    QuestionIs there any benefit using 'struct' instead of 'class' to define the interface? PinsussAnonymous26-Sep-00 9:36 
    AnswerRe: Is there any benefit using 'struct' instead of 'class' to define the interface? PinsussSherwood26-Sep-00 11:51 
    AnswerRe: Is there any benefit using 'struct' instead of 'class' to define the interface? PinsussMarius Cabas1-Oct-00 21:26 

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