Question

In my application I have a modal dialog which contains about 20 different combo boxes which are bind to certain fields in the databases. The database is huge and on the loading of dialog I have to load all the combo boxes from the databases. So I setup 20 threads (1 each for every combo box).

Everything works fine, but the problem only occurs when the user closes the dialog with close or cancel button or OK button while the threads are running; in that case the application crashes.

I have tried to terminate the threads prematurely as well but that does not help. Here is the thread termination code

if(m_iNoOfThreadsCompleted != m_iTotalThreads)      
{
        for(int i = 0; i < m_iTotalThreads - 1; i++)
    {
            if (m_threads[i] != NULL)
        {
            GetExitCodeThread(m_threads[i]->m_hThread, &exit_code);
            if(exit_code == STILL_ACTIVE)
                CloseHandle(m_threads[i]->m_hThread);
        }
        if(m_iNoOfThreadsCompleted == m_iTotalThreads)
            break;
    }
}

What is the issue? Or do I need to use a better approach?

Answer 1

Synchronizing threads is generally done using events.

// Before Creating threads
HANDLE hEndEvent = CreateEvent(NULL,FALSE,FALSE,NULL);
// Pass handle to threads

Then on termination

SetEvent(hEndEvent);
WaitForMultipleObjects(m_iTotalThreads,m_threads,TRUE,INFINITE); // Wait for all threads to end

// Loop through and close all the thread handles

Note that you need to be occasionally looking for the end event to be set otherwise your threads won’t end.

// In Thread
if (WaitForSingleObject(hEndEvent,0)==WAIT_OBJECT_0) {
    // Clean up
    return 0;
}