Re: Problem with MFC Thread

From:
David Wilkinson <no-reply@effisols.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Tue, 16 Sep 2008 10:01:55 -0400
Message-ID:
<OJEKITAGJHA.5572@TK2MSFTNGP03.phx.gbl>
Lucress Carol wrote:

Hi everyone,
I've created a MFC Dialog with a Progress Bar Control, a Stop Button
and a Start Buttton.The idea is to start the progress bar Control by
clicking on the Start Button and I would like to pause (Stop Button)
the process at anytime and continue it when I click on the Start
Button again.
I 'm able to stop the process of the Progress Bar but when I try to
continue the process the whole thing crash...
Here is how my code looks like:

// CProgressBarExampleDlg.h
class CProgressBarExampleDlg : public CDialog
{
  public :
 CProgressBarExampleDlg(CWnd* pParent = NULL);
 UINT Execute(); // here should be the process of the Progress Bar
executed
 static UINT WorkerThreadLauncher(LPVOID pvParam);
 HANDLE m_hEndThread;
 ...
 ...
protected:
void ProcessMessage();
volatile bool m_StopThread;
CWinThread* m_Thread;
...
...
};

//CProgressBarExampleDlg.cpp

BOOL CProgressBarExampleDlg::OnInitDialog()
{
 ...
 m_progress.SetRange(5, 100);
m_StopThread=false;
 HANDLE m_hEndThread = CreateEvent(0, TRUE, FALSE, 0);
...
return TRUE;
}

void CProgressBarExampleDlg::ProcessMessage()
{
     MSG msg;

         if (::PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
    {
        ::TranslateMessage(&msg);
        ::DispatchMessage(&msg);
    }
}

UINT CProgressBarExampleDlg::WorkerThreadLauncher(LPVOID pvParam)
{
   CProgressBarExampleDlg* pThreadInstance=
reinterpret_cast<CProgressBarExampleDlg*>(pvParam);
   return pThreadInstance->Execute();
}

UINT CProgressBarExampleDlg::Execute()
{
    int i, count;
    count=0;

    while (count< 180 && !m_StopThread)
    {
        for (i=0;i<30;i++)
        {
            m_progress.SetPos(i+10);
            Sleep(10);
        }
        count++;
        ProcessMessage();
    }
    return 0;
}

void CProgressBarExampleDlg::OnBnStart()
{
     this->m_Thread=AfxBeginThread(WorkerThreadLauncher,this);
}

void CProgressBarExampleDlg::OnBnStop()
{
      MSG msg;
       DWORD dwResult = WaitForSingleObject( m_hEndThread, 0 );

    if ( dwResult =! WAIT_OBJECT_0 )
                   {
         this->m_StopThread = true;
                   }
}

I guess in the OnBnStart() function I maybe need a if-clause to start
the process again when it has been previously interrupted?


Lucress:

Your Execute() method is running in the worker thread, so

1. It should not be manipulating the progress control directly (though it may
work because CProgressCtrl::SetPos() is implemented by SendMessage() in a very
simple way).

2. What is the purpose of the ProcessMessage() method? The main purpose of a
worker thread is to not block the main thread, so that its message queue can
operate in a normal manner. So you do not need to use PeekMessage().

--
David Wilkinson
Visual C++ MVP

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