Re: MFC and PostMessage problem in Release build

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 05 Feb 2009 23:28:38 -0600

Message-ID:

<cthno4lv1jkp3smb2tk8pu6cs7uslf1oc3@4ax.com>

On Thu, 5 Feb 2009 21:10:40 -0800 (PST), Faisal <faisalm83@gmail.com>
wrote:

I 've an application developed with MFC, which behaves abnormally in
the release build.
It's a dialog-based application with two buttons START and STOP. While
clicking the START, it starts a thread. The thread just sleeps 2000ms
and posts a user-defined message to the dialog. In this message
handler the START button is enabled and STOP is disabled.

My implementation is given below.

#define UWM_STOP (WM_USER + 124)

BEGIN_MESSAGE_MAP(CPostTestDlg, CDialog)
    //{{AFX_MSG_MAP(CPostTestDlg)
    ON_BN_CLICKED(IDC_BTN_START, OnBtnStart)
    ON_BN_CLICKED(IDC_BTN_STOP, OnBtnStop)
    ON_MESSAGE(UWM_STOP, OnBtnStop )
    //}}AFX_MSG_MAP
END_MESSAGE_MAP()

You should move your ON_MESSAGE after the AFX comments, but you can't use
the same handler function in ON_BN_CLICKED and ON_MESSAGE. See below for
more.

DWORD WINAPI CPostTestDlg::ThreadFn( LPVOID lpParam )
{
    CPostTestDlg* pThis = static_cast<CPostTestDlg*>(lpParam);

    while( 1 )
    {
        Sleep( 2000 );

        TRACE(_T("Posting message\n"));
        ::PostMessage( pThis->m_hWnd, UWM_STOP, 0, 0 );
        break;
    }

    return 0;
}

void CPostTestDlg::OnBtnStart()
{
    GetDlgItem( IDC_BTN_START )->EnableWindow( FALSE );
    GetDlgItem( IDC_BTN_STOP )->EnableWindow( TRUE );

    DWORD dwThreadID;
    m_hThread = ::CreateThread(NULL, 0, ThreadFn, (void*)this, NULL,
&dwThreadID);
}

void CPostTestDlg::OnBtnStop()
{
    TRACE(_T("Stop receieved\n"));

    ::WaitForSingleObject( m_hThread, INFINITE );
    ::CloseHandle( m_hThread );

    GetDlgItem( IDC_BTN_START )->EnableWindow( TRUE );
    GetDlgItem( IDC_BTN_STOP )->EnableWindow( FALSE );

}

These code runs smoothly in debug build. When I run it in release
mode, for the first two START and STOP it works fine. When I click
the start third time it crashes.

I've encountered this problem in a complex project. In order to
confirm this issue, I tried this in a sample project (code listed
above). But this problem occurs in this simple project too.

Could someone see something wrong in my code?

You're using the same message handler for ON_BN_CLICKED and ON_MESSAGE,
whose handler functions are totally different. The ON_MESSAGE handler is
declared like this:

LRESULT Handler(WPARAM, LPARAM);

Also, you're using the raw API to manage your threads, when you should be
using AfxBeginThread. See this page for some very important info on using
MFC's CWinThread correctly:

http://members.cox.net/doug_web/threads.htm

--
Doug Harrison
Visual C++ MVP