Re: MFC and PostMessage problem in Release build

From:

Faisal <faisalm83@gmail.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 5 Feb 2009 21:53:33 -0800 (PST)

Message-ID:

<f147b366-838a-4773-b724-c6fd491f8012@r10g2000prf.googlegroups.com>

On Feb 6, 10:28 am, "Doug Harrison [MVP]" <d...@mvps.org> wrote:

On Thu, 5 Feb 2009 21:10:40 -0800 (PST), Faisal <faisal...@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,

Is this a coding practice? Or necessary?

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, NUL=

&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

Thanks Doug.
The type of Handler was the problem.