Re: How to current close window while messages still in queue

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>
Tue, 4 Nov 2008 14:05:49 -0500
"vvf" <> wrote in message

Hi All,

Here is my scenario:

I have an MFC application. In one of the dialogs, I have a worker thread.

Here's how I start the thread:

 m_pThread = AfxBeginThread((AFX_THREADPROC)LoadThread, this, 0, 0,

 m_pThread->m_bAutoDelete = FALSE;

The thread reads some rows from a database (SELECT * ..), and then
iterates through the result set and sends the data rows one by one to the
GUI to update a GUI control:

 for (int i = 0; i <= iUpperBound && (WaitForSingleObject(m_hQuitEvent, 0)
== WAIT_TIMEOUT); ++i)
         // Construct data, etc...
         CData* pData = new CData; // pseudocode
         PostMessage(UpdateMessage, (WPARAM)pData, ... ) // Update the GUI
and delete pData

After the for loop is over, the thread function just finishes and this
thread ends. The m_hQuitEvent is there so that I can set it if I want to
abort the processing.

Here is how the message handler looks like:

LRESULT CWhateverDialog::OnUpdateMessage(WPARAM wParam, ...)
 CData* pData = (CData*)wParam;
 // update GUI control w/ pData information

 delete pData;
  return 0;

The problem is that when I close the dialog, even though I wait for the
thread to complete (WaitForSingleObject on its handle -
CWinThread::m_hThread), there are still some messages in the message queue
that are not yet processed and so I end up having some memory leaks
(because the handler never gets a chance to be called to de-allocate the
objects allocated and postmessage'ed to the GUI.)

What is the correct way to handle this situation ?

The WaitForSingleObject in your main thread stops all message processing.
So don't do that. What you can do is ask the secondary thread to end in
OnOK, and DO NOT call CDialog::OnOK there. Then have the secondary thread
PostMessage(MSG_OkToQuit, ... ) as the last thing it does before exiting.

The message handler for MSG_OkToQuit can call CDialog::OnOK().

Scott McPhillips [VC++ MVP]

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