Threads, Message Pump and Sync

Hi All,

Disclaimer: This may be a relatively long message but please bare with
me since I will attempt to describe the problem thoroughly. Thank you!

I am writing a dialog based application that uses worker threads. That
is, one of the dialogs needs to read a large number of items from a
database and uses a worker thread for that.

The items from the database are sent to the UI thread to be displayed.
Therefore, the whole thing may be summarized as follows:

The worker thread allocates some memory on the heap for the item read
from the database and then uses PostMessage to send it to the UI
thread. The UI thread does whatever it needs to do with the item and
then it adds it to a "deallocation" list that will be traversed by
another worker thread responsable w/ deallocation. The reason for not
deleting the item right away is because I needed it for the entire
life span of the dialog and, as many items may be added to this list,
I don't want to delete the items in the UI thread when dismissing the
dialog.

Anyway, here is some pseudocode:

OnInitDialog:

Starts the worker thread and saves its handle so that I can
WaitForSingleObject on it when I exit the dialog.

The worker thread looks like this:

HANDLE objects[2];

objects[0] = m_hQuitEvent;
objects[1] = m_hProcessEvent;
m_bThreadRunning = TRUE;

while (m_bThreadRunning)
{
   switch(WaitForMultipelObjects(2, objects, FALSE, INFINITE)
   {
     case WAIT_OBJECT_0: m_bThreadRunning = FALSE; break;
     case WAIT_OBJECT_0+1: ProcessItems(); break;
   }
}

For the simplicity of the discussion, I will substitute the items from
the database with a long list of CString's.

Therefore, ProcessItems looks like this:

for (int i = 0; i < 10000000 && m_bThreadRunning; ++i)
{
   CString* pString = new CString;
   PostMessage(VEMsg_AddItem, (WPARAM)pString, 0);
}

The UI thread has a message handler that my be summarized as this:

LRESULT CWhatever::OnAddItem(WPARAM wParam, LPARAM lParam);
{
  CString* pString = static_cast<CString*>(wParam);
  // do whatever
  AddToCleanup(pString);
  return 0;
}

Anyway, when closing the dialog I basically do something like this:

m_bThreadRunning = FALSE; // to break the for loop in ProcessItems
SetEvent(m_hQuitEvent);
WaitForSingleObject(m_pThread->m_hThread, iTimeout);

Anyway, everything works correctly. However, if I quit BEFORE all the
messages in the message pump are processed, as you can imagine, I get
memory leaks. Moreover, these message won't have any place "to go"
since the window will be long gone by the time some of them arrive at
their destination.

The question is: How can I "wait" for the last message sent and only
allow the dialog to be dismissed when the last message has been
processed ? [and thus added to the clean-up list].

I mean, as far as synchronization, I think I did everything right; I
signal the thread to exit, I wait for it to complete and only then I
dismiss the dialog. However, this way I have no idea if all the
messages have been processed.

I thought of the following solution that that is not quite nice, IMHO:

Mark the last package PostMessage'd with some sort of a flag and then
check in the message handler for that flag. If I find the flag,
quitting is allowed, if not, I have to wait.

Thanks!
Marius