How to design cleaner PostMessage chain in WinApi/MFC

Question

I have a MFC GUI app that has multiple frames (sort of like Outlook'ish behavior with main window, and message/appointment windows being created in new frames, or Skype like multi frame syncronization), and I need to PostMessage malloc'ed data through the window hierarchy.

Say, I get the string, _wcsdup it, PostMessage(WM_NEWSTRING, ...), and, the control somewhere deep down the hierarchy processes it, or if there are no subscribers, the message get's cleaned.

What I am looking into now, is that all messages are posted to application thread, thread finds the active frame or best fit frame, passes the message to it, frame passes the message to it's view, the view passes message to subview and so on, if there is no view to process the message, it get's free'd.

The problem is that these chaining commands are pretty tiring to write, as I have to duplicate the message forwarding code in each CWnd class I have. At the same time, resource cleanup is pretty unpleasant, because if there is no window to catch the message, someone has to call the free. Therefore simply posting the message to the main message pump without extra handling, hoping that someone will always catch it, is not a valid approach. PostMessage returns S_OK, no one sees the message as processable, and it's left dangling.

Is there a better, correct approach for what I'm looking for?

There's no reason to not just use SendMessage, trivially solves the memory management problem. Hard to see why you wouldn't just use a method call. — Hans Passant
Multiple threads... SendMessage is effective serialization + context switch. — Coder
If you're dead set on using this method, why not add a message sink to the very end of your message passing chain that will cleanup any message that makes it that far? — Jon

l33t l33t · Accepted Answer · 2011-09-26T07:26:55

I would never use PostMessage as you describe. My solution often involves a hand-shake:

// From CNotifierBlah
PostMesssage(hWnd, UWM_NEW_DATA, 0, 0);
//
LRESULT CDestinationWnd::OnNewData(WPARAM wParam, LPARAM lParam)
{
    CNewData newData = GetNotifierBlah().GetNewData(); // Thread-safe getter!
}

Pretty much the same as Observer pattern.

How to design cleaner PostMessage chain in WinApi/MFC

1 Answers