🚀 go-pugleaf

Should a message queue that receives a message from PostThreadMessage() also 
receive one from PostMessage() with HWND_BROADCAST as the first parameter 
(assuming the queue belongs to a primary thread of a process)?

I have situation in which a main app starts a background process using 
CreateProcess() and then sends a registered message to the background app to 
register (the background app just keeps a reference count of the number of 
main apps).  The main app uses the following during processing of its 
WM_CREATE message.

PostMessage(HWND_BROADCAST, uiAppRegisterMsgID, KBLOCKREGISTER, NULL);

The background app does not have any windows and does not receive user 
input, so there are no calls in the message loop to TranslateMessage() and 
DispatchMessage().  The message loop just watches for the registered message 
to arrive:

while (GetMessage(&msg, NULL, 0, 0)) {
  if (msg.message == uiAppRegisterMsgID) {
    MessageBox(NULL, "App Message retrieved from queue", "KBLockExe message 
loop", MB_OK);
    if (msg.wParam == 0) {
      if ((--nAppRefCount) <= 0) {
        lpfnUnsetHook(hKBHook);
        CloseHandle(hReadyEvent);
        CloseHandle(hKBLockExeMux);
        FreeLibrary(hDllInst);
        ExitProcess(0);
      }
    }
    else if (msg.wParam == 1) {
      nAppRefCount++;
      MessageBox(NULL, "Application registered", "Registration", MB_OK);
    }
  }
}

The message loop never sees the registered message, though.  If the call to 
PostMessage() is replaced by PostThreadMessage() using the threadID of the 
background app, the message loop above responds as it should.

The problem is I cannot guarantee that the main app will always have the 
threadID it needs to send the message, so broadcasting using PostMessage() 
would be preferable.

Any suggestions as to why my approach is not working would be appreciated.

Thanks -- Steve