Is it possible to send WM_QUERYENDSESSION messages to a window in a different process?

Question

I want to debug a windows C++ application I've written to see why it isn't responding to WM_QUERYENDSESSION how I expect it to. Clearly it's a little tricky to do this by just shutting the system down. Is there any utility or code which I can use to send a fake WM_QUERYENDSESSION to my application windows myself?

Answer 1

Yes. If you can get the window handle (maybe using FindWindow()), you can send/post any message to it as long as the WPARAM & LPARAM aren't pointers.

Answer 2

I've used the Win32::GuiTest Perl module to do this kind of thing in the past.

Answer 3

The Windows API SendMessage can be used to do this. http://msdn.microsoft.com/en-us/library/ms644950(VS.85).aspx

IS ti possible it's not responding because some other running process has responded with a zero (making the system wait on it.)

Answer 4

Yes of course, it possible. I faced a similar issue some months ago where some (unknown, but probably mine) app was preventing shutdown, so I wrote some quick code that used EnumWindows to enumerate all the top level windows, sent each one a WM_QUERYENDSESSION message, noted what the return value from SendMessage was and stopped the enumeration if anyone returned FALSE. Took about ten minutes in C++/MFC. This was the guts of it:

void CQes_testDlg::OnBtnTest()  
{  
   // enumerate all the top-level windows.  
   m_ctrl_ListMsgs.ResetContent();  
   EnumWindows (EnumProc, 0);  
}  


BOOL CALLBACK EnumProc (HWND hTarget, LPARAM lParam)  
{  
   CString csTitle;  
   CString csMsg;  
   CWnd *  pWnd = CWnd::FromHandle (hTarget);  
   BOOL    bRetVal = TRUE;  
   DWORD   dwPID;  

   if (pWnd)  
   {  
      pWnd->GetWindowText (csTitle);  
      if (csTitle.GetLength() == 0)  
      {  
         GetWindowThreadProcessId (hTarget, &dwPID);  
         csTitle.Format ("<PID=%d>", dwPID);  
      }  

      if (pWnd->SendMessage (WM_QUERYENDSESSION, 0, ENDSESSION_LOGOFF))  
      {  
         csMsg.Format ("window 0x%X (%s) returned TRUE", hTarget, csTitle);  
      }  
      else   
      {    
         csMsg.Format ("window 0x%X (%s) returned FALSE", hTarget, csTitle);  
         bRetVal = FALSE;  
      }  

      mg_pThis->m_ctrl_ListMsgs.AddString (csMsg);
   }
   else  
   {  
      csMsg.Format ("Unable to resolve HWND 0x%X to a CWnd", hTarget);  
      mg_pThis->m_ctrl_ListMsgs.AddString (csMsg);  
   }  
   return bRetVal;  
}

mg_pThis was just a local copy of the dialog's this pointer, so the helper callback could access it. I told you it was quick and dirty :-)