Block $WM_QUERYENDSESSION

[lJoel]

Hi,

I am using the following code to detect and block shutdowns on XP:

RegisterShutdownBlocker()

Func CancelShutdown($hWndGUI, $MsgID, $WParam, $LParam)
    return False
EndFunc 

Func RegisterShutdownBlocker()

    ; $WM_QUERYENDSESSION, xp
    GUIRegisterMsg(0x11, "CancelShutdown")

    ; Vista, W7, etc
    $shutdownBlocker = GUICreate("PreventShutdown",250,0)
    DllCall("User32.dll", "int", "ShutdownBlockReasonCreate", "hwnd", $shutdownBlocker, "wstr", "Unload joebox")

EndFunc

This works perfectly fine in most cases. However I experienced that the block (AutoIt terminates after the return False call) does not work if the shutdown is initiated with:

#include <stdio.h>

int main(int argc, char* argv[])
{
    DWORD a = 0;

    BroadcastSystemMessage(2, &a ,0x11, 0, 1);

    return 0;
}

Any ideas how to handle / block the WM_QUERYENDSESSION broadcast case correctly?

-- Joe

[Bowmore]

ShutdownBlockReasonCreate only works on Windows Vista or greater and only for desktop applications. You should check for errors after the DLL call. Edited December 9, 2013 by Bowmore

[JohnOne]

Any ideas how to handle / block the WM_QUERYENDSESSION broadcast case correctly?

If any application returns zero, the session is not ended. The system stops sending WM_QUERYENDSESSION messages as soon as one application returns zero.