257917 - nsWindow::DispatchPendingEvents, Hwnd must not be NULL in call to EnumChildWindows

Status: NEW

(Core :: XUL, defect)

Description

[Henrik Lynggaard Hansen]

In widget\src\windows\nswindow.cpp, nsWindow::DispatchPendingEvents We are 
calling ::EnumChildWindows() with a NULL Hwnd.

This is not allowed on Windows 95/98/ME.

If it is null in Win2000+ then its the same as a call to to ::EnumWindows, so 
why not use this directly ?

Comment 1

[Christian :Biesinger (don't email me, ping me on IRC)]

it looks like this can only happen when GetTopLevelHWND returns NULL... why does it?

Comment 2

[Henrik Lynggaard Hansen]

I believe when the call to ::GetParent(...) has a NULL for Hwnd. Thats what my
traces tell me.

However my tree is approx two days old, from before the GetTopLevelHwnd was used.

What currently is:
3747   // Quickly check to see if there are any
3748   // paint events pending.
3749   if (::GetQueueStatus(QS_PAINT)) {
3750     // Find the top level window.
3751     HWND topWnd = GetTopLevelHWND(mWnd);
3752 
3753     // Dispatch pending paints for all topWnd's descendant windows.
3754     // Note: EnumChildWindows enumerates all descendant windows not just
3755     // it's children.
3756     ::EnumChildWindows(topWnd, nsWindow::DispatchStarvedPaints, NULL);
3757   }

is in my tree:

  // Quickly check to see if there are any
  // paint events pending.
  if (::GetQueueStatus(QS_PAINT)) {
    // Find the top level window.
    HWND topWnd = mWnd;
    // mWnd  is somehow NULL !!??
    HWND parentWnd = ::GetParent(mWnd);
    while (parentWnd) { 
      topWnd = parentWnd;
      parentWnd = ::GetParent(parentWnd);
    }
  
    // Dispatch pending paints for all topWnd's descendant windows. 
    // Note: EnumChildWindows enumerates all descendant windows not just
    // it's children.
    ::EnumChildWindows(topWnd, nsWindow::DispatchStarvedPaints, NULL);
  }

Comment 3

[Henrik Lynggaard Hansen]

Attachment: Stack traces for the 3 time this error occurs (during my 15 min surf)

These tree stack traces shows the problem