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List:       kde-core-devel
Subject:    Re: KToolBar problem
From:       David Faure <david () mandrakesoft ! com>
Date:       2000-10-07 2:28:36
[Download RAW message or body]

On Fri, 06 Oct 2000, Reginald Stadlbauer wrote :
>On Fri, 06 Oct 2000, Michael Reiher wrote:
>
>> > Hi
>>
>> There is some evil problem in KToolBar which leads to weird crashes in
>> Konqueror in certain cases when you manipulate your boorkmarks. The most
>> relieable way is probably deleting a bunch of bookmarks at once.
>>
>> The problem is that KToolBar keeps a second list of widgets which is read
>> during rebuildLayout() and if there are illegal pointers in it -> crash.
>> Widgets are removed from that list either explicitly or by a ChildRemove
>> event. So normally when you delete a widget it gets cleand out by the
>> event. However if you delete it so quickly that the ChildInserted event
>> dosnīt get posted QObject simply deletes the Remove(and the Inserted)
>> event. So KToolBar doesnīt get notifyed about the remove. And this is the
>> case when modifying bookmarks. KBookmarkBar runs slotBookmarksChanged()
>> which rebuilds the bookmarkbar. There is some kind of placeholder widget or
>> whatever which gets simply deleted. KBookmarkbar doesnīt get the Removed
>> event and keeps it -> crash on next layout.
>>
>> Iīm kinda unsure what to do now. Possible solutions:
>> 1. Remove the placeholder widget. Doesnīt seem to serve any useful purpose
>> anyway.
>> 2. Explicitly remove it when clearing KBookmarkBar
>> But these two are actually cheating and donīt fix the real Problem;-)
>>
>> 3. Implement some mechanism which compares KToolBars "widgets" list with
>> the children() list and throw out illegal pointers. Though this one would
>> have to be put in *every* place which accesses the widget list. Hmm...
>>
>> IMO all three are sub optimal. With regard to the current freeze Iīd go for
>> 1. or 2. as they are the least dangerous. Attached a patch for 2.
>>
>> Any comments, please? Has anyone a better idea? Perhaps someone with more
>> insight into
>> KToolBar?
>
>Ok, following patch in KToolBar fixes the problem for me. Could be done 
>cleaner with using QGuarderPtr<QWidget> in the list and maps instead of 
>QWidget, but I think this wouldn't be binary compatible. So please review and 
>test this one:
[...]

Looks very good to me.
Currently testing it.

BTW an unrelated problem in KToolbar, as detected by Insure++ :

[ktoolbar.cpp:1297] **FREE_DANGLING**
>>     delete layout();

  Freeing dangling pointer: layout()

  Pointer : 0x0816c230
  In block: 0x00000002 thru 0x00000000 (-1 bytes)
                   freed at .psrc, 0

  Stack trace where the error occurred:
         KToolBar::rebuildLayout()  ktoolbar.cpp, 1297
             KToolBar::showEvent()  ktoolbar.cpp, 1371
                  QWidget::event()
                 QToolBar::event()
                 KToolBar::event()  ktoolbar.cpp, 1674
            QApplication::notify()
            KApplication::notify()  kapp.cpp, 506
                   QWidget::show()
                  QToolBar::show()
                  KToolBar::show()  ktoolbar.cpp, 1425
                   QWidget::show()
               QMainWindow::show()
KonqMisc::createBrowserWindowFromProfile()  konq_misc.cc, 96
                            main()  konq_main.cc, 88

**Memory corrupted.  Program may crash!!**


I love this last statement :-)

Also, the QBoxLayout built there is leaked according to insure++, but I'm quite surprised
(it's given "this" as parent, so it's not a leak AFAICS). Really strange, because all other cases
of something being build with a parent doesn't make insure believe there's a leak.......

[ktoolbar.cpp:1331] **LEAK_SCOPE**
>> }

  Memory leaked leaving scope: bl

  Lost block : 0x0816abc0 thru 0x0816ac17 (88 bytes, 1 element)
               bl, allocated at:
         KToolBar::rebuildLayout()  ktoolbar.cpp, 1298
             KToolBar::showEvent()  ktoolbar.cpp, 1371
                  QWidget::event()
                 QToolBar::event()
                 KToolBar::event()  ktoolbar.cpp, 1674
            QApplication::notify()
            KApplication::notify()  kapp.cpp, 506
                   QWidget::show()

  Stack trace where the error occurred:
         KToolBar::rebuildLayout()  ktoolbar.cpp, 1331
             KToolBar::showEvent()  ktoolbar.cpp, 1371
                  QWidget::event()
                 QToolBar::event()
                 KToolBar::event()  ktoolbar.cpp, 1674
            QApplication::notify()
            KApplication::notify()  kapp.cpp, 506
                   QWidget::show()
                  QToolBar::show()
                  KToolBar::show()  ktoolbar.cpp, 1425
                   QWidget::show()
               QMainWindow::show()
KonqMisc::createBrowserWindowFromProfile()  konq_misc.cc, 96
                            main()  konq_main.cc, 88



-- 
David FAURE, david@mandrakesoft.com, faure@kde.org
http://www.mandrakesoft.com/~david/, http://www.konqueror.org/
KDE, Making The Future of Computing Available Today
See http://www.kde.org/kde1-and-kde2.html for how to set up KDE 2

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