Hey Pau, Dmitriy,
Wt's signals are resilient to this (i.e. the signal can be deleted from a
slot connected to it), and so should Wt widgets be designed (they should
only emit a slot at the very end and be cautious that 'this' may be no
longer valid after doing that).
So it is a bug in Wt (WMenu/WMenuItem).
Regards,
koen
2013/4/16 Pau Garcia i Quiles <[email protected]>
> Hello,
>
> These kind of bugs are well known, see for instance these two in Qt
> applications (which Wt is heavily inspired on)
>
>
> http://blogs.kde.org/2009/03/26/how-crash-almost-every-qtkde-application-and-how-fix-it-0
>
> http://agateau.com/2010/09/29/fun-with-event-loops-and-qobjectdeletelater/
>
>
>
> On Tue, Apr 16, 2013 at 12:30 PM, Dmitriy Igrishin <[email protected]>wrote:
>
>> Hey all,
>>
>> Recently I catched a bug (or misdesign) in WMenu and
>> concluded for myself that slots should never perform
>> deletion of the objects which methods emit the related
>> signals. This may leads to undefined behavior.
>>
>> Consider:
>>
>> // WARNING: bad code!
>> //
>> // Gdb run command: run --docroot . --http-address 0.0.0.0 --http-port
>> 8888
>> #include <Wt/WApplication>
>> #include <Wt/WMenu>
>> #include <Wt/WPopupMenu>
>> #include <Wt/WStackedWidget>
>>
>> namespace {
>>
>> class App : public Wt::WApplication {
>> public:
>> App(const Wt::WEnvironment& env);
>> private:
>> void del();
>>
>> Wt::WMenu* m_;
>> };
>>
>> void App::del()
>> {
>> // This slot will be called from WMenu::select():
>> // ...
>> // item->triggered().emit(item);
>> // itemSelected_.emit(item);
>> // ...
>> // and thus leads to undefined behaviour, since `this'
>> // will point to the deleted WMenu after item->triggered().emit(item).
>> delete m_;
>> m_ = 0;
>> }
>>
>> App::App(const Wt::WEnvironment& env)
>> : WApplication(env)
>> {
>> using Wt::WText;
>>
>> Wt::WStackedWidget* const c = new Wt::WStackedWidget;
>> root()->addWidget(c);
>>
>> // Menu
>> m_ = new Wt::WMenu(c);
>> root()->addWidget(m_);
>>
>> // Submenu
>> Wt::WPopupMenu* const pm = new Wt::WPopupMenu(c);
>> m_->addMenu("User Foo", pm);
>> pm->addItem("Logout", this, &App::del);
>> }
>>
>> Wt::WApplication* createApp(const Wt::WEnvironment& env)
>> {
>> return new App(env);
>> }
>>
>> } // namespace
>>
>> int main(int argc, char* argv[])
>> {
>> return Wt::WRun(argc, argv, createApp);
>> }
>>
>> While the example above demonstrates a bug (or invalid usage
>> due to the lack of documentary cautions from such use) in WMenu,
>> IMO it demonstrates unrecommened and dangerous pratice in general.
>> Thus, I think that the rule: "slots should never perform deletion of the
>> objects which methods emit the related signals" should be documented
>> to prevent users from corresponding gotchas.
>>
>> Thoughts?
>>
>> --
>> // Dmitriy.
>>
>>
>>
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>>
>
>
> --
> Pau Garcia i Quiles
> http://www.elpauer.org
> (Due to my workload, I may need 10 days to answer)
>
>
> ------------------------------------------------------------------------------
> Precog is a next-generation analytics platform capable of advanced
> analytics on semi-structured data. The platform includes APIs for building
> apps and a phenomenal toolset for data science. Developers can use
> our toolset for easy data analysis & visualization. Get a free account!
> http://www2.precog.com/precogplatform/slashdotnewsletter
> _______________________________________________
> witty-interest mailing list
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> https://lists.sourceforge.net/lists/listinfo/witty-interest
>
>
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Precog is a next-generation analytics platform capable of advanced
analytics on semi-structured data. The platform includes APIs for building
apps and a phenomenal toolset for data science. Developers can use
our toolset for easy data analysis & visualization. Get a free account!
http://www2.precog.com/precogplatform/slashdotnewsletter
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