Just to be clear for those of us who are wobbly on C++, this is because during the constructor or destructor, your object is of the class in question, NOT of the class it will finally be, because in the constructor the subclass has not been constructed, yet, and in the destructor the subclass was already destructed. So calling to the subclass virtual implementation would be bad.
Scott Meyers says: http://www.artima.com/cppsource/nevercall.html Is there any way we could modify an object to assert that it can't happen in development? Like scoped_vtable_killer declared in the constructor and destructor which makes calling a virtual method on that object fatal? -scott On Fri, Oct 30, 2009 at 3:12 PM, Jeremy Orlow <jor...@chromium.org> wrote: > I've spent a good deal of this week trying to track down what turned out to > be a simple but fairly common problem: I forgot virtual dispatch only > partially works in destructors. There have been several email threads about > this, but it still bites us form time to time, so I thought it was worth > another reminder. > > Details: > I subclassed ChromeThread which subclasses base::Thread. base::Thread calls > CleanUp on the thread right before termination. CleanUp is virtual. Both > ChromeThread and my class override CleanUp(). base::Thread calls Stop() in > its destructor to stop the thread (if it hasn't already been stopped). But > by the time you hit destruction, the vtable is no longer available and thus > the destructor of base::Thread (and anything it calls) does NOT have access > to the vtable of ChromeThread (or my class). So, if you don't explicitly > call Stop(), your subclass's CleanUp method will NOT be called. Thus the > thread was going away without my CleanUp method ever being called. > Obviously this affects more than just base::Thread. And this is also how > you can hit errors with pure virtual methods being called. > J > > > --~--~---------~--~----~------------~-------~--~----~ Chromium Developers mailing list: chromium-dev@googlegroups.com View archives, change email options, or unsubscribe: http://groups.google.com/group/chromium-dev -~----------~----~----~----~------~----~------~--~---
