On Fri, Nov 20, 2009 at 12:05:55PM -0800, Evan Martin wrote:
> On Fri, Nov 20, 2009 at 4:23 AM, rahul <rahulsin...@gmail.com> wrote:
> > I was trying to compile chromium today on Linux and I got this error.
> > This error occurred because of -Werror CFLAG set in the Makefile. I
> > remedied by writing a one-liner to delete all occurrences of -Werror
> > from CFLAGS in all Makefiles.
> >
> > However, this error intrigued me. I saw through the code and the
> > classes in question have declared virtual methods but haven't declared
> > a destructor. In that case, the compiler generates the destructor.
> >
> >
> > Base *b = new Sub();
> > delete b;
> >
> > To the best of my knowledge, if Base is the class which defines
> > virtual methods but non-virtual destructor, delete can cause a memory
> > leak if Sub happens to be taking more memory than Base. I think that
> > the destructor for a class with virtual methods has either to be
> > "public virtual" or "protected non-virtual" for the proper freeing of
> > memory.
> >
> >
> > Would someone help me clarify this?
> >
> > I know there might be some scenarios where this can be done
> > intentionally but looks like there are more arguments for adding a
> > virtual destructor than not adding one. I see that this is done for
> > the Delegates. Also, if this is one of the intended special cases, can
> > someone explain how to compile chromium then? Deleting -Werror from
> > CFLAGS is an ugly hack at best.
>
> Your analysis is correct. However, a virtual destructor is not needed
> in the case where you never delete through the Base*. It turns out
> for our codebase that is very common (due to lots of "observer"-like
> patterns), so we decided to not rely on this compiler warning. It's
> only caused horrible bugs once or twice! :)
>
> The correct fix would be to disable this particular warning in
> build/common.gypi.
> However, I'm puzzled why nobody else has encountered the problem
> you're mentioning.
> Can you provide some details about your compiler, system configuration, etc.?
I encountered this, by turning on -Wextra which included -Wnon-virtual-dtor,
and submitted some patches to clean it up, which were rejected.
(So, add on -Wno-non-virtual-dtor to get a build.)
-- Jacob
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