Re: [sigc] Re: [gtkmm] libsigcx and gtkmm 2.4

[Daniel Elstner <daniel elstner gmx net>]

Am So, den 13.06.2004 um 18:30 Uhr +0200 schrieb Martin Schulze:
> > 
> > > knows of it. Note that sigc::bind does not take arguments as
> > references
> > > by default if this is where you are heading.
> > 
> > std::string can be implemented with reference counting, and the
> > libstdc++ shipped with GCC does exactly that.
> 
> Meaning that no deep copy of the string is made although it is passed  
> "by value"?! Then I understand the problem here.

Exactly.

> (However, if you pass a "const char*" into the std::string ctor as in  
> my example the copy is being created at once, isn't it?)

Right.  But you have to lock *before* creating the std::string object!

> I still don't see the problem in the case where no references/pointers  
> are being passed around: The list of slots the dispatcher operates on  
> _is_ protected by memory barriers (there might be bugs in my code but  
> it is perfectly possible to simply use a mutex around 'std::list:: 
> push_back()' / 'std::list::pop_front()' as I pointed out in a comment  
> and as Christer does).

Sure, but the caller passes in an already constructed std::string.  As I
said above, you need to lock before constructing the object.  The only
alternative is a deep copy (that's what I'm proposing for the improved
Glib::Dispatcher implementation).

--Daniel