Subj : Re: Can C++ local static objects be made thread safe?
To   : comp.programming.threads
From : gniccolai
Date : Wed Feb 16 2005 07:01 am

David Hopwood <david.nospam.hopwood@blueyonder.co.uk> wrote in message news:<YpyQd.100014$B8.71590@fe3.news.blueyonder.co.uk>...
> Giancarlo Niccolai wrote:
> > So, the thing here is not what happens in that COFU, but that there is
> > someone saying (and from Mariani sayings, CURRENTLY putting in a
> > compiler) THIS scheme:
> > 
> > the_safe_initializer() {
> >    acquire_mutex()
> >    if (! cls.initialized)  //a classwide static or something the like
> >       cls.construct() // a classwide constructor or something the like
> >    release_mutex()
> > }
> > 
> > Now, we all know here that THIS may deadlock, even (or especially) if
> > applied to correct/legal MT code, as we don't know what
> > cls.construct() is doing, and as someone may i.e. legitimaly do:
> > 
> > acquire_recursive_mutex_used_in_cls_constructor()
> > the_safe_initializer()
> > cls.something = change()
> > release_recursive_mutex_used_in_cls_constructor()
> > 
> > and this is just one of the endless *legal* pattern that may bring
> > the_safe_initializer() to deadlock.
> 
> How can the program refer to the same mutex that is generated by the
> compiler? There is no program variable referring to it. Only the
> generated code can refer to it.

acquire_recursive_mutex_used_in_cls_constructor() IS NOT REFERRING TO
ANY MUTEX GENERATED BY THE COMPILER, but to a recursive mutex used in
cls.constructor() for its own internal needs. It's used by the
application to do something in cls, not by the compiler. See the
previous mail.

Bests,
Gian.

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