Re: Boost.Threads: concept requirements

From: davlet_panech (davlet_panech_at_[hidden])
Date: 2002-01-30 12:50:13

--- In boost_at_y..., "bill_kempf" <williamkempf_at_h...> wrote:
> --- In boost_at_y..., "davlet_panech" <davlet_panech_at_y...> wrote:
> > Hi,
> > 
> > It seems that the current implementation of some Boost.Threads 
> > classes violates it's concept requirements, for example, here's 
how 
> > condition::wait() looks like:
> > 
> >     template <typename L>
> >     void wait(L& lock)
> >     {
> >         if (!lock)
> >             throw lock_error();
> > 
> >         do_wait(lock.m_mutex);
> >     }
> > 
> > 
> > Type L is supposed to implement ScopedLock concept, which, unless 
I 
> > am mistaken, doesn't mention anything named `m_mutex'. Am I 
missing 
> > something here?
> 
> Not exactly.  The m_mutex parameter is a private parameter, and 
thus 
> not part of the concept requirements.  It's an implementation 
detail 
> requirement.  If an implementation for a given platform can be 
coded 
> with out this requirement there's nothing wrong with that.
> 
> However, I can see problems with someone trying to extend the 
library 
> with their own Mutex and ScopedLock variants that they want to work 
> with boost::condition, and this sort of implementation detail 
> prevents this.  So, there may be a small flaw in the design.
> 
> Anyone have any ideas about whether we should do something about 
> this, and if so, what?
> 
> Bill Kempf

This issue affects a number of other places, too. For example, the 
documentation for scoped_lock states:

"The type used to instantiate the class must meet the Mutex 
requirements"

However the Mutex requirements are clearly insufficient for the 
scoped_lock template to work. Perhaps we could introduce (and 
document!) a traits class for mutex operations?

Thanks,
D.P.