Re: [boost] Re: Threads: New Win32 Implementation

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2000-09-08 15:45:57

From: William Kempf <sirwillard_at_[hidden]>
> --- In boost_at_[hidden], "Greg Colvin" <gcolvin_at_u...> wrote:
> > From: William Kempf <sirwillard_at_m...>
> > I agree that throwing an exception is a much safer interface, and
> > reasonably clean to use.  I don't see that this
> > 
> >    try {
> >       mutex::try_lock tlk(mx);
> >       cond.wait(tlk, ...);
> >       DoSomethingInteresting();
> >    } catch (failed_try) {
> >       DoSomethingElse();
> >    }
> > 
> > is any harder to write than this
> > 
> >    mutex::try_lock tlk(mx);
> >    if (tlk)
> >    {
> >      cond.wait(tlk, ...);
> >      DoSomethingInteresting();
> >    } else {
> >      DoSomethingElse();
> >    }
> 
> The real issue is performance.  Exceptions are expensive, and the 
> main reason to use a try lock is to try and eke out the best possible 
> performance (there's other reasons, yes).  It might be nice to have 
> multiple types of try locks, compile time options on behavior, or to 
> make use of the nothrow concept of new.  We've been down this road 
> before, so I don't expect a concesus of opinion on this one yet, but 
> I bet we come back to this at some point.

I'm not that sold on the need for try_lock at all, so I'm
not that concerned about performance.  Timeouts are another
matter.

Nevertheless, if performance and safety both matter couldn't
we do some like the following?

    mutex::try_lock tlk(mx);
    if (cond.wait(tlk, ...))
    {
      DoSomethingInteresting();
    } else {
      DoSomethingElse();
    }