[Ace-users] [ace-users] ACE_Process_Mutex has different lifetime on Windows and GNU/Linux

[Steve Huston]

Hi Lars,

> I'm glad to see that my report/question generated some discussion.

Definitely - it's a topic that should be addressed!

> I look forward to seeing this feature in some future ACE release!

I do too - to give this idea the best chance of getting into code, I
recommend one of the following:

1. Partner with someone to work out the rationale of why the
differences exist and find a way to resolve them, develop the code,
integrate and test across all ACE platforms.

2. Make sure this information is recorded in a Bugzilla entry so it
doesn't get lost; when someone has time and/or sufficient motivation,
the details will be available to jump start the work.

Best regards,
-Steve

--
Steve Huston, Riverace Corporation
Want to take ACE training on YOUR schedule?
See http://www.riverace.com/training.htm

> Douglas C. Schmidt wrote:
> > Hi J.T.,
> > 
> >> I think there are several questions:
> >>
> >> * What should be the semantics of ACE_Process_Semaphore when
using
> >>   POSIX semaphores?
> >>
> >> * If a system supports both POSIX and SysV semaphores, which
should
> >>   ACE prefer, and how is this preference specified by feature
test
> >>   macros.
> >>
> >> The answers to the above will answer, what, if any, 
> changes need to be
> >> made to the autoconf machinery.
> > 
> > Right!
> > 
> >> For the first, the fact that ACE allows named semaphores to
outlive
> >> their creating process with Windows and SysV semaphores 
> but not with
> >> POSIX semaphores sounds undesirable and avoidable.  I'll let
Steve
> >> weigh in on this.
> > 
> > Ok, sounds good.  Steve, please let us know your $0.02 worth on
this
> > matter.
> > 
> >> The second question is harder, or at least has broader 
> implications.
> >> In almost all cases, the ACE_HAS_* and ACE_LACKS_* feature 
> test macros
> >> are defined based on whether the system simply *has* or *lacks*
the
> >> particular feature.
> > 
> > Yes, I agree that isn't sufficiently helpful for situations 
> like this.
> > 
> >> In cases where the system supports several ways to do 
> essentially the
> >> same thing, usually there is an implicit choice made within the
ACE
> >> code to use prefer one over the other(s). In many cases 
> the choice is
> >> the obviously correct one, made on suitability or 
> portability or some
> >> other -ibility. But there are cases where it's not so 
> clear cut. ACE
> >> should probably provide some way for the developer to 
> indicate their
> >> preference.
> > 
> > Right, we need an "ACE_PREFERS_*" macro or something like that ;-)
> >  
> >> One way to do that would be to simply not define the feature test
> >> macro for alternate implementation.  I believe this is what Lars'
> >> experienced when he changed from the autoconf generated to canned
> >> config.h, which didn't define ACE_HAS_POSIX_SEM.
> >>
> >> However, this complicates and confuses the definitions of those
> >> feature test macros, as it overloads them to mean the system
> >> *has/lacks* the feature *and* for ACE to *use/avoid* the feature.
> >> This is where whatever choice we make impacts the autoconf 
> machinery,
> >> as it currently only checks for the existence of the features.
> >> Because this muddles the definition of ACE_HAS_* and ACE_LACKS_*,
I
> >> tend to think that there should be an ACE_USE_* or some 
> such feature
> >> test macro for the user to explicitly express their preference.
> >>
> >> Perhaps this all becomes moot, at least as Semaphores are 
> concerned,
> >> if it turns out that they are changed not to delete the 
> file and then
> >> POSIX semaphores are the obviously correct choice. If not, 
> we'll need
> >> to agree on a strategy/roadmap and migrate towards that over
time.
> > 
> > I agree that we need a multi-faceted approach here.  
> Perhaps the way to
> > proceed is:
> > 
> > . Figure out what to do for the ACE_Process_Mutex stuff so 
> that it has
> >   common semantics regardless of whether it uses POSIX semaphores
or
> >   SysV semaphores.  Steve, do you have any thoughts to 
> share on this?
> >   
> > . Devise a more sophisticated set of autoconf capabilities 
> that allow
> >   users to express their preferences when there's no clear
"winner".
> >   
> > Thanks!
> > 
> >         Doug
> 
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