Re: [boost] [thread] semaphore

Subject: Re: [boost] [thread] semaphore
From: Tim Blechmann (tim_at_[hidden])
Date: 2013-09-21 03:38:37

>> sorry, but i strongly disagree: i think that boost is the place for
>> high-performance code, that power users can rely on. i don't know how
>> many `power users' have to maintain abstractions for low-level
>> primitives. regarding semaphores, can you please mention one operating
>> system, that does not support them natively?
> 
> I agree. But we should also try to guess what memory order guarantees 
> should a boost/standard semaphore offer. Interprocess currently uses 
> full-fence operations on spin-semaphores (just like in other primivites, 
> like mutexes, which is too strong for mutexes and maybe for semaphores).
> 
> To be used as a binary semaphore, I guess wait()/post() could be just 
> acquire/release. But I don't know if this applies to counting semaphores 
> (and specially get_value(). I can read an old thread on this:
> 
> https://groups.google.com/forum/#!topic/comp.programming.threads/HpUwUUjgLK8

i was also under the impression that wait/post should be
acquire/release, both for semaphores and for events. get_value() may
need some special care, but i'm not planning to add this to the
sync::semaphore interface, because it is not widely supported: neither
mach nor dispatch semaphores provide an API for accessing the semaphore
count.

cheers,
tim