Re: [boost] [thread] semaphore

Subject: Re: [boost] [thread] semaphore
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2013-09-21 05:07:55

> 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.

Ok, nice. In any case, if sem_getvalue or similar should synchronize 
with boty post() and wait() and read the most recent value, if the 
semaphore is emulated with an atomic emulation on an integer I think a 
Read-Modify-Write operation with memory_order_acq_rel be the answer 
(something like fetch_add with argument 0?) Reading the count while the 
mutex is hold shouldn't also work?

Best,

Ion