[Boost-users] Re: Re: Re: Semaphore and barriers for boost-threads?

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-02-19 02:08:59

Craig Rodrigues wrote:

>> Look the the phrase "Much experience with semaphores shows" and futher
>> paragraphs. In essense, it's says that semaphores are for signal handlers
>> and for inter-process synchronization and discourages their use anywhere
>> else.
> 
> That's an interesting link, thanks!
> I don't interpret the text in the same way that you do, but
> maybe I am not understanding something properly.

Maybe I don't, either. The standard cannot make definitive statements that
"semaphore is bad". Folks on comp.programming.threads newsgroup seem to
make such statements in more clear language ;-)

> Further down from "Much experience with semaphores shows",
> there is this text:
> 
> "Counting semaphores are well matched to dealing with producer/consumer
> problems, including those that might exist between threads of
> different processes, or between a signal handler and a thread. In
> the former case, there may be little or no memory shared by the
> processes; in the latter case, one is not communicating between
> co-equal threads, but between a thread and an interrupt-like entity.
> It is for these reasons that IEEE Std 1003.1-2001 allows semaphores
> to be used by threads."

Doesn't it say that semaphores are retained for inter-process communication
and for signal handlers? 

> This is the use-case that I am interested in.

Which one? Signal handler or inter-process communication?

- Volodya