[boost] Re: no semaphores in boost::thread

From: Nicolas Fleury (nfleury_at_[hidden])
Date: 2003-06-04 17:42:34

William E. Kempf wrote:
> Stefan Seefeld said:
>>As boost doesn't, there must clearly be other reasons for them not to do
>>that.
> 
> There is, but the explanations are long and quite complex.  That's why the
> FAQ points you at a seminal paper on the subject, rather than attempting

Correct me if I'm wrong, but isn't the FAQ pointing to a seminal paper 
only when justiying the absence of events, not semaphores?

What is the paper you have in mind to justify the absence of semaphores? 
  I would like very much to understand and be convinced.  It would also 
be nice if the #10 of the FAQ would point to this paper.

> to explain it.  Like I've said in numerous arguments about the Event
> concept, the problem with the concept isn't that it's broken or unusable,
> only that it's difficult to actually use correctly.  Most users think
> their code is correct, when in fact they have race conditions waiting to
> bite them.  When Mutexes and Condition variables provide everything that
> Semaphores and Events do, but in a way that's easier to use correctly, the
> choice to not include Event's or Semaphore's is reasonable.

I highly respect and esteem people working on boost, and I strongly 
expect the removal of semaphore was reasonable.  It's just that the 
current explanation I see is not convincing for me and probably others: 
"Semaphore was removed as too error prone. The same effect can be 
achieved with greater safety by the combination of a mutex and a 
condition variable."  I guess the answer is in the papers referred in 
the events versus conditions question; it's just that people coming from 
Posix environments would not care about the event topic and would feel 
the semaphore absence justification is incomplete.

Regards,
Nicolas Fleury