Re: Review: Boost.Threads

From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2001-09-25 05:06:02

>   1) "Increment" and "decrement" are verbs.  While "up" and "down"
> also have verb uses, their use as adjectives, adverbs, etc. is much
> more common.  A verb naming implies an action being done; an
> adjectival naming implies a property being returned.  Since the
> latter is obviously not the case here, "increment" and "decrement"
> are the less ambiguous and thus, IMO, the better choices.
>
>   2) Since a "semaphore" (in English) is "a system of visual
> signaling by two flags held one in each hand" (from www.m-w.com), the
> names "up" and "down" make the subtle implication to an inexperienced
> user that a semaphore can be only "up" or "down" (as a flag can only
> be up or down) -- which is obviously not the case with a
> boost::semaphore.  Rather, since these are counting
> semaphores, "increment" and "decrement" instantly convey the multi-
> valued possibilities of the semaphore rather than that of boolean
> up/down values.
>
> Is there something about semaphores that I am just not understanding
> here?  I don't think so, but I'd be happy to learn otherwise.

semaphores provide synchronization operations (with
the primary purpose to impose a limit with respect
to concurrent execution of code regions "protected"
by semaphores) named by POSIX committee and approved
by IEEE/ISO as "Semaphore *Lock* Operation" and
"Semaphore *Unlock* Operation":

"Semaphore Unlock Operation

 An operation that is applied to a semaphore. If, prior to the
 operation, there are any threads in the set of threads awaiting
 the semaphore, then some thread from that set shall be removed
 from the set and becomes unblocked; ..."

a) !! NO INCREMENT !!

"...otherwise, the semaphore value shall be incremented."

b) INCREMENT; increase level of allowed concurrency.

"Semaphore Lock Operation

 An operation that is applied to a semaphore. If, prior to the
 operation, the value of the semaphore is zero, the semaphore
 lock operation shall cause the calling thread to be blocked
 and added to the set of threads awaiting the semaphore; ..."

a) !! NO DECREMENT !!

"...otherwise, the value shall be decremented."

b) DECREMENT; decrease level of allowed concurrency.

regards,
alexander.