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RE: FW: sem_getvalue()
- From: Blanco Alejandro-EAB005 <Alex dot Blanco at motorola dot com>
- To: "'Ross Johnson'" <rpj at ise dot canberra dot edu dot au>
- Cc: pthreads-win32 at sources dot redhat dot com
- Date: Thu, 9 Sep 2004 08:58:21 -0400
- Subject: RE: FW: sem_getvalue()
I got an answer on a different email thread from one of the people who worked on the spec. The answer I got was that the "or" in the statement was just to deal with the temporal concerns - i.e. that at some time during the call, the number of threads waiting may be changing, so 0 or a negative number are valid, but that the important part of the statement is:
"The updated value represents an actual semaphore value..."
and that the intent was definitely that the number be negative when it is known threads are waiting. I'm not familiar enough with the code to offer a patch, but is it an easy update to support this? I looked at where the value is determined, but I could not really figure out whether it was possible.
From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of Ross Johnson
Sent: Thursday, September 09, 2004 5:11 AM
Subject: Re: FW: sem_getvalue()
The pthreads-win32 implementation never returns a negative
number, only zero or a positive number (i.e. the actual
semaphore value as close as can be determined). I read it as
optional because it could easily be written unambiguously.
However, it would be worth asking the austin group list for
Blanco Alejandro-EAB005 wrote:
>I experienced an unusual return value from sem_getValue(), and traced
>it back to the actual POSIX spec that is troubling. I had thought this
>would return a value < 0 if there are threads waiting on the semaphore,
>where the absolute value is the number of threads waiting. I saw that
>it was returning 0 when I had a thread waiting. I looked up the spec
>tml), and it says:
>>The sem_getvalue() function shall update the location referenced by
>>the sval argument to have the value of the semaphore referenced by sem without affecting the state of the semaphore. The updated value represents an actual semaphore value that occurred at some unspecified time during the call, but it need not be the actual value of the semaphore when it is returned to the calling process.
>If sem is locked, then the object to which sval points shall either be
>set to zero **or** to a negative number whose absolute value represents
>the number of processes waiting for the semaphore at some unspecified
>time during the call.
>Is it really optional to return the negative number? Does the
>implementation, at least sometimes, return 0 only?