topic Re: Support for POSIX semaphores? in Operating System - OpenVMS

Support for POSIX semaphores?

Mark Fletcher_4 — Mon, 14 Mar 2005 16:38:45 GMT

Is there any add-on functionality for POSIX semaphores for OpenVMS?

Thanks.

Re: Support for POSIX semaphores?

Mark Fletcher_4 — Mon, 14 Mar 2005 17:00:32 GMT

Oops, I meant UNIX System V-style semaphore system calls (semget, semop, semctl). Are these available or obtainable?

Thanks.

Re: Support for POSIX semaphores?

Wim Van den Wyngaert — Tue, 15 Mar 2005 02:15:54 GMT

http://h71000.www7.hp.com/portability/future_plans.html

I guess not yet.

Wim

Re: Support for POSIX semaphores?

Kris Clippeleyr — Tue, 15 Mar 2005 03:16:57 GMT

Mark,
AFAIK, and I checked the info on the latest version of the CRTL, there is no support for POSIX style semaphores.
The closest you can get, is writing your own routines based on VMS mutexes (mutual exclusion semaphores). There are (undocumented) routines that allow for manipulation of semaphores
( SCH$LOCKR(_QUAD), SCH$LOCKW(_QUAD), SCH$LOCKWNOWAIT(_QUAD), SCH$UNLOCK(_QUAD) )

Hope this helps,
Kris (aka Qkcl)

Re: Support for POSIX semaphores?

Ian Miller. — Tue, 15 Mar 2005 05:03:19 GMT

You would be better using locks ($ENQ etc) that the undocumented routines that may change whenever HP want to.

Re: Support for POSIX semaphores?

Mark Fletcher_4 — Tue, 15 Mar 2005 09:14:06 GMT

Thank you for your help. $ENQ sounds like the best bet.

Mark

Re: Support for POSIX semaphores?

Bruce Visscher_1 — Tue, 15 Mar 2005 10:02:20 GMT

Perhaps the best solution has already been discussed but I wonder if pthread condition variables might not be another, perhaps more portable solution. If synchronization between processes (vs threads) is desired then aren't shared mutexes and condition variables available with the latest pthreads implementation for OpenVMS?

Of course the problem with this solution is that there isn't a portable solution for shared memory that I know of. I guess on VMS you'd have to use global sections.

Caveat: I haven't actually tried using shared pthread mutexes and conditions in a global section on VMS.

Re: Support for POSIX semaphores?

Galen Tackett — Tue, 15 Mar 2005 12:24:26 GMT

The Rolling Roadmap has something about semaphores where it talks about GNV and VMS V8.3. Go to http://h71000.www7.hp.com/openvms/roadmap/openvms_roadmaps.htm and download the "PDF W/Speaker Notes." If you search it for "semaphores" you'll find this text in between two bullets about GNV on page 15:

"Semaphores are similar to VMS locking and is used to coordinating or synchronizing activities in which multiple processes compete for the same operating system resources."

The chart accompanying that text includes "Semaphores" in the OpenVMS V8.3 box, which is shown elsewhere in the presentation as projected for H1 2006.

Re: Support for POSIX semaphores?

Galen Tackett — Tue, 15 Mar 2005 12:27:02 GMT

Oops. I forgot to state:

Mark, I don't know if the usage of Semaphores in the roadmap corresponds with the System V functionality you're looking for. And it certainly isn't of any immediate help to you...

Re: Support for POSIX semaphores?

Mark Fletcher_4 — Tue, 15 Mar 2005 14:08:04 GMT

Correct me if I am wrong, but the $ENQ and $DEQ system calls do not appear to provide "counting" functionality, as in counting semaphores.

Re: Support for POSIX semaphores?

Ian Miller. — Wed, 16 Mar 2005 04:49:02 GMT

Mark, parhaps you can explain the counting function then someone may be able to suggest how to do it.

Re: Support for POSIX semaphores?

Mark Fletcher_4 — Wed, 16 Mar 2005 16:05:26 GMT

Counting semaphores are/were provided by PPL routines:

PPL$CREATE_SEMAPHORE Creates and initializes a semaphore with a
waiting queue
PPL$DECREMENT_SEMAPHORE Waits for the semaphore to have a value
greater than zero and then decrements the
semaphore
PPL$INCREMENT_SEMAPHORE Increments the value of a semaphore by 1

but these do not seem to work in 7.2-3. I can't get a valid semaphore ID back from PPL$CREATE_SEMAPHORE.