On Thursday 22 October 2009 5:17:07 pm Daniel Eischen wrote: > On Thu, 22 Oct 2009, Andrew Gallatin wrote: > > > Daniel Eischen wrote: > >> On Thu, 22 Oct 2009, Andrew Gallatin wrote: > >> > >>> Hi, > >>> > >>> We're designing some software which has to lock access to > >>> shared memory pages between several processes, and has to > >>> run on Linux, Solaris, and FreeBSD. We were planning to > >>> have the lock be a pthread_mutex_t residing in the > >>> shared memory page. This works well on Linux and Solaris, > >>> but FreeBSD (at least 7-stable) does not support > >>> PTHREAD_PROCESS_SHARED mutexes. > >>> > >>> We then moved on to posix semaphores. Using sem_wait/sem_post > >>> with the sem_t residing in a shared page seems to work on > >>> all 3 platforms. However, the FreeBSD (7-stable) man page > >>> for sem_init(3) has this scary text regarding the pshared > >>> value: > >>> > >>> The sem_init() function initializes the unnamed semaphore pointed to > >>> by > >>> sem to have the value value. A non-zero value for pshared specifies a > >>> shared semaphore that can be used by multiple processes, which this > >>> implementation is not capable of. > >>> > >>> Is this text obsolete? Or is my test just "getting lucky"? > >> > >> I think you're getting lucky. > > > > Yes, after playing with the code some, I now see that. :( > > > >>> Is there recommended way to do this? > >> > >> I believe the only way to do this is with SYSV semaphores > >> (semop, semget, semctl). Unfortunately, these are not as > >> easy to use, IMHO. > > > > Yes, they are pretty ugly, and we were hoping to avoid them. > > Are there any plans to support either PTHREAD_PROCESS_SHARED > > mutexes, or pshared posix semaphores in FreeBSD? > > It's planned, just not (yet) being actively worked on. > It's a API change mostly, and then adding in all the > compat hooks so we don't break ABI.
There are also an alternate set of patches on threads@ to allow just shared semaphores I think w/o the changes to the pthread types. I can't recall exactly what they did, but I think rrs@ was playing with using umtx directly to implement some sort of process-shared primitive. -- John Baldwin _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
