What is the status of thread process-shared synchronization?

[Alexander Churanov]

Hi folks!

The FreeBSD 8.1 manual pages state that pthread process-shared
synchronization option is not supported, at least for some primitives.

1) Are there any plans to implement this option?
2) Is anybody working on that?
3) What are the main obstacles which prevent us from having the option
implemented?

I am teaching students UNIX-like systems in general and FreeBSD in
particular. I've set them a task on synchronizing processes reading
and writing from a shared-memory cache. But then found that in spite
of PTHREAD_PROCESS_SHARED being available, it is not supported. I've
endeavored to fix POSIX rwlocks by making pthread_rwlock_t a
structure, but then found that POSIX semaphores do not support
process-shared attribute either.

4) Do we have any synchronization primitive capable of synchronizing
threads in different processes in FreeBSD?

I've found a related discussion, named "A mutex for inter-process",
but there is no conclusion or action items in it.

Alexander Churanov