POSIX semaphores and fork() -- when any process exits, they all lose , access

[Robert Watson]

I was writing some code to exercise POSIX semaphores this morning, and ran
into the following issue:

If I create a named POSIX semaphore in a process, then fork(), the
semaphore appears to be visible to both the parent and child.  However, as
soon as the child exits, the semaphore disappears from the parent.  This
seems likely incorrect, although I don't have a copy of the spec in
question so couldn't say for sure.  It strikes me that the semaphores
should either be shared as of exit, with the child and the parent both
having references to it, or they should remain only with the parent, and
the childs semaphores should be invalidated/corrupted/something.  No doubt
POSIX has something to say on the topic.

Looking at the kernel code, it looks like the semaphore code is aware of
process exit() and exec(), but not fork(), which is probably what leads to
this behavior.  Since POSIX semaphores in the threaded case involve
cooperation between the library and kernel to implement, I suspect getting
the semantics right may require a bit of work.

Does anyone know what the semantics should be, and/or is interested in
making our implementation fit those semantics? 

Thanks,

Robert N M Watson