svn commit: r200274 - head/lib/libc/gen

Jilles Tjoelker jilles at
Tue Dec 8 14:10:30 PST 2009

On Tue, Dec 08, 2009 at 04:45:37PM -0500, John Baldwin wrote:
> On Tuesday 08 December 2009 3:48:06 pm Jilles Tjoelker wrote:
> > Author: jilles
> > Date: Tue Dec  8 20:48:06 2009
> > New Revision: 200274
> > URL:

> > Log:
> >   sem_init(3): document process shared semaphores and their restrictions

> I think the other language was more accurate.  The new language has
> far less detail such as no longer documenting EPERM.

It seems that EPERM longer happens, at least not for any process-shared
semaphore at all.

What's missing is the SIGSYS/ENOSYS you'll get if sem.ko is not loaded,
and you're requesting a process-shared semaphore or not linking with
the threading library.

> I think it is also quite accurate to say that the current
> implementation is not capable of process shared semaphores.  Several
> things would need to be changed including moving away from using file
> descriptors.

There are some lines of code dedicated to make it work, and some people
seem to use it, although they notice that it does not work very well.
This topic has come up on the mailing lists several times recently.

Jilles Tjoelker

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