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Date: Wed, 2 Dec 2009 16:19:24 -0500 (EST)
From: Daniel Eischen <deischen@freebsd.org>
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To: Andrew Gallatin <gallatin@cs.duke.edu>
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Cc: freebsd-current@freebsd.org
Subject: Re: process shared semaphores?
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On Wed, 2 Dec 2009, Andrew Gallatin wrote:

>
> The man page for sem_init(3) says:
>
>     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 still correct?   I'm asking, both because it seems strange to
> not return an error if the implementation does not support pshared
> semaphores, and because the threads library seems to expect
> it to work.  Eg:
>
> int
> _sem_init(sem_t *sem, int pshared, unsigned int value)
> {
>        semid_t semid;
>
>        semid = (semid_t)SEM_USER;
>        if ((pshared != 0) && (ksem_init(&semid, value) != 0))
>                return (-1);
> <....
>
>
> So is the man page out of date, or is the userspace code future-proof
> for when the kernel catches up?

The code should probably return -1 and ENOTSUP.

Why don't you use named semaphores if you want
process shared (sem_open)?  Shouldn't those work?

-- 
DE