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From: John Baldwin <jhb@freebsd.org>
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Cc: threads@freebsd.org, David Xu <davidxu@freebsd.org>
Subject: Re: first patch for process-shared semaphore
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On Wednesday 23 December 2009 10:12:19 pm Alexander Kabaev wrote:
> On Thu, 24 Dec 2009 09:58:50 +0800
> David Xu <davidxu@freebsd.org> wrote:
> 
> > Alexander Kabaev wrote:
> > > On Thu, 24 Dec 2009 09:22:34 +0800
> > > David Xu <davidxu@freebsd.org> wrote:
> > >> libthr does not require semaphore, it implements semaphore,
> > >> it is easier than other ways to implement the process-shared.
> > >>
> > > Let me rephrase: I do not think semaphores belong in libthr. They
> > > should be either in libc or in librt.
> > > 
> > > 
> > OK, does others really implement semaphore in librt ?
> > unfortunately, the librt already requires libpthread to implement
> > SIGEV_THREAD.
> 
> I retract that. It appears that there is no consistency - Solaris put
> these into libc, Linux into libpthread ans SUSv2 hints that these
> belong with realtime functions. libthr is fine.

I vote for libc.  Single-threaded processes can use sem_open() and PSHARED 
sem_init() as well.  Single-threaded processes can even use non-PSHARED 
sem_init() by using fork() to create new "threads" that share the semaphore.

-- 
John Baldwin