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Date: Mon, 28 Dec 2009 15:18:17 +0800
From: David Xu <davidxu@freebsd.org>
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To: John Baldwin <jhb@freebsd.org>
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Cc: Daniel Eischen <deischen@freebsd.org>, freebsd-threads@freebsd.org
Subject: Re: first patch for process-shared semaphore
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John Baldwin wrote:
> 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.
> 
May I can move all semaphore functions into libc and remove all
semaphore related symbols from libthr ? In pratical, this is not a
problem, because libthr itself is not dlopen-safe, all missing semaphore
functions in libthr will be found in libc by rtld.