Date: Mon, 28 Dec 2009 11:21:30 -0500 From: John Baldwin <jhb@freebsd.org> To: David Xu <davidxu@freebsd.org> Cc: Daniel Eischen <deischen@freebsd.org>, freebsd-threads@freebsd.org Subject: Re: first patch for process-shared semaphore Message-ID: <200912281121.30939.jhb@freebsd.org> In-Reply-To: <4B385BB9.3010109@freebsd.org> References: <4B317741.8080004@freebsd.org> <200912240759.47703.jhb@freebsd.org> <4B385BB9.3010109@freebsd.org>
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On Monday 28 December 2009 2:18:17 am David Xu wrote: > 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. I would go with this approach. There is also some discussion about moving all of libthr into libc as well and having a dummy libpthread now that we are back to a single threading library and to avoid issues with dlopen() of libpthread, etc. -- John Baldwin
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