From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/9497 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: FreeBSD's Google Summer of Code 2016 Date: Sat, 5 Mar 2016 20:08:43 -0500 Message-ID: <20160306010843.GQ9349@brightrain.aerifal.cx> References: <56DB3D70.8010601@FreeBSD.org> <20160305212517.GK9349@brightrain.aerifal.cx> <56DB6095.4060204@FreeBSD.org> <20160305233254.GL9349@brightrain.aerifal.cx> <56DB766A.3050500@FreeBSD.org> <20160306002547.GM9349@brightrain.aerifal.cx> <56DB80F7.8030700@FreeBSD.org> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1457226546 18119 80.91.229.3 (6 Mar 2016 01:09:06 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 6 Mar 2016 01:09:06 +0000 (UTC) Cc: musl@lists.openwall.com To: Pedro Giffuni Original-X-From: musl-return-9510-gllmg-musl=m.gmane.org@lists.openwall.com Sun Mar 06 02:09:06 2016 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1acNBv-000439-3q for gllmg-musl@m.gmane.org; Sun, 06 Mar 2016 02:09:03 +0100 Original-Received: (qmail 13380 invoked by uid 550); 6 Mar 2016 01:09:01 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 13360 invoked from network); 6 Mar 2016 01:09:00 -0000 Content-Disposition: inline In-Reply-To: <56DB80F7.8030700@FreeBSD.org> User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:9497 Archived-At: On Sat, Mar 05, 2016 at 07:59:35PM -0500, Pedro Giffuni wrote: > > > On 03/05/16 19:25, Rich Felker wrote: > >On Sat, Mar 05, 2016 at 07:14:34PM -0500, Pedro Giffuni wrote: > >> > >> > >>On 03/05/16 18:32, Rich Felker wrote: > >>>On Sat, Mar 05, 2016 at 05:41:25PM -0500, Pedro Giffuni wrote: > >>>>First of all, great to hear there is interest on the musl side too. > >>>> > >>>>I think the biggest precedent of porting linux-oriented C libraries > >>>>came from Debian's kFreeBSD. We accomodated a little by for them > >>>>by defining __FreeBSD_kernel__ in sys/param.h. > >>>> > >>>>While using the optional linux-abi futex in FreeBSD could be an option, > >>>>it is not really the cleanest option. The Debian guys did a port of > >>>>NPTL using regular pthreads: > >>>> > >> > >>Of course I ahould have meant "based on regular FreeBSD kernel services". > >> > >>>>http://thread.gmane.org/gmane.linux.debian.ports.bsd/11702 > >>>> > >>>>I am certain this will require more research but it would be useful > >>>>for other ports as well. > >>> > >> > >>We could ask Petr Salinger for the details, but I am pretty sure > >>FreeBSD has the required functionality natively. > >> > >>>Glibc/NPTL has a lot of what I'd call "gratuitous abstraction" (like > >>>the lll stuff) in their pthread primitives which makes this > >>>"possible". I call it gratuitous because it's really really hard to > >>>achieve correct implementations of the pthread sync primitives that > >>>don't have serious corner-case bugs, and it's unlikely that their > >>>abstractions actually suffice to make correct alternate > >>>implementations. > >>> > >>>musl does not have any such abstraction. We require a compare-and-swap > >>>operation or equivalent on which arbitrary atomic operations can be > >>>constructed, a futex or equivalent operation that's roughly > >>>while(*addr==expected) sleep(), and implement all the sync primitives > >>>just once on top of these. > >>> > >> > >>I am not a threading expert (or even a CS guy), but it sounds like > >>mutex(9) with condvar(9) would do [1]: > > > >No, they don't satisfy the needs of musl; they have their own > >additional storage requirements and are probably not AS-safe. It might > >be possible to use them to implement a userspace-emulated futex queue > >(only if they are AS-safe), but I don't see a way to extend that to > >the process-shared case. > > > > OK, it looks like sema(9) may be nearer (and also simpler but slower). > For the process-shared case libthr(2) uses the stuff in sys/utmx.h, > shich should be looked at but it is not documented[1]. > > Luckily Ed, the developer that would be mentoring the project, knows > this stuff better than I do. OK, well let's see if there are any proposals and what ideas people come up with. Rich