From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/5755 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: Explaining cond var destroy [Re: [musl] C threads, v3.0] Date: Wed, 06 Aug 2014 12:32:52 +0200 Message-ID: <1407321172.24324.287.camel@eris.loria.fr> References: <1407144603.8274.248.camel@eris.loria.fr> <20140806035213.GR1674@brightrain.aerifal.cx> <1407314595.24324.277.camel@eris.loria.fr> <1407318064.24324.282.camel@eris.loria.fr> <20140806100335.GV1674@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-TgmiVasuMI0a6gMCLjfM" X-Trace: ger.gmane.org 1407321196 32381 80.91.229.3 (6 Aug 2014 10:33:16 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 6 Aug 2014 10:33:16 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-5760-gllmg-musl=m.gmane.org@lists.openwall.com Wed Aug 06 12:33:10 2014 Return-path: Envelope-to: gllmg-musl@plane.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1XEyWo-0004Y3-0p for gllmg-musl@plane.gmane.org; Wed, 06 Aug 2014 12:33:06 +0200 Original-Received: (qmail 11981 invoked by uid 550); 6 Aug 2014 10:33:05 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 11973 invoked from network); 6 Aug 2014 10:33:05 -0000 X-IronPort-AV: E=Sophos;i="5.01,811,1400018400"; d="scan'";a="88460479" In-Reply-To: <20140806100335.GV1674@brightrain.aerifal.cx> Face: 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Cj15cu23XZI4/826Px/xqB37z547sPH374oOvnKTsOb+1zuCoImZARM8ZiLlKkXcWOcoFRJ+Do/CwFO4e2DEe+9Ti+ZXA8ny/cU+X4bMKRZxZIVEiqXI6/+NKuUzPHb7z40ovnX3zx+Ctuq38HyuqWG7Tu+A0AAAAASUVORK5CYII= X-Mailer: Evolution 3.4.4-3 Xref: news.gmane.org gmane.linux.lib.musl.general:5755 Archived-At: --=-TgmiVasuMI0a6gMCLjfM Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable Am Mittwoch, den 06.08.2014, 06:03 -0400 schrieb Rich Felker: > On Wed, Aug 06, 2014 at 11:41:04AM +0200, Jens Gustedt wrote: > > I am not sure that this would easily be possible with the current > > implementation, but I think that this would be ideal. >=20 > Yes, that would be my ideal too, but I'm not sure it's possible. Well, > not with an efficient implementation anyway. There's a trivial > implementation where pthread_cond_timedwait is basically just: >=20 > a_store(&c->_tid, self->tid); > pthread_mutex_unlock(mtx); > __timedwait(&c->tid, self->tid, ts, clock, ts, cleanup, mtx, 0); > pthread_mutex_lock(mtx); >=20 > This makes signal and broadcast operations utterly trivial (just set > c->tid to 0 and call __wake with 1 or INT_MAX as the argument), but it > has lots of spurious wakes under contention, yes > I think, and perhaps > other serious drawbacks too. If I remember correctly, musl's original > implementation looked something like the above, but I was also having > a hard time figuring out how to work requeue-to-mutex (which makes a > big deal to performance on big broadcasts) into it. Look into pthread_cond_broadcast. I think this could do better bookkeeping. Currently it does its case analysis with a mildly complicated expression in preparing the arguments to the requeue-syscall. I think we could be better off by doing a case analysis beforehand and update the different "waiters" variables accordingly *before* the syscall. So the targeted threads wouldn't have to do any bookkeeping when coming back from wait. Maybe this even would help to reduce the condition state from two "waiters" fields to a single one. Jens --=20 :: INRIA Nancy Grand Est ::: AlGorille ::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt :: --=-TgmiVasuMI0a6gMCLjfM Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEABECAAYFAlPiBFQACgkQD9PoadrVN+JYIACfTFqY3wcZcedjBw8hmZ9jnb3D JnkAn0+cKKjQYMCEc0dLCR8sK0MaW0xb =TVJ+ -----END PGP SIGNATURE----- --=-TgmiVasuMI0a6gMCLjfM--