From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/8176 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH] fix atexit when it is called from an atexit handler Date: Thu, 23 Jul 2015 07:54:03 +0200 Message-ID: <1437630843.3270.1.camel@inria.fr> References: <20150722234406.GA382@port70.net> <20150723011816.GT1173@brightrain.aerifal.cx> <20150723030719.GB382@port70.net> 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="=-LUmxzdTBTdn1a/37GKGe" X-Trace: ger.gmane.org 1437630858 31853 80.91.229.3 (23 Jul 2015 05:54:18 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 23 Jul 2015 05:54:18 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-8189-gllmg-musl=m.gmane.org@lists.openwall.com Thu Jul 23 07:54:18 2015 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Cj15cu23XZI4/826Px/xqB37z547sPH374oOvnKTsOb+1zuCoImZARM8ZiLlKkXcWOcoFRJ+Do/CwFO4e2DEe+9Ti+ZXA8ny/cU+X4bMKRZxZIVEiqXI6/+NKuUzPHb7z40ovnX3zx+Ctuq38HyuqWG7Tu+A0AAAAASUVORK5CYII= X-Mailer: Evolution 3.12.9-1+b1 Xref: news.gmane.org gmane.linux.lib.musl.general:8176 Archived-At: --=-LUmxzdTBTdn1a/37GKGe Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Am Donnerstag, den 23.07.2015, 05:07 +0200 schrieb Szabolcs Nagy: > * Rich Felker [2015-07-22 21:18:16 -0400]: > > On Thu, Jul 23, 2015 at 01:44:06AM +0200, Szabolcs Nagy wrote: > > > void __funcs_on_exit() > > > { > > > int i; > > > void (*func)(void *), *arg; > > > LOCK(lock); > > > - for (; head; head=3Dhead->next) for (i=3DCOUNT-1; i>=3D0; i--) { > > > - if (!head->f[i]) continue; > > > + for (;;) { > > > + i =3D next(); > > > + if (i<0) break; > > > func =3D head->f[i]; > > > arg =3D head->a[i]; > > > head->f[i] =3D 0; > >=20 > > I agree that this change should be made, but I don't like the > > particulars of the patch. It seems to increase exit handler runtime to > > O(n=C2=B2) even in the case where no atexit is happening during exit, a= nd > > it's not very elegant. I think a simpler solution would be to reset i > > to COUNT after calling f[i] if either (1) head has changed, or (2) > > i=20 > (2) should be 'f[i] is nonzero'. >=20 > i didnt think about detecting the change of head, > but it is simpler and better for the common case. I'd think this could be done even simpler by running the handlers in batches. Something like (a) take the lock and save the head of the current list in a tmp variable (b) release the lock (c) iterate through the list that was saved in tmp (d) if now head is non-zero, goto (a) This is clearly linear in the number of handlers that are ever insert to the list. For the current implementation this would need a bit of change in __cxa_atexit because 0 for head wouldn't mean that it hasn't been used, yet. A similar improvement could be done for at_quick_exit. There I think it makes not much sense accepting new handlers during processing. So the strategy could just be (i) Take the lock and save count in a tmp (ii) set count to 32 (iii) unlock (iv) do the processing But looking at it, I think that one can even be more improved. We could just use count as atomic, and so we wouldn't need a lock. I can prepare a patch for that, if you like. Jens --=20 :: INRIA Nancy Grand Est ::: Camus ::::::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt :: --=-LUmxzdTBTdn1a/37GKGe 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 v2 iEYEABECAAYFAlWwgXsACgkQD9PoadrVN+LOWgCfZCmeKErKRt7nyJqv7jfYiPwp TB8AniE/7nXFMaN3VOb1yBxbHVnx1d4F =ZZSV -----END PGP SIGNATURE----- --=-LUmxzdTBTdn1a/37GKGe--