{"id":2230562,"url":"http://patchwork.ozlabs.org/api/patches/2230562/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/or7bppmq6y.fsf_-_@lxoliva.fsfla.org/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"","list_archive_url":null,"date":"2026-04-29T21:06:45","name":"[FYI,PATCHv2] testsuite: semaphore/try_acquire_until: reorder clock::now calls","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"e6f8b3db8f219a3480503c1f13276d9aa8c745d2","submitter":{"id":74937,"url":"http://patchwork.ozlabs.org/api/people/74937/?format=json","name":"Alexandre Oliva","email":"oliva@adacore.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/or7bppmq6y.fsf_-_@lxoliva.fsfla.org/mbox/","series":[{"id":502151,"url":"http://patchwork.ozlabs.org/api/series/502151/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=502151","date":"2026-04-29T21:06:45","name":"[FYI,PATCHv2] testsuite: semaphore/try_acquire_until: reorder clock::now calls","version":1,"mbox":"http://patchwork.ozlabs.org/series/502151/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2230562/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2230562/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n secure) header.d=adacore.com header.i=@adacore.com header.a=rsa-sha256\n header.s=google header.b=N2+l67cv;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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Reordering the calls avoids false positives.\n>> \n>> Regstrapped on x86_64-linux-gnu. Also tested on ppc-vx7r2 with gcc-15,\n>> with an analogous patch for try_acquire_posix.cc. Ok to install?\n\n> OK for trunk (and branches if you want, but wait until after 16.1 is released).\n\nThanks, I'm going for trunk only, at least for now.\n\nIn internal review, Olivier Hainque suggested a comment justifying the\nasymmetry, so here's what I plan to check in, barring any objections:\n\n\nClock calls on VxWorks are slow, so the odds that the consecutive\ncalls of *clock::now() will yield a different result are not\nnegligible. Reordering the calls avoids false positives.\n\n\nfor libstdc++-v3/ChangeLog\n\n\t* testsuite/30_threads/semaphore/try_acquire_until.cc\n\t(test01): Reorder calls.\n---\n .../30_threads/semaphore/try_acquire_until.cc | 5 ++++-\n 1 file changed, 4 insertions(+), 1 deletion(-)","diff":"diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc\nindex 44b2b90431a41..a22799d88508a 100644\n--- a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc\n+++ b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc\n@@ -43,8 +43,11 @@ void test01()\n }\n \n {\n- auto const at = std::chrono::system_clock::now() + dur;\n+ // Set the base time T0 first, so that even if there's a delay before the\n+ // deadline AT is computed, it won't shrink the measured DIFF to the point\n+ // of making it seem shorter than the required wait DURation.\n auto const t0 = std::chrono::steady_clock::now();\n+ auto const at = std::chrono::system_clock::now() + dur;\n VERIFY( !s.try_acquire_until(at) );\n auto const diff = std::chrono::steady_clock::now() - t0;\n VERIFY( diff >= dur );\n","prefixes":["FYI","PATCHv2"]}