From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from rock.gnat.com (rock.gnat.com [IPv6:2620:20:4000:0:a9e:1ff:fe9b:1d1]) by sourceware.org (Postfix) with ESMTP id EDA9B38708D6; Thu, 14 Jan 2021 18:57:48 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org EDA9B38708D6 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=adacore.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=oliva@adacore.com Received: from localhost (localhost.localdomain [127.0.0.1]) by filtered-rock.gnat.com (Postfix) with ESMTP id 992325624A; Thu, 14 Jan 2021 13:57:48 -0500 (EST) X-Virus-Scanned: Debian amavisd-new at gnat.com Received: from rock.gnat.com ([127.0.0.1]) by localhost (rock.gnat.com [127.0.0.1]) (amavisd-new, port 10024) with LMTP id xc5bLMXtN5hS; Thu, 14 Jan 2021 13:57:48 -0500 (EST) Received: from free.home (tron.gnat.com [IPv6:2620:20:4000:0:46a8:42ff:fe0e:e294]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by rock.gnat.com (Postfix) with ESMTPS id 5D97B56248; Thu, 14 Jan 2021 13:57:48 -0500 (EST) Received: from livre (livre.home [172.31.160.2]) by free.home (8.15.2/8.15.2) with ESMTPS id 10EIvaeu237631 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 14 Jan 2021 15:57:36 -0300 From: Alexandre Oliva To: Jonathan Wakely Cc: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: Re: calibrate intervals to avoid zero in futures poll test Organization: Free thinker, does not speak for AdaCore References: <20210114125408.GA7692@redhat.com> Errors-To: aoliva@lxoliva.fsfla.org Date: Thu, 14 Jan 2021 15:57:36 -0300 In-Reply-To: <20210114125408.GA7692@redhat.com> (Jonathan Wakely's message of "Thu, 14 Jan 2021 12:54:08 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.84 X-Spam-Status: No, score=-12.5 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 14 Jan 2021 18:57:50 -0000 On Jan 14, 2021, Jonathan Wakely wrote: >> + /* Got for some 10 cycles, but we're already past that and still > I can't parse "Got for some 10 cycles". If that's just a typo Yeah, I meant "Go for ... but if ..." and managed to double-mangle it. Thanks for spotting it. Here's the patch I'm installing, with the typos fixed. Thanks! calibrate intervals to avoid zero in futures poll test From: Alexandre Oliva We get occasional failures of 30_threads/future/members/poll.cc on some platforms whose high resolution clock doesn't have such a high resolution; wait_for_0 ends up as 0, and then some asserts fail as intervals measured as longer than zero are tested for less than several times zero. This patch adds some calibration in the iteration count to set a measurable base time interval with some additional margin. for libstdc++-v3/ChangeLog * testsuite/30_threads/future/members/poll.cc: Calibrate iteration count. --- .../testsuite/30_threads/future/members/poll.cc | 33 +++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) diff --git a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc index 91f685b172d73..133dae15ac471 100644 --- a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc +++ b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc @@ -25,7 +25,7 @@ #include #include -const int iterations = 200; +int iterations = 200; using namespace std; @@ -45,10 +45,41 @@ int main() promise p; future f = p.get_future(); + start_over: auto start = chrono::high_resolution_clock::now(); for(int i = 0; i < iterations; i++) f.wait_for(chrono::seconds(0)); auto stop = chrono::high_resolution_clock::now(); + + /* We've run too few iterations for the clock resolution. + Attempt to calibrate it. */ + if (start == stop) + { + /* Loop until the clock advances, so that start is right after a + time increment. */ + do + start = chrono::high_resolution_clock::now(); + while (start == stop); + int i = 0; + /* Now until the clock advances again, so that stop is right + after another time increment. */ + do + { + f.wait_for(chrono::seconds(0)); + stop = chrono::high_resolution_clock::now(); + i++; + } + while (start == stop); + /* Go for some 10 cycles, but if we're already past that and + still get into the calibration loop, double the iteration + count and try again. */ + if (iterations < i * 10) + iterations = i * 10; + else + iterations *= 2; + goto start_over; + } + double wait_for_0 = print("wait_for(0s)", stop - start); start = chrono::high_resolution_clock::now(); -- Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ Free Software Activist GNU Toolchain Engineer Vim, Vi, Voltei pro Emacs -- GNUlius Caesar