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From: Alexandre Oliva <aoliva@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc(refs/users/aoliva/heads/testme)] improve future::poll calibration loop Date: Tue, 23 Mar 2021 12:34:10 +0000 (GMT) [thread overview] Message-ID: <20210323123410.C6178385701F@sourceware.org> (raw) https://gcc.gnu.org/g:9bc8a66862f6660b3d423f2c930b1e1691a412c7 commit 9bc8a66862f6660b3d423f2c930b1e1691a412c7 Author: Alexandre Oliva <oliva@adacore.com> Date: Tue Mar 23 09:27:56 2021 -0300 improve future::poll calibration loop The calibration loop I've recently added to the libstdc++ future/members/poll.cc tests could still select iteration counts that might yield zero-time measurements for the wait_for when ready loop. Waiting for a future that has already had a value set is presumably uniformly faster than a zero-timed wait for a result, so I've changed the calibration loop to use the former. We might still be unlucky and get nonzero from the initial loop, so that the calibration is skipped altogether, but then get zero from the later when-ready loop. I'm not dealing with this case in this patch. for libstdc++-v3/ChangeLog * testsuite/30_threads/future/members/poll.cc: Use faster after-ready call in the calibration loop. Diff: --- libstdc++-v3/testsuite/30_threads/future/members/poll.cc | 8 +++++++- 1 file changed, 7 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 133dae15ac4..4c846d0b7ba 100644 --- a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc +++ b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc @@ -55,6 +55,12 @@ int main() Attempt to calibrate it. */ if (start == stop) { + /* After set_value, wait_for is faster, so use that for the + calibration to avoid zero at low clock resultions. */ + promise<int> pc; + future<int> fc = pc.get_future(); + pc.set_value(1); + /* Loop until the clock advances, so that start is right after a time increment. */ do @@ -65,7 +71,7 @@ int main() after another time increment. */ do { - f.wait_for(chrono::seconds(0)); + fc.wait_for(chrono::seconds(0)); stop = chrono::high_resolution_clock::now(); i++; }
next reply other threads:[~2021-03-23 12:34 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-03-23 12:34 Alexandre Oliva [this message] 2021-03-24 6:29 Alexandre Oliva 2021-03-24 9:07 Alexandre Oliva 2021-03-24 9:15 Alexandre Oliva
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