On Thu, 14 Jan 2021 at 19:57, Alexandre Oliva <ol...@adacore.com> wrote:
>
> On Jan 14, 2021, Jonathan Wakely <jwak...@redhat.com> 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 <ol...@adacore.com>
>
> 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.
>
Seeing such random errors when testing arm target under qemu
on shared servers. I noticed several such errors on gcc-testresults, too.
So I guess this is a ping for this patch, to clear this noise in the results?
Thanks,
Christophe
>
> 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 <iostream>
> #include <testsuite_hooks.h>
>
> -const int iterations = 200;
> +int iterations = 200;
>
> using namespace std;
>
> @@ -45,10 +45,41 @@ int main()
> promise<int> p;
> future<int> 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
