[gcc(refs/users/aoliva/heads/testme)] calibrate intervals to avoid zero in futures poll test
Alexandre Oliva
aoliva@gcc.gnu.org
Fri Jan 1 01:31:12 GMT 2021
https://gcc.gnu.org/g:64c7b51992d9b738ba5c245ba9474e733e6c7bf4
commit 64c7b51992d9b738ba5c245ba9474e733e6c7bf4
Author: Alexandre Oliva <oliva@adacore.com>
Date: Thu Dec 31 21:38:29 2020 -0300
calibrate intervals to avoid zero in futures poll test
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.
Diff:
---
.../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 fff9bea899c..7b41411a543 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);
+ /* Got for some 10 cycles, but 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();
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