On 22/06/2022 08:22, Sebastian Huber wrote:
On 22/06/2022 08:01, Alexandre Oliva via Gcc-patches wrote:
On rtems under qemu, the frequently-interrupted nanosleep ends up
sleeping shorter than expected, by a margin of less than 0,3%.
I figured failing the library test over a system (emulator?) bug is
undesirable, so I put in some tolerance for the drift.
Regstrapped on x86_64-linux-gnu, also tested with a cross to
aarch64-rtems6. Ok to install?
PS: I see nothing wrong with the implementation of clock_nanosleep (used
by nanosleep) on rtems6 that could cause it to wake up too early. I
suspect some artifact of the emulation environment.
for libstdc++-v3/ChangeLog
* testsuite/30_threads/this_thread/60421.cc: Tolerate a
slightly early wakeup.
---
.../testsuite/30_threads/this_thread/60421.cc | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
index 12dbeba1cc492..f3a5af453c4ad 100644
--- a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
+++ b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
@@ -51,9 +51,10 @@ test02()
std::thread t([&result, &sleeping] {
auto start = std::chrono::system_clock::now();
auto time = std::chrono::seconds(3);
+ auto tolerance = std::chrono::milliseconds(10);
sleeping = true;
std::this_thread::sleep_for(time);
- result = std::chrono::system_clock::now() >= (start + time);
+ result = std::chrono::system_clock::now() + tolerance >= (start +
time);
sleeping = false;
});
while (!sleeping)
This looks like a bug in RTEMS or the BSP for the test platform. I would
first investigate this and then change the test which looks all right to
me.
This is a problem in RTEMS. RTEMS uses the FreeBSD timecounters to
maintain CLOCK_REALTIME and provides two methods to get the time in a
coarse and fine resolution. The std::chrono::system_clock::now() uses
the fine resolution (higher overhead). The clock_nanosleep() uses the
coarse resolution which may give a time before now().
--
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