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* [Bug libstdc++/103187] New: std::counting_semaphore::try_acquire_for does not unblock during wait duration
@ 2021-11-11 10:54 s.zvyagin83 at gmail dot com
2021-11-11 12:08 ` [Bug libstdc++/103187] " redi at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: s.zvyagin83 at gmail dot com @ 2021-11-11 10:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103187
Bug ID: 103187
Summary: std::counting_semaphore::try_acquire_for does not
unblock during wait duration
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: s.zvyagin83 at gmail dot com
Target Milestone: ---
According to C++ standart https://eel.is/c++draft/thread.sema.cnt#18.2
try_acquire_for/until should block until counter is greater than zero or until
timeout expires.
But semaphores implemented with atomic_wait blocks for whole timeout even if
semaphore released during wait.
minimal repoduce code:
g++ -std=c++20 -lpthread
#include <thread>
#include <semaphore>
#include <time.h>
#include <stdio.h>
using namespace std::chrono_literals;
int main()
{
std::binary_semaphore sem{0};
auto begin = std::chrono::steady_clock::now();
auto time = [&begin] {
return
std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now()-begin).count();
};
std::jthread jthr(
[&sem, &time] {
printf("[%ld] thread start\n", time());
std::this_thread::sleep_for(1s);
printf("[%ld] sem.release\n", time());
sem.release();
});
printf("[%ld] sem.try_acquire_for\n", time());
if (sem.try_acquire_for(10s))
printf("[%ld] sem.acquired\n", time());
else
printf("[%ld] failed to acquire sem\n", time());
}
output:
[0] sem.try_acquire_for
[0] thread start
[1000] sem.release
[10000] sem.acquired
POSIX semaphores with same code work correctly and unblock immediately when
semaphore released
g++ -std=c++20 -lpthread -D_GLIBCXX_USE_POSIX_SEMAPHORE=1
output:
[0] sem.try_acquire_for
[0] thread start
[1000] sem.release
[1000] sem.acquired
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/103187] std::counting_semaphore::try_acquire_for does not unblock during wait duration
2021-11-11 10:54 [Bug libstdc++/103187] New: std::counting_semaphore::try_acquire_for does not unblock during wait duration s.zvyagin83 at gmail dot com
@ 2021-11-11 12:08 ` redi at gcc dot gnu.org
2021-11-11 12:17 ` redi at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2021-11-11 12:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103187
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to fail| |11.2.1
Known to work| |12.0
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2021-11-11
Target Milestone|--- |11.3
CC| |rodgertq at gcc dot gnu.org
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Already fixed on trunk, I think we just need a backport.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/103187] std::counting_semaphore::try_acquire_for does not unblock during wait duration
2021-11-11 10:54 [Bug libstdc++/103187] New: std::counting_semaphore::try_acquire_for does not unblock during wait duration s.zvyagin83 at gmail dot com
2021-11-11 12:08 ` [Bug libstdc++/103187] " redi at gcc dot gnu.org
@ 2021-11-11 12:17 ` redi at gcc dot gnu.org
2021-11-23 21:19 ` redi at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2021-11-11 12:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103187
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The relevant commit seems to be g:aeaea265cea3a2b2e772af7825351a4ceef29aac but
that *should* only be an optimization to use futexes when available. The fact
it times out without that change suggests the non-futex code has a bug, and
it's probably still there on trunk.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/103187] std::counting_semaphore::try_acquire_for does not unblock during wait duration
2021-11-11 10:54 [Bug libstdc++/103187] New: std::counting_semaphore::try_acquire_for does not unblock during wait duration s.zvyagin83 at gmail dot com
2021-11-11 12:08 ` [Bug libstdc++/103187] " redi at gcc dot gnu.org
2021-11-11 12:17 ` redi at gcc dot gnu.org
@ 2021-11-23 21:19 ` redi at gcc dot gnu.org
2022-04-21 7:50 ` rguenth at gcc dot gnu.org
2022-08-04 13:29 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2021-11-23 21:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103187
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I've backported that fix for GCC 11.3 but I want to keep this open to get to
the bottom of the underlying bug.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/103187] std::counting_semaphore::try_acquire_for does not unblock during wait duration
2021-11-11 10:54 [Bug libstdc++/103187] New: std::counting_semaphore::try_acquire_for does not unblock during wait duration s.zvyagin83 at gmail dot com
` (2 preceding siblings ...)
2021-11-23 21:19 ` redi at gcc dot gnu.org
@ 2022-04-21 7:50 ` rguenth at gcc dot gnu.org
2022-08-04 13:29 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-04-21 7:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103187
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|11.3 |11.4
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11.3 is being released, retargeting bugs to GCC 11.4.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/103187] std::counting_semaphore::try_acquire_for does not unblock during wait duration
2021-11-11 10:54 [Bug libstdc++/103187] New: std::counting_semaphore::try_acquire_for does not unblock during wait duration s.zvyagin83 at gmail dot com
` (3 preceding siblings ...)
2022-04-21 7:50 ` rguenth at gcc dot gnu.org
@ 2022-08-04 13:29 ` redi at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2022-08-04 13:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103187
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|11.4 |11.3
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #2)
> The relevant commit seems to be g:aeaea265cea3a2b2e772af7825351a4ceef29aac
> but that *should* only be an optimization to use futexes when available.
Ah no, because the HAVE_PLATFORM_WAIT macro was being set, but too late to
affect the value of the __platform_wait_uses_type variable template, it meant
that _S_wait_addr always returned &_M_w._M_ver and did a futex wait on that,
but the semaphore release() was doing a futex wake on &_M_counter instead.
> The
> fact it times out without that change suggests the non-futex code has a bug,
> and it's probably still there on trunk.
I think it's fixed by the above commit, which is in GCC 11.3 and later.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2022-08-04 13:29 UTC | newest]
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2021-11-11 10:54 [Bug libstdc++/103187] New: std::counting_semaphore::try_acquire_for does not unblock during wait duration s.zvyagin83 at gmail dot com
2021-11-11 12:08 ` [Bug libstdc++/103187] " redi at gcc dot gnu.org
2021-11-11 12:17 ` redi at gcc dot gnu.org
2021-11-23 21:19 ` redi at gcc dot gnu.org
2022-04-21 7:50 ` rguenth at gcc dot gnu.org
2022-08-04 13:29 ` redi at gcc dot gnu.org
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