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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
end of thread, other threads:[~2022-08-04 13:29 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
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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