From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 16F3C385841A; Thu, 11 Nov 2021 10:54:09 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 16F3C385841A
From: "s.zvyagin83 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/103187] New: std::counting_semaphore::try_acquire_for
 does not unblock during wait duration
Date: Thu, 11 Nov 2021 10:54:08 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 11.2.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: s.zvyagin83 at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-103187-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Thu, 11 Nov 2021 10:54:09 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103187

            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 un=
til
timeout expires.=20

But semaphores implemented with atomic_wait blocks for whole timeout even if
semaphore released during wait.=20

minimal repoduce code:
g++ -std=3Dc++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 =3D std::chrono::steady_clock::now();
  auto time =3D [&begin] {
      return
std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_c=
lock::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=3Dc++20 -lpthread -D_GLIBCXX_USE_POSIX_SEMAPHORE=3D1

output:
[0] sem.try_acquire_for
[0] thread start
[1000] sem.release
[1000] sem.acquired=