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
