https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78237
Bug ID: 78237
Summary: std::timed_mutex::try_lock_for/until affected by
system realtime clock
Product: gcc
Version: 6.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: marejde at gmail dot com
Target Milestone: ---
The following program:
#include <chrono>
#include <iostream>
#include <mutex>
#include <thread>
int main(void)
{
std::recursive_timed_mutex mutex;
bool ret = mutex.try_lock_for(std::chrono::seconds(2));
std::cout << "ret = " << ret << "\n";
std::thread thread([&mutex]() {
std::this_thread::sleep_for(std::chrono::seconds(1));
auto now = std::chrono::steady_clock::now();
bool ret = mutex.try_lock_until(now +
std::chrono::seconds(60));
std::cout << "ret = " << ret << "\n";
});
thread.join();
return 0;
}
does not work as expected when modifying the system time. try_lock_until()
returns false immediately when time is advanced passed now + 60s.
Compiling with Clang and libc++ try_lock_until() waits for 60 seconds
regardless of what the system time is changed to.
Looking at the implementation in libstdc++ it looks like it ends up calling
pthread_mutex_timedwait() (that uses CLOCK_REALTIME) while the libc++
implementation implements the methods with a condition variable.
