[Bug libstdc++/57641] std::timed_mutex.try_lock_until() is broken

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57641

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Testcase using clock with an earlier epoch:

#include <chrono>
#include <thread>
#include <mutex>
#include <assert.h>

namespace C = std::chrono;

struct clock
{

    typedef C::system_clock::rep rep;
    typedef C::system_clock::period period;
    typedef C::system_clock::duration duration;
    typedef std::chrono::time_point<clock> time_point;
    static constexpr bool is_steady = C::system_clock::is_steady;

    static time_point now() {
        return time_point(C::system_clock::now().time_since_epoch() +
C::seconds(10));
    }
};

std::timed_mutex mx;

void f()
{
    mx.try_lock_until(clock::now() + C::milliseconds(1));
}

int main()
{
    std::lock_guard<std::timed_mutex> l(mx);
    auto start = C::system_clock::now();
    std::thread t(f);
    t.join();
    auto stop = C::system_clock::now();
    assert( (stop - start) < C::seconds(9) );
}