Daily bit(e) of C++ | std::timed_mutex, std::recursive_timed_mutex, std::shared_timed_mutex

Daily bit(e) of C++ #19, The timed mutex variants: std::timed_mutex, std::recursive_timed_mutex, std::shared_timed_mutex

Timed mutex variants (std::timed_mutex, std::recursive_timed_mutex and std::shared_timed_mutex) offer support for timeouts when waiting on a lock. The timeout the be specified as either a time point or a duration.

Adding timeouts to mutexes allows a program to give up waiting on a lock and potentially report an error instead of being stuck in a hard-to-detect state.

#include <thread>
#include <mutex>
#include <chrono>
#include <syncstream>
#include <iostream>

using namespace std::chrono_literals;

std::timed_mutex mux;
// This thread will hold the lock for 2 seconds
auto t = std::jthread([&mux]{
    std::unique_lock lock(mux);
    std::this_thread::sleep_for(2s);
});

auto runner = [&mux]{
    // Try to obtain the lock for 200ms
    std::unique_lock lock(mux, 200ms);
    if (!lock.owns_lock()) {
        std::osyncstream(std::cerr) << "Unable to obtain lock.\n";
        return;
    }
    std::osyncstream(std::cerr) << "Lock was obtained.\n";
};

// Generally, first two attempts will time out
// the other two attempts should succeed.
auto r1 = std::jthread(runner);
std::this_thread::sleep_for(1s);
auto r2 = std::jthread(runner);
std::this_thread::sleep_for(1s);
auto r3 = std::jthread(runner);
std::this_thread::sleep_for(1s);
auto r4 = std::jthread(runner);

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