rippled/include/xrpl/basics/UptimeClock.h

#ifndef XRPL_BASICS_UPTIMETIMER_H_INCLUDED
#define XRPL_BASICS_UPTIMETIMER_H_INCLUDED

#include <atomic>
#include <chrono>
#include <ratio>
#include <thread>

namespace xrpl {

/** Tracks program uptime to seconds precision.

    The timer caches the current time as a performance optimization.
    This allows clients to query the current time thousands of times
    per second.
*/

class UptimeClock
{
public:
    using rep = int;
    using period = std::ratio<1>;
    using duration = std::chrono::duration<rep, period>;
    using time_point = std::chrono::time_point<UptimeClock>;
    static constexpr bool is_steady = std::chrono::system_clock::is_steady;

    explicit UptimeClock() = default;

    static time_point
    now();  // seconds since rippled program start

private:
    static std::atomic<rep> now_;
    static std::atomic<bool> stop_;

    struct update_thread : private std::thread
    {
        ~update_thread();
        update_thread(update_thread&&) = default;

        using std::thread::thread;
    };

    static update_thread
    start_clock();
};

}  // namespace xrpl

#endif