ticker.hpp

#include <atomic>
#include <chrono>
#include <condition_variable>
#include <cstdint>
#include <iostream>
#include <thread>

// Executes a function f in a fixed interval,
// i.e. an average timespan between two consecutive calls of f,
// given in microseconds.
// f is a unary function, taking the time delta (in microseconds)
// between the last and the current call as its argument.
// In case of a delay outdated calls are be executed immediately.
// So the average executation time of f should be way shorter
// than the requested interval.
// Call ticker::start() to run.
// The ticker stops when ticker::stop() is called
// or the instance runs out of scope.
//
// Example usage:
//
// void say_hi(std::int64_t)
// {
//     std::cout << "hi " << std::endl;
// }
// int main()
// {
//     ticker hi_ticker(say_hi, 2 * 1000 * 1000);
//     hi_ticker.start();
//     std::this_thread::sleep_for(std::chrono::milliseconds(4500));
// }
class ticker
{
public:
    typedef std::function<void(std::int64_t)> function;
    ticker(const function& f, std::int64_t interval_us) :
        f_(f),
        interval_us_(interval_us),
        control_mutex_(),
        is_running_(false),
        thread_(),
        stop_mutex_()
    {
    }
    bool is_running()
    {
        std::lock_guard<std::mutex> lock(control_mutex_);
        return is_running_;
    }
    bool start()
    {
        std::lock_guard<std::mutex> lock(control_mutex_);
        if (is_running_)
            return false;
        stop_mutex_.lock();
        thread_ = std::thread([this]() { thread_function(); });
        is_running_ = true;
        return true;
    }
    bool stop()
    {
        std::lock_guard<std::mutex> lock(control_mutex_);
        if (!is_running_)
            return false;
        stop_mutex_.unlock();
        if (thread_.joinable())
        {
            thread_.join();
            thread_ = std::thread();
        }
        is_running_ = false;
        return true;
    }
    ~ticker()
    {
        stop();
    }
private:
    void thread_function()
    {
        auto last_wake_up_time = std::chrono::steady_clock::now();
        auto last_time = last_wake_up_time;
        bool quit = false;
        while (!quit)
        {
            const auto wake_up_time =
                last_wake_up_time + std::chrono::microseconds{ interval_us_ };
            const auto sleep_time =
                wake_up_time - std::chrono::steady_clock::now();
            if (stop_mutex_.try_lock_for(sleep_time))
            {
                stop_mutex_.unlock();
                quit = true;
            }
            const auto current_time = std::chrono::steady_clock::now();
            const auto elapsed = current_time - last_time;
            last_wake_up_time = wake_up_time;
            last_time = current_time;
            const auto elapsed_us =
                std::chrono::duration_cast<std::chrono::microseconds>(
                    elapsed).count();
            try
            {
                f_(elapsed_us);
            }
            catch (...)
            {
            }
        }
    }
    const function f_;
    const std::int64_t interval_us_;
    std::mutex control_mutex_;
    bool is_running_;
    std::thread thread_;
    std::timed_mutex stop_mutex_;
};