periodic timer intervals in C++

Question

I'm converting a code from C# to C++. I want to call a function every at periodic time intervals. My original function in C# is:

private void Init_timerGetData()
{
    timerGetData = new Timer();
    timerGetData.Interval = 5;
    timerGetData.Tick += new EventHandler(ReadData_Tick);
}

private void ReadData_Tick(object sender, EventArgs e)
   {...}

How to re-write this function in C++ in order to get the same functionality?

Answer 1

You can roll your own with a class that launches a thread to do the calls. Here's a simple one I use that will call every period until the class's destructor runs. You can tweak the details of the implementation to achieve most anything you want:

#include <atomic>
#include <chrono>
#include <functional>
#include <thread>

class call_every
{
    std::function<void()> f_;
    std::chrono::system_clock::duration d_;
    std::chrono::system_clock::time_point run_now_;
    std::atomic_bool quit_;
    std::thread thr_;

public:
    ~call_every()
    {
        quit_ = true;
        thr_.join();
    }

    template <class F>
    explicit call_every(F f, std::chrono::system_clock::duration d)
        : f_{std::move(f)}
        , d_{d}
        , run_now_{std::chrono::system_clock::now()}
        , quit_{false}
        , thr_{&call_every::run, this}
        {}

private:
    void run()
    {
        while (!quit_)
        {
            f_();
            run_now_ += d_;
            std::this_thread::sleep_until(run_now_);
        }
    }
};

#include <iostream>

int
main()
{
    using namespace std;
    using namespace std::chrono;
    call_every x{[]{cout << "Hi" << endl;}, 5s};
    this_thread::sleep_for(15s);
}

$ a.out
Hi
Hi
Hi
Hi
$

Here's a variant of the above that will be more responsive to the quit_ command. Instead of unconditionally sleeping for the duration, it uses a condition_variable with a wait_until which ~call_every() can interrupt before the duration times out. This ensures a more timely shutdown, should that be important.

#include <chrono>
#include <condition_variable>
#include <functional>
#include <mutex>
#include <thread>

class call_every
{
    std::mutex mut_;
    std::condition_variable cv_;
    std::function<void()> f_;
    std::chrono::system_clock::duration d_;
    std::chrono::system_clock::time_point run_now_;
    bool quit_;
    std::thread thr_;

public:
    ~call_every()
    {
        {
            std::lock_guard lock{mut_};
            quit_ = true;
        }
        cv_.notify_one();
        thr_.join();
    }

    template <class F>
    explicit call_every(F f, std::chrono::system_clock::duration d)
        : f_{std::move(f)}
        , d_{d}
        , run_now_{std::chrono::system_clock::now()}
        , quit_{false}
        , thr_{&call_every::run, this}
        {
        }

private:
    void run()
    {
        while (true)
        {
            f_();
            run_now_ += d_;
            std::unique_lock lock{mut_};
            if (cv_.wait_until(lock, run_now_, [this]() {return quit_;}))
                break;
        }
    }
};