How to create timer events using C++ 11?

Question

How to create timer events using C++ 11?

I need something like: “Call me after 1 second from now”.

Is there any library?

Answer 1

Made a simple implementation of what I believe to be what you want to achieve. You can use the class later with the following arguments:

• int (milliseconds to wait until to run the code)
• bool (if true it returns instantly and runs the code after specified time on another thread)
• variable arguments (exactly what you'd feed to std::bind)

---

You can change std::chrono::milliseconds to std::chrono::nanoseconds or microseconds for even higher precision and add a second int and a for loop to specify for how many times to run the code.

Here you go, enjoy:

#include <functional>
#include <chrono>
#include <future>
#include <cstdio>

class later
{
public:
    template <class callable, class... arguments>
    later(int after, bool async, callable&& f, arguments&&... args)
    {
        std::function<typename std::result_of<callable(arguments...)>::type()> task(std::bind(std::forward<callable>(f), std::forward<arguments>(args)...));

        if (async)
        {
            std::thread([after, task]() {
                std::this_thread::sleep_for(std::chrono::milliseconds(after));
                task();
            }).detach();
        }
        else
        {
            std::this_thread::sleep_for(std::chrono::milliseconds(after));
            task();
        }
    }

};

void test1(void)
{
    return;
}

void test2(int a)
{
    printf("%i\n", a);
    return;
}

int main()
{
    later later_test1(1000, false, &test1);
    later later_test2(1000, false, &test2, 101);

    return 0;
}

Outputs after two seconds:

101

Answer 2

The asynchronous solution from Edward:

• create new thread
• sleep in that thread
• do the task in that thread

is simple and might just work for you.

I would also like to give a more advanced version which has these advantages:

• no thread startup overhead
• only a single extra thread per process required to handle all timed tasks

This might be in particular useful in large software projects where you have many task executed repetitively in your process and you care about resource usage (threads) and also startup overhead.

Idea: Have one service thread which processes all registered timed tasks. Use boost io_service for that.

Code similar to: http://www.boost.org/doc/libs/1_65_1/doc/html/boost_asio/tutorial/tuttimer2/src.html

#include <cstdio>
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

int main()
{
  boost::asio::io_service io;

  boost::asio::deadline_timer t(io, boost::posix_time::seconds(1));
  t.async_wait([](const boost::system::error_code& /*e*/){
    printf("Printed after 1s\n"); });

  boost::asio::deadline_timer t2(io, boost::posix_time::seconds(1));
  t2.async_wait([](const boost::system::error_code& /*e*/){
    printf("Printed after 1s\n"); });

  // both prints happen at the same time,
  // but only a single thread is used to handle both timed tasks
  // - namely the main thread calling io.run();

  io.run();

  return 0;
}