asio/src/examples/cpp03/timers/time_t_timer.cpp

//
// time_t_timer.cpp
// ~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#include <asio.hpp>
#include <ctime>
#include <iostream>

// A custom implementation of the Clock concept from the standard C++ library.
struct time_t_clock
{
  // The duration type.
  typedef asio::chrono::steady_clock::duration duration;

  // The duration's underlying arithmetic representation.
  typedef duration::rep rep;

  // The ratio representing the duration's tick period.
  typedef duration::period period;

  // An absolute time point represented using the clock.
  typedef asio::chrono::time_point<time_t_clock> time_point;

  // The clock is not monotonically increasing.
  static const bool is_steady = false;

  // Get the current time.
  static time_point now()
  {
    return time_point() + asio::chrono::seconds(std::time(0));
  }
};

// The asio::basic_waitable_timer template accepts an optional WaitTraits
// template parameter. The underlying time_t clock has one-second granularity,
// so these traits may be customised to reduce the latency between the clock
// ticking over and a wait operation's completion. When the timeout is near
// (less than one second away) we poll the clock more frequently to detect the
// time change closer to when it occurs. The user can select the appropriate
// trade off between accuracy and the increased CPU cost of polling. In extreme
// cases, a zero duration may be returned to make the timers as accurate as
// possible, albeit with 100% CPU usage.
struct time_t_wait_traits
{
  // Determine how long until the clock should be next polled to determine
  // whether the duration has elapsed.
  static time_t_clock::duration to_wait_duration(
      const time_t_clock::duration& d)
  {
    if (d > asio::chrono::seconds(1))
      return d - asio::chrono::seconds(1);
    else if (d > asio::chrono::seconds(0))
      return asio::chrono::milliseconds(10);
    else
      return asio::chrono::seconds(0);
  }

  // Determine how long until the clock should be next polled to determine
  // whether the absoluate time has been reached.
  static time_t_clock::duration to_wait_duration(
      const time_t_clock::time_point& t)
  {
    return to_wait_duration(t - time_t_clock::now());
  }
};

typedef asio::basic_waitable_timer<
  time_t_clock, time_t_wait_traits> time_t_timer;

void handle_timeout(const asio::error_code&)
{
  std::cout << "handle_timeout\n";
}

int main()
{
  try
  {
    asio::io_context io_context;

    time_t_timer timer(io_context);

    timer.expires_after(asio::chrono::seconds(5));
    std::cout << "Starting synchronous wait\n";
    timer.wait();
    std::cout << "Finished synchronous wait\n";

    timer.expires_after(asio::chrono::seconds(5));
    std::cout << "Starting asynchronous wait\n";
    timer.async_wait(&handle_timeout);
    io_context.run();
    std::cout << "Finished asynchronous wait\n";
  }
  catch (std::exception& e)
  {
    std::cout << "Exception: " << e.what() << "\n";
  }

  return 0;
}