107 lines
3.2 KiB
C++
107 lines
3.2 KiB
C++
//
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// time_t_timer.cpp
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// ~~~~~~~~~~~~~~~~
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//
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// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#include <boost/asio.hpp>
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#include <ctime>
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#include <chrono>
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#include <iostream>
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// A custom implementation of the Clock concept from the standard C++ library.
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struct time_t_clock
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{
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// The duration type.
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typedef std::chrono::steady_clock::duration duration;
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// The duration's underlying arithmetic representation.
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typedef duration::rep rep;
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// The ratio representing the duration's tick period.
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typedef duration::period period;
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// An absolute time point represented using the clock.
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typedef std::chrono::time_point<time_t_clock> time_point;
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// The clock is not monotonically increasing.
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static constexpr bool is_steady = false;
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// Get the current time.
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static time_point now() noexcept
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{
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return time_point() + std::chrono::seconds(std::time(0));
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}
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};
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// The boost::asio::basic_waitable_timer template accepts an optional WaitTraits
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// template parameter. The underlying time_t clock has one-second granularity,
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// so these traits may be customised to reduce the latency between the clock
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// ticking over and a wait operation's completion. When the timeout is near
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// (less than one second away) we poll the clock more frequently to detect the
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// time change closer to when it occurs. The user can select the appropriate
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// trade off between accuracy and the increased CPU cost of polling. In extreme
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// cases, a zero duration may be returned to make the timers as accurate as
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// possible, albeit with 100% CPU usage.
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struct time_t_wait_traits
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{
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// Determine how long until the clock should be next polled to determine
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// whether the duration has elapsed.
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static time_t_clock::duration to_wait_duration(
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const time_t_clock::duration& d)
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{
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if (d > std::chrono::seconds(1))
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return d - std::chrono::seconds(1);
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else if (d > std::chrono::seconds(0))
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return std::chrono::milliseconds(10);
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else
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return std::chrono::seconds(0);
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}
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// Determine how long until the clock should be next polled to determine
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// whether the absoluate time has been reached.
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static time_t_clock::duration to_wait_duration(
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const time_t_clock::time_point& t)
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{
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return to_wait_duration(t - time_t_clock::now());
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}
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};
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typedef boost::asio::basic_waitable_timer<
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time_t_clock, time_t_wait_traits> time_t_timer;
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int main()
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{
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try
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{
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boost::asio::io_context io_context;
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time_t_timer timer(io_context);
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timer.expires_after(std::chrono::seconds(5));
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std::cout << "Starting synchronous wait\n";
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timer.wait();
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std::cout << "Finished synchronous wait\n";
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timer.expires_after(std::chrono::seconds(5));
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std::cout << "Starting asynchronous wait\n";
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timer.async_wait(
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[](const boost::system::error_code& /*error*/)
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{
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std::cout << "timeout\n";
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});
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io_context.run();
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std::cout << "Finished asynchronous wait\n";
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}
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catch (std::exception& e)
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{
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std::cout << "Exception: " << e.what() << "\n";
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}
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return 0;
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}
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