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1 | // |
2 | // time_t_timer.cpp | |
3 | // ~~~~~~~~~~~~~~~~ | |
4 | // | |
f67539c2 | 5 | // Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com) |
92f5a8d4 TL |
6 | // |
7 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | |
8 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
9 | // | |
10 | ||
11 | #include <boost/asio.hpp> | |
12 | #include <ctime> | |
13 | #include <chrono> | |
14 | #include <iostream> | |
15 | ||
16 | // A custom implementation of the Clock concept from the standard C++ library. | |
17 | struct time_t_clock | |
18 | { | |
19 | // The duration type. | |
20 | typedef std::chrono::steady_clock::duration duration; | |
21 | ||
22 | // The duration's underlying arithmetic representation. | |
23 | typedef duration::rep rep; | |
24 | ||
25 | // The ratio representing the duration's tick period. | |
26 | typedef duration::period period; | |
27 | ||
28 | // An absolute time point represented using the clock. | |
29 | typedef std::chrono::time_point<time_t_clock> time_point; | |
30 | ||
31 | // The clock is not monotonically increasing. | |
32 | static constexpr bool is_steady = false; | |
33 | ||
34 | // Get the current time. | |
35 | static time_point now() noexcept | |
36 | { | |
37 | return time_point() + std::chrono::seconds(std::time(0)); | |
38 | } | |
39 | }; | |
40 | ||
41 | // The boost::asio::basic_waitable_timer template accepts an optional WaitTraits | |
42 | // template parameter. The underlying time_t clock has one-second granularity, | |
43 | // so these traits may be customised to reduce the latency between the clock | |
44 | // ticking over and a wait operation's completion. When the timeout is near | |
45 | // (less than one second away) we poll the clock more frequently to detect the | |
46 | // time change closer to when it occurs. The user can select the appropriate | |
47 | // trade off between accuracy and the increased CPU cost of polling. In extreme | |
48 | // cases, a zero duration may be returned to make the timers as accurate as | |
49 | // possible, albeit with 100% CPU usage. | |
50 | struct time_t_wait_traits | |
51 | { | |
52 | // Determine how long until the clock should be next polled to determine | |
53 | // whether the duration has elapsed. | |
54 | static time_t_clock::duration to_wait_duration( | |
55 | const time_t_clock::duration& d) | |
56 | { | |
57 | if (d > std::chrono::seconds(1)) | |
58 | return d - std::chrono::seconds(1); | |
59 | else if (d > std::chrono::seconds(0)) | |
60 | return std::chrono::milliseconds(10); | |
61 | else | |
62 | return std::chrono::seconds(0); | |
63 | } | |
64 | ||
65 | // Determine how long until the clock should be next polled to determine | |
66 | // whether the absoluate time has been reached. | |
67 | static time_t_clock::duration to_wait_duration( | |
68 | const time_t_clock::time_point& t) | |
69 | { | |
70 | return to_wait_duration(t - time_t_clock::now()); | |
71 | } | |
72 | }; | |
73 | ||
74 | typedef boost::asio::basic_waitable_timer< | |
75 | time_t_clock, time_t_wait_traits> time_t_timer; | |
76 | ||
77 | int main() | |
78 | { | |
79 | try | |
80 | { | |
81 | boost::asio::io_context io_context; | |
82 | ||
83 | time_t_timer timer(io_context); | |
84 | ||
85 | timer.expires_after(std::chrono::seconds(5)); | |
86 | std::cout << "Starting synchronous wait\n"; | |
87 | timer.wait(); | |
88 | std::cout << "Finished synchronous wait\n"; | |
89 | ||
90 | timer.expires_after(std::chrono::seconds(5)); | |
91 | std::cout << "Starting asynchronous wait\n"; | |
92 | timer.async_wait( | |
93 | [](const boost::system::error_code& /*error*/) | |
94 | { | |
95 | std::cout << "timeout\n"; | |
96 | }); | |
97 | io_context.run(); | |
98 | std::cout << "Finished asynchronous wait\n"; | |
99 | } | |
100 | catch (std::exception& e) | |
101 | { | |
102 | std::cout << "Exception: " << e.what() << "\n"; | |
103 | } | |
104 | ||
105 | return 0; | |
106 | } |