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1 | // |
2 | // composed_7.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/compose.hpp> | |
12 | #include <boost/asio/io_context.hpp> | |
13 | #include <boost/asio/ip/tcp.hpp> | |
14 | #include <boost/asio/steady_timer.hpp> | |
15 | #include <boost/asio/use_future.hpp> | |
16 | #include <boost/asio/write.hpp> | |
17 | #include <functional> | |
18 | #include <iostream> | |
19 | #include <memory> | |
20 | #include <sstream> | |
21 | #include <string> | |
22 | #include <type_traits> | |
23 | #include <utility> | |
24 | ||
25 | using boost::asio::ip::tcp; | |
26 | ||
27 | // NOTE: This example requires the new boost::asio::async_compose function. For | |
28 | // an example that works with the Networking TS style of completion tokens, | |
29 | // please see an older version of asio. | |
30 | ||
31 | //------------------------------------------------------------------------------ | |
32 | ||
33 | // This composed operation shows composition of multiple underlying operations. | |
34 | // It automatically serialises a message, using its I/O streams insertion | |
35 | // operator, before sending it N times on the socket. To do this, it must | |
36 | // allocate a buffer for the encoded message and ensure this buffer's validity | |
37 | // until all underlying async_write operation complete. A one second delay is | |
38 | // inserted prior to each write operation, using a steady_timer. | |
39 | ||
40 | template <typename T, typename CompletionToken> | |
41 | auto async_write_messages(tcp::socket& socket, | |
42 | const T& message, std::size_t repeat_count, | |
43 | CompletionToken&& token) | |
44 | // The return type of the initiating function is deduced from the combination | |
45 | // of CompletionToken type and the completion handler's signature. When the | |
46 | // completion token is a simple callback, the return type is always void. | |
47 | // In this example, when the completion token is boost::asio::yield_context | |
48 | // (used for stackful coroutines) the return type would be also be void, as | |
49 | // there is no non-error argument to the completion handler. When the | |
50 | // completion token is boost::asio::use_future it would be std::future<void>. | |
51 | // | |
52 | // In C++14 we can omit the return type as it is automatically deduced from | |
53 | // the return type of boost::asio::async_initiate. | |
54 | { | |
55 | // Encode the message and copy it into an allocated buffer. The buffer will | |
56 | // be maintained for the lifetime of the composed asynchronous operation. | |
57 | std::ostringstream os; | |
58 | os << message; | |
59 | std::unique_ptr<std::string> encoded_message(new std::string(os.str())); | |
60 | ||
61 | // Create a steady_timer to be used for the delay between messages. | |
62 | std::unique_ptr<boost::asio::steady_timer> delay_timer( | |
63 | new boost::asio::steady_timer(socket.get_executor())); | |
64 | ||
65 | // To manage the cycle between the multiple underlying asychronous | |
66 | // operations, our implementation is a state machine. | |
67 | enum { starting, waiting, writing }; | |
68 | ||
69 | // The boost::asio::async_compose function takes: | |
70 | // | |
71 | // - our asynchronous operation implementation, | |
72 | // - the completion token, | |
73 | // - the completion handler signature, and | |
74 | // - any I/O objects (or executors) used by the operation | |
75 | // | |
76 | // It then wraps our implementation, which is implemented here as a state | |
77 | // machine in a lambda, in an intermediate completion handler that meets the | |
78 | // requirements of a conforming asynchronous operation. This includes | |
79 | // tracking outstanding work against the I/O executors associated with the | |
80 | // operation (in this example, this is the socket's executor). | |
81 | // | |
82 | // The first argument to our lambda is a reference to the enclosing | |
83 | // intermediate completion handler. This intermediate completion handler is | |
84 | // provided for us by the boost::asio::async_compose function, and takes care | |
85 | // of all the details required to implement a conforming asynchronous | |
86 | // operation. When calling an underlying asynchronous operation, we pass it | |
87 | // this enclosing intermediate completion handler as the completion token. | |
88 | // | |
89 | // All arguments to our lambda after the first must be defaulted to allow the | |
90 | // state machine to be started, as well as to allow the completion handler to | |
91 | // match the completion signature of both the async_write and | |
92 | // steady_timer::async_wait operations. | |
93 | return boost::asio::async_compose< | |
94 | CompletionToken, void(boost::system::error_code)>( | |
95 | [ | |
96 | // The implementation holds a reference to the socket as it is used for | |
97 | // multiple async_write operations. | |
98 | &socket, | |
99 | ||
100 | // The allocated buffer for the encoded message. The std::unique_ptr | |
101 | // smart pointer is move-only, and as a consequence our lambda | |
102 | // implementation is also move-only. | |
103 | encoded_message = std::move(encoded_message), | |
104 | ||
105 | // The repeat count remaining. | |
106 | repeat_count, | |
107 | ||
108 | // A steady timer used for introducing a delay. | |
109 | delay_timer = std::move(delay_timer), | |
110 | ||
111 | // To manage the cycle between the multiple underlying asychronous | |
112 | // operations, our implementation is a state machine. | |
113 | state = starting | |
114 | ] | |
115 | ( | |
116 | auto& self, | |
117 | const boost::system::error_code& error = {}, | |
118 | std::size_t = 0 | |
119 | ) mutable | |
120 | { | |
121 | if (!error) | |
122 | { | |
123 | switch (state) | |
124 | { | |
125 | case starting: | |
126 | case writing: | |
127 | if (repeat_count > 0) | |
128 | { | |
129 | --repeat_count; | |
130 | state = waiting; | |
131 | delay_timer->expires_after(std::chrono::seconds(1)); | |
132 | delay_timer->async_wait(std::move(self)); | |
133 | return; // Composed operation not yet complete. | |
134 | } | |
135 | break; // Composed operation complete, continue below. | |
136 | case waiting: | |
137 | state = writing; | |
138 | boost::asio::async_write(socket, | |
139 | boost::asio::buffer(*encoded_message), std::move(self)); | |
140 | return; // Composed operation not yet complete. | |
141 | } | |
142 | } | |
143 | ||
144 | // This point is reached only on completion of the entire composed | |
145 | // operation. | |
146 | ||
147 | // Deallocate the encoded message and delay timer before calling the | |
148 | // user-supplied completion handler. | |
149 | encoded_message.reset(); | |
150 | delay_timer.reset(); | |
151 | ||
152 | // Call the user-supplied handler with the result of the operation. | |
153 | self.complete(error); | |
154 | }, | |
155 | token, socket); | |
156 | } | |
157 | ||
158 | //------------------------------------------------------------------------------ | |
159 | ||
160 | void test_callback() | |
161 | { | |
162 | boost::asio::io_context io_context; | |
163 | ||
164 | tcp::acceptor acceptor(io_context, {tcp::v4(), 55555}); | |
165 | tcp::socket socket = acceptor.accept(); | |
166 | ||
167 | // Test our asynchronous operation using a lambda as a callback. | |
168 | async_write_messages(socket, "Testing callback\r\n", 5, | |
169 | [](const boost::system::error_code& error) | |
170 | { | |
171 | if (!error) | |
172 | { | |
173 | std::cout << "Messages sent\n"; | |
174 | } | |
175 | else | |
176 | { | |
177 | std::cout << "Error: " << error.message() << "\n"; | |
178 | } | |
179 | }); | |
180 | ||
181 | io_context.run(); | |
182 | } | |
183 | ||
184 | //------------------------------------------------------------------------------ | |
185 | ||
186 | void test_future() | |
187 | { | |
188 | boost::asio::io_context io_context; | |
189 | ||
190 | tcp::acceptor acceptor(io_context, {tcp::v4(), 55555}); | |
191 | tcp::socket socket = acceptor.accept(); | |
192 | ||
193 | // Test our asynchronous operation using the use_future completion token. | |
194 | // This token causes the operation's initiating function to return a future, | |
195 | // which may be used to synchronously wait for the result of the operation. | |
196 | std::future<void> f = async_write_messages( | |
197 | socket, "Testing future\r\n", 5, boost::asio::use_future); | |
198 | ||
199 | io_context.run(); | |
200 | ||
201 | try | |
202 | { | |
203 | // Get the result of the operation. | |
204 | f.get(); | |
205 | std::cout << "Messages sent\n"; | |
206 | } | |
207 | catch (const std::exception& e) | |
208 | { | |
209 | std::cout << "Error: " << e.what() << "\n"; | |
210 | } | |
211 | } | |
212 | ||
213 | //------------------------------------------------------------------------------ | |
214 | ||
215 | int main() | |
216 | { | |
217 | test_callback(); | |
218 | test_future(); | |
219 | } |