| // |
| // composed_8.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 <boost/asio/compose.hpp> |
| #include <boost/asio/io_context.hpp> |
| #include <boost/asio/ip/tcp.hpp> |
| #include <boost/asio/steady_timer.hpp> |
| #include <boost/asio/use_future.hpp> |
| #include <boost/asio/write.hpp> |
| #include <functional> |
| #include <iostream> |
| #include <memory> |
| #include <sstream> |
| #include <string> |
| #include <type_traits> |
| #include <utility> |
| |
| using boost::asio::ip::tcp; |
| |
| // NOTE: This example requires the new boost::asio::async_compose function. For |
| // an example that works with the Networking TS style of completion tokens, |
| // please see an older version of asio. |
| |
| //------------------------------------------------------------------------------ |
| |
| // This composed operation shows composition of multiple underlying operations, |
| // using asio's stackless coroutines support to express the flow of control. It |
| // automatically serialises a message, using its I/O streams insertion |
| // operator, before sending it N times on the socket. To do this, it must |
| // allocate a buffer for the encoded message and ensure this buffer's validity |
| // until all underlying async_write operation complete. A one second delay is |
| // inserted prior to each write operation, using a steady_timer. |
| |
| #include <boost/asio/yield.hpp> |
| |
| // In this example, the composed operation's logic is implemented as a state |
| // machine within a hand-crafted function object. |
| struct async_write_messages_implementation |
| { |
| // The implementation holds a reference to the socket as it is used for |
| // multiple async_write operations. |
| tcp::socket& socket_; |
| |
| // The allocated buffer for the encoded message. The std::unique_ptr smart |
| // pointer is move-only, and as a consequence our implementation is also |
| // move-only. |
| std::unique_ptr<std::string> encoded_message_; |
| |
| // The repeat count remaining. |
| std::size_t repeat_count_; |
| |
| // A steady timer used for introducing a delay. |
| std::unique_ptr<boost::asio::steady_timer> delay_timer_; |
| |
| // The coroutine state. |
| boost::asio::coroutine coro_; |
| |
| // The first argument to our function object's call operator is a reference |
| // to the enclosing intermediate completion handler. This intermediate |
| // completion handler is provided for us by the boost::asio::async_compose |
| // function, and takes care of all the details required to implement a |
| // conforming asynchronous operation. When calling an underlying asynchronous |
| // operation, we pass it this enclosing intermediate completion handler |
| // as the completion token. |
| // |
| // All arguments after the first must be defaulted to allow the state machine |
| // to be started, as well as to allow the completion handler to match the |
| // completion signature of both the async_write and steady_timer::async_wait |
| // operations. |
| template <typename Self> |
| void operator()(Self& self, |
| const boost::system::error_code& error = boost::system::error_code(), |
| std::size_t = 0) |
| { |
| reenter (coro_) |
| { |
| while (repeat_count_ > 0) |
| { |
| --repeat_count_; |
| |
| delay_timer_->expires_after(std::chrono::seconds(1)); |
| yield delay_timer_->async_wait(std::move(self)); |
| if (error) |
| break; |
| |
| yield boost::asio::async_write(socket_, |
| boost::asio::buffer(*encoded_message_), std::move(self)); |
| if (error) |
| break; |
| } |
| |
| // Deallocate the encoded message and delay timer before calling the |
| // user-supplied completion handler. |
| encoded_message_.reset(); |
| delay_timer_.reset(); |
| |
| // Call the user-supplied handler with the result of the operation. |
| self.complete(error); |
| } |
| } |
| }; |
| |
| #include <boost/asio/unyield.hpp> |
| |
| template <typename T, typename CompletionToken> |
| auto async_write_messages(tcp::socket& socket, |
| const T& message, std::size_t repeat_count, |
| CompletionToken&& token) |
| // The return type of the initiating function is deduced from the combination |
| // of CompletionToken type and the completion handler's signature. When the |
| // completion token is a simple callback, the return type is always void. |
| // In this example, when the completion token is boost::asio::yield_context |
| // (used for stackful coroutines) the return type would be also be void, as |
| // there is no non-error argument to the completion handler. When the |
| // completion token is boost::asio::use_future it would be std::future<void>. |
| -> typename boost::asio::async_result< |
| typename std::decay<CompletionToken>::type, |
| void(boost::system::error_code)>::return_type |
| { |
| // Encode the message and copy it into an allocated buffer. The buffer will |
| // be maintained for the lifetime of the composed asynchronous operation. |
| std::ostringstream os; |
| os << message; |
| std::unique_ptr<std::string> encoded_message(new std::string(os.str())); |
| |
| // Create a steady_timer to be used for the delay between messages. |
| std::unique_ptr<boost::asio::steady_timer> delay_timer( |
| new boost::asio::steady_timer(socket.get_executor())); |
| |
| // The boost::asio::async_compose function takes: |
| // |
| // - our asynchronous operation implementation, |
| // - the completion token, |
| // - the completion handler signature, and |
| // - any I/O objects (or executors) used by the operation |
| // |
| // It then wraps our implementation in an intermediate completion handler |
| // that meets the requirements of a conforming asynchronous operation. This |
| // includes tracking outstanding work against the I/O executors associated |
| // with the operation (in this example, this is the socket's executor). |
| return boost::asio::async_compose< |
| CompletionToken, void(boost::system::error_code)>( |
| async_write_messages_implementation{socket, |
| std::move(encoded_message), repeat_count, |
| std::move(delay_timer), boost::asio::coroutine()}, |
| token, socket); |
| } |
| |
| //------------------------------------------------------------------------------ |
| |
| void test_callback() |
| { |
| boost::asio::io_context io_context; |
| |
| tcp::acceptor acceptor(io_context, {tcp::v4(), 55555}); |
| tcp::socket socket = acceptor.accept(); |
| |
| // Test our asynchronous operation using a lambda as a callback. |
| async_write_messages(socket, "Testing callback\r\n", 5, |
| [](const boost::system::error_code& error) |
| { |
| if (!error) |
| { |
| std::cout << "Messages sent\n"; |
| } |
| else |
| { |
| std::cout << "Error: " << error.message() << "\n"; |
| } |
| }); |
| |
| io_context.run(); |
| } |
| |
| //------------------------------------------------------------------------------ |
| |
| void test_future() |
| { |
| boost::asio::io_context io_context; |
| |
| tcp::acceptor acceptor(io_context, {tcp::v4(), 55555}); |
| tcp::socket socket = acceptor.accept(); |
| |
| // Test our asynchronous operation using the use_future completion token. |
| // This token causes the operation's initiating function to return a future, |
| // which may be used to synchronously wait for the result of the operation. |
| std::future<void> f = async_write_messages( |
| socket, "Testing future\r\n", 5, boost::asio::use_future); |
| |
| io_context.run(); |
| |
| try |
| { |
| // Get the result of the operation. |
| f.get(); |
| std::cout << "Messages sent\n"; |
| } |
| catch (const std::exception& e) |
| { |
| std::cout << "Error: " << e.what() << "\n"; |
| } |
| } |
| |
| //------------------------------------------------------------------------------ |
| |
| int main() |
| { |
| test_callback(); |
| test_future(); |
| } |