| // |
| // 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 <asio/compose.hpp> |
| #include <asio/coroutine.hpp> |
| #include <asio/io_context.hpp> |
| #include <asio/ip/tcp.hpp> |
| #include <asio/steady_timer.hpp> |
| #include <asio/use_future.hpp> |
| #include <asio/write.hpp> |
| #include <functional> |
| #include <iostream> |
| #include <memory> |
| #include <sstream> |
| #include <string> |
| #include <type_traits> |
| #include <utility> |
| |
| using asio::ip::tcp; |
| |
| // NOTE: This example requires the new 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 <asio/yield.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 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 asio::use_future it would be std::future<void>. |
| // |
| // In C++14 we can omit the return type as it is automatically deduced from |
| // the return type of asio::async_initiate. |
| { |
| // 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<asio::steady_timer> delay_timer( |
| new asio::steady_timer(socket.get_executor())); |
| |
| // The 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, which is implemented here as a stackless |
| // coroutine in a lambda, 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). |
| // |
| // The first argument to our lambda is a reference to the enclosing |
| // intermediate completion handler. This intermediate completion handler is |
| // provided for us by the 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 to our lambda 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. |
| return asio::async_compose< |
| CompletionToken, void(std::error_code)>( |
| [ |
| // The implementation holds a reference to the socket as it is used for |
| // multiple async_write operations. |
| &socket, |
| |
| // The allocated buffer for the encoded message. The std::unique_ptr |
| // smart pointer is move-only, and as a consequence our lambda |
| // implementation is also move-only. |
| encoded_message = std::move(encoded_message), |
| |
| // The repeat count remaining. |
| repeat_count, |
| |
| // A steady timer used for introducing a delay. |
| delay_timer = std::move(delay_timer), |
| |
| // The coroutine state. |
| coro = asio::coroutine() |
| ] |
| ( |
| auto& self, |
| const std::error_code& error = {}, |
| std::size_t = 0 |
| ) mutable |
| { |
| 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 asio::async_write(socket, |
| 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); |
| } |
| }, |
| token, socket); |
| } |
| |
| #include <asio/unyield.hpp> |
| |
| //------------------------------------------------------------------------------ |
| |
| void test_callback() |
| { |
| 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 std::error_code& error) |
| { |
| if (!error) |
| { |
| std::cout << "Messages sent\n"; |
| } |
| else |
| { |
| std::cout << "Error: " << error.message() << "\n"; |
| } |
| }); |
| |
| io_context.run(); |
| } |
| |
| //------------------------------------------------------------------------------ |
| |
| void test_future() |
| { |
| 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, 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(); |
| } |