213 lines
7.3 KiB
C++
213 lines
7.3 KiB
C++
//
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// composed_8.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/compose.hpp>
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#include <boost/asio/coroutine.hpp>
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#include <boost/asio/io_context.hpp>
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#include <boost/asio/ip/tcp.hpp>
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#include <boost/asio/steady_timer.hpp>
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#include <boost/asio/use_future.hpp>
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#include <boost/asio/write.hpp>
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#include <functional>
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#include <iostream>
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#include <memory>
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#include <sstream>
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#include <string>
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#include <type_traits>
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#include <utility>
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using boost::asio::ip::tcp;
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// NOTE: This example requires the new boost::asio::async_compose function. For
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// an example that works with the Networking TS style of completion tokens,
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// please see an older version of asio.
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//------------------------------------------------------------------------------
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// This composed operation shows composition of multiple underlying operations,
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// using asio's stackless coroutines support to express the flow of control. It
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// automatically serialises a message, using its I/O streams insertion
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// operator, before sending it N times on the socket. To do this, it must
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// allocate a buffer for the encoded message and ensure this buffer's validity
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// until all underlying async_write operation complete. A one second delay is
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// inserted prior to each write operation, using a steady_timer.
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#include <boost/asio/yield.hpp>
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template <typename T, typename CompletionToken>
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auto async_write_messages(tcp::socket& socket,
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const T& message, std::size_t repeat_count,
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CompletionToken&& token)
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// The return type of the initiating function is deduced from the combination
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// of CompletionToken type and the completion handler's signature. When the
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// completion token is a simple callback, the return type is always void.
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// In this example, when the completion token is boost::asio::yield_context
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// (used for stackful coroutines) the return type would be also be void, as
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// there is no non-error argument to the completion handler. When the
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// completion token is boost::asio::use_future it would be std::future<void>.
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//
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// In C++14 we can omit the return type as it is automatically deduced from
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// the return type of boost::asio::async_initiate.
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{
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// Encode the message and copy it into an allocated buffer. The buffer will
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// be maintained for the lifetime of the composed asynchronous operation.
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std::ostringstream os;
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os << message;
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std::unique_ptr<std::string> encoded_message(new std::string(os.str()));
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// Create a steady_timer to be used for the delay between messages.
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std::unique_ptr<boost::asio::steady_timer> delay_timer(
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new boost::asio::steady_timer(socket.get_executor()));
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// The boost::asio::async_compose function takes:
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//
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// - our asynchronous operation implementation,
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// - the completion token,
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// - the completion handler signature, and
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// - any I/O objects (or executors) used by the operation
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//
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// It then wraps our implementation, which is implemented here as a stackless
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// coroutine in a lambda, in an intermediate completion handler that meets the
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// requirements of a conforming asynchronous operation. This includes
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// tracking outstanding work against the I/O executors associated with the
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// operation (in this example, this is the socket's executor).
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//
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// The first argument to our lambda is a reference to the enclosing
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// intermediate completion handler. This intermediate completion handler is
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// provided for us by the boost::asio::async_compose function, and takes care
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// of all the details required to implement a conforming asynchronous
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// operation. When calling an underlying asynchronous operation, we pass it
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// this enclosing intermediate completion handler as the completion token.
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//
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// All arguments to our lambda after the first must be defaulted to allow the
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// state machine to be started, as well as to allow the completion handler to
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// match the completion signature of both the async_write and
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// steady_timer::async_wait operations.
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return boost::asio::async_compose<
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CompletionToken, void(boost::system::error_code)>(
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[
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// The implementation holds a reference to the socket as it is used for
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// multiple async_write operations.
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&socket,
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// The allocated buffer for the encoded message. The std::unique_ptr
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// smart pointer is move-only, and as a consequence our lambda
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// implementation is also move-only.
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encoded_message = std::move(encoded_message),
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// The repeat count remaining.
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repeat_count,
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// A steady timer used for introducing a delay.
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delay_timer = std::move(delay_timer),
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// The coroutine state.
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coro = boost::asio::coroutine()
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]
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(
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auto& self,
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const boost::system::error_code& error = {},
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std::size_t = 0
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) mutable
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{
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reenter (coro)
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{
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while (repeat_count > 0)
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{
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--repeat_count;
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delay_timer->expires_after(std::chrono::seconds(1));
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yield delay_timer->async_wait(std::move(self));
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if (error)
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break;
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yield boost::asio::async_write(socket,
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boost::asio::buffer(*encoded_message), std::move(self));
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if (error)
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break;
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}
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// Deallocate the encoded message and delay timer before calling the
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// user-supplied completion handler.
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encoded_message.reset();
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delay_timer.reset();
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// Call the user-supplied handler with the result of the operation.
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self.complete(error);
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}
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},
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token, socket);
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}
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#include <boost/asio/unyield.hpp>
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//------------------------------------------------------------------------------
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void test_callback()
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{
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boost::asio::io_context io_context;
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tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
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tcp::socket socket = acceptor.accept();
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// Test our asynchronous operation using a lambda as a callback.
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async_write_messages(socket, "Testing callback\r\n", 5,
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[](const boost::system::error_code& error)
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{
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if (!error)
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{
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std::cout << "Messages sent\n";
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}
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else
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{
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std::cout << "Error: " << error.message() << "\n";
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}
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});
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io_context.run();
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}
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//------------------------------------------------------------------------------
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void test_future()
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{
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boost::asio::io_context io_context;
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tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
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tcp::socket socket = acceptor.accept();
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// Test our asynchronous operation using the use_future completion token.
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// This token causes the operation's initiating function to return a future,
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// which may be used to synchronously wait for the result of the operation.
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std::future<void> f = async_write_messages(
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socket, "Testing future\r\n", 5, boost::asio::use_future);
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io_context.run();
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try
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{
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// Get the result of the operation.
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f.get();
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std::cout << "Messages sent\n";
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}
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catch (const std::exception& e)
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{
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std::cout << "Error: " << e.what() << "\n";
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}
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}
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//------------------------------------------------------------------------------
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int main()
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{
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test_callback();
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test_future();
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}
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