asio/example/cpp14/operations/composed_8.cpp

213 lines
7.3 KiB
C++

//
// composed_8.cpp
// ~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2019 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/coroutine.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>
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>.
//
// In C++14 we can omit the return type as it is automatically deduced from
// the return type of boost::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<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, 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 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 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 boost::asio::async_compose<
CompletionToken, void(boost::system::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 = boost::asio::coroutine()
]
(
auto& self,
const boost::system::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 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);
}
},
token, socket);
}
#include <boost/asio/unyield.hpp>
//------------------------------------------------------------------------------
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();
}