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//
// completion_executor.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2025 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.hpp>
#include <concepts>
#include <iostream>
using boost::asio::ip::tcp;
//----------------------------------------------------------------------
// The logging_executor class implements a minimal executor that satisfies the
// requirements for use as a completion executor. This means it may be bound to
// a handler using bind_executor.
class logging_executor
{
public:
// All executors must be no-throw equality comparable.
bool operator==(const logging_executor&) const noexcept = default;
// All executors must provide a const member function execute().
void execute(std::invocable auto handler) const
{
try
{
std::cout << "handler invocation starting\n";
std::move(handler)();
std::cout << "handler invocation complete\n";
}
catch (...)
{
std::cout << "handler invocation completed with exception\n";
throw;
}
}
};
// Confirm that a logging_executor satisfies the executor requirements.
static_assert(boost::asio::execution::executor<logging_executor>);
// Confirm that a logging_executor can be used as a completion executor.
static_assert(std::convertible_to<
logging_executor, boost::asio::any_completion_executor>);
//----------------------------------------------------------------------
int main()
{
boost::asio::io_context io_context(1);
// Post a completion handler to be run immediately.
boost::asio::post(io_context,
boost::asio::bind_executor(logging_executor{},
[]{ std::cout << "post complete\n"; }));
// Start an asynchronous accept that will complete immediately.
tcp::endpoint endpoint(boost::asio::ip::address_v4::loopback(), 0);
tcp::acceptor acceptor(io_context, endpoint);
tcp::socket server_socket(io_context);
acceptor.async_accept(
boost::asio::bind_executor(logging_executor{},
[](auto...){ std::cout << "async_accept complete\n"; }));
tcp::socket client_socket(io_context);
client_socket.connect(acceptor.local_endpoint());
// Set a timer to expire immediately.
boost::asio::steady_timer timer(io_context);
timer.expires_at(boost::asio::steady_timer::clock_type::time_point::min());
timer.async_wait(
boost::asio::bind_executor(logging_executor{},
[](auto){ std::cout << "async_wait complete\n"; }));
io_context.run();
return 0;
}
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