How to start Boost echo server in a separate thread - boost

Question

I was using boost version boost 1_64_0 to run a Tcp server in a seprate thread
This was the code for the server.
https://www.boost.org/doc/libs/1_52_0/doc/html/boost_asio/example/echo/async_tcp_echo_server.cpp
in the Main loop i could spawn a new thread like this.
int main()
{
// Run the boost echo server as a different thread
boost::asio::io_service io_service;
server server1(io_service, 1980);
boost::thread t(boost::bind(&io_service::run, &io_service));
// when about to close the program
io_service.stop(); // stop the server
t.join();
}
Now i have changed the boost version to boost_1_73_0 and i am using this example to create a server
https://www.boost.org/doc/libs/1_71_0/doc/html/boost_asio/example/cpp11/echo/async_tcp_echo_server.cpp
how do to create a new thread ?
The existing code to create a new thread gives error.
io_service: left of :: must be a class/struct/union
run : undeclared identifier

Answer 1

In &io_service::run, io_service is not a type but the local variable by that name.
Starting from https://www.boost.org/doc/libs/1_74_0/doc/html/boost_asio/example/cpp11/echo/async_tcp_echo_server.cpp
io_context.run();
Needs to be like
std::thread t([&] { io_context.run(); });
// ...
t.join();
Or if you insist:
std::thread t(boost::bind(&boost::asio::io_context::run, &io_context));
I would use a thread_pool to shortcut all the complexities¹:
boost::asio::thread_pool io(1);
server s(io.get_executor(), std::atoi(argv[1]));
// ...
io.join();
A trivial edit to the class interface is required (see e.g. Boost 1.70 io_service deprecation)
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//
// async_tcp_echo_server.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2020 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 <boost/bind/bind.hpp>
#include <cstdlib>
#include <iostream>
#include <memory>
#include <utility>
using boost::asio::ip::tcp;
class session : public std::enable_shared_from_this<session> {
public:
session(tcp::socket socket) : socket_(std::move(socket)) {}
void start() { do_read(); }
private:
void do_read() {
auto self(shared_from_this());
socket_.async_read_some(
boost::asio::buffer(data_, max_length),
[this, self](boost::system::error_code ec, std::size_t length) {
if (!ec) {
do_write(length);
}
});
}
void do_write(std::size_t length) {
auto self(shared_from_this());
boost::asio::async_write(
socket_, boost::asio::buffer(data_, length),
[this, self](boost::system::error_code ec, std::size_t /*length*/) {
if (!ec) {
do_read();
}
});
}
tcp::socket socket_;
enum { max_length = 1024 };
char data_[max_length];
};
class server {
public:
template <typename Executor>
server(Executor ex, short port)
: acceptor_(ex, tcp::endpoint(tcp::v4(), port)) {
do_accept();
}
private:
void do_accept() {
acceptor_.async_accept(
[this](boost::system::error_code ec, tcp::socket socket) {
if (!ec) {
std::make_shared<session>(std::move(socket))->start();
}
do_accept();
});
}
tcp::acceptor acceptor_;
};
int main(int argc, char* argv[]) {
try {
if (argc != 2) {
std::cerr << "Usage: async_tcp_echo_server <port>\n";
return 1;
}
boost::asio::thread_pool io(1);
server s(io.get_executor(), std::atoi(argv[1]));
// ...
io.join();
} catch (std::exception& e) {
std::cerr << "Exception: " << e.what() << "\n";
}
}
¹ see e.g. Should the exception thrown by boost::asio::io_service::run() be caught?