Boost asio and array of sockets - c++

Question

I have to write a program that initializes a array of TCP sockets, and use async i/o to read data using a thread pool. Im new to async io, thread pools, shared_ptrs. What I now have is a working program with one socket. Heres the clipping:
boost::shared_ptr< asio::ip::tcp::socket > sock1(
new asio::ip::tcp::socket( *io_service )
);
boost::shared_ptr< asio::ip::tcp::acceptor > acceptor( new asio::ip::tcp::acceptor( *io_service ) );
asio::ip::tcp::endpoint endpoint(asio::ip::tcp::v4(), portNum);
acceptor->open( endpoint.protocol() );
acceptor->set_option( asio::ip::tcp::acceptor::reuse_address( false ) );
acceptor->bind( endpoint );
acceptor->listen();
I am stuck in getting similar code for an "array of sockets", that is, I want to have acceptor[], that are binded to endpoint[]. I must pass around pointers to the acceptors an sockets, so shared_ptr comes in, and am unable to get it right.
for (i=0; i<10; i++) {
// init socket[i] with *io_service
// init endpoint[i]
// init acceptor[i] with *io_service
acceptor[i]->listen()
}
(btw, do I really need an socket[] array for this porpose?) Can someone please help me?

Answer 1

Here is a full example for using Boost ASIO to implement a TCP echo server listening to multiple ports, with a thread pool to distribute work across multiple cores. It is based on this example from the Boost documentation (providing a single-threaded TCP echo server).
Session class
The session class represents a single active socket connection with a client. It reads from the socket and then writes the same data into the socket to echo it back to the client. The implementation uses the async_... functions provided by Boost ASIO: These functions register a callback at the I/O service that will be triggered when the I/O operation has finished.
session.h
#pragma once
#include <array>
#include <memory>
#include <boost/asio.hpp>
/**
* A TCP session opened on the server.
*/
class session : public std::enable_shared_from_this<session> {
using endpoint_t = boost::asio::ip::tcp::endpoint;
using socket_t = boost::asio::ip::tcp::socket;
public:
session(boost::asio::io_service &service);
/**
* Start reading from the socket.
*/
void start();
/**
* Callback for socket reads.
*/
void handle_read(const boost::system::error_code &ec,
size_t bytes_transferred);
/**
* Callback for socket writes.
*/
void handle_write(const boost::system::error_code &ec);
/**
* Get a reference to the session socket.
*/
socket_t &socket() { return socket_; }
private:
/**
* Session socket
*/
socket_t socket_;
/**
* Buffer to be used for r/w operations.
*/
std::array<uint8_t, 4096> buffer_;
};
session.cpp
#include "session.h"
#include <functional>
#include <iostream>
#include <thread>
using boost::asio::async_write;
using boost::asio::buffer;
using boost::asio::io_service;
using boost::asio::error::connection_reset;
using boost::asio::error::eof;
using boost::system::error_code;
using boost::system::system_error;
using std::placeholders::_1;
using std::placeholders::_2;
session::session(io_service &service) : socket_{service} {}
void session::start() {
auto handler = std::bind(&session::handle_read, shared_from_this(), _1, _2);
socket_.async_read_some(buffer(buffer_), handler);
}
void session::handle_read(const error_code &ec, size_t bytes_transferred) {
if (ec) {
if (ec == eof || ec == connection_reset) {
return;
}
throw system_error{ec};
}
std::cout << "Thread " << std::this_thread::get_id() << ": Received "
<< bytes_transferred << " bytes on " << socket_.local_endpoint()
<< " from " << socket_.remote_endpoint() << std::endl;
auto handler = std::bind(&session::handle_write, shared_from_this(), _1);
async_write(socket_, buffer(buffer_.data(), bytes_transferred), handler);
}
void session::handle_write(const error_code &ec) {
if (ec) {
throw system_error{ec};
}
auto handler = std::bind(&session::handle_read, shared_from_this(), _1, _2);
socket_.async_read_some(buffer(buffer_), handler);
}
Server class
The server class creates an acceptor for each given port. The acceptor will listen to the port and dispatch a socket for each incoming connection request. The waiting for an incoming connection is again implemented with a async_... function.
server.h
#pragma once
#include <vector>
#include <boost/asio.hpp>
#include "session.h"
/**
* Listens to a socket and dispatches sessions for each incoming request.
*/
class server {
using acceptor_t = boost::asio::ip::tcp::acceptor;
using endpoint_t = boost::asio::ip::tcp::endpoint;
using socket_t = boost::asio::ip::tcp::socket;
public:
server(boost::asio::io_service &service, const std::vector<uint16_t> &ports);
/**
* Start listening for incoming requests.
*/
void start_accept(size_t index);
/**
* Callback for when a request comes in.
*/
void handle_accept(size_t index, std::shared_ptr<session> new_session,
const boost::system::error_code &ec);
private:
/**
* Reference to the I/O service that will call our callbacks.
*/
boost::asio::io_service &service_;
/**
* List of acceptors each listening to (a different) socket.
*/
std::vector<acceptor_t> acceptors_;
};
server.cpp
#include "server.h"
#include <functional>
#include <boost/asio.hpp>
using std::placeholders::_1;
using std::placeholders::_2;
using boost::asio::io_service;
using boost::asio::error::eof;
using boost::system::error_code;
using boost::system::system_error;
server::server(boost::asio::io_service &service,
const std::vector<uint16_t> &ports)
: service_{service} {
auto create_acceptor = [&](uint16_t port) {
acceptor_t acceptor{service};
endpoint_t endpoint{boost::asio::ip::tcp::v4(), port};
acceptor.open(endpoint.protocol());
acceptor.set_option(acceptor_t::reuse_address(false));
acceptor.bind(endpoint);
acceptor.listen();
return acceptor;
};
std::transform(ports.begin(), ports.end(), std::back_inserter(acceptors_),
create_acceptor);
for (size_t i = 0; i < acceptors_.size(); i++) {
start_accept(i);
}
}
void server::start_accept(size_t index) {
auto new_session{std::make_shared<session>(service_)};
auto handler =
std::bind(&server::handle_accept, this, index, new_session, _1);
acceptors_[index].async_accept(new_session->socket(), handler);
}
void server::handle_accept(size_t index, std::shared_ptr<session> new_session,
const boost::system::error_code &ec) {
if (ec) {
throw system_error{ec};
}
new_session->start();
start_accept(index);
}
Main
The main function creates the server for a series of ports.
For this example, the ports are set to 5000,...,5010. It then spawns a series of threads for each CPU core that calls the run function of the I/O service provided by Boost ASIO. The I/O service is capable of handling such a multi-threading scenario, dispatching work among the threads that have called its run function (reference):
Multiple threads may call the run() function to set up a pool of threads from which the io_context may execute handlers. All threads that are waiting in the pool are equivalent and the io_context may choose any one of them to invoke a handler.
server_main.cpp
#include "server.h"
#include <numeric>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
int main() {
std::vector<uint16_t> ports{};
// Fill ports with range [5000,5000+n)
ports.resize(10);
std::iota(ports.begin(), ports.end(), 5000);
boost::asio::io_service service{};
server s{service, ports};
// Spawn thread group for running the I/O service
size_t thread_count = std::min(
static_cast<size_t>(boost::thread::hardware_concurrency()), ports.size());
boost::thread_group tg{};
for (size_t i = 0; i < thread_count; ++i) {
tg.create_thread([&]() { service.run(); });
}
tg.join_all();
return 0;
}
You could compile the server for example with g++ -O2 -lboost_thread -lpthread {session,server,server_main}.cpp -o server. If you run the server with clients that send it random data, you would get output such as:
Thread 140043413878528: Received 4096 bytes on 127.0.0.1:5007 from 127.0.0.1:40856
Thread 140043405485824: Received 4096 bytes on 127.0.0.1:5000 from 127.0.0.1:42556
Thread 140043388700416: Received 4096 bytes on 127.0.0.1:5005 from 127.0.0.1:58582
Thread 140043388700416: Received 4096 bytes on 127.0.0.1:5001 from 127.0.0.1:40192
Thread 140043388700416: Received 4096 bytes on 127.0.0.1:5003 from 127.0.0.1:42508
Thread 140043397093120: Received 4096 bytes on 127.0.0.1:5008 from 127.0.0.1:37808
Thread 140043388700416: Received 4096 bytes on 127.0.0.1:5006 from 127.0.0.1:35440
Thread 140043397093120: Received 4096 bytes on 127.0.0.1:5009 from 127.0.0.1:58306
Thread 140043405485824: Received 4096 bytes on 127.0.0.1:5002 from 127.0.0.1:56300
You can see the server handling multiple ports, with work being distributed among the worker threads (not necessarily restricting each thread to a specific port).