c++ boost: how to implement session per thread - c++

Question

I want to implement there is one thread for each connected session in a server. However, the handle accept callback is called in the same thread.I am not quite familiar the threading model in asio. Is there website mentioned about it?
Edit: I try to write a chat room server based on the example from boost.
as you can see the same thread is used to handle the connection request. So I don't know how to make it into separated thread.
output:
[00410190] main Thread Start
[00410860] Thread Start
[00410898] Thread Start
[00410190] start accept
[00410898] handle accept
[00410898] start accept
[00410898] handle accept
[00410898] start accept
code:
#include "stdafx.h"
#include <algorithm>
#include <cstdlib>
#include <deque>
#include <iostream>
#include <list>
#include <set>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/asio.hpp>
#include "chat_message.h"
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
using boost::asio::ip::tcp;
//----------------------------------------------------------------------
typedef std::deque<chat_message> chat_message_queue;
boost::mutex global_stream_lock;
//----------------------------------------------------------------------
class chat_participant
{
public:
virtual ~chat_participant() {}
virtual void deliver(const chat_message& msg) = 0;
};
typedef boost::shared_ptr<chat_participant> chat_participant_ptr;
//----------------------------------------------------------------------
class chat_room
{
public:
void join(chat_participant_ptr participant)
{
participants_.insert(participant);
std::for_each(recent_msgs_.begin(), recent_msgs_.end(),
boost::bind(&chat_participant::deliver, participant, _1));
}
void leave(chat_participant_ptr participant)
{
participants_.erase(participant);
}
void deliver(const chat_message& msg)
{
recent_msgs_.push_back(msg);
while (recent_msgs_.size() > max_recent_msgs)
recent_msgs_.pop_front();
std::for_each(participants_.begin(), participants_.end(),
boost::bind(&chat_participant::deliver, _1, boost::ref(msg)));
}
private:
std::set<chat_participant_ptr> participants_;
enum { max_recent_msgs = 100 };
chat_message_queue recent_msgs_;
};
//----------------------------------------------------------------------
class chat_session
: public chat_participant,
public boost::enable_shared_from_this<chat_session>
{
public:
chat_session(boost::asio::io_service& io_service, chat_room& room)
: socket_(io_service),
room_(room)
{
}
tcp::socket& socket()
{
return socket_;
}
void start()
{
room_.join(shared_from_this());
boost::asio::async_read(socket_,
boost::asio::buffer(read_msg_.data(), chat_message::header_length),
boost::bind(
&chat_session::handle_read_header, shared_from_this(),
boost::asio::placeholders::error));
}
void deliver(const chat_message& msg)
{
bool write_in_progress = !write_msgs_.empty();
write_msgs_.push_back(msg);
if (!write_in_progress)
{
boost::asio::async_write(socket_,
boost::asio::buffer(write_msgs_.front().data(),
write_msgs_.front().length()),
boost::bind(&chat_session::handle_write, shared_from_this(),
boost::asio::placeholders::error));
}
}
void handle_read_header(const boost::system::error_code& error)
{
if (!error && read_msg_.decode_header())
{
boost::asio::async_read(socket_,
boost::asio::buffer(read_msg_.body(), read_msg_.body_length()),
boost::bind(&chat_session::handle_read_body, shared_from_this(),
boost::asio::placeholders::error));
}
else
{
room_.leave(shared_from_this());
}
}
void handle_read_body(const boost::system::error_code& error)
{
if (!error)
{
room_.deliver(read_msg_);
std::string s(read_msg_.data(), read_msg_.length());
std::cout << s<< std::endl;
boost::asio::async_read(socket_,
boost::asio::buffer(read_msg_.data(), chat_message::header_length),
boost::bind(&chat_session::handle_read_header, shared_from_this(),
boost::asio::placeholders::error));
}
else
{
room_.leave(shared_from_this());
}
}
void handle_write(const boost::system::error_code& error)
{
if (!error)
{
write_msgs_.pop_front();
if (!write_msgs_.empty())
{
boost::asio::async_write(socket_,
boost::asio::buffer(write_msgs_.front().data(),
write_msgs_.front().length()),
boost::bind(&chat_session::handle_write, shared_from_this(),
boost::asio::placeholders::error));
}
}
else
{
room_.leave(shared_from_this());
}
}
private:
tcp::socket socket_;
chat_room& room_;
chat_message read_msg_;
chat_message_queue write_msgs_;
};
typedef boost::shared_ptr<chat_session> chat_session_ptr;
//----------------------------------------------------------------------
class chat_server
{
public:
chat_server(boost::asio::io_service& io_service,
const tcp::endpoint& endpoint)
: io_service_(io_service),
acceptor_(io_service, endpoint)
{
start_accept();
}
void start_accept()
{
global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] start accept" << std::endl;
global_stream_lock.unlock();
chat_session_ptr new_session(new chat_session(io_service_, room_));
acceptor_.async_accept(new_session->socket(),
boost::bind(&chat_server::handle_accept, this, new_session,
boost::asio::placeholders::error));
}
void handle_accept(chat_session_ptr session,
const boost::system::error_code& error)
{
global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] handle accept" << std::endl;
global_stream_lock.unlock();
if (!error)
{
session->start();
}
start_accept();
}
private:
boost::asio::io_service& io_service_;
tcp::acceptor acceptor_;
chat_room room_;
};
typedef boost::shared_ptr<chat_server> chat_server_ptr;
typedef std::list<chat_server_ptr> chat_server_list;
void WorkerThread( boost::shared_ptr< boost::asio::io_service > io_service )
{
global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] Thread Start" << std::endl;
global_stream_lock.unlock();
io_service->run();
global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] Thread Finish" << std::endl;
global_stream_lock.unlock();
}
//----------------------------------------------------------------------
int _tmain(int argc, char* argv[])
{
try
{
if (argc < 2)
{
std::cerr << "Usage: chat_server <port> [<port> ...]\n";
return 1;
}
boost::shared_ptr< boost::asio::io_service > io_service(
new boost::asio::io_service
);
boost::shared_ptr< boost::asio::io_service::work > work(
new boost::asio::io_service::work( *io_service )
);
//boost::asio::io_service::strand strand( *io_service );
global_stream_lock.lock();
std::cout << "[" << boost::this_thread::get_id()
<< "] main Thread Start" << std::endl;
global_stream_lock.unlock();
boost::thread_group worker_threads;
for( int x = 0; x < 2; ++x )
{
worker_threads.create_thread( boost::bind( &WorkerThread,
io_service ) );
}
chat_server_list servers;
for (int i = 1; i < argc; ++i)
std::cout<<argv[i] << std::endl;
for (int i = 1; i < argc; ++i)
{
using namespace std; // For atoi.
tcp::endpoint endpoint(tcp::v4(), atoi(argv[i]));
chat_server_ptr server(new chat_server(*io_service, endpoint));
servers.push_back(server);
}
work.reset();
worker_threads.join_all();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}

Answer 1

This boost asio example shows an HTTP server using a single io_service and a thread pool to handle incoming sessions. It might help.