首先,这段代码。
现在我不明白为什么他们要在
//
// chat_client.cpp
// ~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2010 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 <cstdlib>
#include <deque>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
#include "chat_message.hpp"
using boost::asio::ip::tcp;
typedef std::deque<chat_message> chat_message_queue;
class chat_client
{
public:
chat_client(boost::asio::io_service& io_service,
tcp::resolver::iterator endpoint_iterator)
: io_service_(io_service),
socket_(io_service)
{
tcp::endpoint endpoint = *endpoint_iterator;
socket_.async_connect(endpoint,
boost::bind(&chat_client::handle_connect, this,
boost::asio::placeholders::error, ++endpoint_iterator));
}
void write(const chat_message& msg)
{
io_service_.post(boost::bind(&chat_client::do_write, this, msg));
}
void close()
{
io_service_.post(boost::bind(&chat_client::do_close, this));
}
private:
void handle_connect(const boost::system::error_code& error,
tcp::resolver::iterator endpoint_iterator)
{
if (!error)
{
boost::asio::async_read(socket_,
boost::asio::buffer(read_msg_.data(), chat_message::header_length),
boost::bind(&chat_client::handle_read_header, this,
boost::asio::placeholders::error));
}
else if (endpoint_iterator != tcp::resolver::iterator())
{
socket_.close();
tcp::endpoint endpoint = *endpoint_iterator;
socket_.async_connect(endpoint,
boost::bind(&chat_client::handle_connect, this,
boost::asio::placeholders::error, ++endpoint_iterator));
}
}
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_client::handle_read_body, this,
boost::asio::placeholders::error));
}
else
{
do_close();
}
}
void handle_read_body(const boost::system::error_code& error)
{
if (!error)
{
std::cout.write(read_msg_.body(), read_msg_.body_length());
std::cout << "\n";
boost::asio::async_read(socket_,
boost::asio::buffer(read_msg_.data(), chat_message::header_length),
boost::bind(&chat_client::handle_read_header, this,
boost::asio::placeholders::error));
}
else
{
do_close();
}
}
void do_write(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_client::handle_write, this,
boost::asio::placeholders::error));
}
}
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_client::handle_write, this,
boost::asio::placeholders::error));
}
}
else
{
do_close();
}
}
void do_close()
{
socket_.close();
}
private:
boost::asio::io_service& io_service_;
tcp::socket socket_;
chat_message read_msg_;
chat_message_queue write_msgs_;
};
int main(int argc, char* argv[])
{
try
{
if (argc != 3)
{
std::cerr << "Usage: chat_client <host> <port>\n";
return 1;
}
boost::asio::io_service io_service;
tcp::resolver resolver(io_service);
tcp::resolver::query query(argv[1], argv[2]);
tcp::resolver::iterator iterator = resolver.resolve(query);
chat_client c(io_service, iterator);
boost::thread t(boost::bind(&boost::asio::io_service::run, &io_service));
char line[chat_message::max_body_length + 1];
while (std::cin.getline(line, chat_message::max_body_length + 1))
{
using namespace std; // For strlen and memcpy.
chat_message msg;
msg.body_length(strlen(line));
memcpy(msg.body(), line, msg.body_length());
msg.encode_header();
c.write(msg);
}
c.close();
t.join();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
现在我不明白为什么他们要在
io_service
中使用write
函数来进行调用?这样可以保证线程安全,确保没有其他人会同时使用套接字吗?这是否可以确保没有两个async_write
会同时发生?而且async_write
和async_read
也不会同时使用?
我需要确保asynch_write
和async_read
不会同时发生吗?或者同时进行是安全的吗?
另外,如果我想让代码运行得更快,我了解到可以使用2(或更多)线程来执行io_service::run()
,那么在这种情况下,我需要使用互斥锁来确保上述事项不会发生吗?