最近在看 asio 的帮助文档，看到了官方的 demo ，请问大家 conn 的引用计数增加为什么是 1 ，2 ，3 ，4 呢？
``` c++
std::cout << "3: " << new_connection.use_count() << std::endl;
```
bind 可以增加引用计数的话，这个位置 conn 的引用计数应该是 2 吧，因为 start_accept 运行完毕后，引用计数要减 1
``` c++
//
// serfer.cpp
// ~~~~~~~~~~
//
// Copyright (c) 2003-2023 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 <ctime>
#include <iostream>
#include <string>
#include <boost/bind/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
std::string make_daytime_string()
{
using namespace std; // For time_t, time and ctime;
time_t now = time(0);
return ctime(&now);
}
class tcp_connection
: public boost::enable_shared_from_this<tcp_connection>
{
public:
typedef boost::shared_ptr<tcp_connection> pointer;
static pointer create(boost::asio::io_context& io_context)
{
return pointer(new tcp_connection(io_context));
}
tcp::socket& socket()
{
return socket_;
}
void start()
{
message_ = make_daytime_string();
boost::asio::async_write(socket_, boost::asio::buffer(message_),
boost::bind(&tcp_connection::handle_write, shared_from_this(),
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
~tcp_connection() { std::cout << "conn descontruct" << std::endl;}
private:
tcp_connection(boost::asio::io_context& io_context)
: socket_(io_context)
{
}
void handle_write(const boost::system::error_code& /*error*/,
size_t /*bytes_transferred*/)
{
}
tcp::socket socket_;
std::string message_;
};
class tcp_serfer
{
public:
tcp_serfer(boost::asio::io_context& io_context)
: io_context_(io_context),
acceptor_(io_context, tcp::endpoint(tcp::v4(), 13))
{
start_accept();
}
private:
void start_accept()
{
tcp_connection::pointer new_connection =
tcp_connection::create(io_context_);
std::cout << "1: " << new_connection.use_count() << std::endl;
acceptor_.async_accept(new_connection->socket(),
boost::bind(&tcp_serfer::handle_accept, this, new_connection,
boost::asio::placeholders::error));
std::cout << "2: " << new_connection.use_count() << std::endl;
}
void handle_accept(tcp_connection::pointer new_connection,
const boost::system::error_code& error)
{
std::cout << "3: " << new_connection.use_count() << std::endl;
if (!error)
{
new_connection->start();
}
start_accept();
std::cout << "4: " << new_connection.use_count() << std::endl;
}
boost::asio::io_context& io_context_;
tcp::acceptor acceptor_;
};
int main()
{
try
{
boost::asio::io_context io_context;
tcp_serfer serfer(io_context);
io_context.run();
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return 0;
}
```
1. 编译完成，运行程序
2. 新开一个终端，运行 `nc 127.0.0.1 13`
输出为：
``` html
1: 1
2: 2
3: 3
1: 1
2: 2
4: 4
conn descontruct
``` |
|
