boost asio 疑问

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？

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

//
// server.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 
#include 
#include 
#include 
#include 
#include 
#include 

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
{
public:
  typedef boost::shared_ptr 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_server
{
public:
  tcp_server(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_server::handle_accept, this, new_connection,
          boost::asio::placeholders::error));
    std::cout <<"2:" << new_connection.use_count() <start();}

    start_accept();
    std::cout <<"4:" << new_connection.use_count() <

1: 1
2: 2
3: 3
1: 1
2: 2
4: 4
conn descontruct