3

首先，代码

//
// 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;
}

现在我不明白他们为什么write要发布电话io_service？所以这将是线程安全的，并且 no1 会同时使用套接字？这能确保async_write不会发生 2X 吗？并且没有async_write并且async_read会一起使用吗？我是否必须确保这asynch_write两者async_read不会同时发生？或者同时做这两件事是否安全？顺便说一句，如果我想让代码运行得更快，我知道我可以创建 2 个（或更多）线程来这样做io_service::run()，在这种情况下，我是否必须使用互斥锁来确保我上面写的事情不会发生？

4

1 回答 1

2

io_service::post从chat_client::write公共方法中使用，因为async_write它是一个组合操作，并且应用程序需要确保在流完成之前不会对流执行其他操作。

此操作通过对流的 async_write_some 函数的零次或多次调用来实现，称为组合操作。在此操作完成之前，程序必须确保流不执行其他写入操作（例如 async_write、流的 async_write_some 函数或执行写入的任何其他组合操作）。

真正的工作是在chat_client::do_write使用传出消息队列的地方完成的。

编辑：

在聊天客户端示例中，只有一个线程调用io_service::run，因此处理程序中没有线程安全问题。如果您有多个线程调用io_service::run，您应该调查 strands 而不是我在上一个问题中描述的互斥锁。

于 2010-11-03T21:58:59.607 回答