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我正在使用 boost 示例 httpserver3： http: //www.boost.org/doc/libs/1_53_0/doc/html/boost_asio/examples.html#boost_asio.examples.http_server_3

我无法清楚地理解调用 new_connection_ 的 reset 方法时会发生什么

void server::start_accept()
{
  new_connection_.reset(new connection(io_service_, request_handler_));
  acceptor_.async_accept(new_connection_->socket(),
      boost::bind(&server::handle_accept, this,
        boost::asio::placeholders::error));
}

void server::handle_accept(const boost::system::error_code& e)
{
  if (!e)
  {
    new_connection_->start();
  }
    std::cout<<"handle_accept"<<std::endl;
  start_accept();
}

我知道“重置”将导致先前的对象被删除，如文档所述。如果服务器对象在前一个连接对象正在处理它的请求时接受一个新连接会发生什么？之前的连接会立即被破坏还是会收到错误并退出？

void connection::handle_read(const boost::system::error_code& e,
    std::size_t bytes_transferred)
{
  if (!e)
  {
    boost::tribool result;
    boost::tie(result, boost::tuples::ignore) = request_parser_.parse(
        request_, buffer_.data(), buffer_.data() + bytes_transferred);

    if (result)
    {
      request_handler_.handle_request(request_, reply_);
      boost::asio::async_write(socket_, reply_.to_buffers(),
          strand_.wrap(
            boost::bind(&connection::handle_write, shared_from_this(),
              boost::asio::placeholders::error)));
    }
    else if (!result)
    {
      reply_ = reply::stock_reply(reply::bad_request);
      boost::asio::async_write(socket_, reply_.to_buffers(),
          strand_.wrap(
            boost::bind(&connection::handle_write, shared_from_this(),
              boost::asio::placeholders::error)));
    }
    else
    {
      socket_.async_read_some(boost::asio::buffer(buffer_),
          strand_.wrap(
            boost::bind(&connection::handle_read, shared_from_this(),
              boost::asio::placeholders::error,
              boost::asio::placeholders::bytes_transferred)));
    }
  }

  // If an error occurs then no new asynchronous operations are started. This
  // means that all shared_ptr references to the connection object will
  // disappear and the object will be destroyed automatically after this
  // handler returns. The connection class's destructor closes the socket.
}

void connection::handle_write(const boost::system::error_code& e)
{
  if (!e)
  {
    // Initiate graceful connection closure.
    boost::system::error_code ignored_ec;
    socket_.shutdown(boost::asio::ip::tcp::socket::shutdown_both, ignored_ec);
  }

  // No new asynchronous operations are started. This means that all shared_ptr
  // references to the connection object will disappear and the object will be
  // destroyed automatically after this handler returns. The connection class's
  // destructor closes the socket.
}
4

1 回答 1

1

啊，的魔力shared_from_this()。您错过了这部分代码：

void connection::start()
{
  socket_.async_read_some(boost::asio::buffer(buffer_),
      strand_.wrap(
        boost::bind(&connection::handle_read, shared_from_this(),
          boost::asio::placeholders::error,
          boost::asio::placeholders::bytes_transferred)));
}

会发生什么：

  1. server::handle_accept()来电new_connection_->start()。
  2. connection::start()调度读取操作，并通过这样做，创建原始共享指针的副本与shared_from_this()调用。
  3. 现在 server::handle_accept()调用server::start_accept().
  4. server::start_accept()做reset()原始共享指针，但 ASIO 服务有它的副本，所以只要连接的回调继续使用 调度更多操作shared_from_this()，连接就不会被破坏（因为至少有一个共享指针仍然指向堆分配的connection对象）。
于 2013-09-14T20:18:49.937 回答