在boost :: asio中，为什么异步接受处理程序需要重启异步接受？

Question

In the Daytime.3 tutorial for boost::asio (asynchronous TCP server), the class tcp_server contains the following two methods:

void start_accept()
{
  tcp_connection::pointer new_connection =
    tcp_connection::create(acceptor_.get_io_service());

  acceptor_.async_accept(new_connection->socket(),
      boost::bind(&tcp_server::handle_accept, this, new_connection,
        boost::asio::placeholders::error));
}

void handle_accept(tcp_connection::pointer new_connection,
    const boost::system::error_code& error)
{
  if (!error) new_connection->start(); // ***

  start_accept();
}

My concern is the line marked *** . What if this operation takes a long time to complete? Even if it doesn't, there must be some time gap between the *** line and the call to start_accept , during which the server will fail to accept incoming connections. Wouldn't it make more sense for async_accept to register an OS handler that doesn't halt when it accepts its first connection? Also, is this a real issue and how would I fix it?

Answer 1

The server won't "fail to accept incoming connections"; that's what the second parameter of the listen() function is for in the sockets API. But you are correct that the server can have a delay in handling the client request. A single-threaded application that requires lots of computation will cause issues, hence why this particular example really only performs IO. If your server really does need to perform something CPU intensive, then the handler should be passed to a task manager of some sort.