用boost库实现socket编程，遇到几个问题，求大神指导

boost::asio::socket_base::bytes_readable command(true);
socket_.io_control(command);
上面这段代码是干什么用的啊？？
还有socket_.read_some()  ,boost::asio::async_read(),这两个函数有什么区别啊

http://stackoverflow.com/questions/12708558/c-multiple-multicast-receiver-with-boost-asio/12749727

google
socket控制
socket的读，异步读

异步读，同步读~~~~