boost中async_read和async_read_some的区别

boost中async_read和async_read_some的区别
假设原型如下

async_read(
	socket_,
	boost::asio::buffer(read_msg_.data(),512),
	readHandler
)

和

socket_.async_read_some(
	boost::asio::buffer(read_msg_.data(),512),
	readHandler
)

async_read：只有读满512字节或出错才会调用readHandler，
async_read_some：只要有消息或出错就会调用readHandler