/**
\page designcloseascancel Close as Cancel

In asio, asynchronous socket operations can be cancelled by closing the socket.
There is no separate cancel operation for a socket, nor is there a way to
cancel individual operations. This approach was selected as the best balance
between utility, portability and efficiency.

For example, although Win32 provides a CancelIo function which can be used to
cancel outstanding operations, this only works if CancelIo is invoked from the
thread that initiated the operation. This restriction was considered too
onerous for a portable networking library. Closing the socket will cancel the
operation from any thread.

*/
