I work in WINNT.I use IO completion port mode in server program,and use nonblocking socket in client program.Both they are TCP stream socket.When I closesocket the socket which connect to the client,client can't always receive the last message from server. I know tcp socket ought to ensure all message has been received before close.But why IO completion port mode socket not?What can I do? Thank you very much! regards

Before calling closesocket, call shutdown.

yes,thanks!