Problems with nonblocking sockets in Windows

When I work in full-duplex mode with sockets (server & clients send & receive data through the same port ) I have the following results:
1. Blocking mode - works properly from 2 sides - server sends and receives data without problems and also client sends and receives data without problems.

2. Unblocking mode - server sends and receives data properly, but client only sends data properly, but
does not receives data (I use recv()). Recv in Client does not wait data and immedeatelly goes to the next operator after recv.
What's is it needed to add in my appl. to work in nonblocking mode with full-duplex socket?