The function wait-for-input-streams and wait-for-input-streams-returning-first are a convenient interface for waiting for input from socket streams. The standard I/O functions (cl:read, cl:read-char and so on) can also wait properly. You can also use process-wait and similar functions with cl:listen in the wait-function, but you will need to use with-noticed-socket-stream.
LispWorks User Guide and Reference Manual - 13 Feb 2015