25.1 Running a server that accepts connections

The function start-up-server starts a new thread which:

1. Creates a socket, then:
2. Prepares it (that is, binds it to the address and port and does various other settings) and then:
3. Waits for connections to it ("accepting connections").

When a connection is made, a programmer-supplied function is called with the new socket. Typically this function create a stream of type socket-stream with this socket, and then uses the stream for communication through the socket using standard Common Lisp I/O functions.