How does one create a dispatch source that responds to multiple
connections on the same socket, that is, listening on a socket with a
backlog larger than 1?

In the online doc it seems that you should have a connected socket to
read from, the same way as reading from a file. But documentation also
says you need a socket returned from listen().

So where does the accept() call fit into this? Specifically it would
be nice to avoid blocking on accept() before creating a read source.