If force is
start-tty-listener checks whether the default listener process is alive or if there is a live process with name "TTY Listener". If such a process exists,
start-tty-listener simply returns
nil and does not start a new process. If no such process exists, or if force was
start-tty-listener starts a new listener process named "TTY Listener", and returns it.
If a REPL with I/O through
*terminal-io* (such as a REPL started by
start-tty-listener) is in the debugger, then by default it blocks multiprocessing. This behavior is controlled by the value of *terminal-debugger-block-multiprocessing*.
LispWorks User Guide and Reference Manual - 13 Feb 2015