Without keyword arguments,
unblocks the barrier, which means that any thread that is waiting on the barrier wakes and returns from barrier-wait, and the arriver count is reset to 0.
is true, or if
is not passed and the barrier was made with
also disables the barrier, so any further calls to barrier-wait return
is true, instead of waking up the waiting threads,
kills them (by process-kill).
LispWorks User Guide and Reference Manual - 21 Dec 2011