Without keyword arguments,
barrier-unblock 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.
If disable is true, or if disable is not passed and the barrier was made with disable-on-unblock true, then
barrier-unblock also disables the barrier, so any further calls to barrier-wait return
If kill-waiting is true, instead of waking up the waiting threads,
barrier-unblock kills them (by process-terminate).
LispWorks User Guide and Reference Manual - 13 Feb 2015