The lock to be relinquished.
When this is
t, an error is signaled if *current-process* is not the owner of the lock. The default is
Attempts to release a lock. If the lock is owned by *current-process*,
process-unlock decrements an internal count. If this lock count is then zero, the lock is released. Note that
process-unlock relates only on Lisp processes.
process-sharing-unlock is guaranteed to successfully unlock the lock, but is not guaranteed to return, as described in Guarantees and limitations when locking and unlocking.
LispWorks User Guide and Reference Manual - 13 Feb 2015