A condition variable
nil or a positive real
condition-variable-wait waits at most timeout seconds for the condition variable condvar to be signaled. The lock lock is released while waiting and claimed again before returning. The caller must be holding the lock lock before calling this function.
It is recommended that you use lock-and-condition-variable-wait or simple-lock-and-condition-variable-wait instead of
condition-variable-wait. The locking functions make it easier to avoid mistakes, and can be more efficient.
LispWorks User Guide and Reference Manual - 13 Feb 2015