semaphore-release sem &key count => flag
A non negative fixnum.
A generalized boolean.
semaphore-release releases count units back to the semaphore sem.
It atomically increments the semaphore's unit count by count (which defaults to 1).
The returned flag is true if any other thread was waiting for the semaphore and false otherwise
LispWorks User Guide and Reference Manual - 20 Sep 2017