Like process-unlock, but on a "sharing" lock.
The function process-exclusive-unlock is the same as process-unlock but for a "sharing" lock.
Calls to process-exclusive-unlock should be paired with process-exclusive-lock calls. In most cases the macro with-exclusive-lock the best way to achieve this.
process-exclusive-unlock is guaranteed to successfully unlock sharing-lock, but is not guaranteed to return, as described in Guarantees and limitations when locking and unlocking.
LispWorks User Guide and Reference Manual - 20 Sep 2017