Holds a lock in shared mode while executing a body of code.
A sharing lock.
The status of the process while the lock is locked, as seen in the Process Browser.
A timeout period, in seconds.
The forms to execute
The values returned from evaluating body.
is like with-lock, but the lock must be "sharing" and the lock will be locked in shared mode. That means that other threads can also lock it in shared mode.
Before locking this waits for the lock to be free of any exclusive lock, but it does not check for other shared mode use of the same lock.
It is possible to lock for sharing inside the scope of sharing lock and inside the scope of an exclusive lock.
LispWorks User Guide and Reference Manual - 21 Dec 2011