6.5 SCM Mutual Exclusion
These 2 calls can be used for locking and synchronizing processes.
— Scheme Procedure: bt:put han key val
Associates key with val in the bt han only if
key was previously empty. Returns #t for success, #f for failure.
— Scheme Procedure: bt:rem han key
Removes key and it's associated value from bt han only if
key is present. Returns key's value for success, #f for
failure (not present).