Database Systems 6th Edition by Ramez Elmasri, Shamkant B. Navathe

تمرين 4

Modify the data structures for multiple-mode locks and the algorithms for read_lock(X), write_lock(X), and unlock(X) so that upgrading and downgrading of locks are possible. (Hint: The lock needs to keep track of the transaction id(s) that hold the lock, if any.)