Week 12 (16)

Synchronise access to shared data items via following rules:

before reading X, get read (shared) lock on X
before writing X, get write (exclusive) lock on X
a tx attempting to get a read lock on X is blocked if another tx already has write lock on X
a tx attempting to get an write lock on X is blocked if another tx has any kind of lock on X

These rules alone do not guarantee serializability.