Editing Linearizability (section)

=== Linearizability versus serializability ===
Consider the following history, again of two objects interacting with a lock:

{| border="1" cellspacing="0"
| A invokes lock
| A successfully locks
| B invokes unlock
| B successfully unlocks
| A invokes unlock
| A successfully unlocks
|}

This history is not valid because there is a point at which both A and B hold the lock; moreover, it cannot be reordered to a valid sequential history without violating the ordering rule. Therefore, it is not linearizable. However, under serializability, B's unlock operation may be moved to ''before'' A's original lock, which is a valid history (assuming the object begins the history in a locked state):

{| border="1" cellspacing="0"
| B invokes unlock
| B successfully unlocks
| A invokes lock
| A successfully locks
| A invokes unlock
| A successfully unlocks
|}

This reordering is sensible provided there is no alternative means of communicating between A and B. Linearizability is better when considering individual objects separately, as the reordering restrictions ensure that multiple linearizable objects are, considered as a whole, still linearizable.