I hope you will share my delight in watching as simple, even naive, questions lead to remarkable solutions and purely theoretical discoveries find unanticipated applications.
The developerWorks tutorial "Locking down your PHP applications" (see Resources) talks about SQL injections: the art of sending malformed data to a database to cause harm or unwarranted access.
In short, locking is the means by which data integrity can be maintained when two or more application processes simultaneously request access to the same data.
Versions each class and resource individually instead of reloading the whole application, avoiding the problems associated with container redeployment and rolling upgrades.