record_locking 0.01

record_locking 0.01 is yet another powerful package for web developers. It actually offers PHP/Ajax method of implementing dynamic application level record locking.

There has been a lot of effort to create enterprise grade multiuser LAMP applications, since this approach promises to solve a lot of major problems - such as platform independence, eliminating the overhead of maintaining software on the user's workstation, etc.

However, one of the dirty secrets of LAMP apps is that the record locking provided by the database server only functions for the duration of the transaction - which in the case of a browser based UI is only during a single html request/event. There isn't any established means of maintaining a record lock over multiple html "interactions" with the user - i.e: during the time while the user has the record in his browser window for editing.

A true multi-user app requires "application level" record locking to ensure that only one user can change a record at a time. Enabling members to change (parts of) their own records creates a non-zero possibility of race conflicts with the office manager or other authorized admins attempting to change the same record.

Each status check updates the lock timestamp, confirming that the user is still connected and actively editing the record. Locks are normally released when the user saves the record or navigates to a different screen. If the user fails to properly close/release the record - abandons the record or his browser crashes - locks go stale if not updated for 5 minutes. The next status request or attempt to lock the record will delete or overwrite any stale lock.

Saving a record requires a current lock owned by the user. This protects against obsolete cached data being resubmitted to the database. The user must remain in effectively continuous contact with the database in order to successfully change a record - emulating the behavior of a conventional "closely linked" application.

The user's background javascript process requests a special php file that manages the lock directory and generates a minimal html response back to the calling javascript process with the current lock status. The javascript process parses this returned html message and updates the lock status window. In order to avoid hammering the hard disk with lock traffic, the special php file and lock directory are loaded into a ramdrive mounted as the lock/ directory tree.