Using the Locking Hierarchy

An application should obtain a level 1 lock before beginning an operation, such as a complete defragmentation or compression. The application should release the level 1 lock only after the entire operation is finished. This approach prevents other processes from obtaining a lock on the same disk, which would keep the lock owner from finishing its work.

To minimize the time spent in the level 3 lock, a process should remain in the level 2 lock to perform certain tasks, such as computing disk statistics and preparing data packets to be written before actually writing them in the level 3 lock. As soon as a process enters the level 3 lock, the application must call Get Lock Flag State (Interrupt 21h Function 440Dh Minor Code 6Ch) to determine if anything on the disk has changed, such as the swap file growing or shrinking. If a change has occurred, the process should release the level 3 lock, return to the level 2 lock to recompute any needed information, and then obtain the level 3 lock again. If Get Lock Flag State shows that the disk has not changed, the process should do its writing and then release the level 3 lock.