Avoiding deadlocks in concurrent programming

[Eloff]

Hi Steve,

The backup thread only holds the lock long enough to create an
in-memory representation of the data. It writes to disk on it's own
time after it has released the lock, so this is not an issue.

If you're saying what I think you are, then a single lock is actually
better for performance than multiple locks so long as one avoids
waiting for other resources like I/O.

-Dan