How to safely maintain a status file

[Plumo]

> What are you keeping in this status file that needs to be saved
> several times per second?  Depending on what type of state you're
> storing and how persistent it needs to be, there may be a better way
> to store it.
>
> Michael

This is for a threaded web crawler. I want to cache what URL's are
currently in the queue so if terminated the crawler can continue next
time from the same point.