File sharing, locking, etc... between multiple users...

[Rob Cozens]

Jonathan:

> My brother, who is a much more experienced programmer than myself, 
> gave me a
> long explanation about collisions, that can occur in the following 
> order of
> events:
>
> 1) User A reads the file, and determines it is not owned
> 2) In the few milliseconds between when User A reads the file, and 
> resaves
> it, user B reads the file and also reads that it is not owned.
> 3) User A makes changes and saves the data
> 4) User B, who should have been locked out but was not, makes changes 
> and
> saves his data, overwriting the changes made by User A.
>

Absolutely!  That's why between steps 2 and 3 each user must reread the 
file to confirm she/he has acquired access.

Rob Cozens
CCW, Serendipity Software Company

"And I, which was two fooles, do so grow three;
Who are a little wise, the best fooles bee."

from "The Triple Foole" by John Donne (1572-1631)