Tim -

> Think about the issues here - two copies of the same image running,
> recording changes to the same changes file. You open the changes file
> for write from the first image to get to a point where it records a
> change. You try to open the changes file again for the second image.
> Does your OS allow opening a file multiple times to write? Does it even
> allow opening to read once it's already open for write?

Actually it allows all of them. I made the decision for having an exclusive 
write lock on files opened with read-write since Squeak doesn't give us much 
control about the intended behavior and in the past I was bitten many a time 
by having different programs (or even the same program!) write to a file 
concurrently. This can actually be a problem if you know what you're doing 
but unless we have better control from Squeak directly I don't see any 
better solution.

Cheers,
  - Andreas