I'd strongly recomment that you follow
kschwab's advice and rename the
data file to the same directory before you start to copy
or process it. Copying takes time, and you don't want
the remote process to start updating the file
while your process in in the middle of copying it.
Renaming it first will help prevent that.
Then, after you rename it, check to see if
it's still changing, because it's possible that
the remote process opened the file just before you renamed it.
There's still a race condition, but it's much smaller.
Proper design would have been for the remote program to never send
the same data twice and never use the same filename twice.
I also recommend that you find the person who designed
this broken protocol and kick them in the ass.
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