Interesting idea...this seems similar (and maybe easier):

Open .dat file (need to do either way)
Write contents (need to do either way)
Close .dat file (need to do either way)
rename .dat file to .dat.ok (instead of creating a 0 len file)

Then I only look for ".ok" files, but I don't have 2x the files

--OR-- the 2nd process could open the file using "r+"...seems like this would also work and maybe it wouldn't slow down the writer process???

Hard to know what is best...

thanks!