Is there any instance in a multi-user environment where two computers/sessions might both open up a file exclusively for read-access without giving me an error when it can't write after reading? Here's the problem I'm currently facing:


I have a POS app which has run for years(originally written in Clipper and released in VFP form roughly 1 year ago). In the past 4 months or so, I've had roughly 3 of these occurences(50-500 orders each day per turnkey system-- about 40 VFP turnkey systems in current use), giving me an approximate .00031% occurence rate(200 orders a day on 40 systems for 120 days(approximately 4 months)). Very rare, but people notice when things go wrong. Here's the scenario:

When saving an order, the programs uses an ORDER_NO dbf file exclusively(on record, one field). It tries 8 times with a delay between retries-- it will give an error if it can't open the file after 8 retries. Once the program has the ORDER_NO file, it reads the current Order Number(6-7 digit depending upon system's history/original setup) then increments the order number in ORDER_NO by 1(uses a simple REPLACE command). Then it closes the file, and continues saving the order. Exclusive use of the ORDER_NO file prevents other users from opening it up at the same time and getting duplicate order numbers. However, as I said before, I've had roughly 3 reports of duplicate order numbers in the past 4 months. Is there any bug, issue, problem, or my favorite-- undocumented feature in VFP I should be aware of that would cause this? Any proposed workarounds/checks? Thanks.