(off list) John, Thank you for the concrete example. I think you may have made a minor error when you wrote, "B updates the record to reflect a new count of 20 pairs." I think you may have meant that B writes the record with its new count of 15 pairs. I don't know if anyone will be confused by this, and I didn't want to add to the clutter on the list by posting this there.
On Mon, 16 Jun 2014 17:29:37 -0400, John Gilmore <jwgli...@gmail.com> wrote: >When two competent people disagree about a well-settled technical >issue there is a possibility that they are talking at cross purposes. > >Consider an inventory record, for concreteness one that contains a >count of the number of pairs of size 13EEE black oxfords in some >wholesaler's stock, and two programs, A and B. > >B queries this record, finds that it contains a count of 20 pairs, and >withdraws 5 pairs from and updates the record to reflect the new count >of 15. After B's query but before but before B's update A also >queries this record and withdraws 10 pairs. B updates the record to >reflect a new count of 20 pairs. A then updates it to reflect a new >count of 10 pairs. In the upshot the inventory record reflects a >balance of 10 pairs when it should reeflect a balance of only 5 pairs. > >Scenarios of this kind that differ only in detail can be multiplied ad >infinitum et nauseam. Does either of you judge > >o that they are innocuous, > >o that serialization cannot prevent them, or > >o that such serialization requirements are different > for programs having different levels of reusability? > >John Gilmore, Ashland, MA 01721 - USA > >---------------------------------------------------------------------- >For IBM-MAIN subscribe / signoff / archive access instructions, >send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
