In a recent note, Barry Merrill said: > Date: Wed, 1 Jun 2005 13:56:17 -0500 > > It's my understanding that the Exclusive ENQUEUE on SYS1.UADS > for a TSO user came about during the last night of testing for > the initial release of TSO, the design of which was based on > models of how TSO should work by Alan Scheer > (and when TSO didn't match his model, unlike most modelers, > he changed TSO to match the model, rather than changing the model). > > The TSO development group had a room with a dozen or so terminals, > and Alan took a break about midnight, and came back to a terminal, > logged on, but was unable to get any reply messages to his commands, > although the commands were obviously being accepted. A few minutes > later, a compatriot called from across the room "There are a bunch > of messages to you on this terminal over here, Alan", and he realized > that he had remained logged on at one terminal, and had then logged > on a second time from the second terminal, and there had been no > specification for protection for multiple logons by a single user! > > The exclusive Enqueue was added to prevent duplicate logons about 2am, > and the first iteration of TSO Product was delivered, on schedule, > to PID at 6am that same morning. > So an onerous restriction, peculiar to IBM, came about through a late-night patch for a bad design.
If there was no specification of preventing multiple logons, then preventing multiple logons to circumvent misrouting of messages was a change in the specification, and, I'd say, of the model. The correct fix would have been to route messages to the originating session, rather than brute-force prohibition of multiple sessions. It was a fundamental design flaw to confuse session-id with user-id. TSO has institutionalized this rather than attempting to correct it. -- gil -- StorageTek INFORMATION made POWERFUL ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
