On 11 November 2013 20:15, Jon Perryman <jperr...@pacbell.net> wrote: > L R2,QUEUE > L R3,NEXT_ENTRY > CS R2,R3,QUEUE New queue head > While this seems bullet proof, it's not. If there is a long delay between > between the L instructions then next entry could > have been freed causing an abend.
If your code is referencing an item that may have been freed, then your design is wrong. > While the delay is very unlikely, it is still a possiblity (e.g. swapout > after first "L"). This example is just removing the first > entry. If you try to remove an entry in the middle of the chain, you run a > larger risk. > > Some of the techniques we use to minimize risk: > 1. Abend recovery > 2. don't overload the entry - only contains shared information. > 3. Place entry on a timeout queue before placing on a free queue or freeing. > 4. Copy the entry to workarea - reduces reference time of actual entry > 5. Eyecatchers that can be verified. > 6. Unique identifier for each entry that can be verified. > 7. Turn off interrupts. Most of these are indicative of incorrect design rather than of careful attention to risk. If it's unclear whether a queue entry is eligible to be worked on or even to be looked at unless you do it in a hurry, then there is something quite wrong. By all means provide abend recovery, but don't make it part of the queue handling design. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
