Deciding what to include in the parameter area

Your mainline routine can put whatever information it wants in the parameter area. Remember that the object is to provide the recovery routine with as much useful information as possible so the recovery routine can be effective. Here are some suggestions for important information to place in the parameter area:

• The base registers for the mainline. The recovery routine must be able to establish addressability to whatever resources the mainline is holding.
• The addresses of all dynamically acquired storage.
• The location of a work area for use by the recovery routine.
• Indications of what resources are held or serialized, such as ENQs, locks, data sets, and so on.
• Footprints indicating the processing being performed by the mainline when the error occurred. Using footprints is a technique whereby the mainline sets bits as it goes through its processing. When the recovery routine gets control, it can check the parameter area to see which bits have been turned on, and thus can tell how far along the mainline was. The recovery routine can pinpoint what the mainline was doing at the time of error. If the mainline was done with its processing when the error occurred, the recovery routine might not need to retry, but might just clean up resources.
• An indication of whether a retry is desired.
• The input parameter list to the mainline. When the mainline received control, it might have received an input parameter list. The mainline can preserve this in the parameter area intended for use by the recovery routine. The recovery routine can then inspect the input parameter list to determine if the mainline received input that was not valid.
• Whatever register contents (both GPRs and ARs) the mainline wants to save (they might need to be restored upon retry).
• The location of important data areas used by the mainline. Errors often occur because of damage to information in a data area. The recovery routine might need to repair one or more of these data areas, and so must be able to access them. The recovery routine might also want to include these data areas when it specifies the areas of storage to dump.
• The addresses of any user-written routines available to repair damage. You might have separate routines designed to scan and repair queues, repair data areas, and so on. The recovery routine might want to call these other routines for assistance.