COBOL Manual for TNS and TNS/R Programs

Libraries and Utility Routines
HP COBOL Manual for TNS and TNS/R Programs—522555-006
13-35
Checkpoint Lists for Process Pairs
These routines operate upon copies of the process-creation messages that establish
the execution environment of the program. Copies of these messages are not saved
automatically and must be requested by a SAVE directive in the main program. For
information on the SAVE directive, see SAVE.
Topics:
•
Checkpoint Lists for Process Pairs (non-CRE environment only)
•
Defined Portions of Saved Messages
Checkpoint Lists for Process Pairs
This topic applies only to non-CRE SMU routines, as CRE SMU routines do not
support checkpointing.
In an HP COBOL program, the saved message storage space is not part of the direct
variable space. When a program designed to run as a process pair needs to change or
delete saved messages, it needs a checkpoint list.
A checkpoint list is a COBOL record with a specific structure in which the message
changes are recorded. (Examples of checkpoint lists are given in the individual routine
descriptions in Saved Message Utility (SMU) Routines where required.)
The information in a checkpoint list must be transmitted to the backup member of a
process pair, just as values of critical HP COBOL program variables must. This is the
purpose of the CHECKPOINT statement. When a checkpoint list appears in a
CHECKPOINT statement, the reserved word QUEUE must precede its name.
Checkpoint lists can be mixed with any of the other items that are legal in a
CHECKPOINT statement, as in this example:
CHECKPOINT ITEM-1, QUEUE CP-LIST-1, ITEM-2, FILE ITEM-3.
The compiler interprets CP-LIST-1 as a checkpoint list and checkpoints the information
it contains and the values of the other items. It then resets CP-LIST-1 to empty so that
its information storage space is available to record further message changes.
Caution. An HP COBOL program must not modify the contents of a checkpoint list directly.
The execution logic of the routines and the CHECKPOINT statement maintain checkpoint lists
without any other program action.