Synchronization point processing

When IMS is restarted or resets to an earlier checkpoint, it is possible that a previously-issued command will be rescheduled for execution.

When the automated operator (AO) application regains control after a CMD call, IMS produces an initial response to the command. Command processing might be incomplete because additional IMS processing initiated by the command is still in progress.

Command responses that are not retrieved by a GCMD call are discarded at a synchronization point or by another CMD call.

A synchronization point is reached when any of the following events occur:

• The AO application requests the next input message with a GU call, assuming the program is defined as MODE=SINGLE on the TRANSACT macro statement.
• The program makes a CHKP call.
• The program makes a SYNC call.
• The program terminates.

Therefore, when IMS is restarted or resets to an earlier checkpoint, it is possible that a previously-issued command will be rescheduled for execution. An input message, generated by an AO exit routine and destined for an AO application, could be rescheduled although the resources are no longer held by the AO application. PCB status codes indicate more precisely which condition, or combination of conditions, exists.