SNAX/APC Application Programming Manual

Using the Application Program Interface
SNAX/APC Application Programming Manual—138786
1-10
Fault-Tolerant Programming
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General Conversational Verbs: If any verb other than those previously listed is in
progress when SNAX/APC receives a CANCEL system message, SNAX/APC
deactivates the session and replies to the cancelled IPC. SNAX/APC frees the
internal resources after finishing the processing of the verb.
Fault-Tolerant Programming
The SNAX/APC server can be configured to run as a NonStop process pair. If the
primary process fails, the backup SNAX/APC server process reinitializes the SNAX/XF,
SNAX/APN, or SNAX/CDF interface. The local TP is notified of the failure by
operating system error 201 on the current I/O request.
When the TP receives operating system error 201, its conversation and LU-LU session
are lost. The TP must issue a TP-READY request. If the TP initiated the previous
conversation, it can issue a new (MC)ALLOCATE request to start the conversation
again. In this way, even though the session itself has been interrupted, the integrity of
the operating environment remains intact, and the conversation can be restarted by the
application without operator intervention.
If the TP does issue a new TP-READY request, the TP receives the IPC return code
SERVICE-DENIED (PROCESS-RESET) or INVALID-RESOURCE-ID.
If a TP is configured to operate as a NonStop process pair and the primary TP in the pair
fails, the SNAX/APC server detects duplicate messages from the newly activated backup
and thus maintains session and conversation integrity. Duplicate messages from a newly
activated backup process are replied to with the same reply as was sent to the original
message.