SNAX/APC Application Programming Manual

Using the Application Program Interface
SNAX/APC Application Programming Manual—138786
1-9
Error Handling
IPC; the file system discards the reply. Thus, a CANCEL message cancels the entire
IPC, not just the single verb being processed when the message arrives. Every response
to every verb in the outstanding IPC is lost when that IPC is cancelled.
Support for CANCEL messages must be specifically enabled by specifying the
CANCELSUPPORT startup parameter. If the CANCELSUPPORT parameter is not
enabled, SNAX/APC ignores all CANCEL system messages except for those from the
SNAX/APC Dispatcher process. In this case the outstanding DISPATCHER-READY
request is cancelled.
If the CANCELSUPPORT parameter is enabled, SNAX/APC handles CANCEL system
messages that come from application programs. The particular processing performed by
SNAX/APC depends on the particular verb that is being process when the CANCEL
message arrives.
In all cases (except operator control verbs), when a CANCEL system message is
received during an existing conversation, that conversation is terminated.with a
DEALLOCATE (ABEND) verb or the underlying session is terminated with an
UNBIND. Following a CANCEL system message, the application must issue a new TP-
READY verb
When SNAX/APC receives a CANCEL message, SNAX/APC determines what to do
based on which verb is currently being processed. The following list summarizes that
CANCEL processing action that is taken for each verb.
•
ACTIVATE-SESSION and DEACTIVATE-SESSION verbs: If an ACTIVATE-
SESSION or DEACTIVATE-SESSION verb is in progress when SNAX/APC
receives a CANCEL system message, SNAX/APC replies to the cancelled IPC
immediately. The verb is allowed to finish normally. After SNAX/APC finishes
processing the verb, SNAX/APC deallocates the conversation and frees the internal
resources.
•
ALLOCATE, and MC-ALLOCATE verbs: If an ALLOCATE or MC-ALLOCATE
verb is in progress when SNAX/APC receives a CANCEL system message,
SNAX/APC replies to the cancelled IPC immediately. The verb is allowed to finish
normally. After SNAX/APC finishes processing the verb, SNAX/APC deallocates
the conversation and frees the internal resources.
•
DEALLOCATE and MC-DEALLOCATE verbs: If a DEALLOCATE or MC-
DEALLOCATE verb is in progress when SNAX/APC receives a CANCEL system
message, SNAX/APC replies to the cancelled IPC immediately. The verb is allowed
to finish normally unless SNAX/APC is waiting for a response from the remote TP.
In this case, SNAX/APC deactivates the session.
•
TP-END Verb: If a TP-END verb is in progress when SNAX/APC receives a
CANCEL system message, the TP-END verb is allowed to finish normally.
•
TP-READY Verb: If a TP-READY verb is in progress when SNAX/APC receives a
CANCEL system message, SNAX/APC replies to the cancelled IPC immediately
and removes the TP-READY request from its internal queues. In the case of a
remote TP-READY, that TP-READY is no longer available to service incoming
attaches.