Channel message retry exit program

The channel message-retry exit is called when an attempt to open the target queue is unsuccessful. We can use the exit to determine under which circumstances to retry, how many times to retry, and how frequently.

This exit is also called at the receiving end of the channel at MCA initiation and termination.

The channel message-retry exit is passed an agent buffer containing the transmission queue header, MQXQH, and the application message text as retrieved from the queue. The format of MQXQH is given in Overview for MQXQH.

The exit is invoked for all reason codes; the exit determines for which reason codes it wants the MCA to retry, for how many times, and at what intervals. (The value of the message-retry count set when the channel was defined is passed to the exit in the MQCD, but the exit can ignore this value.)

The MsgRetryCount field in MQCXP is incremented by the MCA each time the exit is invoked, and the exit returns either MQXCC_OK with the wait time contained in the MsgRetryInterval field of MQCXP, or MQXCC_SUPPRESS_FUNCTION. Retries continue indefinitely until the exit returns MQXCC_SUPPRESS_FUNCTION in the ExitResponse field of MQCXP. See MQCXP for information about the action taken by the MCA for these completion codes.

If all the retries are unsuccessful, the message is written to the dead-letter queue. If there is no dead-letter queue available, the channel stops.

If we do not define a message-retry exit for a channel and a failure occurs that is likely to be temporary, for example MQRC_Q_FULL, the MCA uses the message-retry count and message-retry intervals set when the channel was defined. If the failure is of a more permanent nature and we have not defined an exit program to handle it, the message is written to the dead-letter queue.