Error handling by the CICS bridge

Errors detected by the CICS bridge cause the bridge to:

• Back out the unit of work
• Copy request messages to the dead-letter queue
• Send an error reply message back to the client if a reply-to queue is available
• Write a CSQC7nn message to the CICS CSMQ transient data queue or issue a transaction abend. Where it is possible to put a message on the reply-to queue, the message will contain this abend code

Any further request messages in the same unit of work are removed from the request queue and copied to the dead-letter queue, either during error processing for this unit of work or at the next initialization of the monitor. No further error messages are generated.

Unexpected messages are removed from the request queue during monitor initialization and put on the dead-letter queue, passing all context. No error reply messages are generated.

If sending a reply message fails, the CICS Bridge puts the reply on the dead-letter queue, passing identity context from the CICS bridge request queue. A unit of work is not backed out if the reply message is successfully put on the dead-letter queue. Failure to put a reply message on the dead-letter queue is treated as a request error, and the unit of work is backed out.

If the CICS bridge fails to put a request message on the dead-letter queue, the CICS bridge task abends and leaves the CICS bridge monitor to process the error. If the monitor fails to copy the request to the dead-letter queue, the monitor abends.

Failure to put an error reply is ignored by the CICS bridge. The request message has already been copied to the dead-letter queue and the unit of work has been backed out by WebSphere MQ.

Figure 18 shows what happens when an error occurs in a unit of work.

Figure 18. User program abends (only program in the unit of work)

In this figure:

• The client application sends a request message to run a CICS program named P1. The queue manager used by the client receives the message.

The monitor task browses the request queue awaiting the arrival of a message. When a message arrives, it:

• Gets the request message with browse
• Checks for any problems with the request message
• Starts a CICS bridge task
• Continues browsing the request queue

The CICS bridge task

• Gets the request message from the request queue under syncpoint control
• Takes the information in the request message and builds a COMMAREA for program P1
• Issues an EXEC CICS LINK call to program P1
• Waits for program P1 to complete

When these tasks are complete, the user program abends.

The CICS bridge task abend handler is driven, which:

• Issues an EXEC CICS SYNCPOINT ROLLBACK which:
  • Backs out all the changes made by P1
  • Reinstates the request message on the request queue
• Gets the request message a second time from the request queue, again under syncpoint control
• Copies the request to the dead-letter queue
• Puts an error reply to the reply-to queue

If the request message includes the name of a reply-to queue:

• Writes a CSQC7nn message to the CICS CSMT transient data queue