Background to CICS-z/OS Communications Server error handling

Errors detected by CICS-z/OS Communications Server LU control are queued for handling by a special task, the CICS® node error handler (transaction CSNE).

CICS uses the same task for some housekeeping work, such as sending “good morning” messages, and logging session starts and ends, which are not errors.

In a few cases, exceptions signaled to CICS by z/OS® Communications Server are not treated as errors, and are not passed to the node error handler. For example, CICS often sends a z/OS Communications Server BID command as part of automatic transaction initiation. Rejection of the BID with exception code ‘0813' (wait) is a standard response, and CICS handles the retry in terminal control without calling this an error. In the rest of this description, only the errors are considered.

The CSNE task runs as a “background” task, meaning that it is not associated with any one CICS terminal. At any time, there is at most one such task, working on the single node error queue.

All node errors on the queue are analyzed in turn by a table-driven, CICS-supplied program called DFHZNAC (node abnormal condition program). It is not intended that you should ever modify this.

DFHZNAC links to a module called DFHZNEP (if present in the CICS system) when processing most node errors. (It does not link to DFHZNEP for errors that are not related to a specific node—for example, those caused by a z/OS Communications Server shutdown.) The interface for this link is described in When an abnormal condition occurs. This formal DFHZNAC to DFHZNEP interface gives you the opportunity to supply your own code to analyze error conditions, change default actions by setting various “action flags”, and take additional actions specific to your applications.

CICS supplies a pregenerated default DFHZNEP, which sets the “print TCTTE” action flag if a z/OS Communications Server storage problem is detected, and returns control to DFHZNAC. Because it leaves all other action flags unchanged, DFHZNAC's default actions are not otherwise affected. (DFHZNAC's default actions for different error conditions are listed in Default actions of the node abnormal condition program.)