DFHSKE (subtask exit program)

When the subtask manager DFHSKM, executing on behalf of a CICS task, decides that a subtask is to be started, it attaches a CICS task using the DFHKC ATTACH macro and specifying the entry point of DFHSKCNA. This CICS task attaches the subtask and waits for subtask completion by means of the ECB parameter coded in the ATTACH macro.

The ATTACH macro specifies an entry point in DFHSIP (known to MVS by an IDENTIFY macro issued in DFHSIP). DFHSIP then branches to the entry point of DFHSKE, whose address is in the subtask control area.

The subtask reverses the order of the in-progress queue to service requests on a first-come, first-served basis. It then loops round the in-progress queue and, for each WQE, branches to the program specified in the WQE (the SK exit routine).

The exit routine returns control to DFHSKE, either indicating that the exit routine has completed by issuing a DFHSK CTYPE=RETURN macro or requesting that execution of the SK exit is suspended until an ECB specified by the exit is posted by some component of the operating system.

When a return is requested, the ECB in the WQE is posted, causing the dispatcher domain to resume the CICS task that was waiting for the SK exit to be complete. When a wait is requested, the WQE is added to the waiting queue, which is processed later.

When all WQEs in the in-progress queue have been processed, DFHSKE examines the waiting queue. If any WQEs are on this queue, their ECB addresses are inserted into an operating-system multiple-wait queue. The subtask work ECB (posted when a WQE is added to the work queue) is put at the top of this multiple-wait list. An operating-system multiple-wait is then issued.

When the subtask regains control, an ECB has been posted. This can be because more work has arrived or because an ECB belonging to an exit routine has been posted.

The WQEs on the waiting queue are scanned, and those whose ECB has been posted are moved to the in-progress queue, with a flag on indicating that an SK exit routine is to be resumed.

Control returns to the beginning of this program which examines the work queue and proceeds as described earlier.

DFHSKE handles program checks and operating system abends. If an abend exit is driven when processing a WQE, that WQE is blamed and processing of it terminates. The CICS task requesting the processing is informed of the problem.

If an abend exit is driven when a WQE is not being processed, it is assumed to be a problem in the subtasking program. The abend is handled, and a count of failures is increased. When a threshold is reached, the subtask terminates.

The MVS exits are ESTAE and SPIE.

For normal termination, DFHSKE loops, processing WQEs and waiting when there is no work to do. The subtask checks a flag in the subtask control area to see if it has been requested to terminate. If the flag is set, the subtask terminates, indicating normal termination by setting a response code in the subtask control area for the attacher, DFHSKC.

Abnormal termination may occur when the error threshold has been reached. The subtask terminates, but sets an error return code in the subtask control area for the attacher to see. The attacher, DFHSKC, then cleans up any outstanding WQEs on the subtask queues.