Design overview

When the recommended initialization routine DFHSSIN is specified, the CICS® subsystem is initialized during the master scheduler initialization phase of the MVS™ IPL. The CICS-specific subsystem parameters are read from SYS1.PARMLIB, and the subsystem vector table is created. The supporting subsystem function routines are loaded into common memory and their addresses are stored into the subsystem vector table. If everything is successful, the CICS subsystem is made active by storing the address of the subsystem vector table in the subsystem communication table.

Console message handling

At startup, a CICS region that supports console message handling notifies the CICS subsystem of its existence, by using the CICS SVC to issue a subsystem interface call for the ‘generic connect’ function with a CONNECT subfunction. The subsystem notes the creation of the new region and, if this is the first such CICS region to become active, invokes a service of MVS console support called "subsystem console message broadcasting". The message broadcasting service causes all subsequent console messages to be broadcast to all subsystems that have expressed an interest in receiving them, including the CICS subsystem. This MVS service can also be activated by other products, for example, NetView®.

If the message broadcasting service has been activated, either by CICS or by another product, the CICS subsystem examines all messages issued by WTO macros in any address space, but it intercepts and modifies only the following:

As each TCB terminates, it issues an ‘end of task’ subsystem call, which is broadcast to all active subsystems. Likewise, as each address space terminates, it issues an ‘end of memory’ subsystem call, which is also broadcast to all active subsystems. When it receives either of these calls, the CICS subsystem first calls the end-of-memory routine in DFHIRP; then, if the terminating address space is known by the subsystem, it invokes the ‘generic connect’ function with a DISCONNECT subfunction.

The DISCONNECT subfunction notes the termination of the CICS address space and, if this is the last CICS containing console message handling support to terminate, notifies the "subsystem console message broadcasting" support that the CICS subsystem is no longer interested in receiving broadcast console messages. Nevertheless, if another product has kept console message broadcasting active, the CICS subsystem continues to reformat messages from CICS regions that do not have console message handling support.

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