Each CICS® region operating with CICS BAC support performs a CICS BAC startup procedure. This is initiated either by an entry for the startup processor in the CICS region PLTPI, or by a supplied transaction. The primary function of the CICS startup processor is to ensure that all resources reflect their states as known to CICS BAC by means of the control file. For example, if a CICS region named CICSHUR1 is not running, and a CICS BAC batch job issues a request to close FILEA on CICSHUR1, the batch request utility itself updates the CICS region control file with the new file state (CLOSED), then continues processing. If CICSHUR1 is then started before the batch job issues a CICS BAC request to re-open the file, the startup processor running during PLTPI processing recognizes that FILEA should remain closed, and issues the appropriate CICS commands to ensure FILEA stays closed.
The startup processor also starts the CICS BAC request server subtask. This ensures that the control file is allocated uniquely to the CICS region and prevents either the communication server or a batch request utility allocating and accessing the file directly.
When the startup processor has completed its work, it terminates, leaving the CICS BAC request server subtask running to handle batch request utility or communication server requests that are sent to the CICS region, and which require control file access. This is illustrated in Figure 1.
For information about initiating the CICS BAC startup processor, see Setting up and starting the CICS component