Control blocks

IRC uses two levels of control blocks:

  1. A CICS/MRO terminal control layer
  2. An interregion SVC layer interfaced by the DFHIR macro.

Terminal control layer

The CICS/MRO terminal control layer is shown in Figure 60.

This layer uses the cross-region block (CRB). This is a global (that is, one per CICS® system) block that is created in the CICS dynamic storage area above the 16MB line (the ECDSA) when IRC is initialized, and provides information to communicate with the IRC SVC. See Figure 61.

Figure 60. CICS/MRO terminal control layer of control blocks
 This is the first part of a technical drawing showing the CICS/MRO terminal control layer of control blocks.
 This is the second part of a technical drawing showing the CICS/MRO terminal control layer of control blocks.
Notes:
  1. The first TCTTE on the chain is not necessarily the TCTTE for the task’s primary terminal.
  2. A task has allocated MRO sessions to other systems.
  3. TCTTEs are described more fully in Terminal control.
  4. Primary TCTTEs relate to Receive sessions, and secondary TCTTEs relate to Send sessions.
  5. TCSEVC1 is the label on the address of the TCTTE of the first primary session. TCSEVC2 is that of the first secondary session.
  6. The primary and secondary sessions each have sets of TCTTEs. These are found by using the DFHTC CTYPE=LOCATE macro.
  7. A TCTTE is allocated for a surrogate session in transaction routing.
Figure 61. Cross-region block (CRB)
 This is a technical drawing showing the structure of the cross-region block (CRB).

DFHIR layer

The interregion SVC layer interfaced by the DFHIR macro is shown in Figure 62.

Figure 62. Interregion SVC layer of control blocks interfaced by the DFHIR macro
 This is a technical drawing showing the structure of the interregion SVC layer of control blocks interfaced by the DFHIR macro.

This layer uses the following control blocks, which, unless otherwise stated, reside in subpool 241 in MVS™ storage:

Terminal control layer and DFHIR layer

Figure 63 shows the control blocks that are accessed by both the terminal control layer and the DFHIR layer. Figure 64 shows the location of these control blocks in MVS virtual storage.

Figure 63. Control blocks accessed by CICS/MRO terminal-control layer of control blocks and by interregion SVC layer of control blocks
 This is a technical drawing showing the control blocks accessed by both the terminal control layer and the DFHIR layer.

The following blocks are used by both the terminal control layer and the DFHIR layer. These blocks are allocated at logon time within a single MVS GETMAIN, and, unless otherwise stated, reside in subpool 251 of MVS storage.

Subsystem logon control block (SLCB)
The SLCB is used by the IRC SVC and region and contains the master ECB, posted when the region has IRC activity. It is pointed to by the CRB and LCB.
Subsystem connection address control block (SCACB)
The SCACB contains entries allowing the addressing of SCCBs from the SLCB.
Subsystem connection control block (SCCB)
The SCCB is created for each IRC send-receive session, and is allocated at logon. It contains the ECB, posted when input for the session is available.
Note:
There is a one-to-one relationship between TCTTEs and SCCBs when they are in use.

Figure 64. Location of control blocks in MVS virtual storage
 This is a technical drawing showing the location of the control blocks in MVS virtual storage.

MRO ECB summary

The following is a summary of the MRO event control blocks (ECBs):

Name           Location    Who waits                  Who posts
Dependent ECB    SCCB    Application (TC WAIT)          DFHIRP
LOGON ECB        SLCB    CICS (KCP, Op sys WAIT list)   DFHIRP
Link ECB         LCB     DFHIRP (Op sys WAIT)           DFHIRP
Work queue ECB   QUEUE   CSNC transaction               DFHIRP
                                                        DFHZIS2
                                                        DFHZLOC

See the CICS Data Areas manual for a detailed description of the CICS control blocks.

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