Implementing and Managing APPC Protected Conversations

68 Implementing and Managing APPC Protected Conversations

5.1 Description

For IMS-to-IMS APPC protected conversations we wanted to test the interaction between two

IMS application programs running in two different IMS systems. We wanted to verify actions

taken for normal processing and for failure scenarios. IMS requires APPC/MVS and MVS

Recoverable Resource Management Services to enable APPC protected conversations.

APPC/IMS is an APPC/MVS scheduler that supports implicit and explicit APPC application

programming. An implicit application program uses IMS DL/I message calls for the

communication interface and APPC/IMS provides the interaction with APPC. This means that

existing IMS applications are able to participate in an APPC environment without

modification.

An explicit application uses APPC calls for direct interaction with an APPC partner program.

IMS supports the following explicit application programs:

򐂰 Modified Standard

򐂰 CPI-C Driven

The Modified Standard application program uses a combination of IMS DL/I message calls

and the APPC calls to communicate directly with APPC/MVS as shown in Figure 5-1.

Figure 5-1 Sample of modified standard application program

An IMS Modified Standard application program can initiate an APPC Protected Conversation;

however, APPC/IMS has to initiate the coordinated syncpoint process. When the IMS

Modified Standard application program Deallocates the protected conversation, the APPC

conversation is in a Defer-Deallocate state. The IMS syncpoint manager recognizes that

APPC/MVS has expressed interest in the Context and Unit of Recovery associated with the

GU I/O PCB

Allocate

Send

Send

Receive

Send

Deallocate

Access IMS DB

Access DB2

ISRT I/O PCB

Modified Standard

Chapter 5. Sample scenario: IMS to IMS 69

IMS Modified Standard application program. At the start of the IMS syncpoint process IMS

will issue the ATRCMIT call to RRS to initiate the coordinated syncpoint process. The Partner

Program will be notified to issue a Commit when it Receives Take_Commit_Deallocate.

RRS is the syncpoint coordinator that drives Two-Phase commit flows to IMS and to

APPC/MVS. APPC/MVS provides the Communication Resource Manager support to flow

Two-Phase commit protocols using the protected conversation as shown in Figure 5-2.

Figure 5-2 Syncpoint flow

IMS only schedules a CPI-C Driven application program and the application program has to

issue the X/OPEN CPI-C calls or the APPC/MVS-specific API calls to communicate with the

APPC partner program, as illustrated in Figure 5-3 on page 70.

APPC/IMS

ATRCMIT

IMS Modified

Application

GU

Allocate

Send

Send

Receive

Deallocate

ISRT

APPC Partner

Accept

Receive

Receive

Send

Receive

Take-Commit_Deallocate

SRRCMIT

Deallocate

APPC/MVS

RRS

Syncpoint Flows

70 Implementing and Managing APPC Protected Conversations

Figure 5-3 CPI-C Driver application flow

An IMS CPI-C Driven application program uses SRRCMIT to participate in an APPC

protected conversation coordinated syncpoint process. When the IMS CPI-C Driven

application program receives Take_Commit on a Receive verb, it uses SRRCMIT to activate

its syncpoint. In the case of Take_Commit_Deallocate the IMS CPI-C Driven application

program issues the SRRCMIT call and Deallocates the protected conversation.

Our sample IMS PL/I application programs consisted of the following:

IMSH IMSI

IMS1TR1

Modified

IMS2IMP Implicit

IMS1TR2

Modified

IMS2EXP Explicit

Note: To re-create the environment we used:

Refer to Appendix A, “Installation definitions for Protected Conversation exploiters” on

page 113 for detailed installation instructions required to set up the sample systems used

throughout this book.

Refer to Appendix B, “APPC exploiter sample source code” on page 155 for the source

code used in our examples.

CPI

CPI

-

-

C Driven

C Driven

Accept

Receive

Receive

Access IMS DB / DB2

Send

Receive

Take_Commit

SRRCMIT

…

Receive

Take_Commit_Deallocate

SRRCMIT

Deallocate