CICS Runtime Concepts

This chater contas the following topics:

Purpose

CICS Runtime Goals

CICS Runtime Architecture

System Administration Perspective

CICS Runtime Cobol

CICS Runtime C

Purpose

There are different approaches to migrating CICS applications to a UNIX/Linux environment. The purpose of this section is to give an understanding not only of what CICS Runtime is and what it does, but also what it is not and what it does not do. Particularly the aim is to explain that CICS Runtime is not an emulation of the CICS application environment on a UNIX/Linux system. CICS Runtime keeps the application logic contained in the COBOL programs but is totally compatible with the Tuxedo client/server architecture for the execution of that logic. CICS Runtime provides a middleware between the CICS coding in the programs and the Tuxedo OLTP system, UNIX\Linux OS and Oracle database responsible for executing transactions and providing persistence.

CICS Runtime Goals

The first aim of CICS Runtime is to preserve the considerable investment already made in CICS applications by allowing migrated programs to run unchanged (except for a syntactic adaptation) by using an API emulation runtime on top of native Tuxedo features. This means the impact of migration is limited on:

•	3270 screens and BMS management; there is no impact on application end-users.

•	EXEC CICS calls; there is no impact on developers.

At the same time, CICS Runtime is run entirely on a robust production environment based on Tuxedo that protects and guarantees application functionality.

In fact, CICS Runtime gives customers the benefits of Tuxedo distributed architecture without impacting application APIs. It allows the key strengths of Tuxedo to be leveraged and allows routes to the future including SOA to be opened.

CICS Runtime Architecture

Software Development Perspective

The following diagram shows the software bricks used to create the application environment on the migration source and target platforms.

Figure 2‑1 Migration Software Environments

Except for the top and bottom bricks, there is little else that changes for the software developer.

Programmatic Interface

CICS Runtime offers a library of CICS API reproducing the functionality of the z/OS CICS API and offering equivalent services to the migrated CICS applications, and in addition it offers BMS capabilities with support for 3270 screens.

In a CICS application on a z/OS platform all interactions with resources are done thru the EXEC CICS API (with the exception of DB2).

The CICS Preprocessor (on Z/OS) transforms these EXEC CICS into calls to the CICS library.

On the target platform, the same philosophy is used; an CICS Runtime Preprocessor (an CICS Runtime compile-time tool) transforms these EXEC CICS into calls to the CICS Runtime library.

For the software developer, there is little that changes. The CICS Runtime preprocessor automatically changes the CICS API that is called. There are some limitations in the command that can be used; these are described in CICS Commands and Parameters Coverage.

System Administration Perspective

For a software administrator, there is little that remains the same. There are the same applications to be executed and end-users still access applications using the same 3270 terminals. Apart from that, everything else is different and relies on a native Tuxedo architecture to manage transactions with the aid of CICS Runtime to provide an API between the COBOL programs and Tuxedo.

Figure 2‑2 CICS Runtime Architecture

CICS Runtime provides the run-time support to allow converted CICS applications to run in a robust production ready environment based on TUXEDO /T, while offering applications functionally equivalent behavior.

In term of deployment, the system is distributable on one or multiple machines in a single TUXEDO domain, or several domains communicating through a TUXEDO domain.

In term of administration, the administration is native TUXEDO, with all tuxedo administration tools being normally usable, plus a few administration tables for CICS only concepts, like terminal definitions, and Transaction - First Program table.

z/OS CICS Concepts in a CICS Runtime Environment

Developers and administrators used to working in a z/OS CICS environment naturally want to know how concepts familiar on the source platform are implemented on the target platform.

Table 2‑1 gives an overview of how the source platform notions have an equivalent on the target platform.

 

Table 2‑1 Source Platform Notions

z/OS CICS	CICS Runtime
CICS Session	TUXEDO Session
Transaction Transaction First Program	Tuxedo Service Program associated with service
L.U.W. SYNCPOINT [ROLLBACK]	Transaction tpcommit() / tpabort()
COBOL Program	COBOL Program
CALL "SUBPGMX"	CALL "SUBPGMX"
EXEC CICS LINK local	Local call with memory stacking and isolation.
DPL (Distributed Program Link)	Tpcall to a tuxedo service
Conversational Programs Pseudo-Conversational	tpconnect()/tpsend()/tpreceive() Request/Response tpcall()/tpreply()
COMMAREA (State Info/Context)	Tuxedo is stateless, context passed through buffers

Administrative Tasks

Most of this guide describes how to administer resources for CICS application running with CICS Runtime on a Tuxedo system. CICS Runtime uses Tuxedo natively with the addition of a few extra resource files and servers.

This provides all the robust characteristics of Tuxedo including:

•	Load balancing, priority management, Dynamic routing,

•	Supervision, automatic restart of servers,

•	Transparent distribution on multiple machines,

•	Server migration from one machine to another,

•	The distribution of the load of a new machine is very simple.

•	Declare the machine in the UBBCONFIG

•	Launch a few servers offering transactions on this machine

CICS Runtime Cobol

ART CICS Runtime runs in Cobol Micro Focus or Cobol IT.

Micro Focus Cobol is still a reference. The Micro Focus features not supported by Cobol IT cannot be included in this product.

To keep compatible with ART CICS runtime:

•	Cobol IT should be version 3.3.12 and later.

•	CICS programs should be compiled with -fthread-safe option when using COBOL-IT.

•	CICS programs are required to be recompiled if once compiled by Cobol IT in previous version before.

BDB files can be used with Cobol IT only in XA mode.

Subprogram Calls and Link Level in Micro Focus Cobol

Subprogram working storage is initialized when the subprogram is called for the first time in a link level. After the return link, the working storage is initialized again when the subprogram is called for the first time in a new link at the same level.

For example:

LINK (level 1)+

SP1 first call -(working initialized)

RETURN

LINK (lev 1)

SP1 first call -(working initialized)

Working storage is not initialized when subprogram is called in lower link levels.

For example:

LINK (lev 1)

SP1 first call -(working initialized)

LINK (Lev 2)

SP1 first call -(working not initialized)

This behavior is specific to Micro Focus Cobol and not applicable to Cobol IT. On Cobol IT, there is no initialization no matter in which links level subprograms are called.

CICS Runtime C

ART CICS Runtime C support is still COBOL depended. All CICS C programs are required to be complied with COBOL/cob complier and are executed in COBOL runtime. Therefore, COBOL installer is mandatory and currently only Microfocus COBOL is supported.

For more information about CICS Runtime C, please refer to CICS Runtime C Program Support.