Using API mode

API mode is the most generalized way to use QUICKSTART. It supports a wider range of languages, access methods, and DBMSs than other QUICKSTART checkpointing modes. Although API mode requires source code modification (Transparent mode, MVS Checkpoint mode, and IMS Extended Checkpoint/Restart Replacement mode do not), it supports programming languages and DBMSs that the other three modes do not.

The concept of API mode is that the application program must contain a few Application Programming Interface (API) CALLs to the QUICKSTART for MVS product to perform the checkpointing and restarting activities. In addition, depending on the programming language used, the application program may be required to issue API CALLs for sequential file I/O requests. Finally, some control blocks in Working Storage are needed to delimit the Checkpoint Area. Since the application issues the API CALLs, the application is in complete control of when these activities take place. This provides for maximum flexibility in accommodating complex checkpoint/restart requirements.

This section describes the application program modifications and design considerations which are necessary to realize the full benefits of the API Mode. While examples presented in this section are for the COBOL programming language, all concepts presented are applicable to all programming languages. Supplemental sections are provided to describe programming language variances and examples, for the programming languages PL/I, Assembler, and IEF.

You must continue with COBOL Programming language supplement to get a base knowledge of the inner workings of QUICKSTART checkpointing, even if QUICKSTART Transparent Mode is to be used ultimately.

If you are using a programming language other than COBOL, see the appropriate section for language-specific information:

See Application-requirements-for-restartability for specific information regarding designing restartable programs and the Logical Unit of Work (LUW), which discusses different types of application LUWs, and techniques to make these applications restartable.

See also Testing-restartable-code for detailed information regarding testing the application program's restartability.

This section contains the following topics:

 

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