CPP - CICS Problem Program

Enhanced Definition

A CICS Problem Program (CPP) is an application program, typically written in COBOL, PL/I, or Assembler, designed to execute within an IBM CICS (Customer Information Control System) region. Its primary purpose is to perform specific business logic, data processing, or interactive tasks, usually as part of an online transaction processing (OLTP) system.

Key Characteristics

- Execution Environment: Runs under the control of the CICS Transaction Server, which provides an execution environment, resource management, and services.
- CICS API Usage: Interacts with CICS services (e.g., terminal I/O, file I/O, database access, program control) exclusively through EXEC CICS commands.
- Language Support: Commonly developed in traditional mainframe languages like COBOL, PL/I, and Assembler, though C/C++ and Java are also supported.
- Quasi-Reentrancy: Often designed to be quasi-reentrant, meaning that multiple CICS tasks can share a single copy of the program in memory, provided the program does not modify itself or its static working storage.
- Transaction-Oriented: Typically associated with a CICS transaction, processing a single logical unit of work from initiation to completion.
- Resource Management: CICS manages the allocation and deallocation of system resources (e.g., memory, files, databases) on behalf of the CPP.

Use Cases

- Online Transaction Processing (OLTP): Handling real-time business transactions such as customer inquiries, order entry, inventory updates, and financial transfers.
- Data Entry and Validation: Providing interactive screens for users to input data, with immediate validation and feedback.
- Customer Service Applications: Enabling call center agents to access and update customer information, service requests, and account details.
- Integration with Databases: Accessing and manipulating data in mainframe databases like DB2 (via DB2 DLI or SQL), IMS DB, or VSAM files.

Related Concepts

A CPP is the core executable component of a CICS Transaction, which is defined in the Program Control Table (PCT) and specifies the program to be executed. It runs within a CICS Region, which is the operating environment providing the necessary services and resources. CPPs often interact with CICS System Services like File Control, Program Control, Terminal Control, and Task Control, and access data stored in VSAM, DB2, or IMS DB/DC via CICS-provided interfaces. The CICS region itself is started and managed using JCL.

Best Practices:

Design for Quasi-Reentrancy: Ensure programs are quasi-reentrant by avoiding modification of static storage and using WORKING-STORAGE SECTION for task-specific data, to maximize resource sharing and performance.
Robust Error Handling: Implement comprehensive error handling using EXEC CICS HANDLE CONDITION or checking RESP and RESP2 codes after CICS commands to gracefully manage exceptions and prevent abnormal terminations.
Efficient Resource Management: Acquire and release CICS resources (e.g., ENQs, temporary storage, TSQs) promptly to avoid contention, deadlocks, and resource exhaustion.
Performance Optimization: Minimize I/O operations, optimize database calls, and avoid unnecessary processing loops to ensure fast transaction response times.
Security Considerations: Adhere to CICS security best practices, using RACF or equivalent to authorize access to transactions, programs, and resources, and validate all user input.