MainframeMaster

COBOL DISABLE Statement

Master the DISABLE statement for controlling communication channels, terminal devices, and system resources in COBOL mainframe applications.

Overview

The DISABLE statement in COBOL is used to deactivate communication channels, terminal devices, or other system resources in mainframe environments. This statement is particularly important in Message Control System (MCS) applications where you need to control the flow of messages and manage terminal access dynamically.

DISABLE provides a mechanism for temporarily or permanently stopping the processing of messages through specific terminals or communication paths. This is essential for maintenance procedures, error handling, controlled shutdowns, and resource management in complex mainframe applications.

The statement works in conjunction with the ENABLE statement, allowing programs to dynamically control system resources based on application logic, system conditions, or administrative requirements. Understanding DISABLE is crucial for developing robust mainframe applications that can handle various operational scenarios.

Basic Syntax and Usage

The basic syntax of the DISABLE statement varies depending on the specific implementation and target system:

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DISABLE terminal-name
    [WITH KEY identifier-1]
    [INVALID KEY imperative-statement-1]
    [NOT INVALID KEY imperative-statement-2]
    [END-DISABLE].

The terminal-name specifies the communication resource to be disabled. The optional WITH KEY clause provides additional identification or security information.

Simple Terminal Disable

Here's a basic example of disabling a terminal:

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DISABLE TERMINAL-01
    INVALID KEY 
        DISPLAY "Unable to disable TERMINAL-01"
    NOT INVALID KEY
        DISPLAY "TERMINAL-01 successfully disabled"
END-DISABLE.

This example attempts to disable TERMINAL-01 and provides appropriate feedback based on the success or failure of the operation.

Communication Control Examples

Message Queue Management

DISABLE is commonly used in message queue management to control message flow:

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WORKING-STORAGE SECTION.
01 WS-TERMINAL-STATUS   PIC X(2).
01 WS-QUEUE-NAME        PIC X(8) VALUE "MSGQ001".
 
PROCEDURE DIVISION.
DISABLE-QUEUE.
    DISABLE WS-QUEUE-NAME
        INVALID KEY
            MOVE "ER" TO WS-TERMINAL-STATUS
            DISPLAY "Queue disable failed: " WS-QUEUE-NAME
        NOT INVALID KEY
            MOVE "OK" TO WS-TERMINAL-STATUS
            DISPLAY "Queue disabled: " WS-QUEUE-NAME
    END-DISABLE.

This example demonstrates disabling a message queue and tracking the operation status for error handling.

Conditional Terminal Control

You can implement conditional logic to disable terminals based on specific criteria:

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WORKING-STORAGE SECTION.
01 WS-MAINTENANCE-MODE  PIC X(1) VALUE "N".
01 WS-TERMINAL-TABLE.
    05 WS-TERMINAL OCCURS 10 TIMES.
        10 WS-TERM-ID   PIC X(8).
        10 WS-TERM-TYPE PIC X(1).
 
PROCEDURE DIVISION.
MAINTENANCE-DISABLE.
    IF WS-MAINTENANCE-MODE = "Y"
        PERFORM VARYING WS-INDEX FROM 1 BY 1
            UNTIL WS-INDEX > 10
            IF WS-TERM-TYPE(WS-INDEX) = "U"
                DISABLE WS-TERM-ID(WS-INDEX)
                    INVALID KEY
                        DISPLAY "Failed to disable user terminal"
                    NOT INVALID KEY
                        DISPLAY "User terminal disabled for maintenance"
                END-DISABLE
            END-IF
        END-PERFORM
    END-IF.

This routine disables user terminals during maintenance mode while potentially leaving administrative terminals active.

Advanced Control Techniques

Security-Based Disabling

DISABLE can be used with security keys for controlled access management:

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WORKING-STORAGE SECTION.
01 WS-SECURITY-KEY      PIC X(8) VALUE "ADMIN001".
01 WS-TERMINAL-ID       PIC X(8).
01 WS-DISABLE-REASON    PIC X(50).
 
PROCEDURE DIVISION.
SECURE-DISABLE.
    MOVE "TERM005" TO WS-TERMINAL-ID
    MOVE "Security violation detected" TO WS-DISABLE-REASON
    
    DISABLE WS-TERMINAL-ID
        WITH KEY WS-SECURITY-KEY
        INVALID KEY
            DISPLAY "Unauthorized disable attempt"
            PERFORM LOG-SECURITY-EVENT
        NOT INVALID KEY
            DISPLAY "Terminal secured: " WS-DISABLE-REASON
            PERFORM LOG-DISABLE-EVENT
    END-DISABLE.

This example shows how to use security keys with DISABLE operations and implement appropriate logging.

Batch Terminal Management

For managing multiple terminals efficiently:

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WORKING-STORAGE SECTION.
01 WS-TERMINAL-LIST.
    05 WS-TERM-COUNT    PIC 9(2) VALUE 5.
    05 WS-TERMINALS     PIC X(8) OCCURS 10 TIMES.
01 WS-DISABLE-COUNT     PIC 9(2) VALUE ZERO.
01 WS-ERROR-COUNT       PIC 9(2) VALUE ZERO.
 
PROCEDURE DIVISION.
BATCH-DISABLE.
    PERFORM VARYING WS-INDEX FROM 1 BY 1
        UNTIL WS-INDEX > WS-TERM-COUNT
        
        DISABLE WS-TERMINALS(WS-INDEX)
            INVALID KEY
                ADD 1 TO WS-ERROR-COUNT
                DISPLAY "Error disabling: " 
                        WS-TERMINALS(WS-INDEX)
            NOT INVALID KEY
                ADD 1 TO WS-DISABLE-COUNT
                DISPLAY "Disabled: " WS-TERMINALS(WS-INDEX)
        END-DISABLE
    END-PERFORM
    
    DISPLAY "Summary: " WS-DISABLE-COUNT " disabled, "
            WS-ERROR-COUNT " errors".

This batch processing approach allows efficient management of multiple terminals with comprehensive error tracking.

Error Handling and Recovery

Comprehensive Error Management

Implementing robust error handling for DISABLE operations:

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WORKING-STORAGE SECTION.
01 WS-ERROR-HANDLING.
    05 WS-RETRY-COUNT   PIC 9(2) VALUE ZERO.
    05 WS-MAX-RETRIES   PIC 9(2) VALUE 3.
    05 WS-WAIT-TIME     PIC 9(3) VALUE 100.
 
PROCEDURE DIVISION.
DISABLE-WITH-RETRY.
    MOVE ZERO TO WS-RETRY-COUNT
    
    PERFORM UNTIL WS-RETRY-COUNT > WS-MAX-RETRIES
        DISABLE WS-TARGET-TERMINAL
            INVALID KEY
                ADD 1 TO WS-RETRY-COUNT
                IF WS-RETRY-COUNT <= WS-MAX-RETRIES
                    DISPLAY "Disable failed, retry " WS-RETRY-COUNT
                    CALL "WAIT" USING WS-WAIT-TIME
                ELSE
                    DISPLAY "Disable operation failed permanently"
                    PERFORM ESCALATE-ERROR
                END-IF
            NOT INVALID KEY
                DISPLAY "Terminal disabled successfully"
                MOVE 999 TO WS-RETRY-COUNT
        END-DISABLE
    END-PERFORM.

This retry mechanism provides resilience against temporary system issues.

Status Monitoring

Implementing status monitoring for disabled resources:

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WORKING-STORAGE SECTION.
01 WS-TERMINAL-STATUS-TABLE.
    05 WS-STATUS-ENTRY OCCURS 50 TIMES.
        10 WS-TERM-NAME     PIC X(8).
        10 WS-TERM-STATUS   PIC X(1).
        10 WS-DISABLE-TIME  PIC X(14).
 
PROCEDURE DIVISION.
UPDATE-STATUS-TABLE.
    ACCEPT WS-CURRENT-TIME FROM DATE-TIME
    
    PERFORM VARYING WS-INDEX FROM 1 BY 1
        UNTIL WS-INDEX > 50
        IF WS-TERM-NAME(WS-INDEX) = WS-TARGET-TERMINAL
            MOVE "D" TO WS-TERM-STATUS(WS-INDEX)
            MOVE WS-CURRENT-TIME TO WS-DISABLE-TIME(WS-INDEX)
            EXIT PERFORM
        END-IF
    END-PERFORM.

This status tracking helps maintain awareness of which resources are disabled and when.

Best Practices and Guidelines

Operational Guidelines

Follow these best practices when using DISABLE:

  • Always implement proper error handling with INVALID KEY clauses
  • Maintain logs of disable operations for audit and troubleshooting
  • Use descriptive terminal names for better maintainability
  • Implement timeout mechanisms for disable operations
  • Provide user feedback for disable operations
  • Test disable/enable cycles thoroughly

Security Considerations

Security aspects of DISABLE operations:

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WORKING-STORAGE SECTION.
01 WS-SECURITY-CONTEXT.
    05 WS-USER-ID       PIC X(8).
    05 WS-AUTH-LEVEL    PIC 9(1).
    05 WS-OPERATION-LOG PIC X(100).
 
PROCEDURE DIVISION.
AUTHORIZED-DISABLE.
    IF WS-AUTH-LEVEL >= 5
        DISABLE WS-TARGET-TERMINAL
            INVALID KEY
                STRING "DISABLE FAILED: " WS-TARGET-TERMINAL
                       " BY USER: " WS-USER-ID
                       INTO WS-OPERATION-LOG
                PERFORM LOG-SECURITY-EVENT
            NOT INVALID KEY
                STRING "DISABLE SUCCESS: " WS-TARGET-TERMINAL
                       " BY USER: " WS-USER-ID
                       INTO WS-OPERATION-LOG
                PERFORM LOG-OPERATION
        END-DISABLE
    ELSE
        DISPLAY "Insufficient privileges for disable operation"
        PERFORM LOG-ACCESS-DENIED
    END-IF.

This example demonstrates authorization checking and comprehensive logging for security compliance.

Integration with System Management

Automated Resource Management

Integrating DISABLE with automated system management:

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WORKING-STORAGE SECTION.
01 WS-SYSTEM-STATUS.
    05 WS-CPU-USAGE     PIC 9(3).
    05 WS-MEMORY-USAGE  PIC 9(3).
    05 WS-LOAD-FACTOR   PIC 9(3).
 
PROCEDURE DIVISION.
ADAPTIVE-DISABLE.
    CALL "GET-SYSTEM-STATUS" USING WS-SYSTEM-STATUS
    
    IF WS-CPU-USAGE > 90 OR WS-MEMORY-USAGE > 85
        PERFORM DISABLE-NON-CRITICAL-TERMINALS
        DISPLAY "System overload: Non-critical terminals disabled"
    END-IF
    
    IF WS-LOAD-FACTOR > 95
        PERFORM EMERGENCY-DISABLE-SEQUENCE
        DISPLAY "Emergency shutdown: All user terminals disabled"
    END-IF.

This adaptive approach automatically manages terminal resources based on system load conditions.

Scheduled Maintenance Integration

Coordinating DISABLE operations with maintenance schedules:

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WORKING-STORAGE SECTION.
01 WS-MAINTENANCE-SCHEDULE.
    05 WS-MAINT-START   PIC X(14).
    05 WS-MAINT-END     PIC X(14).
    05 WS-CURRENT-TIME  PIC X(14).
 
PROCEDURE DIVISION.
SCHEDULED-DISABLE.
    ACCEPT WS-CURRENT-TIME FROM DATE-TIME
    
    IF WS-CURRENT-TIME >= WS-MAINT-START AND
       WS-CURRENT-TIME <= WS-MAINT-END
        PERFORM DISABLE-ALL-USER-TERMINALS
        DISPLAY "Maintenance mode: User access disabled"
    ELSE
        PERFORM ENABLE-ALL-USER-TERMINALS
        DISPLAY "Normal operations: User access enabled"
    END-IF.

This scheduling approach ensures terminals are automatically disabled during maintenance windows.

Hands-on Exercise

Exercise: Terminal Control System

Create a COBOL program that implements a comprehensive terminal control system using DISABLE and ENABLE statements.

Requirements:

  • Implement selective terminal disable based on terminal type
  • Include error handling with retry mechanisms
  • Maintain status tracking for all terminals
  • Implement security authorization for disable operations
  • Provide comprehensive logging and reporting
View Solution
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IDENTIFICATION DIVISION.
PROGRAM-ID. TERMINAL-CONTROL.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-CONTROL-TABLE.
    05 WS-TERMINAL OCCURS 20 TIMES.
        10 WS-TERM-ID       PIC X(8).
        10 WS-TERM-TYPE     PIC X(1).
        10 WS-TERM-STATUS   PIC X(1).
        10 WS-LAST-ACTION   PIC X(14).
 
01 WS-OPERATION-COUNTERS.
    05 WS-DISABLE-COUNT     PIC 9(3) VALUE ZERO.
    05 WS-ENABLE-COUNT      PIC 9(3) VALUE ZERO.
    05 WS-ERROR-COUNT       PIC 9(3) VALUE ZERO.
 
01 WS-SECURITY.
    05 WS-USER-AUTH         PIC 9(1) VALUE 1.
    05 WS-REQUIRED-AUTH     PIC 9(1) VALUE 3.
 
PROCEDURE DIVISION.
MAIN-CONTROL.
    PERFORM INITIALIZE-TERMINALS
    PERFORM SECURITY-CHECK
    IF WS-USER-AUTH >= WS-REQUIRED-AUTH
        PERFORM TERMINAL-MANAGEMENT-MENU
    ELSE
        DISPLAY "Insufficient authorization"
    END-IF
    PERFORM DISPLAY-SUMMARY
    GOBACK.
 
TERMINAL-MANAGEMENT-MENU.
    DISPLAY "1=Disable User Terminals"
    DISPLAY "2=Enable All Terminals"
    DISPLAY "3=Status Report"
    ACCEPT WS-CHOICE
    
    EVALUATE WS-CHOICE
        WHEN "1" PERFORM DISABLE-USER-TERMINALS
        WHEN "2" PERFORM ENABLE-ALL-TERMINALS
        WHEN "3" PERFORM STATUS-REPORT
    END-EVALUATE.
 
DISABLE-USER-TERMINALS.
    PERFORM VARYING WS-INDEX FROM 1 BY 1
        UNTIL WS-INDEX > 20
        IF WS-TERM-TYPE(WS-INDEX) = "U"
            DISABLE WS-TERM-ID(WS-INDEX)
                INVALID KEY
                    ADD 1 TO WS-ERROR-COUNT
                    MOVE "E" TO WS-TERM-STATUS(WS-INDEX)
                NOT INVALID KEY
                    ADD 1 TO WS-DISABLE-COUNT
                    MOVE "D" TO WS-TERM-STATUS(WS-INDEX)
                    ACCEPT WS-LAST-ACTION(WS-INDEX) FROM DATE-TIME
            END-DISABLE
        END-IF
    END-PERFORM.

Quiz

Test Your Knowledge

1. What is the primary purpose of the DISABLE statement?

2. Which clause is used to handle failed DISABLE operations?

3. How do you reverse the effect of a DISABLE statement?

View Answers

1. To deactivate communication channels or terminals - DISABLE is used to temporarily or permanently stop message processing through specified resources.

2. INVALID KEY - The INVALID KEY clause handles situations where the DISABLE operation cannot be completed successfully.

3. Use the ENABLE statement - ENABLE reverses the effect of DISABLE, reactivating the disabled resource for normal operation.

Frequently Asked Questions

Related Concepts

Message Control System (MCS)

Understanding COBOL message control systems and communication handling

Terminal Management

Managing terminal devices and user interfaces in COBOL applications

System Resource Control

Controlling and managing system resources in mainframe environments

Communication Protocols

Understanding communication protocols and data exchange in COBOL