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COBOL SHARING Clause - Quick Reference

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Overview

The SHARING clause is used to control file sharing and record area sharing in COBOL. It specifies how files can be accessed by multiple programs or processes simultaneously, ensuring data integrity and preventing conflicts.

Purpose and Usage

  • Concurrent access control - Control multi-program file access
  • Data integrity - Prevent data corruption
  • File locking - Implement file locking mechanisms
  • Performance optimization - Optimize concurrent access
  • Conflict prevention - Prevent access conflicts

Syntax

The SHARING clause is used in the FILE-CONTROL paragraph of the ENVIRONMENT DIVISION.

Basic Syntax

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* Basic SHARING syntax
SELECT file-name
ASSIGN TO physical-file-name
ORGANIZATION IS organization-type
ACCESS MODE IS access-mode
SHARING IS sharing-mode.
 
* Complete example
IDENTIFICATION DIVISION.
PROGRAM-ID. SHARING-EXAMPLE.
 
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT SHARED-FILE
    ASSIGN TO 'DATA/SHARED.DAT'
    ORGANIZATION IS SEQUENTIAL
    ACCESS MODE IS SEQUENTIAL
    SHARING IS ALLOWED
    FILE STATUS IS WS-FILE-STATUS.
 
DATA DIVISION.
FILE SECTION.
FD  SHARED-FILE.
01  FILE-RECORD.
    05  RECORD-DATA    PIC X(80).
 
WORKING-STORAGE SECTION.
01  WS-FILE-STATUS     PIC XX.
 
PROCEDURE DIVISION.
MAIN-LOGIC.
    OPEN INPUT SHARED-FILE
    READ SHARED-FILE
    CLOSE SHARED-FILE
    STOP RUN.

SHARING controls concurrent file access.

Practical Examples

Examples of using the SHARING clause in different scenarios.

Read-Only Sharing

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* Allow multiple programs to read the same file
SELECT READ-ONLY-FILE
ASSIGN TO 'DATA/REFERENCE.DAT'
ORGANIZATION IS SEQUENTIAL
ACCESS MODE IS SEQUENTIAL
SHARING IS ALLOWED
FILE STATUS IS WS-READ-STATUS.
 
* Multiple programs can read simultaneously
PROCEDURE DIVISION.
READ-SHARED-FILE.
    OPEN INPUT READ-ONLY-FILE
    READ READ-ONLY-FILE
        AT END
            MOVE 'Y' TO END-OF-FILE-FLAG
        NOT AT END
            PERFORM PROCESS-RECORD
    END-READ
    CLOSE READ-ONLY-FILE.

SHARING ALLOWED for read-only access.

Exclusive Access

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* Exclusive access for write operations
SELECT EXCLUSIVE-FILE
ASSIGN TO 'DATA/EXCLUSIVE.DAT'
ORGANIZATION IS INDEXED
ACCESS MODE IS RANDOM
RECORD KEY IS FILE-KEY
SHARING IS NO OTHER
FILE STATUS IS WS-EXCLUSIVE-STATUS.
 
* Only one program can access at a time
PROCEDURE DIVISION.
WRITE-EXCLUSIVE-FILE.
    OPEN I-O EXCLUSIVE-FILE
    MOVE "KEY001" TO FILE-KEY
    READ EXCLUSIVE-FILE
    REWRITE FILE-RECORD
    CLOSE EXCLUSIVE-FILE.

SHARING NO OTHER for exclusive access.

Controlled Sharing

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* Controlled sharing with specific modes
SELECT CONTROLLED-FILE
ASSIGN TO 'DATA/CONTROLLED.DAT'
ORGANIZATION IS RELATIVE
ACCESS MODE IS RANDOM
RELATIVE KEY IS REL-KEY
SHARING IS READ ONLY
FILE STATUS IS WS-CONTROLLED-STATUS.
 
* Allow read access but control write access
PROCEDURE DIVISION.
ACCESS-CONTROLLED-FILE.
    OPEN INPUT CONTROLLED-FILE
    MOVE 1 TO REL-KEY
    READ CONTROLLED-FILE
    CLOSE CONTROLLED-FILE.

SHARING READ ONLY for controlled access.

Best Practices

Understanding best practices ensures effective use of the SHARING clause.

Best Practices

  • Choose appropriate sharing mode - Select sharing mode based on access needs
  • Consider data integrity - Ensure data integrity with proper sharing
  • Minimize conflicts - Use sharing modes that minimize conflicts
  • Monitor performance - Monitor performance impact of sharing
  • Handle errors properly - Handle sharing-related errors

Test Your Knowledge

1. What is the primary purpose of the SHARING clause in COBOL?

  • To share data between programs
  • To control file sharing and record area sharing
  • To share memory between processes
  • To share variables between procedures

2. In which COBOL division is the SHARING clause typically used?

  • IDENTIFICATION DIVISION
  • ENVIRONMENT DIVISION
  • DATA DIVISION
  • PROCEDURE DIVISION

3. What does SHARING control in file operations?

  • File access permissions
  • How files can be shared between programs
  • File organization
  • File status codes

4. Can SHARING be used with all file types?

  • Yes, with all file types
  • No, only with sequential files
  • No, only with indexed files
  • Only with specific file organizations

5. What is the relationship between SHARING and file locking?

  • They are the same thing
  • SHARING controls access, locking prevents conflicts
  • SHARING is obsolete, locking is modern
  • They cannot be used together

Frequently Asked Questions

Related Concepts

File Processing

File processing techniques in COBOL.

File Organization Types

Different file organization types in COBOL.

Concurrent Programming

Concurrent programming concepts in COBOL.

SET StatementSIGN Clause