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COBOL THREAD-LOCAL-STORAGE - Quick Reference

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Overview

THREAD-LOCAL-STORAGE is a COBOL feature that provides thread-specific data storage in multithreaded programs. Each thread gets its own copy of the data declared in the THREAD-LOCAL-STORAGE SECTION, ensuring data isolation and thread safety without the need for complex synchronization mechanisms.

Purpose and Usage

  • Thread-specific data isolation
  • Thread safety without synchronization
  • Automatic cleanup when threads terminate
  • Simplified thread management
  • Performance optimization in multithreaded applications

Syntax

THREAD-LOCAL-STORAGE is declared in the DATA DIVISION:

Basic Declaration

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* Basic THREAD-LOCAL-STORAGE declaration
DATA DIVISION.
THREAD-LOCAL-STORAGE SECTION.
01  thread-counter PIC 9(6) VALUE ZERO.
01  thread-temp-data.
    05  temp-field1 PIC X(20).
    05  temp-field2 PIC 9(5).
01  thread-status PIC X(10) VALUE "ACTIVE".
 
WORKING-STORAGE SECTION.
01  shared-data PIC X(50).

Each thread gets its own copy of data in THREAD-LOCAL-STORAGE SECTION.

Thread-Specific Data Usage

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* Using thread-local storage in procedures
PROCEDURE DIVISION.
THREAD-PROCEDURE.
    * Each thread has its own counter
    ADD 1 TO thread-counter.
    DISPLAY "Thread counter: " thread-counter.
    
    * Each thread has its own temp data
    MOVE "Thread data" TO temp-field1.
    MOVE 100 TO temp-field2.
    
    * Update thread status
    MOVE "PROCESSING" TO thread-status.
    
    PERFORM thread-processing.
    
    EXIT THREAD.
 
THREAD-PROCESSING.
    * Access thread-specific data
    IF thread-status = "PROCESSING"
        PERFORM process-data
    END-IF.
    
    * Use thread counter for logging
    DISPLAY "Processing record " thread-counter.

Practical Examples

Here are some practical uses of THREAD-LOCAL-STORAGE in COBOL:

Thread-Specific Counters

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* Thread-specific counters and processing
DATA DIVISION.
THREAD-LOCAL-STORAGE SECTION.
01  thread-stats.
    05  records-processed PIC 9(8) VALUE ZERO.
    05  errors-encountered PIC 9(4) VALUE ZERO.
    05  processing-time PIC 9(6) VALUE ZERO.
01  thread-id PIC X(10).
 
PROCEDURE DIVISION.
PROCESS-RECORDS.
    * Each thread processes its own records
    PERFORM UNTIL end-of-records
        READ input-file
            AT END
                MOVE "Y" TO end-of-records-flag
            NOT AT END
                PERFORM process-single-record
        END-READ
    END-PERFORM.
    
    * Display thread-specific statistics
    DISPLAY "Thread " thread-id " processed " 
            records-processed " records".
    DISPLAY "Errors: " errors-encountered.
    DISPLAY "Time: " processing-time " seconds".
    
    EXIT THREAD.
 
PROCESS-SINGLE-RECORD.
    * Increment thread-specific counter
    ADD 1 TO records-processed.
    
    * Process the record
    IF record-valid
        PERFORM valid-record-processing
    ELSE
        ADD 1 TO errors-encountered
        PERFORM error-handling
    END-IF.

Each thread maintains its own processing statistics.

Thread-Specific Temporary Storage

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* Thread-specific temporary storage
DATA DIVISION.
THREAD-LOCAL-STORAGE SECTION.
01  thread-temp-storage.
    05  temp-buffer PIC X(1000).
    05  temp-counter PIC 9(4).
    05  temp-status PIC X(20).
01  thread-work-area.
    05  work-field1 PIC X(50).
    05  work-field2 PIC 9(6).
    05  work-field3 PIC X(10).
 
PROCEDURE DIVISION.
THREAD-WORK-PROCESS.
    * Initialize thread-specific work area
    MOVE "READY" TO temp-status.
    MOVE ZERO TO temp-counter.
    
    * Use thread-specific buffer for processing
    PERFORM UNTIL work-complete
        * Load data into thread-specific buffer
        MOVE input-data TO temp-buffer.
        
        * Process using thread-specific work area
        PERFORM process-data-chunk.
        
        * Update thread-specific status
        MOVE "PROCESSING" TO temp-status.
        
        ADD 1 TO temp-counter
    END-PERFORM.
    
    * Final status update
    MOVE "COMPLETE" TO temp-status.
    DISPLAY "Thread completed " temp-counter " chunks".

Each thread has its own temporary storage and work area.

Best Practices

  • Use THREAD-LOCAL-STORAGE for data that should not be shared between threads.
  • Keep thread-local data minimal to avoid excessive memory usage.
  • Initialize thread-local data appropriately for each thread.
  • Use thread-local storage for temporary data and counters.
  • Document which data is thread-local versus shared.
  • Consider the memory overhead of thread-local storage.

Common Pitfalls

  • Using thread-local storage for data that should be shared.
  • Excessive memory usage from large thread-local data structures.
  • Not initializing thread-local data properly.
  • Confusing thread-local and shared data access patterns.
  • Not considering the cleanup behavior of thread-local storage.

Test Your Knowledge

1. What is THREAD-LOCAL-STORAGE in COBOL?

  • A global data storage area
  • Thread-specific data storage
  • A file storage mechanism
  • A database storage type

2. What is the primary purpose of THREAD-LOCAL-STORAGE?

  • To share data between threads
  • To provide thread-specific data isolation
  • To improve performance
  • To reduce memory usage

3. When should you use THREAD-LOCAL-STORAGE?

  • In single-threaded programs
  • In multithreaded programs where threads need their own data
  • For global data sharing
  • For file operations

4. What happens to THREAD-LOCAL-STORAGE when a thread terminates?

  • It becomes global
  • It is automatically freed
  • It remains in memory
  • It is shared with other threads

5. How do you declare THREAD-LOCAL-STORAGE?

  • In the PROCEDURE DIVISION
  • In the DATA DIVISION using THREAD-LOCAL-STORAGE SECTION
  • In the ENVIRONMENT DIVISION
  • In the WORKING-STORAGE SECTION

Frequently Asked Questions

Related Concepts

Multithreading

Multithreaded programming in COBOL.

Thread Synchronization

Managing concurrent access to shared resources.

Memory Management

Efficient memory usage in COBOL programs.

Concurrent Programming

Patterns for concurrent execution.

Performance Optimization

Optimizing COBOL program performance.

SAME RECORD AREAUSE AFTER STANDARD EXCEPTION PROCEDURE