What is concurrent programming in COBOL?

Designing COBOL programs to handle multiple simultaneous operations, often using CICS or other transaction processing environments.

How do I design thread-safe COBOL programs?

Use proper locking mechanisms, avoid shared state, implement atomic operations, and handle race conditions carefully.

What are synchronization primitives?

Mechanisms like locks, semaphores, and barriers that coordinate access to shared resources between concurrent processes.

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COBOL Concurrent Programming

Concurrent programming in COBOL involves designing programs that can handle multiple simultaneous operations safely. Focus on thread safety, synchronization, and avoiding race conditions.

Thread-Safe Data Access

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       *> Use atomic operations for counters
       ADD 1 TO RECORD-COUNT
       *> Avoid: COMPUTE RECORD-COUNT = RECORD-COUNT + 1
       
       *> Thread-safe flag setting
       MOVE 'Y' TO PROCESSING-FLAG
       *> Check flag atomically
       IF PROCESSING-FLAG = 'Y'
           PERFORM CONTINUE-PROCESSING
       END-IF.

Use atomic operations like ADD and MOVE for simple updates. Avoid complex computations that might be interrupted. Design data structures to minimize shared state between threads.

Synchronization Patterns

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       *> Producer-Consumer pattern
       PERFORM PRODUCER-LOOP UNTIL EOF
           PERFORM ENQUEUE-DATA
           PERFORM SIGNAL-CONSUMER
       END-PERFORM.
       
       PERFORM CONSUMER-LOOP UNTIL DONE
           PERFORM WAIT-FOR-DATA
           PERFORM DEQUEUE-DATA
           PERFORM PROCESS-DATA
       END-PERFORM.

Implement classic synchronization patterns like producer-consumer using queues and signals. Use proper locking around shared data structures to prevent corruption.

Critical Section Protection

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       *> Protect shared resource access
       PERFORM ENTER-CRITICAL-SECTION
       READ SHARED-FILE
       COMPUTE NEW-VALUE = CURRENT-VALUE + INCREMENT
       MOVE NEW-VALUE TO CURRENT-VALUE
       REWRITE SHARED-RECORD
       PERFORM EXIT-CRITICAL-SECTION.

Wrap critical sections that access shared resources with proper locking. Keep critical sections short to minimize contention. Always release locks in the same order they were acquired.

Deadlock Prevention

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       *> Consistent lock ordering
       IF RESOURCE-A-ID < RESOURCE-B-ID
           PERFORM LOCK-RESOURCE-A
           PERFORM LOCK-RESOURCE-B
       ELSE
           PERFORM LOCK-RESOURCE-B
           PERFORM LOCK-RESOURCE-A
       END-IF.

Establish consistent lock ordering across all programs to prevent deadlocks. Use timeouts to detect and break deadlock situations. Log deadlock occurrences for analysis.

Race Condition Handling

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       *> Check-then-act pattern (problematic)
       IF COUNTER < MAX-LIMIT
           ADD 1 TO COUNTER  *> Race condition possible
       END-IF.
       
       *> Better: atomic check-and-increment
       PERFORM ATOMIC-INCREMENT
       IF INCREMENT-SUCCESSFUL
           PERFORM CONTINUE-PROCESSING
       ELSE
           PERFORM HANDLE-LIMIT-REACHED
       END-IF.

Avoid check-then-act patterns that create race conditions. Use atomic operations or proper locking to ensure operations complete without interruption.

Minimize shared state between concurrent processes.
Use atomic operations for simple updates.
Protect critical sections with proper locking.
Order lock acquisition consistently to prevent deadlocks.
Test with multiple concurrent users and high loads.

Concurrent Processing

Parallel execution patterns

CICS Programming

Transaction processing environment