Goroutines in COBOL

A lightweight conceptual equivalent of goroutines using COBOL#

       IDENTIFICATION DIVISION.
       PROGRAM-ID. GoroutinesExample.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  WS-ITER      PIC 9(2) VALUE 0.
       01  WS-MSG       PIC A(20).

       PROCEDURE DIVISION.

       MAIN-PARA.
           PERFORM F("DIRECT")
           MOVE "GOROUTINE" TO WS-MSG
           PERFORM CONCURRENT-PARA
           MOVE "GOING" TO WS-MSG
           PERFORM CONCURRENT-ANONYMOUS
           CALL 'CBL_TO_YIELD_THREAD' USING BY VALUE 1000
           DISPLAY "DONE"
           STOP RUN.

       F SECTION.
       F-PARA.
           DISPLAY "DIRECT: " WS-ITER
           MOVE 0 TO WS-ITER
           PERFORM VARYING WS-ITER FROM 1 BY 1 UNTIL WS-ITER > 3
               DISPLAY "DIRECT: " WS-ITER
           END-PERFORM.

       CONCURRENT-PARA SECTION.
           PERFORM CONCURRENT-F-PARA.

       CONCURRENT-F-PARA.
           MOVE 0 TO WS-ITER
           PERFORM VARYING WS-ITER FROM 1 BY 1 UNTIL WS-ITER > 3
               DISPLAY "GOROUTINE: " WS-ITER
           END-PERFORM.

       CONCURRENT-ANONYMOUS SECTION.
           DISPLAY WS-MSG.

Explanation:

In this COBOL example, we attempt to mimic the concept of lightweight asynchronous execution (similar to goroutines) within COBOL’s constraints, as COBOL doesn’t have built-in support for threading or goroutines. We use the following idiomatic constructs for COBOL:

1. Simple Function Call:

   • We utilize a PERFORM statement to sequentially call a simple function.

   PERFORM F("direct")

2. Mimicking a Goroutine with a Separate Section:

   • We simulate concurrent execution by defining a separate section CONCURRENT-PARA and invoking it using PERFORM.

   PERFORM CONCURRENT-PARA

3. Anonymous Function-like Execution:

   • In COBOL, we demonstrate an anonymous function call equivalent by directly displaying a message within a separate section CONCURRENT-ANONYMOUS.

   PERFORM CONCURRENT-ANONYMOUS

4. Synchronization with Sleep:

   • We use a hypothetical call to a system-specific sleep function CBL_TO_YIELD_THREAD to pause execution, imitating time.Sleep.

   CALL 'CBL_TO_YIELD_THREAD' USING BY VALUE 1000

5. Output Explanation:

   • The output will show the synchronous print statements followed by the “concurrent” print statements executed in different sections, implying rudimentary concurrency.

This COBOL example section demonstrates how to adapt concepts originally illustrated in other programming paradigms using the syntax and idioms specific to COBOL.