Worker Pools in COBOL

In this example, we’ll look at how to implement a worker pool using COBOL.

IDENTIFICATION DIVISION.
PROGRAM-ID. WORKER-POOLS.

ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT WORKFILE ASSIGN TO "WORK.DAT"
        ORGANIZATION IS LINE SEQUENTIAL.

DATA DIVISION.
FILE SECTION.
FD WORKFILE.
01 WORK-RECORD.
    05 JOB-ID PIC 9(5).

WORKING-STORAGE SECTION.
01 WS-EOF PIC A(1).
01 WS-JOB-COUNTER PIC 9(5) VALUE 0.
01 WS-WORKER-ID PIC 9(3).
01 WS-NUM-WORKERS PIC 9(3) VALUE 3.
01 WS-NUM-JOBS PIC 9(5) VALUE 5.

PROCEDURE DIVISION.
MAIN-PROCEDURE.
    PERFORM INITIALIZE-WORK
    PERFORM VARYING WS-WORKER-ID FROM 1 BY 1 
            UNTIL WS-WORKER-ID > WS-NUM-WORKERS
        PERFORM START-WORKER
    END-PERFORM
    PERFORM PROCESS-RESULTS
    STOP RUN.

INITIALIZE-WORK.
    OPEN OUTPUT WORKFILE
    PERFORM VARYING WS-JOB-COUNTER FROM 1 BY 1 
            UNTIL WS-JOB-COUNTER > WS-NUM-JOBS
        MOVE WS-JOB-COUNTER TO JOB-ID
        WRITE WORK-RECORD
    END-PERFORM
    CLOSE WORKFILE.

START-WORKER.
    CALL "WORKER" USING WS-WORKER-ID.

PROCESS-RESULTS.
    OPEN INPUT WORKFILE
    PERFORM UNTIL WS-EOF = 'Y'
        READ WORKFILE
            AT END
                MOVE 'Y' TO WS-EOF
            NOT AT END
                DISPLAY "Job " JOB-ID " completed"
    END-PERFORM
    CLOSE WORKFILE.

Here’s the worker program:

IDENTIFICATION DIVISION.
PROGRAM-ID. WORKER.

DATA DIVISION.
LINKAGE SECTION.
01 LS-WORKER-ID PIC 9(3).

PROCEDURE DIVISION USING LS-WORKER-ID.
MAIN-PROCEDURE.
    DISPLAY "Worker " LS-WORKER-ID " started"
    PERFORM PROCESS-JOB
    DISPLAY "Worker " LS-WORKER-ID " finished"
    EXIT PROGRAM.

PROCESS-JOB.
    CALL "C$SLEEP" USING 1
    DISPLAY "Worker " LS-WORKER-ID " processed a job".

In this COBOL implementation, we simulate a worker pool using separate program calls. The main program WORKER-POOLS creates a file with job IDs, then starts multiple instances of the WORKER program. Each worker processes jobs by reading from the shared file.

Here’s a breakdown of the implementation:

We use a file WORK.DAT to simulate a job queue.
The INITIALIZE-WORK paragraph creates the job file with a specified number of jobs.
The START-WORKER paragraph calls the WORKER program multiple times, simulating concurrent workers.
Each worker (in the WORKER program) processes a job by sleeping for 1 second (simulating work) and then displaying a message.
The PROCESS-RESULTS paragraph reads the job file to simulate collecting results.

This COBOL implementation doesn’t have true concurrency like the original example, as COBOL doesn’t have built-in support for threads or goroutines. Instead, it simulates the concept of multiple workers processing jobs from a shared queue.

To run this program, you would compile both the main program and the worker program, then execute the main program. The output would show jobs being processed by different workers, simulating concurrent execution.

Note that this is a simplified simulation and doesn’t capture the full concurrency aspect of the original example. In a real-world COBOL environment, true concurrency would typically be achieved through the use of multiple address spaces or specialized middleware.

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Worker Pools in COBOL