Channel Buffering in COBOL

IDENTIFICATION DIVISION.
PROGRAM-ID. CHANNEL-BUFFERING.

ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.

DATA DIVISION.
FILE SECTION.
WORKING-STORAGE SECTION.
01 MESSAGES.
   05 MESSAGE-VALUE PIC X(20) OCCURS 2 TIMES.
01 MESSAGE-COUNT PIC 9 VALUE 0.
01 I PIC 9.

PROCEDURE DIVISION.
MAIN-PROCEDURE.
    PERFORM INITIALIZE-MESSAGES
    PERFORM SEND-MESSAGES
    PERFORM RECEIVE-MESSAGES
    STOP RUN.

INITIALIZE-MESSAGES.
    MOVE SPACES TO MESSAGES.

SEND-MESSAGES.
    MOVE "buffered" TO MESSAGE-VALUE(1)
    MOVE "channel" TO MESSAGE-VALUE(2)
    ADD 2 TO MESSAGE-COUNT.

RECEIVE-MESSAGES.
    PERFORM VARYING I FROM 1 BY 1 UNTIL I > MESSAGE-COUNT
        DISPLAY MESSAGE-VALUE(I)
    END-PERFORM.

By default, COBOL doesn’t have a built-in concept of channels or buffering as seen in modern concurrent programming languages. However, we can simulate a similar behavior using arrays and counters.

In this example, we create a table (array) called MESSAGES that can hold up to 2 string values, simulating a buffered channel with a capacity of 2.

The SEND-MESSAGES paragraph demonstrates adding values to our simulated channel. We can add these values without immediately processing them, similar to sending to a buffered channel.

SEND-MESSAGES.
    MOVE "buffered" TO MESSAGE-VALUE(1)
    MOVE "channel" TO MESSAGE-VALUE(2)
    ADD 2 TO MESSAGE-COUNT.

Later, we can process these values using the RECEIVE-MESSAGES paragraph, which iterates through the messages and displays them:

RECEIVE-MESSAGES.
    PERFORM VARYING I FROM 1 BY 1 UNTIL I > MESSAGE-COUNT
        DISPLAY MESSAGE-VALUE(I)
    END-PERFORM.

When you run this COBOL program, it will output:

buffered
channel

This example demonstrates how we can simulate buffered channel-like behavior in COBOL, even though the language doesn’t natively support such concepts. It’s important to note that this is not truly concurrent or asynchronous, as COBOL programs typically run sequentially.