Select in COBOL

Our program demonstrates the concept of handling multiple concurrent operations. In COBOL, we don’t have direct equivalents to Go’s channels and select statement, but we can simulate similar behavior using file handling and timed waits.

IDENTIFICATION DIVISION.
PROGRAM-ID. SELECT-EXAMPLE.

ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT FILE1 ASSIGN TO "file1.txt"
        ORGANIZATION IS LINE SEQUENTIAL.
    SELECT FILE2 ASSIGN TO "file2.txt"
        ORGANIZATION IS LINE SEQUENTIAL.

DATA DIVISION.
FILE SECTION.
FD FILE1.
01 FILE1-RECORD PIC X(10).
FD FILE2.
01 FILE2-RECORD PIC X(10).

WORKING-STORAGE SECTION.
01 WS-EOF        PIC X VALUE 'N'.
01 WS-TIMER      PIC 9(8) VALUE 0.
01 WS-COUNTER    PIC 9 VALUE 0.

PROCEDURE DIVISION.
MAIN-PROCEDURE.
    PERFORM SIMULATE-CONCURRENT-OPS
    PERFORM PROCESS-FILES 2 TIMES
    STOP RUN.

SIMULATE-CONCURRENT-OPS.
    OPEN OUTPUT FILE1
    OPEN OUTPUT FILE2
    CALL "C$SLEEP" USING 1
    MOVE "one" TO FILE1-RECORD
    WRITE FILE1-RECORD
    CALL "C$SLEEP" USING 1
    MOVE "two" TO FILE2-RECORD
    WRITE FILE2-RECORD
    CLOSE FILE1
    CLOSE FILE2.

PROCESS-FILES.
    OPEN INPUT FILE1
    OPEN INPUT FILE2
    PERFORM UNTIL WS-COUNTER = 2
        CALL "C$SLEEP" USING 0.1
        ADD 1 TO WS-TIMER
        IF WS-TIMER > 30
            DISPLAY "Timeout occurred"
            EXIT PERFORM
        END-IF
        READ FILE1
            AT END
                CONTINUE
            NOT AT END
                DISPLAY "received " FILE1-RECORD
                ADD 1 TO WS-COUNTER
        END-READ
        READ FILE2
            AT END
                CONTINUE
            NOT AT END
                DISPLAY "received " FILE2-RECORD
                ADD 1 TO WS-COUNTER
        END-READ
    END-PERFORM
    CLOSE FILE1
    CLOSE FILE2.

In this COBOL example, we simulate concurrent operations by writing to two separate files with a delay between writes. Then, we repeatedly check these files for new content, simulating the behavior of selecting from multiple channels.

To run the program, compile it with a COBOL compiler and execute the resulting binary.

$ cobc -x select-example.cob
$ ./select-example
received one
received two

Note that the execution time will be approximately 2 seconds, simulating the concurrent operations in the original Go example. The COBOL version uses file I/O and timed waits to achieve a similar effect to Go’s goroutines and channels.

This example demonstrates how to handle multiple concurrent operations in COBOL, even though the language doesn’t have built-in constructs for concurrency like Go does. We’ve used file handling and timed waits to simulate similar behavior.

Channel Directions in COBOL

Timeouts in COBOL

Learn X By Example

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Select in COBOL