Practical RPG: Queueing, Part I: Data Queues

[DaleB63]

Back in the early 90's, I had a need to do depth-first and breadth-first searches on some data. These algorithms are relatively simple with recursion; not so much in iterative languages like RPG or COBOL. Wound up developing a way to use an array to simulate a stack, and came up with an iterative algorithm.

Anyway, at the time I didn't know about data queues. A *LIFO data queue *is* a stack. Push and Pop are simply QDNDDTAQ and QRCVDTAQ. Even without recursion, using a data queue for the stack might have made for simpler code than what I came up with. Faster is debatable, but definitely simpler.

[Mirco Cortesi]

I used a data queue in As400 to communicate with a server computer running a Windows system.
In windows i referenced the cwbx.dll in the ToolBox equipment of Client Access.
In As400 I created a simple data queue.

If you plan to use a data queue, please keep in mind:
- the receiving machine could be slower than the sending one
- the data queue has a maximum capacity

So I want to highly recommend to insert a MONMSG CPF950A after each send data to a queue, followed by a waiting command and a retry.
Otherwise you will experiment a loss of data.

Here below is an example of a safe procedure to send data and receive data from the queue.
I hope to have been helpful.


PGM PARM(&FN)
/* Simple sequential data queue */
/* Queue name */
DCL VAR(&QN) TYPE(*CHAR) LEN(10) VALUE('QUEUE')
/* Library of the queue */
DCL VAR(&QL) TYPE(*CHAR) LEN(10) VALUE('QTEMP')
/* String lenghth to manage */
DCL VAR(&FL) TYPE(*DEC) LEN(5 0) VALUE(80)
/* Data to manage */
DCL VAR(&FN) TYPE(*CHAR) LEN(80)
/* Wait */
DCL VAR(&WT) TYPE(*DEC) LEN(5 0)

/* Create the data QUEUE with length = 80 */
CHKOBJ OBJ(QTEMP/QUEUE) OBJTYPE(*DTAQ)
MONMSG MSGID(CPF9801) EXEC(DO)
CRTDTAQ DTAQ(QTEMP/QUEUE) MAXLEN(80)
ENDDO
/* Send data to the queue */
DLY1: CALL PGM(QSNDDTAQ) PARM(&QN &QL &FL &FN)
MONMSG MSGID(CPF9801) /* The queue doesn't exist */
MONMSG MSGID(CPF950A) EXEC(DO)
SNDPGMMSG MSGID(CPF9898) MSGF(QCPFMSG) MSGDTA('The +
queue is full. Please wait...') +
TOPGMQ(*EXT) MSGTYPE(*STATUS)
DLYJOB DLY(10) /* 10 seconds */
GOTO CMDLBL(DLY1)
ENDDO
/* Receive data from the queue */
OVER: CALL PGM(QRCVDTAQ) PARM(&QN &QL &FL &FN &WT)
ENDPGM