Read a message queue like a physical file
Learn how to read a message queue like a physical file in this tip.
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All of us know that we can read a Physical file WR to its RRN (Relative Record Number). But have you ever needed to replicate the same in case of message queues i.e. read a message queue in a similar manner.
I mean how about reading a message queue WR to the position of a message in it? Seems silly at very first thought… But it is possible.
This will be similar to reading a physical file WR to its RRN. It means that if a message queue contains 15 messages and you want to read say the 6th message (from the top) of that message queue, you can do it.
I have made a CL program RRNMSGQ to do this.
You'll need following to run this program:
1. MENU1 is a display file having DDS as shown below:
A R MENU
A CF03(03 'EXIT')
A CA05(05 'REFRESH')
A 7 2'Enter the Message Number :'
A COLOR(YLW) DSPATR(HI CS)
A OPTION 2Y 0I +2
A DSPATR(MDT)
A 22 4'CF03=Exit'
A COLOR(BLU)
A 22 15'CA05=Refresh'
A COLOR(BLU)
2. The name of Message Queue having messages in it is NEW. It is having a number of messages in it.
3. SYNGRAP is my current library.
4. MYMESG is a Message file having the following message ids with the text as shown below:
I.) RAP0014 --
You typed message number as &1. Enter a value from 1-&2.
II.) RAP0034 --
Only &1 messages in total in Message Queue NEW. Enter a value from 1-&1.
In the above two messages, data types of variables &1 and &2 are as follows:
Field Data Type Length
&1 *CHAR 2
&2 *CHAR 2
5. RRNMSGQ (CL Program)
PGM
DCLF FILE(MENU1)
DCL VAR(&MSG) TYPE(*CHAR) LEN(132)
DCL VAR(&KEY) TYPE(*CHAR) LEN(4)
DCL VAR(&KEY1) TYPE(*CHAR) LEN(4)
DCL VAR(&A) TYPE(*DEC) LEN(2 0) VALUE(0)
DCL VAR(&B) TYPE(*CHAR) LEN(2) VALUE('0')
DCL VAR(&T) TYPE(*DEC) LEN(2 0)
DCL VAR(&ABC) TYPE(*CHAR) LEN(2)
MONMSG MSGID(CPF2410)
RCVMSG MSGQ(NEW) MSGTYPE(*FIRST) RMV(*NO) +
KEYVAR(&KEY)
/* Display Error message if Message Queue NEW is Empty */
IF COND(&KEY *EQ ' ') THEN(DO)
SNDPGMMSG MSG('Message Queue NEW is empty. Enter some +
messages in it & then Try again.') +
TOPGMQ(*EXT)
/* RMVMSG PGMQ(*EXT) CLEAR(*ALL) */
GOTO CMDLBL(ENDPGM)
ENDDO
CHGVAR VAR(&T) VALUE(&T + 1)
RCV: RCVMSG MSGQ(NEW) MSGTYPE(*NEXT) MSGKEY(&KEY) +
RMV(*NO) KEYVAR(&KEY1)
IF COND(&KEY1 *NE ' ') THEN(DO)
CHGVAR VAR(&T) VALUE(&T + 1)
CHGVAR VAR(&KEY) VALUE(&KEY1)
GOTO CMDLBL(RCV)
ENDDO
CHGVAR VAR(&ABC) VALUE(&T)
CHGVAR VAR(&KEY) VALUE(' ')
CHGVAR VAR(&KEY1) VALUE(' ')
BEGIN: SNDRCVF RCDFMT(MENU)
CHGVAR VAR(&A) VALUE(0)
/* Quit the program, if F3 is pressed on MENU1 screen*/
IF COND(&IN03 *EQ '1') THEN(DO)
GOTO CMDLBL(ENDPGM)
ENDDO
/* Refresh the MENU1 screen for input capable field "OPTION" +
if F5 is pressed on MENU1 screen */
IF COND(&IN05 *EQ '1') THEN(DO)
CHGVAR VAR(&OPTION) VALUE(0)
CHGVAR VAR(&IN05) VALUE('0')
GOTO CMDLBL(BEGIN)
ENDDO
/* Display Error message if user enters 0(zero) in +
the input capable field "OPTION" on MENU1 screen */
IF COND(&OPTION *EQ 0) THEN(DO)
SNDPGMMSG MSGID(RAP0014) MSGF(MYMESG) MSGDTA(&B *BCAT +
&ABC) TOPGMQ(*EXT)
/* RMVMSG PGMQ(*EXT) CLEAR(*ALL) */
GOTO CMDLBL(BEGIN)
ENDDO
/* Display Error message if user enters a value in +
the input capable field "OPTION" on MENU1 screen which exceeds +
the total number of messages in the message queue NEW. +
For example: Message queue NEW has 12 messages & user enters 14 +
in the "OPTION" field.*/
IF COND(&OPTION *GT &T) THEN(DO)
SNDPGMMSG MSGID(RAP0034) MSGF(SYNGRAP/MYMESG) +
MSGDTA(&ABC) TOPGMQ(*EXT)
CHGVAR VAR(&OPTION) VALUE(0)
/* RMVMSG PGMQ(*EXT) CLEAR(*ALL) */
GOTO CMDLBL(BEGIN)
ENDDO
ELSE CMD(DO)
RCVMSG MSGQ(NEW) MSGTYPE(*FIRST) RMV(*NO) +
KEYVAR(&KEY) MSG(&MSG)
CHGVAR VAR(&A) VALUE(&A + 1)
START: IF COND(&A *NE &OPTION) THEN(DO)
RCVMSG MSGQ(NEW) MSGTYPE(*NEXT) MSGKEY(&KEY) +
RMV(*NO) KEYVAR(&KEY1) MSG(&MSG)
CHGVAR VAR(&A) VALUE(&A + 1)
CHGVAR VAR(&KEY) VALUE(&KEY1)
ENDDO
ELSE CMD(DO)
SNDPGMMSG MSG(&MSG) TOPGMQ(*EXT)
GOTO CMDLBL(BEGIN)
/* RMVMSG PGMQ(*EXT) CLEAR(*ALL) */
ENDDO
GOTO CMDLBL(START)
ENDDO
ENDPGM: ENDPGM
If you want to read 6th message (from top) of message queue NEW, you'll
have to follow these steps :
a. Call CL program RRNMSGQ from command line. This will show a screen to you.
b. Enter 6 in the 'Enter the Message Number :' field shown on this screen and press
key. This will either show you the 6th message (from top) of the message queue NEW
OR
An appropriate error message will be displayed (as described in CL
program) giving you the information regarding the exact cause of error.
As shown above, in CL program RRNMSGQ, appropriate error handling has been done & error messages have been explained with the help of comments.
Note: If, every time you want to refresh the screen on which the messages will be displayed, just uncomment the statement
/* RMVMSG PGMQ(*EXT) CLEAR(*ALL) */
at various places in the CL Program, compile the program again &
then run the program.
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