Example: Waiting for input from a display file and a data queue

The program in Job B is waiting for input from a display file that it is using and for input to arrive on the data queue from Job A. Instead of alternately waiting for the display file and then the data queue, the program waits for one object, the data queue.

The program calls QRCVDTAQ and waits for the placement of an entry on the data queue that was specified on the display file. Job A is also placing entries on the same data queue. There are two types of entries that are put on this queue, the display file entry, and the user-defined entry. Display data management places the display file entry on the data queue when data is available from the display file. Job A places the user-defined entry on the data queue.

The structure of the display file entry is described in the previous example.

The structure of the entry placed on the queue by Job A is defined by the application programmer.

The following example shows coding logic that the application program in Job B might use:

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  OPEN DSPFILE ... /* Open the Display file. DTAQ parameter specified on*/
                   /* CRTDSPF, CHGDSPF, or OVRDSPF for the file.        */
 
 
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 DO
   WRITE DSPFILE   /* Write with Invite for the Display file            */
 
   CALL QRCVDTAQ   /* Receive an entry from the data queue specified    */
                   /* on the DTAQ parameter for the file. Entries       */
                   /* are placed on the data queue either by Job A or   */
                   /* by display data management when data is           */
                   /* available from any invited device on the display  */
                   /* file.                                             */
                   /* After the entry is received, determine what type  */
                   /* of entry it is, process it, and return to receive */
                   /* the next entry on the data queue.                 */
   IF 'ENTRY TYPE' FIELD = '*DSPF     ' THEN   /* Entry is from display */
     DO                                       /*  file. Since this entry*/
                                              /* does not contain the   */
                                              /* data received, the data*/
                                              /* must be read from the  */
                                              /* file before it can be  */
       READ DATA FROM DISPLAY FILE            /* processed.             */
       PROCESS INPUT DATA FROM DISPLAY FILE
       WRITE TO DISPLAY FILE                   /* Write with Invite    */
     END
   ELSE                                        /* Entry is from Job A.  */
                                               /* This entry contains   */
                                               /* the data from Job A,  */
                                               /* so no read is required*/
                                               /* before processing the */
                                               /* data.                 */
       PROCESS DATA QUEUE ENTRY FROM JOB A
   LOOP BACK TO RECEIVE ENTRY FROM DATA QUEUE
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 END