Receive request messages

For example, your procedure or program can obtain input (commands) from a display station and handle the messages that result from the analysis and processing of the input. The commands are sent as request messages so they can be processed. Usually, request messages are received from the external message queue (*EXT) of the job. For batch jobs, the requests received are those read from the input stream. For interactive jobs, the requests received are those the display station user enters one at a time on the Command Entry display. For example, CL commands are requests that are received by the IBM-supplied CL processor QCMD.

Your procedure or program must define the syntax of the data in the request message, interpret the request, and diagnose any errors. While the request is being analyzed or the request function is being run, any number of errors can be detected. As a result of these errors, messages are sent to the call message queue for the procedure or program. The procedure or program handles these messages and then receives the next request message. Thus, a request processing cycle is defined; a request message is received, the request is analyzed and run by your procedure or program with resulting messages displayed, and the next request received. If there are no more request messages to be received in a batch job, an escape message is sent to your procedure or program to indicate this.

More than one OPM program or ILE procedure of a job can receive request messages for processing. The requests received by more recent program calls are considered to be nested within those received by higher level program calls. The request processing cycles at each nesting level are independent of each other. Within an ILE program, one or more procedures within that program can be receiving request messages. If more than one procedure is processing requests then the nesting occurs within the same ILE program and the nesting levels remain independent.

The following diagram shows how request messages are processed by QCMD:

1

The CL processor QCMD receives a request message from *EXT.

2

If there is no request message on *EXT, the Command Entry display is displayed. The display station user enters a command on the display. When the command is entered, it is placed on *EXT as a request message.

3

Since step 2 placed a request on *EXT, now the RCVMSG in step 1 can continue. The command is then moved to the QCMD call message queue and is passed from there to QCMD to complete step 1.

4

The command is analyzed and its command processing program (CPP) is called.

5

The command processing program sends diagnostic messages to the call message queue for QCMD.

6

Then the command processing program sends an escape message to the call message queue for QCMD. The escape message notifies QCMD that diagnostic messages are on the queue and that QCMD should end processing of the CPP.

7

QCMD is monitoring for the arrival of a request-check (CPF9901) or function-check (CPF9999) escape message. QCMD then tries to receive the next request message.

Note: If a request processor receives message CPF9901 or CPF9999, it should run a Reclaim Resources (RCLRSC) command. The request processor should also monitor for messages CPF1907 (end request) and CPF2415 (which indicates that the user pressed F3 or F12 on the Command Entry display).

8

Because a request message was being processed, all the messages on the call message queue for QCMD are written to the Command Entry display, which then prompts the display station user for another command.

9

The previous request message (command) and its associated messages are contained in the job log according to the message logging level specified for the job.