The Inquire sample program on IBM i

The Inquire sample program, AMQ3INQ4, inquires about some of the attributes of a queue using the MQINQ call.

The program is intended to run as a triggered program, so its only input is an MQTMC (trigger message) structure. This structure contains the name of a target queue with attributes that are to be inquired upon.

For the triggering process to work, you must ensure that the Inquire sample program is triggered by messages arriving on queue SYSTEM.SAMPLE.INQ. To do ao, specify the name of the Inquire sample program in the ApplId field of the SYSTEM.SAMPLE.INQPROCESS process definition. (For this, we can use the CHGMQMPRC command, described in Change MQ Process (CHGMQMPRC) ). The sample queue has a trigger type of FIRST, so if there are already messages on the queue before you run the Request sample, the Inquire sample is not triggered by the messages you send.

When we have set the definition correctly, first start AMQ3SRV4 in one job, then start AMQ3REQ4 in another. You could use AMQ3TRG4 instead of AMQ3SRV4, but potential job submission delays might make it less easy to follow what is happening.

Use the Request sample program to send request messages, each containing just a queue name, to queue SYSTEM.SAMPLE.INQ. For each request message, the Inquire sample program sends a reply message containing information about the queue specified in the request message. The replies are sent to the reply-to queue specified in the request message.

Design of the Inquire sample program

When the program is triggered, it explicitly connects to the default queue manager using the MQCONN call. Although not necessary on IBM® i, this design feature means you could use the same program on other platforms without changing the source code.

The program then opens the queue named in the trigger message structure it was passed when it started. (For clarity, we will call this the request queue.) The program uses the MQOPEN call to open this queue for shared input.

The program uses the MQGET call to remove messages from this queue. This call uses the GMATM and GMWT options, with a wait interval of 5 seconds. The program tests the descriptor of each message to see if it is a request message; if it is not, the program discards the message, and displays a warning message.

For each request message removed from the request queue, the program reads the name of the queue (which we will call the target queue ) contained in the data and opens that queue using the MQOPEN call with the OOINQ option. The program then uses the MQINQ call to inquire about the values of the InhibitGet, CurrentQDepth, and OpenInputCount attributes of the target queue.

If the MQINQ call is successful, the program uses the MQPUT call to put a reply message on the reply-to queue. This message contains the values of the three attributes.

If the MQOPEN or MQINQ call is unsuccessful, the program uses the MQPUT call to put a report message on the reply-to queue. In the MDFB field of the message descriptor of this report message is the reason code returned by either the MQOPEN or MQINQ call, depending on which one failed.

After the MQINQ call, the program closes the target queue using the MQCLOSE call.

When there are no messages remaining on the request queue, the program closes that queue and disconnects from the queue manager.