The Set sample program on IBM i

The Set sample program, AMQ3SET4, inhibits put operations on a queue by using the MQSET call to change the queue's InhibitPut attribute.

The program is intended to run as a triggered program, so its only input is an MQTMC (trigger message) structure that 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 Set sample program is triggered by messages arriving on queue SYSTEM.SAMPLE.SET. To do this, specify the name of the Set sample program in the ApplId field of the process definition SYSTEM.SAMPLE.SETPROCESS. (For this, we can use the CHGMQMPRC command, described in the Administer IBM® i .) 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 Set 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 could 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.SET. For each request message, the Set sample program sends a reply message containing a confirmation that put operations have been inhibited on the specified queue. The replies are sent to the reply-to queue specified in the request message.

Design of the Set 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 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 OOSET option. The program then uses the MQSET call to set the value of the InhibitPut attribute of the target queue to QAPUTI.

If the MQSET call is successful, the program uses the MQPUT call to put a reply message on the reply-to queue. This message contains the string PUT inhibited.

If the MQOPEN or MQSET 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 MQSET call, depending on which one failed.

After the MQSET 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.