The Inquire sample programs

The Inquire sample programs inquire about some of the attributes of a queue using the MQINQ call.

See Features demonstrated in the sample programs on Multiplatforms for the names of these programs.

These programs are intended to run as triggered programs, so their only input is an MQTMC2 (trigger message) structure for IBM i, Windows, UNIX and Linux systems. This structure contains the name of a target queue with attributes that are to be inquired upon. The C version also uses the queue manager name. The COBOL version uses the default queue manager.

For the triggering process to work, ensure that the Inquire sample program that we want to use is triggered by messages arriving on queue SYSTEM.SAMPLE.INQ. To do this, specify the name of the Inquire sample program that we want to use in the ApplicId field of the process definition SYSTEM.SAMPLE.INQPROCESS. For IBM i, we can use the CHGMQMPRC command for this; for details, see Change MQ Process (CHGMQMPRC). The sample queue has a trigger type of FIRST; if there are already messages on the queue before you run the request sample, the inquire sample is not triggered by the messages that you send.

• For UNIX, Linux, and Windows, start the runmqtrm program in one session, then start the amqsreq program in another.
• For IBM i, start the AMQSERV4 program in one session, then start the AMQSREQ4 program in another. You could use AMQSTRG4 instead of AMQSERV4, but potential job submission delays could make it less easy to follow what is happening.

Use the Request sample programs to send request messages, each containing just a queue name, to queue SYSTEM.SAMPLE.INQ. For each request message, the Inquire sample programs send 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.

On IBM i, if the sample input file member QMQMSAMP.AMQSDATA(INQ) is used, the last queue named does not exist, so the sample returns a report message with a reason code for the failure.

Design of the Inquire sample program

The program opens the queue named in the trigger message structure that 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 MQGMO_ACCEPT_TRUNCATED_MSG and MQGMO_WAIT 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 MQOO_INQ 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 MQPUT1 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 MQPUT1 call to put a report message on the reply-to queue. In the Feedback 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.