The Asynchronous consumption sample program

The amqscbf sample program demonstrates the use of MQCB and MQCTL to consume messages from multiple queues asynchronously.

amqscbf is provided as C source code, and a binary client and server executable on Windows, UNIX and Linux platforms.

The program is started from the command line and takes the following optional parameters:

Usage: [Options] Queue Name {queue_name}
  where Options are:
    -m Queue Manager Name
    -o Open options
    -r Reconnect Type
       d Reconnect Disabled
       r Reconnect
       m Reconnect Queue Manager

Provide more than one queue name to read messages from multiple queues (a maximum of ten queues are supported by the sample.)

Note: Reconnect type is only valid for client programs.

Example

The example shows amqscbf run as a server program reading one message from QL1 and then being stopped.

Use IBM MQ Explorer to put a test message on QL1. Stop the program by pressing enter.

C:\>amqscbf QL1
Sample AMQSCBF0 start

Press enter to end
Message Call (9 Bytes) :
Message 1

Sample AMQSCBF0 end

What amqscbf demonstrates

The sample shows how to read messages from multiple queues in the order of their arrival. This would require a lot more code using synchronous MQGET. In the case of asynchronous consumption, no polling is required, and thread and storage management is performed by IBM MQ. A "real world" example would need to deal with errors; in the sample errors are written out to the console.

The sample code has the following steps,

Define the single message consumption callback function,

void MessageConsumer(MQHCONN      hConn,
                        MQMD    * pMsgDesc,
                        MQGMO   * pGetMsgOpts,
                        MQBYTE  * Buffer,
                        MQCBC   * pContext)
{ ... }

Connect to the queue manager,

MQCONNX(QMName,&cno,&Hcon,&CompCode,&CReason);

Open the input queues, and associate each one with the MessageConsumer callback function,
```
MQOPEN(Hcon,&od,O_options,&Hobj,&OpenCode,&Reason);
cbd.CallbackFunction = MessageConsumer;
MQCB(Hcon,MQOP_REGISTER,&cbd,Hobj,&md,&gmo,&CompCode,&Reason);
```
cbd.CallbackFunction does not need to be set for each queue; it is an input-only field. But you could associate a different callback function with each queue.

Start consumption of the messages,

MQCTL(Hcon,MQOP_START,&ctlo,&CompCode,&Reason);

Wait until the user has pressed enter and then stop consumption of messages,
```
MQCTL(Hcon,MQOP_STOP,&ctlo,&CompCode,&Reason);
```
Finally disconnect from the queue manager,
```
MQDISC(&Hcon,&CompCode,&Reason);
```

Parent topic: Use the sample programs on Multiplatforms