Working With Consumers

When you create a consumer, you need to make several decisions:

• Do you want to receive messages synchronously or asynchronously?

  If you create a synchronous consumer, you can call one of three kinds of receive functions to receive your messages. If you create an asynchronous consumer, you must specify the name of a callback function that the client runtime can call when a message is delivered to the destination for that consumer. For information about the callback function signature, see Callback Type for Asynchronous Message Consumption .

• If you are consuming messages from a topic, do you want to use a durable or a nondurable consumer?

  A durable consumer receives all the messages published to a topic, including the ones published while the subscriber is inactive. A nondurable consumer only receives messages while the subscriber is active.

  The broker retains a record of this durable subscription and makes sure that all messages from the publishers to this topic are retained until they are either acknowledged by this durable subscriber or until they have expired. Sessions with durable subscribers must always provide the same client identifier. In addition, each consumer must specify a durable name using the durableName parameter, which uniquely identifies (for each client identifier) each durable subscription it creates.

A session’s consumers are automatically closed when you close the session or connection to which they belong. However, messages will be routed to the durable subscriber while it is inactive and delivered when a new durable consumer is recreated. To close a consumer without closing the session or connection to which it belongs, use the MQCloseMessageConsumer() function. If you want to close a durable consumer permanently, you should call the function MQUnsubscribeDurableMessageConsumer after closing it, to delete state information maintained by the broker on behalf of the durable consumer.