NonStop JMS C++ API Programmer's Guide

Using the NSJMS C++ APIs

NonStop Server for Java Message Service C++ API Programmer’s Guide—526459-002

5-9

Receiving a Message

NSJMS C++ APIs client uses a Consumer to receive messages from a specified

destination. A message consumer is created by passing a destination name (queue or

topic) and consumer type to the createConsumer() method supplied by a Session

class. The PTP messaging application and the Pub/Sub messaging application both

use the Consumer class as its message consumer.

Consumer class

The Consumer class supports a single receive() method:

Message* receive(int timeout);

A client can request the next message from a message consumer that uses its

receive() method. This call blocks until a message arrives or the timeout expires.

The receive() method takes a timeout argument in milliseconds. This value defines

how long the receive() method should wait when there are no messages available.

For example:

receive(3000); //wait 3 seconds

A value of zero blocks the receive() call indefinitely.

Receiving Messages from a Queue

To receive a message from a queue, clients create a Consumer object by using the

createConsumer() method from the Session class, which has the

Consumer::RECEIVER constant as the consumer type. This method uses a queue

destination to define the location from which the messages are received.

Creating the consumer for a queue (a receiver), starting a transaction, receiving the

message, and then ending the transaction is shown in this code fragment:

char *queueName = “MyQueue”;

// Creating the Receiver

Consumer *pConsumer = pSes->createConsumer(queueName,

Consumer::RECEIVER);

// Starting Transaction, Receiving the Message

BEGINTRANSACTION();

Message *pMsg = pConsumer->receive(3000);

ENDTRANSACTION();

Free Consumer Resources

The Session class contains the freeConsumer() method for freeing consumer

resources. This method takes a pointer to a Consumer object as an argument. This

Note. The Consumer receive operation must be wrapped within a transaction because the

MESSAGE table is audited.