Chapter 2 Messages : Synchronous and Asynchronous Message Consumption

Synchronous and Asynchronous Message Consumption
The EMS APIs allow for both synchronous or asynchronous message consumption. For synchronous consumption, the message consumer explicitly invokes a receive call on the topic or queue. When synchronously receiving messages, the consumer remains blocked until a message arrives. See Receiving Messages for details.
The consumer can receive messages asynchronously by registering a message listener to receive the messages. When a message arrives at the destination, the message listener delivers the message to the message consumer. The message consumer is free to do other operations between messages. See Creating a Message Listener for Asynchronous Message Consumption for details.