XMS supports persistent and nonpersistent modes of message delivery, and asynchronous and synchronous delivery of messages.
Message delivery mode
- Persistent messages are delivered once. A messaging server takes special precautions, such as logging the messages, to ensure that persistent messages are not lost in transit, even in the event of a failure.
- Nonpersistent messages are delivered no more than once. Nonpersistent messages are less reliable than persistent messages because they can be lost in transit in the event of a failure.
The choice of delivery mode is a trade-off between reliability and performance. Nonpersistent messages are typically transported more quickly than persistent messages.
Asynchronous message delivery
XMS uses one thread to handle all asynchronous
message deliveries for a session. This means that only one message listener function or one
onMessage() method can run at a time.
If more than one message consumer in a session is receiving messages asynchronously, and a
message listener function or
onMessage() method is delivering a message to a
message consumer, then any other message consumers that are waiting for the same message must
continue to wait. Other messages that are waiting to be delivered to the session must also continue
If an application requires concurrent delivery of messages, create more than one session so that
XMS uses more than one thread to handle asynchronous
message delivery. In this way, more than one message listener function or
onMessage() method can run concurrently.
A session is not made asynchronous by assigning a message listener to a consumer. A session
becomes asynchronous only when the
Connection.Start method is called. All
synchronous calls are permitted until the
Connection.Start method is called.
Message delivery to consumers start when the
Connection.Start is called.
If synchronous calls, such as creation of a consumer or producer, must be made on an asynchronous
Connection.Stop must be called. A session can be resumed by calling
Connection.Start method to start delivery of messages. The only exception to
this is the Session message delivery thread, which is the thread that delivers messages to the
callback function. This thread can to make any call on session (except a Close call) in the message
Synchronous message delivery
Messages are delivered synchronously to an application if the application uses the Receive methods of MessageConsumer objects.
Using the Receive methods, an application can wait a specified period of time for a message, or it can wait indefinitely. Alternatively, if an application does not want to wait for a message, it can use the Receive with No Wait method.