Acknowledging Messages

Acknowledging Messages

For each message delivered on a subscription, AMPS counts the message against the subscription backlog until the message is explicitly acknowledged. In addition, when a queue specifies at-least-once delivery, AMPS retains the message in the queue until the message expires or until the message has been explicitly acknowledged and removed from the queue. From the point of view of the AMPS server, acknowledgment is implemented as a sow_delete from the queue with the bookmarks of the messages to remove. The AMPS C# client provides several ways to make it easier for applications to create and send the appropriate sow_delete.

Automatic Acknowledgment

The AMPS client allows you to specify that messages should be automatically acknowledged. When this mode is on, AMPS acknowledges the message automatically in the following cases:

• Asynchronous Message Processing Interface - The message handler returns without throwing an exception.

• Synchronous Message Processing Interface - The application requests the next message from the MessageStream.

AMPS batches acknowledgments created with this method, as described in the following section.

To enable automatic acknowledgment, use the setAutoAck() method.

client.setAutoAck(true);  // enable AutoAck

Message Convenience Method

The AMPS C# client provides a convenience method, ack(), on delivered messages. When the application is finished with the message, the application simply calls ack() on the message. (This, in turn, provides the topic and bookmark to the ack() method of the client that received the message.)

For messages that originated from a queue with at-least-once semantics, this adds the bookmark from the message to the batch of messages to acknowledge. For other messages, this method has no effect.

message.ack(); // Add this message to the next
               // acknowledgment batch.