The Broker guarantees that events from a single publishing Broker client will not be processed out of order. This has important implications when more than one Broker client is sharing the same event queue because the Broker will not return an event to Broker client which is incapable of acknowledging the event.

The following table shows an example event queue containing event received from three different publishing Broker clients; Client A, Client B, and Client C.

Consider these steps:

Since the last event from publishing Broker client A has not yet been acknowledged, the next event in the queue from Broker client A cannot be given to a different receiving client.

By enforcing these acknowledgment rules, the Broker allows you to write client applications that process events from a single queue across multiple threads of control.