7.3. Listener Notifications

Each cache event triggers a notification that is dispatched to listeners. A listener is a simple POJO annotated with @Listener. A Listenable is an interface that denotes that the implementation can have listeners attached to it. Each listener is registered using methods defined in the Listenable.
A listener can be attached to both the cache and Cache Manager to allow them to receive cache-level or cache manager-level notifications.
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7.3.1. About Cache-level Notifications

In Red Hat JBoss Data Grid, cache-level events occur on a per-cache basis, and are global and cluster-wide. Examples of cache-level events include the addition, removal and modification of entries, which trigger notifications to listeners registered on the relevant cache.
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7.3.2. Cache Manager-level Notifications

Examples of events that occur in Red Hat JBoss Data Grid at the cache manager-level are:
  • Nodes joining or leaving a cluster;
  • The starting and stopping of caches
Cache manager-level events are located globally and used cluster-wide, but are restricted to events within caches created by a single cache manager.
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7.3.3. About Synchronous and Asynchronous Notifications

By default, notifications in Red Hat JBoss Data Grid are dispatched in the same thread that generates the event. Therefore the listener must be written in a way that does not block or prevent the thread's progression.
Alternatively, the listener can be annotated as asynchronous, which dispatches notifications in a separate thread and prevents blocking the operations of the original thread.
Annotate listeners using the following: 
@Listener (sync = false)
public class MyAsyncListener { .... }
Use the <asyncListenerExecutor/> element in the configuration file to tune the thread pool that is used to dispatch asynchronous notifications.
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