Examples of org.eclipse.osgi.framework.eventmgr.EventManager

• org.eclipse.osgi.framework.eventmgr.EventManager
  te an EventManager with a name for an asynchronous event dispatch thread EventManager eventManager = new EventManager("SomeEvent Async Event Dispatcher Thread"); // Create a CopyOnWriteIdentityMap to hold the list of SomeEventListeners Map eventListeners = new CopyOnWriteIdentityMap(); // Add a SomeEventListener to the listener list eventListeners.put(someEventListener, null); // Asynchronously deliver a SomeEvent to registered SomeEventListeners // Create the listener queue for this event delivery ListenerQueue listenerQueue = new ListenerQueue(eventManager); // Add the listeners to the queue and associate them with the event dispatcher listenerQueue.queueListeners(eventListeners.entrySet(), new EventDispatcher() { public void dispatchEvent(Object eventListener, Object listenerObject, int eventAction, Object eventObject) { try { (SomeEventListener)eventListener.someEventOccured((SomeEvent)eventObject); } catch (Throwable t) { // properly log/handle any Throwable thrown by the listener } } }); // Deliver the event to the listeners. listenerQueue.dispatchEventAsynchronous(0, new SomeEvent()); // Remove the listener from the listener list eventListeners.remove(someEventListener); // Close EventManager to clean when done to terminate async event dispatch thread. // Note that closing the event manager while asynchronously delivering events // may cause some events to not be delivered before the async event dispatch // thread terminates eventManager.close();

  At first glance, this package may seem more complicated than necessary but it has support for some important features. The listener list supports companion objects for each listener object. This is used by the OSGi framework to create wrapper objects for a listener which are passed to the event dispatcher. The ListenerQueue class is used to build a snap shot of the listeners prior to beginning event dispatch. The OSGi framework uses a 2 level listener list for each listener type (4 types). Level one is managed per framework instance and contains the list of BundleContexts which have registered a listener. Level 2 is managed per BundleContext for the listeners in that context. This allows all the listeners of a bundle to be easily and atomically removed from the level one list. To use a "flat" list for all bundles would require the list to know which bundle registered a listener object so that the list could be traversed when stopping a bundle to remove all the bundle's listeners. When an event is fired, a snapshot list (ListenerQueue) must be made of the current listeners before delivery is attempted. The snapshot list is necessary to allow the listener list to be modified while the event is being delivered to the snapshot list. The memory cost of the snapshot list is low since the ListenerQueue object uses the copy-on-write semantics of the CopyOnWriteIdentityMap. This guarantees the snapshot list is never modified once created. The OSGi framework also uses a 2 level dispatch technique (EventDispatcher). Level one dispatch is used by the framework to add the level 2 listener list of each BundleContext to the snapshot in preparation for delivery of the event. Level 2 dispatch is used as the final event deliverer and must cast the listener and event objects to the proper type before calling the listener. Level 2 dispatch will cancel delivery of an event to a bundle that has stopped between the time the snapshot was created and the attempt was made to deliver the event.

  The highly dynamic nature of the OSGi framework had necessitated these features for proper and efficient event delivery. @since 3.1 @noextend This class is not intended to be subclassed by clients.

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