Class SubscriberRegistry

output/java_guava/1.4.18/SubscriberRegistry.java:54–244

Registry of subscribers to a single event bus. @author Colin Decker

final class SubscriberRegistry {

  /**
   * All registered subscribers, indexed by event type.
   *
   * <p>The {@link CopyOnWriteArraySet} values make it easy and relatively lightweight to get an
   * immutable snapshot of all current subscribers to an event without any locking.
   */
  private final ConcurrentMap<Class<?>, CopyOnWriteArraySet<Subscriber>> subscribers = Maps.newConcurrentMap();

  /**
   * The event bus this registry belongs to.
   */

  @Weak
  private final EventBus bus;

  SubscriberRegistry(EventBus bus) {
    this.bus = checkNotNull(bus);
  }

  /**
   * Registers all subscriber methods on the given listener object.
   */

  void register(Object listener) {
    Multimap<Class<?>, Subscriber> listenerMethods = findAllSubscribers(listener);
    for (Map.Entry<Class<?>, Collection<Subscriber>> entry : listenerMethods.asMap().entrySet()) {
      Class<?> eventType = entry.getKey();
      Collection<Subscriber> eventMethodsInListener = entry.getValue();
      CopyOnWriteArraySet<Subscriber> eventSubscribers = subscribers.get(eventType);
      if (eventSubscribers == null) {
        CopyOnWriteArraySet<Subscriber> newSet = new CopyOnWriteArraySet<Subscriber>();
        eventSubscribers = MoreObjects.firstNonNull(subscribers.putIfAbsent(eventType, newSet), newSet);
      }
      eventSubscribers.addAll(eventMethodsInListener);
    }
  }

  /**
   * Unregisters all subscribers on the given listener object.
   */

  void unregister(Object listener) {
    Multimap<Class<?>, Subscriber> listenerMethods = findAllSubscribers(listener);
    for (Map.Entry<Class<?>, Collection<Subscriber>> entry : listenerMethods.asMap().entrySet()) {
      Class<?> eventType = entry.getKey();
      Collection<Subscriber> listenerMethodsForType = entry.getValue();
      CopyOnWriteArraySet<Subscriber> currentSubscribers = subscribers.get(eventType);
      if (currentSubscribers == null
          || !currentSubscribers.removeAll(listenerMethodsForType)) {
        // if removeAll returns true, all we really know is that at least one subscriber was
        // removed... however, barring something very strange we can assume that if at least one
        // subscriber was removed, all subscribers on listener for that event type were... after
        // all, the definition of subscribers on a particular class is totally static
        throw new IllegalArgumentException("missing event subscriber for an annotated method. Is " + listener
        + " registered?");
      }