core/src/main/java/dev/kske/eventbus/core/EventBus.java

@@ -90,6 +90,16 @@ public final class EventBus {
 	 */
 	private final Map<Class<?>, TreeSet<EventHandler>> bindings = new ConcurrentHashMap<>();
 
+	/**
+	 * A cache mapping an event class to all handlers the event should be dispatched to. This
+	 * includes polymorphic handlers that don't reference the event class explicitly. If an event
+	 * class is not contained inside this cache, the {@link #bindings} have to be traversed manually
+	 * in search of applicable handlers.
+	 *
+	 * @since 1.3.0
+	 */
+	private final Map<Class<?>, TreeSet<EventHandler>> bindingCache = new ConcurrentHashMap<>();
+
 	/**
 	 * Stores all registered event listeners (which declare event handlers) and prevents them from
 	 * being garbage collected.
@@ -175,24 +185,32 @@ public final class EventBus {
 	 * Searches for the event handlers bound to an event class. This includes polymorphic handlers
 	 * that are bound to a supertype of the event class.
 	 *
+	 * @implNote If the given event type was requested in the past, the handlers are retrieved from
+	 *           the {@link #bindingCache}. If not, the entire {@link #bindings} are traversed in
+	 *           search of polymorphic handlers compatible with the event type.
 	 * @param eventType the event type to use for the search
 	 * @return a navigable set containing the applicable handlers in descending order of priority
 	 * @since 1.2.0
 	 */
 	private NavigableSet<EventHandler> getHandlersFor(Class<?> eventType) {
+		if (bindingCache.containsKey(eventType)) {
+			return bindingCache.get(eventType);
+		} else {
 
-		// Get handlers defined for the event class
-		TreeSet<EventHandler> handlers =
-			bindings.getOrDefault(eventType, new TreeSet<>(byPriority));
+			// Get handlers defined for the event class
+			TreeSet<EventHandler> handlers =
+				bindings.getOrDefault(eventType, new TreeSet<>(byPriority));
 
-		// Get polymorphic handlers
-		for (var binding : bindings.entrySet())
-			if (binding.getKey().isAssignableFrom(eventType))
-				for (var handler : binding.getValue())
-					if (handler.isPolymorphic())
-						handlers.add(handler);
+			// Get polymorphic handlers
+			for (var binding : bindings.entrySet())
+				if (binding.getKey().isAssignableFrom(eventType))
+					for (var handler : binding.getValue())
+						if (handler.isPolymorphic())
+							handlers.add(handler);
 
-		return handlers;
+			bindingCache.put(eventType, handlers);
+			return handlers;
+		}
 	}
 
 	/**
@@ -369,15 +387,28 @@ public final class EventBus {
 	}
 
 	/**
-	 * Inserts a new handler into the {@link #bindings} map.
+	 * Inserts a new handler into the {@link #bindings} map. Additionally, the handler is placed
+	 * inside the {@link #bindingCache} where applicable.
 	 *
 	 * @param handler the handler to bind
 	 * @since 1.2.0
 	 */
 	private void bindHandler(EventHandler handler) {
+
+		// Bind handler
 		bindings.putIfAbsent(handler.getEventType(), new TreeSet<>(byPriority));
 		logger.log(Level.DEBUG, "Binding event handler {0}", handler);
 		bindings.get(handler.getEventType()).add(handler);
+
+		// Insert handler into cache
+		bindingCache.putIfAbsent(handler.getEventType(), new TreeSet<>(byPriority));
+		bindingCache.get(handler.getEventType()).add(handler);
+
+		// Handler is polymorphic => insert where applicable
+		if (handler.isPolymorphic())
+			for (var binding : bindingCache.entrySet())
+				if (binding.getKey().isAssignableFrom(handler.getEventType()))
+					binding.getValue().add(handler);
 	}
 
 	/**
@@ -402,6 +433,18 @@ public final class EventBus {
 			}
 		}
 
+		// Remove bindings from cache
+		for (var binding : bindingCache.values()) {
+			var it = binding.iterator();
+			while (it.hasNext()) {
+				var handler = it.next();
+				if (handler.getListener() == listener) {
+					logger.log(Level.TRACE, "Removing event handler {0} from cache", handler);
+					it.remove();
+				}
+			}
+		}
+
 		// Remove the listener itself
 		registeredListeners.remove(listener);
 	}