org.killbill.commons.eventbus.SubscriberRegistry Maven / Gradle / Ivy
/*
* Copyright (C) 2007 The Guava Authors
* Copyright 2020-2022 Equinix, Inc
* Copyright 2014-2022 The Billing Project, LLC
*
* The Billing Project licenses this file to you under the Apache License, version 2.0
* (the "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package org.killbill.commons.eventbus;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CopyOnWriteArraySet;
import javax.annotation.CheckForNull;
import org.killbill.commons.utils.Preconditions;
import org.killbill.commons.utils.Primitives;
import org.killbill.commons.utils.TypeToken;
import org.killbill.commons.utils.annotation.VisibleForTesting;
import org.killbill.commons.utils.cache.Cache;
import org.killbill.commons.utils.cache.DefaultCache;
import org.killbill.commons.utils.cache.DefaultSynchronizedCache;
import org.killbill.commons.utils.collect.Iterators;
import org.killbill.commons.utils.collect.MultiValueHashMap;
import org.killbill.commons.utils.collect.MultiValueMap;
/**
* Registry of subscribers to a single event bus.
*
* @author Colin Decker
*/
final class SubscriberRegistry {
/**
* All registered subscribers, indexed by event type.
*
* 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, CopyOnWriteArraySet> subscribers = new ConcurrentHashMap<>();
/** The event bus this registry belongs to. */
private final EventBus bus;
SubscriberRegistry(final EventBus bus) {
this.bus = Preconditions.checkNotNull(bus);
}
/** Registers all subscriber methods on the given listener object. */
void register(final Object listener) {
final MultiValueMap, Subscriber> listenerMethods = findAllSubscribers(listener);
for (final Entry, List> entry : listenerMethods.entrySet()) {
final Class eventType = entry.getKey();
final Collection eventMethodsInListener = entry.getValue();
CopyOnWriteArraySet eventSubscribers = subscribers.get(eventType);
if (eventSubscribers == null) {
final CopyOnWriteArraySet newSet = new CopyOnWriteArraySet<>();
eventSubscribers = Objects.requireNonNullElse(subscribers.putIfAbsent(eventType, newSet), newSet);
}
eventSubscribers.addAll(eventMethodsInListener);
}
}
/** Unregisters all subscribers on the given listener object. */
void unregister(final Object listener) {
final MultiValueMap, Subscriber> listenerMethods = findAllSubscribers(listener);
for (final Entry, List> entry : listenerMethods.entrySet()) {
final Class eventType = entry.getKey();
final Collection listenerMethodsForType = entry.getValue();
final CopyOnWriteArraySet 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?");
}
// don't try to remove the set if it's empty; that can't be done safely without a lock
// anyway, if the set is empty it'll just be wrapping an array of length 0
}
}
@VisibleForTesting
Set getSubscribersForTesting(final Class eventType) {
return Objects.requireNonNullElse(subscribers.get(eventType), Collections.emptySet());
}
/**
* Gets an iterator representing an immutable snapshot of all subscribers to the given event at
* the time this method is called.
*/
Iterator getSubscribers(final Object event) {
final Set> eventTypes = flattenHierarchy(event.getClass());
final List> subscriberIterators = new ArrayList<>(eventTypes.size());
for (final Class eventType : eventTypes) {
final CopyOnWriteArraySet eventSubscribers = subscribers.get(eventType);
if (eventSubscribers != null) {
// eager no-copy snapshot
subscriberIterators.add(eventSubscribers.iterator());
}
}
return Iterators.concat(subscriberIterators.iterator());
}
/**
* A thread-safe cache that contains the mapping from each class to all methods in that class and
* all super-classes, that are annotated with {@code @Subscribe}. The cache is shared across all
* instances of this class; this greatly improves performance if multiple EventBus instances are
* created and objects of the same class are registered on all of them.
*/
private static final Cache, List> subscriberMethodsCache = new DefaultSynchronizedCache<>(
Integer.MAX_VALUE,
DefaultCache.NO_TIMEOUT,
SubscriberRegistry::getAnnotatedMethodsNotCached
);
/**
* Returns all subscribers for the given listener grouped by the type of event they subscribe to.
*/
private MultiValueMap, Subscriber> findAllSubscribers(final Object listener) {
final MultiValueMap, Subscriber> methodsInListener = new MultiValueHashMap<>();
final Class clazz = listener.getClass();
for (final Method method : subscriberMethodsCache.get(clazz)) {
final Class[] parameterTypes = method.getParameterTypes();
final Class eventType = parameterTypes[0];
methodsInListener.putElement(eventType, Subscriber.create(bus, listener, method));
}
return methodsInListener;
}
private static List getAnnotatedMethodsNotCached(final Class clazz) {
final Set> supertypes = TypeToken.getRawTypes(clazz);
final Map identifiers = new HashMap<>();
for (final Class supertype : supertypes) {
for (final Method method : supertype.getDeclaredMethods()) {
if (method.isAnnotationPresent(Subscribe.class) && !method.isSynthetic()) {
// TODO(cgdecker): Should check for a generic parameter type and error out
final Class[] parameterTypes = method.getParameterTypes();
Preconditions.checkArgument(parameterTypes.length == 1,
"Method %s has @Subscribe annotation but has %s parameters. Subscriber methods must have exactly 1 parameter.",
method,
parameterTypes.length);
Preconditions.checkArgument(!parameterTypes[0].isPrimitive(),
"@Subscribe method %s's parameter is %s. Subscriber methods cannot accept primitives. Consider changing the parameter to %s.",
method,
parameterTypes[0].getName(),
Primitives.wrap(parameterTypes[0]).getSimpleName());
final MethodIdentifier ident = new MethodIdentifier(method);
if (!identifiers.containsKey(ident)) {
identifiers.put(ident, method);
}
}
}
}
return List.copyOf(identifiers.values());
}
/**
* Global cache of classes to their flattened hierarchy of supertypes.
*
* Guava version
* */
private static final Cache, Set>> flattenHierarchyCache = new DefaultSynchronizedCache<>(
// max size in our cache is mandatory. OTOH, guava version of flattenHierarchyCache have no maxSize.
Integer.MAX_VALUE,
DefaultCache.NO_TIMEOUT,
// Note Issue: 1615: Originally, flattenHierarchyCache data type was "LoadingCache" from Guava:
// https://github.com/google/guava/blob/master/guava/src/com/google/common/eventbus/SubscriberRegistry.java#L219
// CacheLoader used ImmutableSet as return value. Somehow ImmutableSet maintains its order, where
// HashSet isn't. This is why we have LinkedHashSet here.
key -> new LinkedHashSet<>(TypeToken.getRawTypes(key)));
/**
* Flattens a class's type hierarchy into a set of {@code Class} objects including all
* superclasses (transitively) and all interfaces implemented by these superclasses.
*/
@VisibleForTesting
static Set> flattenHierarchy(final Class concreteClass) {
return flattenHierarchyCache.get(concreteClass);
}
private static final class MethodIdentifier {
private final String name;
private final List> parameterTypes;
MethodIdentifier(final Method method) {
this.name = method.getName();
this.parameterTypes = Arrays.asList(method.getParameterTypes());
}
@Override
public int hashCode() {
return Objects.hash(name, parameterTypes);
}
@Override
public boolean equals(@CheckForNull final Object o) {
if (o instanceof MethodIdentifier) {
final MethodIdentifier ident = (MethodIdentifier) o;
return name.equals(ident.name) && parameterTypes.equals(ident.parameterTypes);
}
return false;
}
}
}