com.datastax.oss.driver.internal.core.context.EventBus Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF 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 com.datastax.oss.driver.internal.core.context;
import com.datastax.oss.driver.shaded.guava.common.collect.HashMultimap;
import com.datastax.oss.driver.shaded.guava.common.collect.Multimaps;
import com.datastax.oss.driver.shaded.guava.common.collect.SetMultimap;
import java.util.function.Consumer;
import net.jcip.annotations.ThreadSafe;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Barebones event bus implementation, that allows components to communicate without knowing about
* each other.
*
* This is intended for administrative events (topology changes, new connections, etc.), which
* are comparatively rare in the driver. Do not use it for anything on the request path, because it
* relies on synchronization.
*
*
We don't use Guava's implementation because Guava is shaded in the driver, and the event bus
* needs to be accessible from low-level 3rd party customizations.
*/
@ThreadSafe
public class EventBus {
private static final Logger LOG = LoggerFactory.getLogger(EventBus.class);
private final String logPrefix;
private final SetMultimap, Consumer> listeners =
Multimaps.synchronizedSetMultimap(HashMultimap.create());
public EventBus(String logPrefix) {
this.logPrefix = logPrefix;
}
/**
* Registers a listener for an event type.
*
* If the listener has a shorter lifecycle than the {@code Cluster} instance, it is recommended
* to save the key returned by this method, and use it later to unregister and therefore avoid a
* leak.
*
* @return a key that is needed to unregister later.
*/
public Object register(Class eventClass, Consumer listener) {
LOG.debug("[{}] Registering {} for {}", logPrefix, listener, eventClass);
listeners.put(eventClass, listener);
// The reason for the key mechanism is that this will often be used with method references,
// and you get a different object every time you reference a method, so register(Foo::bar)
// followed by unregister(Foo::bar) wouldn't work as expected.
return listener;
}
/**
* Unregisters a listener.
*
* @param key the key that was returned by {@link #register(Class, Consumer)}
*/
public boolean unregister(Object key, Class eventClass) {
LOG.debug("[{}] Unregistering {} for {}", logPrefix, key, eventClass);
return listeners.remove(eventClass, key);
}
/**
* Sends an event that will notify any registered listener for that class.
*
* Listeners are looked up by an exact match on the class of the object, as returned by
* {@code event.getClass()}. Listeners of a supertype won't be notified.
*
*
The listeners are invoked on the calling thread. It's their responsibility to schedule event
* processing asynchronously if needed.
*/
public void fire(Object event) {
LOG.debug("[{}] Firing an instance of {}: {}", logPrefix, event.getClass(), event);
// if the exact match thing gets too cumbersome, we can reconsider, but I'd like to avoid
// scanning all the keys with instanceof checks.
Class eventClass = event.getClass();
for (Consumer l : listeners.get(eventClass)) {
@SuppressWarnings("unchecked")
Consumer