/**
* 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 org.apache.ambari.server.events.publishers;
import org.apache.ambari.server.events.jpa.JPAEvent;
import org.apache.ambari.server.orm.entities.ClusterEntity;
import com.google.common.eventbus.EventBus;
import com.google.inject.Singleton;
/**
* The {@link JPAEventPublisher} is used to publish events pertaining to
* EclipseLink and the persistence layer. This class uses a synchronized bus and
* will therefore run on the current thread. This is desirable since JPA events
* are time-senstive and cannot be executed in an asynchronous manner most of
* the time.
* <p/>
* This publisher was created specifically for AMBARI-17970. The headless server
* thread which monitors the database for things to do (known as the action
* scheduler) polls every second. However, it takes EclipseLink up to 1000ms to
* update L1 persistence context cache references in other threads. Therefore,
* it's possible that the action scheduler can pickup a {@link ClusterEntity}
* with stale data, including stale configurations. Those stale configurations
* can then be sent in commands down to agents.
*/
@Singleton
public class JPAEventPublisher {
/**
* A single threaded, synchronous event bus for processing JPA events.
*/
private final EventBus m_eventBus = new EventBus("ambari-jpa-event-bus");
/**
* Publishes the specified event to all registered listeners that
* {@link com.google.common.eventbus.Subscribe} to any of the
* {@link JPAEventPublisher} instances.
*
* @param event
* the event
*/
public void publish(JPAEvent event) {
m_eventBus.post(event);
}
/**
* Register a listener to receive events. The listener should use the
* {@link com.google.common.eventbus.Subscribe} annotation.
*
* @param object
* the listener to receive events.
*/
public void register(Object object) {
m_eventBus.register(object);
}
}