/**
* 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 java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import org.apache.ambari.server.configuration.Configuration;
import org.apache.ambari.server.controller.utilities.ScalingThreadPoolExecutor;
import org.apache.ambari.server.events.AlertEvent;
import com.google.common.eventbus.AsyncEventBus;
import com.google.common.eventbus.EventBus;
import com.google.common.eventbus.Subscribe;
import com.google.inject.Inject;
import com.google.inject.Singleton;
/**
* The {@link AlertEventPublisher} is used to wrap a customized instance of an
* {@link AsyncEventBus} that is only used for alerts. In general, Ambari should
* have its own application-wide event bus for application events (session
* information, state changes, etc), but since alerts can contain many events
* being published concurrently, it makes sense to encapsulate a specific alert
* bus in this publisher.
*/
@Singleton
public final class AlertEventPublisher {
/**
* A multi-threaded event bus that can handle dispatching {@link AlertEvent}s.
*/
private final EventBus m_eventBus;
/**
* Constructor.
*/
@Inject
public AlertEventPublisher(Configuration config) {
// create an executor which will scale with the number of queued work items
// when handling incoming alerts
int corePoolSize = config.getAlertEventPublisherCorePoolSize();
int maxPoolSize = config.getAlertEventPublisherMaxPoolSize();
int workerQueueSize = config.getAlertEventPublisherWorkerQueueSize();
ThreadPoolExecutor executor = new ScalingThreadPoolExecutor(corePoolSize, maxPoolSize, 0L,
TimeUnit.SECONDS, workerQueueSize);
executor.allowCoreThreadTimeOut(false);
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardOldestPolicy());
executor.setThreadFactory(new AlertEventBusThreadFactory());
m_eventBus = new AsyncEventBus(executor);
}
/**
* Publishes the specified event to all registered listeners that
* {@link Subscribe} to any of the {@link AlertEvent} instances.
*
* @param event
*/
public void publish(AlertEvent event) {
m_eventBus.post(event);
}
/**
* Register a listener to receive events. The listener should use the
* {@link Subscribe} annotation.
*
* @param object
* the listener to receive events.
*/
public void register(Object object) {
m_eventBus.register(object);
}
/**
* A custom {@link ThreadFactory} for the threads that will handle published
* {@link AlertEvent}. Threads created will have slightly reduced priority
* since {@link AlertEvent} instances are not critical to the system.
*/
private static final class AlertEventBusThreadFactory implements
ThreadFactory {
private static final AtomicInteger s_threadIdPool = new AtomicInteger(1);
/**
* {@inheritDoc}
*/
@Override
public Thread newThread(Runnable r) {
Thread thread = new Thread(r, "alert-event-bus-"
+ s_threadIdPool.getAndIncrement());
thread.setDaemon(false);
thread.setPriority(Thread.NORM_PRIORITY - 1);
return thread;
}
}
}