/**
* 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.hadoop.yarn.event;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience.Public;
import org.apache.hadoop.classification.InterfaceStability.Evolving;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.service.AbstractService;
import org.apache.hadoop.util.ShutdownHookManager;
import org.apache.hadoop.yarn.exceptions.YarnRuntimeException;
/**
* Dispatches {@link Event}s in a separate thread. Currently only single thread
* does that. Potentially there could be multiple channels for each event type
* class and a thread pool can be used to dispatch the events.
*/
@SuppressWarnings("rawtypes")
@Public
@Evolving
public class AsyncDispatcher extends AbstractService implements Dispatcher {
private static final Log LOG = LogFactory.getLog(AsyncDispatcher.class);
private final BlockingQueue<Event> eventQueue;
private volatile boolean stopped = false;
// Configuration flag for enabling/disabling draining dispatcher's events on
// stop functionality.
private volatile boolean drainEventsOnStop = false;
// Indicates all the remaining dispatcher's events on stop have been drained
// and processed.
private volatile boolean drained = true;
private Object waitForDrained = new Object();
// For drainEventsOnStop enabled only, block newly coming events into the
// queue while stopping.
private volatile boolean blockNewEvents = false;
private EventHandler handlerInstance = null;
private Thread eventHandlingThread;
protected final Map<Class<? extends Enum>, EventHandler> eventDispatchers;
private boolean exitOnDispatchException;
public AsyncDispatcher() {
this(new LinkedBlockingQueue<Event>());
}
public AsyncDispatcher(BlockingQueue<Event> eventQueue) {
super("Dispatcher");
this.eventQueue = eventQueue;
this.eventDispatchers = new HashMap<Class<? extends Enum>, EventHandler>();
}
Runnable createThread() {
return new Runnable() {
@Override
public void run() {
while (!stopped && !Thread.currentThread().isInterrupted()) {
drained = eventQueue.isEmpty();
// blockNewEvents is only set when dispatcher is draining to stop,
// adding this check is to avoid the overhead of acquiring the lock
// and calling notify every time in the normal run of the loop.
if (blockNewEvents) {
synchronized (waitForDrained) {
if (drained) {
waitForDrained.notify();
}
}
}
Event event;
try {
event = eventQueue.take();
} catch(InterruptedException ie) {
if (!stopped) {
LOG.warn("AsyncDispatcher thread interrupted", ie);
}
return;
}
if (event != null) {
dispatch(event);
}
}
}
};
}
@Override
protected void serviceInit(Configuration conf) throws Exception {
this.exitOnDispatchException =
conf.getBoolean(Dispatcher.DISPATCHER_EXIT_ON_ERROR_KEY,
Dispatcher.DEFAULT_DISPATCHER_EXIT_ON_ERROR);
super.serviceInit(conf);
}
@Override
protected void serviceStart() throws Exception {
//start all the components
super.serviceStart();
eventHandlingThread = new Thread(createThread());
eventHandlingThread.setName("AsyncDispatcher event handler");
eventHandlingThread.start();
}
public void setDrainEventsOnStop() {
drainEventsOnStop = true;
}
@Override
protected void serviceStop() throws Exception {
if (drainEventsOnStop) {
blockNewEvents = true;
LOG.info("AsyncDispatcher is draining to stop, igonring any new events.");
synchronized (waitForDrained) {
while (!drained && eventHandlingThread.isAlive()) {
waitForDrained.wait(1000);
LOG.info("Waiting for AsyncDispatcher to drain.");
}
}
}
stopped = true;
if (eventHandlingThread != null) {
eventHandlingThread.interrupt();
try {
eventHandlingThread.join();
} catch (InterruptedException ie) {
LOG.warn("Interrupted Exception while stopping", ie);
}
}
// stop all the components
super.serviceStop();
}
@SuppressWarnings("unchecked")
protected void dispatch(Event event) {
//all events go thru this loop
if (LOG.isDebugEnabled()) {
LOG.debug("Dispatching the event " + event.getClass().getName() + "."
+ event.toString());
}
Class<? extends Enum> type = event.getType().getDeclaringClass();
try{
EventHandler handler = eventDispatchers.get(type);
if(handler != null) {
handler.handle(event);
} else {
throw new Exception("No handler for registered for " + type);
}
} catch (Throwable t) {
//TODO Maybe log the state of the queue
LOG.fatal("Error in dispatcher thread", t);
// If serviceStop is called, we should exit this thread gracefully.
if (exitOnDispatchException
&& (ShutdownHookManager.get().isShutdownInProgress()) == false
&& stopped == false) {
LOG.info("Exiting, bbye..");
System.exit(-1);
}
}
}
@SuppressWarnings("unchecked")
@Override
public void register(Class<? extends Enum> eventType,
EventHandler handler) {
/* check to see if we have a listener registered */
EventHandler<Event> registeredHandler = (EventHandler<Event>)
eventDispatchers.get(eventType);
LOG.info("Registering " + eventType + " for " + handler.getClass());
if (registeredHandler == null) {
eventDispatchers.put(eventType, handler);
} else if (!(registeredHandler instanceof MultiListenerHandler)){
/* for multiple listeners of an event add the multiple listener handler */
MultiListenerHandler multiHandler = new MultiListenerHandler();
multiHandler.addHandler(registeredHandler);
multiHandler.addHandler(handler);
eventDispatchers.put(eventType, multiHandler);
} else {
/* already a multilistener, just add to it */
MultiListenerHandler multiHandler
= (MultiListenerHandler) registeredHandler;
multiHandler.addHandler(handler);
}
}
@Override
public EventHandler getEventHandler() {
if (handlerInstance == null) {
handlerInstance = new GenericEventHandler();
}
return handlerInstance;
}
class GenericEventHandler implements EventHandler<Event> {
public void handle(Event event) {
if (blockNewEvents) {
return;
}
drained = false;
/* all this method does is enqueue all the events onto the queue */
int qSize = eventQueue.size();
if (qSize !=0 && qSize %1000 == 0) {
LOG.info("Size of event-queue is " + qSize);
}
int remCapacity = eventQueue.remainingCapacity();
if (remCapacity < 1000) {
LOG.warn("Very low remaining capacity in the event-queue: "
+ remCapacity);
}
try {
eventQueue.put(event);
} catch (InterruptedException e) {
if (!stopped) {
LOG.warn("AsyncDispatcher thread interrupted", e);
}
throw new YarnRuntimeException(e);
}
};
}
/**
* Multiplexing an event. Sending it to different handlers that
* are interested in the event.
* @param <T> the type of event these multiple handlers are interested in.
*/
static class MultiListenerHandler implements EventHandler<Event> {
List<EventHandler<Event>> listofHandlers;
public MultiListenerHandler() {
listofHandlers = new ArrayList<EventHandler<Event>>();
}
@Override
public void handle(Event event) {
for (EventHandler<Event> handler: listofHandlers) {
handler.handle(event);
}
}
void addHandler(EventHandler<Event> handler) {
listofHandlers.add(handler);
}
}
}