2 * Copyright (c) 2014 Brocade Communications Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
9 package org.opendaylight.yangtools.util.concurrent;
11 import java.util.ArrayList;
12 import java.util.Arrays;
13 import java.util.List;
14 import java.util.concurrent.BlockingQueue;
15 import java.util.concurrent.ConcurrentHashMap;
16 import java.util.concurrent.ConcurrentMap;
17 import java.util.concurrent.Executor;
18 import java.util.concurrent.LinkedBlockingQueue;
19 import java.util.concurrent.RejectedExecutionException;
20 import java.util.concurrent.TimeUnit;
21 import java.util.concurrent.locks.Lock;
22 import java.util.concurrent.locks.ReentrantLock;
24 import javax.annotation.concurrent.GuardedBy;
26 import org.slf4j.Logger;
27 import org.slf4j.LoggerFactory;
29 import com.google.common.base.Preconditions;
32 * This class manages queuing and dispatching notifications for multiple listeners concurrently.
33 * Notifications are queued on a per-listener basis and dispatched serially to each listener via an
36 * This class optimizes its memory footprint by only allocating and maintaining a queue and executor
37 * task for a listener when there are pending notifications. On the first notification(s), a queue
38 * is created and a task is submitted to the executor to dispatch the queue to the associated
39 * listener. Any subsequent notifications that occur before all previous notifications have been
40 * dispatched are appended to the existing queue. When all notifications have been dispatched, the
41 * queue and task are discarded.
43 * @author Thomas Pantelis
45 * @param <L> the listener type
46 * @param <N> the notification type
48 public class QueuedNotificationManager<L,N> implements NotificationManager<L,N> {
51 * Interface implemented by clients that does the work of invoking listeners with notifications.
53 * @author Thomas Pantelis
55 * @param <L> the listener type
56 * @param <N> the notification type
58 public interface Invoker<L,N> {
61 * Called to invoke a listener with a notification.
63 * @param listener the listener to invoke
64 * @param notification the notification to send
66 void invokeListener( L listener, N notification );
69 private static final Logger LOG = LoggerFactory.getLogger( QueuedNotificationManager.class );
71 private final Executor executor;
72 private final Invoker<L,N> listenerInvoker;
74 private final ConcurrentMap<ListenerKey<L>,NotificationTask>
75 listenerCache = new ConcurrentHashMap<>();
77 private final String name;
78 private final int maxQueueCapacity;
83 * @param executor the {@link Executor} to use for notification tasks
84 * @param listenerInvoker the {@link Invoker} to use for invoking listeners
85 * @param maxQueueCapacity the capacity of each listener queue
86 * @param name the name of this instance for logging info
88 public QueuedNotificationManager( Executor executor, Invoker<L,N> listenerInvoker,
89 int maxQueueCapacity, String name ) {
90 this.executor = Preconditions.checkNotNull( executor );
91 this.listenerInvoker = Preconditions.checkNotNull( listenerInvoker );
92 Preconditions.checkArgument( maxQueueCapacity > 0, "maxQueueCapacity must be > 0 " );
93 this.maxQueueCapacity = maxQueueCapacity;
94 this.name = Preconditions.checkNotNull( name );
98 * @see org.opendaylight.yangtools.util.concurrent.NotificationManager#addNotification(L, N)
101 public void submitNotification( final L listener, final N notification )
102 throws RejectedExecutionException {
104 if( notification == null ) {
108 submitNotifications( listener, Arrays.asList( notification ) );
112 * @see org.opendaylight.yangtools.util.concurrent.NotificationManager#submitNotifications(L, java.util.Collection)
115 public void submitNotifications( final L listener, final Iterable<N> notifications )
116 throws RejectedExecutionException {
118 if( notifications == null || listener == null ) {
122 if( LOG.isTraceEnabled() ) {
123 LOG.trace( "{}: submitNotifications for listener {}: {}",
124 name, listener.toString(), notifications );
127 ListenerKey<L> key = new ListenerKey<>( listener );
128 NotificationTask newNotificationTask = null;
130 // Keep looping until we are either able to add a new NotificationTask or are able to
131 // add our notifications to an existing NotificationTask. Eventually one or the other
136 NotificationTask existingTask = listenerCache.get( key );
138 if( existingTask == null || !existingTask.submitNotifications( notifications ) ) {
140 // Either there's no existing task or we couldn't add our notifications to the
141 // existing one because it's in the process of exiting and removing itself from
142 // the cache. Either way try to put a new task in the cache. If we can't put
143 // then either the existing one is still there and hasn't removed itself quite
144 // yet or some other concurrent thread beat us to the put although this method
145 // shouldn't be called concurrently for the same listener as that would violate
146 // notification ordering. In any case loop back up and try again.
148 if( newNotificationTask == null ) {
149 newNotificationTask = new NotificationTask( key, notifications );
152 existingTask = listenerCache.putIfAbsent( key, newNotificationTask );
153 if( existingTask == null ) {
155 // We were able to put our new task - now submit it to the executor and
156 // we're done. If it throws a RejectedxecutionException, let that propagate
159 LOG.debug( "{}: Submitting NotificationTask for listener {}",
160 name, listener.toString() );
162 executor.execute( newNotificationTask );
167 // We were able to add our notifications to an existing task so we're done.
172 } catch( InterruptedException e ) {
174 // We were interrupted trying to offer to the listener's queue. Somebody's probably
175 // telling us to quit.
177 LOG.debug( "{}: Interrupted trying to add to {} listener's queue",
178 name, listener.toString() );
181 if( LOG.isTraceEnabled() ) {
182 LOG.trace( "{}: submitNotifications dine for listener {}",
183 name, listener.toString() );
188 * Returns {@link ListenerNotificationQueueStats} instances for each current listener
189 * notification task in progress.
191 public List<ListenerNotificationQueueStats> getListenerNotificationQueueStats() {
192 List<ListenerNotificationQueueStats> statsList = new ArrayList<>( listenerCache.size() );
193 for( NotificationTask task: listenerCache.values() ) {
194 statsList.add( new ListenerNotificationQueueStats(
195 task.listenerKey.toString(), task.notificationQueue.size() ) );
202 * Returns the maximum listener queue capacity.
204 public int getMaxQueueCapacity(){
205 return maxQueueCapacity;
209 * Returns the {@link Executor} to used for notification tasks.
211 public Executor getExecutor(){
216 * Used as the listenerCache map key. We key by listener reference identity hashCode/equals.
217 * Since we don't know anything about the listener class implementations and we're mixing
218 * multiple listener class instances in the same map, this avoids any potential issue with an
219 * equals implementation that just blindly casts the other Object to compare instead of checking
222 private static class ListenerKey<L> {
224 private final L listener;
226 public ListenerKey( L listener ) {
227 this.listener = listener;
235 public int hashCode() {
236 return System.identityHashCode( listener );
240 public boolean equals( Object obj ) {
244 if (!(obj instanceof ListenerKey<?>)) {
248 ListenerKey<?> other = (ListenerKey<?>) obj;
249 return listener == other.listener;
253 public String toString() {
254 return listener.toString();
259 * Executor task for a single listener that queues notifications and sends them serially to the
262 private class NotificationTask implements Runnable {
264 private final BlockingQueue<N> notificationQueue;
266 private volatile boolean done = false;
268 @GuardedBy("queuingLock")
269 private boolean queuedNotifications = false;
271 private final Lock queuingLock = new ReentrantLock();
273 private final ListenerKey<L> listenerKey;
275 NotificationTask( ListenerKey<L> listenerKey, Iterable<N> notifications ) {
277 this.listenerKey = listenerKey;
278 this.notificationQueue = new LinkedBlockingQueue<>( maxQueueCapacity );
280 for( N notification: notifications ) {
281 this.notificationQueue.add( notification );
285 boolean submitNotifications( Iterable<N> notifications ) throws InterruptedException {
290 // Check the done flag - if true then #run is in the process of exiting so return
291 // false to indicate such. Otherwise, offer the notifications to the queue.
297 for( N notification: notifications ) {
301 // Try to offer for up to a minute and log a message if it times out.
303 // FIXME: we loop forever to guarantee delivery however this leaves it open
304 // for 1 rogue listener to bring everyone to a halt. Another option is to
305 // limit the tries and give up after a while and drop the notification.
306 // Given a reasonably large queue capacity and long timeout, if we still
307 // can't queue then most likely the listener is an unrecoverable state
308 // (deadlock or endless loop).
310 if( LOG.isDebugEnabled() ) {
311 LOG.debug( "{}: Offering notification to the queue for listener {}: {}",
312 name, listenerKey.toString(), notification );
315 if( notificationQueue.offer( notification, 1, TimeUnit.MINUTES ) ) {
320 "{}: Timed out trying to offer a notification to the queue for listener {}." +
321 "The queue has reached its capacity of {}",
322 name, listenerKey.toString(), maxQueueCapacity );
326 // Set the queuedNotifications flag to tell #run that we've just queued
327 // notifications and not to exit yet, even if it thinks the queue is empty at this
330 queuedNotifications = true;
333 queuingLock.unlock();
343 // Loop until we've dispatched all the notifications in the queue.
347 // Get the notification at the head of the queue, waiting a little bit for one
350 N notification = notificationQueue.poll( 10, TimeUnit.MILLISECONDS );
351 if( notification == null ) {
353 // The queue is empty - try to get the queuingLock. If we can't get the lock
354 // then #submitNotifications is in the process of offering to the queue so
355 // we'll loop back up and poll the queue again.
357 if( queuingLock.tryLock() ) {
360 // Check the queuedNotifications flag to see if #submitNotifications
361 // has offered new notification(s) to the queue. If so, loop back up
362 // and poll the queue again. Otherwise set done to true and exit.
363 // Once we set the done flag and unlock, calls to
364 // #submitNotifications will fail and a new task will be created.
366 if( !queuedNotifications ) {
371 // Clear the queuedNotifications flag so we'll try to exit the next
372 // time through the loop when the queue is empty.
374 queuedNotifications = false;
377 queuingLock.unlock();
382 notifyListener( notification );
384 } catch( InterruptedException e ) {
386 // The executor is probably shutting down so log as debug.
387 LOG.debug( "{}: Interrupted trying to remove from {} listener's queue",
388 name, listenerKey.toString() );
391 // We're exiting, gracefully or not - either way make sure we always remove
392 // ourselves from the cache.
394 listenerCache.remove( listenerKey );
398 private void notifyListener( N notification ) {
400 if( notification == null ) {
406 if( LOG.isDebugEnabled() ) {
407 LOG.debug( "{}: Invoking listener {} with notification: {}",
408 name, listenerKey.toString(), notification );
411 listenerInvoker.invokeListener( listenerKey.getListener(), notification );
413 } catch( RuntimeException e ) {
415 // We'll let a RuntimeException from the listener slide and keep sending any
416 // remaining notifications.
418 LOG.error( String.format( "%1$s: Error notifying listener %2$s", name,
419 listenerKey.toString() ), e );
423 // A JVM Error is severe - best practice is to throw them up the chain. Set done to
424 // true so no new notifications can be added to this task as we're about to bail.