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.Collections;
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 );
72 * Caps the maximum number of attempts to offer notification to a particular listener. Each
73 * attempt window is 1 minute, so an offer times out after roughly 10 minutes.
75 private static final int MAX_NOTIFICATION_OFFER_ATTEMPTS = 10;
77 private final Executor executor;
78 private final Invoker<L,N> listenerInvoker;
80 private final ConcurrentMap<ListenerKey<L>,NotificationTask>
81 listenerCache = new ConcurrentHashMap<>();
83 private final String name;
84 private final int maxQueueCapacity;
89 * @param executor the {@link Executor} to use for notification tasks
90 * @param listenerInvoker the {@link Invoker} to use for invoking listeners
91 * @param maxQueueCapacity the capacity of each listener queue
92 * @param name the name of this instance for logging info
94 public QueuedNotificationManager( Executor executor, Invoker<L,N> listenerInvoker,
95 int maxQueueCapacity, String name ) {
96 this.executor = Preconditions.checkNotNull( executor );
97 this.listenerInvoker = Preconditions.checkNotNull( listenerInvoker );
98 Preconditions.checkArgument( maxQueueCapacity > 0, "maxQueueCapacity must be > 0 " );
99 this.maxQueueCapacity = maxQueueCapacity;
100 this.name = Preconditions.checkNotNull( name );
104 * @see org.opendaylight.yangtools.util.concurrent.NotificationManager#addNotification(L, N)
107 public void submitNotification( final L listener, final N notification )
108 throws RejectedExecutionException {
110 if( notification == null ) {
114 submitNotifications( listener, Collections.singletonList(notification));
118 * @see org.opendaylight.yangtools.util.concurrent.NotificationManager#submitNotifications(L, java.util.Collection)
121 public void submitNotifications( final L listener, final Iterable<N> notifications )
122 throws RejectedExecutionException {
124 if( notifications == null || listener == null ) {
128 if( LOG.isTraceEnabled() ) {
129 LOG.trace( "{}: submitNotifications for listener {}: {}",
130 name, listener.toString(), notifications );
133 ListenerKey<L> key = new ListenerKey<>( listener );
134 NotificationTask newNotificationTask = null;
136 // Keep looping until we are either able to add a new NotificationTask or are able to
137 // add our notifications to an existing NotificationTask. Eventually one or the other
142 NotificationTask existingTask = listenerCache.get( key );
144 if( existingTask == null || !existingTask.submitNotifications( notifications ) ) {
146 // Either there's no existing task or we couldn't add our notifications to the
147 // existing one because it's in the process of exiting and removing itself from
148 // the cache. Either way try to put a new task in the cache. If we can't put
149 // then either the existing one is still there and hasn't removed itself quite
150 // yet or some other concurrent thread beat us to the put although this method
151 // shouldn't be called concurrently for the same listener as that would violate
152 // notification ordering. In any case loop back up and try again.
154 if( newNotificationTask == null ) {
155 newNotificationTask = new NotificationTask( key, notifications );
158 existingTask = listenerCache.putIfAbsent( key, newNotificationTask );
159 if( existingTask == null ) {
161 // We were able to put our new task - now submit it to the executor and
162 // we're done. If it throws a RejectedxecutionException, let that propagate
165 LOG.debug( "{}: Submitting NotificationTask for listener {}",
166 name, listener.toString() );
168 executor.execute( newNotificationTask );
173 // We were able to add our notifications to an existing task so we're done.
178 } catch( InterruptedException e ) {
180 // We were interrupted trying to offer to the listener's queue. Somebody's probably
181 // telling us to quit.
183 LOG.debug( "{}: Interrupted trying to add to {} listener's queue",
184 name, listener.toString() );
187 if( LOG.isTraceEnabled() ) {
188 LOG.trace( "{}: submitNotifications dine for listener {}",
189 name, listener.toString() );
194 * Returns {@link ListenerNotificationQueueStats} instances for each current listener
195 * notification task in progress.
197 public List<ListenerNotificationQueueStats> getListenerNotificationQueueStats() {
198 List<ListenerNotificationQueueStats> statsList = new ArrayList<>( listenerCache.size() );
199 for( NotificationTask task: listenerCache.values() ) {
200 statsList.add( new ListenerNotificationQueueStats(
201 task.listenerKey.toString(), task.notificationQueue.size() ) );
208 * Returns the maximum listener queue capacity.
210 public int getMaxQueueCapacity(){
211 return maxQueueCapacity;
215 * Returns the {@link Executor} to used for notification tasks.
217 public Executor getExecutor(){
222 * Used as the listenerCache map key. We key by listener reference identity hashCode/equals.
223 * Since we don't know anything about the listener class implementations and we're mixing
224 * multiple listener class instances in the same map, this avoids any potential issue with an
225 * equals implementation that just blindly casts the other Object to compare instead of checking
228 private static class ListenerKey<L> {
230 private final L listener;
232 public ListenerKey( L listener ) {
233 this.listener = listener;
241 public int hashCode() {
242 return System.identityHashCode( listener );
246 public boolean equals( Object obj ) {
250 if (!(obj instanceof ListenerKey<?>)) {
254 ListenerKey<?> other = (ListenerKey<?>) obj;
255 return listener == other.listener;
259 public String toString() {
260 return listener.toString();
265 * Executor task for a single listener that queues notifications and sends them serially to the
268 private class NotificationTask implements Runnable {
270 private final BlockingQueue<N> notificationQueue;
272 private volatile boolean done = false;
274 @GuardedBy("queuingLock")
275 private boolean queuedNotifications = false;
277 private final Lock queuingLock = new ReentrantLock();
279 private final ListenerKey<L> listenerKey;
281 NotificationTask( ListenerKey<L> listenerKey, Iterable<N> notifications ) {
283 this.listenerKey = listenerKey;
284 this.notificationQueue = new LinkedBlockingQueue<>( maxQueueCapacity );
286 for( N notification: notifications ) {
287 this.notificationQueue.add( notification );
291 boolean submitNotifications( Iterable<N> notifications ) throws InterruptedException {
296 // Check the done flag - if true then #run is in the process of exiting so return
297 // false to indicate such. Otherwise, offer the notifications to the queue.
303 for( N notification: notifications ) {
304 boolean notificationOfferAttemptSuccess = false;
305 // The offer is attempted for up to 10 minutes, with a status message printed each minute
306 for (int notificationOfferAttempts = 0;
307 notificationOfferAttempts < MAX_NOTIFICATION_OFFER_ATTEMPTS; notificationOfferAttempts++ ) {
309 // Try to offer for up to a minute and log a message if it times out.
310 if( LOG.isDebugEnabled() ) {
311 LOG.debug( "{}: Offering notification to the queue for listener {}: {}",
312 name, listenerKey.toString(), notification );
315 if( notificationOfferAttemptSuccess = notificationQueue.offer(
316 notification, 1, TimeUnit.MINUTES ) ) {
321 "{}: Timed out trying to offer a notification to the queue for listener {} " +
322 "on attempt {} of {}. " +
323 "The queue has reached its capacity of {}",
324 name, listenerKey.toString(), notificationOfferAttempts, MAX_NOTIFICATION_OFFER_ATTEMPTS,
327 if (!notificationOfferAttemptSuccess) {
329 "{}: Failed to offer a notification to the queue for listener {}. " +
330 "Exceeded max allowable attempts of {} in {} minutes; the listener " +
331 "is likely in an unrecoverable state (deadlock or endless loop).",
332 name, listenerKey.toString(), MAX_NOTIFICATION_OFFER_ATTEMPTS,
333 MAX_NOTIFICATION_OFFER_ATTEMPTS );
337 // Set the queuedNotifications flag to tell #run that we've just queued
338 // notifications and not to exit yet, even if it thinks the queue is empty at this
341 queuedNotifications = true;
344 queuingLock.unlock();
354 // Loop until we've dispatched all the notifications in the queue.
358 // Get the notification at the head of the queue, waiting a little bit for one
361 N notification = notificationQueue.poll( 10, TimeUnit.MILLISECONDS );
362 if( notification == null ) {
364 // The queue is empty - try to get the queuingLock. If we can't get the lock
365 // then #submitNotifications is in the process of offering to the queue so
366 // we'll loop back up and poll the queue again.
368 if( queuingLock.tryLock() ) {
371 // Check the queuedNotifications flag to see if #submitNotifications
372 // has offered new notification(s) to the queue. If so, loop back up
373 // and poll the queue again. Otherwise set done to true and exit.
374 // Once we set the done flag and unlock, calls to
375 // #submitNotifications will fail and a new task will be created.
377 if( !queuedNotifications ) {
382 // Clear the queuedNotifications flag so we'll try to exit the next
383 // time through the loop when the queue is empty.
385 queuedNotifications = false;
388 queuingLock.unlock();
393 notifyListener( notification );
395 } catch( InterruptedException e ) {
397 // The executor is probably shutting down so log as debug.
398 LOG.debug( "{}: Interrupted trying to remove from {} listener's queue",
399 name, listenerKey.toString() );
402 // We're exiting, gracefully or not - either way make sure we always remove
403 // ourselves from the cache.
405 listenerCache.remove( listenerKey );
409 private void notifyListener( N notification ) {
411 if( notification == null ) {
417 if( LOG.isDebugEnabled() ) {
418 LOG.debug( "{}: Invoking listener {} with notification: {}",
419 name, listenerKey.toString(), notification );
422 listenerInvoker.invokeListener( listenerKey.getListener(), notification );
424 } catch( RuntimeException e ) {
426 // We'll let a RuntimeException from the listener slide and keep sending any
427 // remaining notifications.
429 LOG.error( String.format( "%1$s: Error notifying listener %2$s", name,
430 listenerKey.toString() ), e );
434 // A JVM Error is severe - best practice is to throw them up the chain. Set done to
435 // true so no new notifications can be added to this task as we're about to bail.