opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/md/sal/dom/store/impl/ResolveDataChangeEventsTask.java

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   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
   7  */
   8 package org.opendaylight.controller.md.sal.dom.store.impl;
   9
  10 import static org.opendaylight.controller.md.sal.dom.store.impl.DOMImmutableDataChangeEvent.builder;
  11
  12 import java.util.Collection;
  13 import java.util.Collections;
  14 import java.util.HashSet;
  15 import java.util.LinkedList;
  16 import java.util.List;
  17 import java.util.Map.Entry;
  18 import java.util.Set;
  19 import java.util.concurrent.Callable;
  20
  21 import org.opendaylight.controller.md.sal.common.api.data.AsyncDataBroker.DataChangeScope;
  22 import org.opendaylight.controller.md.sal.dom.store.impl.DOMImmutableDataChangeEvent.Builder;
  23 import org.opendaylight.controller.md.sal.dom.store.impl.DOMImmutableDataChangeEvent.SimpleEventFactory;
  24 import org.opendaylight.controller.md.sal.dom.store.impl.tree.DataTreeCandidate;
  25 import org.opendaylight.controller.md.sal.dom.store.impl.tree.DataTreeCandidateNode;
  26 import org.opendaylight.controller.md.sal.dom.store.impl.tree.ListenerTree;
  27 import org.opendaylight.controller.md.sal.dom.store.impl.tree.ListenerTree.Node;
  28 import org.opendaylight.controller.md.sal.dom.store.impl.tree.ListenerTree.Walker;
  29 import org.opendaylight.controller.md.sal.dom.store.impl.tree.ModificationType;
  30 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier;
  31 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.NodeIdentifier;
  32 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.NodeIdentifierWithPredicates;
  33 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.NodeWithValue;
  34 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.PathArgument;
  35 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  36 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNodeContainer;
  37 import org.slf4j.Logger;
  38 import org.slf4j.LoggerFactory;
  39
  40 import com.google.common.base.Optional;
  41 import com.google.common.base.Preconditions;
  42 import com.google.common.collect.HashMultimap;
  43 import com.google.common.collect.ImmutableList;
  44 import com.google.common.collect.Iterables;
  45 import com.google.common.collect.Multimap;
  46
  47 /**
  48  * Resolve Data Change Events based on modifications and listeners
  49  *
  50  * Computes data change events for all affected registered listeners in data
  51  * tree.
  52  */
  53 final class ResolveDataChangeEventsTask implements Callable<Iterable<ChangeListenerNotifyTask>> {
  54     private static final Logger LOG = LoggerFactory.getLogger(ResolveDataChangeEventsTask.class);
  55     private static final DOMImmutableDataChangeEvent NO_CHANGE = builder(DataChangeScope.BASE).build();
  56
  57     private final Multimap<ListenerTree.Node, DOMImmutableDataChangeEvent> events = HashMultimap.create();
  58     private final DataTreeCandidate candidate;
  59     private final ListenerTree listenerRoot;
  60
  61     public ResolveDataChangeEventsTask(final DataTreeCandidate candidate, final ListenerTree listenerTree) {
  62         this.candidate = Preconditions.checkNotNull(candidate);
  63         this.listenerRoot = Preconditions.checkNotNull(listenerTree);
  64     }
  65
  66     /**
  67      * Resolves and creates Notification Tasks
  68      *
  69      * Implementation of done as Map-Reduce with two steps: 1. resolving events
  70      * and their mapping to listeners 2. merging events affecting same listener
  71      *
  72      * @return An {@link Iterable} of Notification Tasks which needs to be executed in
  73      *         order to delivery data change events.
  74      */
  75     @Override
  76     public Iterable<ChangeListenerNotifyTask> call() {
  77         try (final Walker w = listenerRoot.getWalker()) {
  78             resolveAnyChangeEvent(candidate.getRootPath(), Collections.singleton(w.getRootNode()), candidate.getRootNode());
  79             return createNotificationTasks();
  80         }
  81     }
  82
  83     /**
  84      *
  85      * Walks map of listeners to data change events, creates notification
  86      * delivery tasks.
  87      *
  88      * Walks map of registered and affected listeners and creates notification
  89      * tasks from set of listeners and events to be delivered.
  90      *
  91      * If set of listeners has more then one event (applicable to wildcarded
  92      * listeners), merges all data change events into one, final which contains
  93      * all separate updates.
  94      *
  95      * Dispatch between merge variant and reuse variant of notification task is
  96      * done in
  97      * {@link #addNotificationTask(com.google.common.collect.ImmutableList.Builder, Node, Collection)}
  98      *
  99      * @return Collection of notification tasks.
 100      */
 101     private Collection<ChangeListenerNotifyTask> createNotificationTasks() {
 102         ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder = ImmutableList.builder();
 103         for (Entry<ListenerTree.Node, Collection<DOMImmutableDataChangeEvent>> entry : events.asMap().entrySet()) {
 104             addNotificationTask(taskListBuilder, entry.getKey(), entry.getValue());
 105         }
 106         return taskListBuilder.build();
 107     }
 108
 109     /**
 110      * Adds notification task to task list.
 111      *
 112      * If entry collection contains one event, this event is reused and added to
 113      * notification tasks for listeners (see
 114      * {@link #addNotificationTaskByScope(com.google.common.collect.ImmutableList.Builder, Node, DOMImmutableDataChangeEvent)}
 115      * . Otherwise events are merged by scope and distributed between listeners
 116      * to particular scope. See
 117      * {@link #addNotificationTasksAndMergeEvents(com.google.common.collect.ImmutableList.Builder, Node, Collection)}
 118      * .
 119      *
 120      * @param taskListBuilder
 121      * @param listeners
 122      * @param entries
 123      */
 124     private static void addNotificationTask(final ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder,
 125             final ListenerTree.Node listeners, final Collection<DOMImmutableDataChangeEvent> entries) {
 126
 127         if (!entries.isEmpty()) {
 128             if (entries.size() == 1) {
 129                 addNotificationTaskByScope(taskListBuilder, listeners, Iterables.getOnlyElement(entries));
 130             } else {
 131                 addNotificationTasksAndMergeEvents(taskListBuilder, listeners, entries);
 132             }
 133         }
 134     }
 135
 136     /**
 137      *
 138      * Add notification deliveries task to the listener.
 139      *
 140      *
 141      * @param taskListBuilder
 142      * @param listeners
 143      * @param event
 144      */
 145     private static void addNotificationTaskByScope(
 146             final ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder, final ListenerTree.Node listeners,
 147             final DOMImmutableDataChangeEvent event) {
 148         DataChangeScope eventScope = event.getScope();
 149         for (DataChangeListenerRegistration<?> listenerReg : listeners.getListeners()) {
 150             DataChangeScope listenerScope = listenerReg.getScope();
 151             List<DataChangeListenerRegistration<?>> listenerSet = Collections
 152                     .<DataChangeListenerRegistration<?>> singletonList(listenerReg);
 153             if (eventScope == DataChangeScope.BASE) {
 154                 taskListBuilder.add(new ChangeListenerNotifyTask(listenerSet, event));
 155             } else if (eventScope == DataChangeScope.ONE && listenerScope != DataChangeScope.BASE) {
 156                 taskListBuilder.add(new ChangeListenerNotifyTask(listenerSet, event));
 157             } else if (eventScope == DataChangeScope.SUBTREE && listenerScope == DataChangeScope.SUBTREE) {
 158                 taskListBuilder.add(new ChangeListenerNotifyTask(listenerSet, event));
 159             }
 160         }
 161     }
 162
 163     /**
 164      *
 165      * Add notification tasks with merged event
 166      *
 167      * Separate Events by scope and creates merged notification tasks for each
 168      * and every scope which is present.
 169      *
 170      * Adds merged events to task list based on scope requested by client.
 171      *
 172      * @param taskListBuilder
 173      * @param listeners
 174      * @param entries
 175      */
 176     private static void addNotificationTasksAndMergeEvents(
 177             final ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder, final ListenerTree.Node listeners,
 178             final Collection<DOMImmutableDataChangeEvent> entries) {
 179
 180         final Builder baseBuilder = builder(DataChangeScope.BASE);
 181         final Builder oneBuilder = builder(DataChangeScope.ONE);
 182         final Builder subtreeBuilder = builder(DataChangeScope.SUBTREE);
 183
 184         boolean baseModified = false;
 185         boolean oneModified = false;
 186         boolean subtreeModified = false;
 187         for (final DOMImmutableDataChangeEvent entry : entries) {
 188             switch (entry.getScope()) {
 189             // Absence of breaks is intentional here. Subtree contains base and
 190             // one, one also contains base
 191             case BASE:
 192                 baseBuilder.merge(entry);
 193                 baseModified = true;
 194             case ONE:
 195                 oneBuilder.merge(entry);
 196                 oneModified = true;
 197             case SUBTREE:
 198                 subtreeBuilder.merge(entry);
 199                 subtreeModified = true;
 200             }
 201         }
 202
 203         if (baseModified) {
 204             addNotificationTaskExclusively(taskListBuilder, listeners, baseBuilder.build());
 205         }
 206         if (oneModified) {
 207             addNotificationTaskExclusively(taskListBuilder, listeners, oneBuilder.build());
 208         }
 209         if (subtreeModified) {
 210             addNotificationTaskExclusively(taskListBuilder, listeners, subtreeBuilder.build());
 211         }
 212     }
 213
 214     private static void addNotificationTaskExclusively(
 215             final ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder, final Node listeners,
 216             final DOMImmutableDataChangeEvent event) {
 217         for (DataChangeListenerRegistration<?> listener : listeners.getListeners()) {
 218             if (listener.getScope() == event.getScope()) {
 219                 Set<DataChangeListenerRegistration<?>> listenerSet = Collections
 220                         .<DataChangeListenerRegistration<?>> singleton(listener);
 221                 taskListBuilder.add(new ChangeListenerNotifyTask(listenerSet, event));
 222             }
 223         }
 224     }
 225
 226     /**
 227      * Resolves data change event for supplied node
 228      *
 229      * @param path
 230      *            Path to current node in tree
 231      * @param listeners
 232      *            Collection of Listener registration nodes interested in
 233      *            subtree
 234      * @param modification
 235      *            Modification of current node
 236      * @param before
 237      *            - Original (before) state of current node
 238      * @param after
 239      *            - After state of current node
 240      * @return Data Change Event of this node and all it's children
 241      */
 242     private DOMImmutableDataChangeEvent resolveAnyChangeEvent(final InstanceIdentifier path,
 243             final Collection<ListenerTree.Node> listeners, final DataTreeCandidateNode node) {
 244
 245         if (node.getModificationType() != ModificationType.UNMODIFIED &&
 246                 !node.getDataAfter().isPresent() && !node.getDataBefore().isPresent()) {
 247             LOG.debug("Modification at {} has type {}, but no before- and after-data. Assuming unchanged.",
 248                     path, node.getModificationType());
 249             return NO_CHANGE;
 250         }
 251
 252         // no before and after state is present
 253
 254         switch (node.getModificationType()) {
 255         case SUBTREE_MODIFIED:
 256             return resolveSubtreeChangeEvent(path, listeners, node);
 257         case MERGE:
 258         case WRITE:
 259             Preconditions.checkArgument(node.getDataAfter().isPresent(),
 260                     "Modification at {} has type {} but no after-data", path, node.getModificationType());
 261             if (node.getDataBefore().isPresent()) {
 262                 return resolveReplacedEvent(path, listeners, node.getDataBefore().get(), node.getDataAfter().get());
 263             } else {
 264                 return resolveCreateEvent(path, listeners, node.getDataAfter().get());
 265             }
 266         case DELETE:
 267             Preconditions.checkArgument(node.getDataBefore().isPresent(),
 268                     "Modification at {} has type {} but no before-data", path, node.getModificationType());
 269             return resolveDeleteEvent(path, listeners, node.getDataBefore().get());
 270         case UNMODIFIED:
 271             return NO_CHANGE;
 272         }
 273
 274         throw new IllegalStateException(String.format("Unhandled node state %s at %s", node.getModificationType(), path));
 275     }
 276
 277     private DOMImmutableDataChangeEvent resolveReplacedEvent(final InstanceIdentifier path,
 278             final Collection<Node> listeners, final NormalizedNode<?, ?> beforeData,
 279             final NormalizedNode<?, ?> afterData) {
 280
 281         if (beforeData instanceof NormalizedNodeContainer<?, ?, ?>) {
 282             // Node is container (contains child) and we have interested
 283             // listeners registered for it, that means we need to do
 284             // resolution of changes on children level and can not
 285             // shortcut resolution.
 286             LOG.trace("Resolving subtree replace event for {} before {}, after {}",path,beforeData,afterData);
 287             @SuppressWarnings("unchecked")
 288             NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> beforeCont = (NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>>) beforeData;
 289             @SuppressWarnings("unchecked")
 290             NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> afterCont = (NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>>) afterData;
 291             return resolveNodeContainerReplaced(path, listeners, beforeCont, afterCont);
 292         } else if (!beforeData.equals(afterData)) {
 293             // Node is either of Leaf type (does not contain child nodes)
 294             // or we do not have listeners, so normal equals method is
 295             // sufficient for determining change.
 296             LOG.trace("Resolving leaf replace event for {} , before {}, after {}",path,beforeData,afterData);
 297             DOMImmutableDataChangeEvent event = builder(DataChangeScope.BASE).setBefore(beforeData).setAfter(afterData)
 298                     .addUpdated(path, beforeData, afterData).build();
 299             addPartialTask(listeners, event);
 300             return event;
 301         } else {
 302             return NO_CHANGE;
 303         }
 304     }
 305
 306     private DOMImmutableDataChangeEvent resolveNodeContainerReplaced(final InstanceIdentifier path,
 307             final Collection<Node> listeners,
 308             final NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> beforeCont,
 309                     final NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> afterCont) {
 310         final Set<PathArgument> alreadyProcessed = new HashSet<>();
 311         final List<DOMImmutableDataChangeEvent> childChanges = new LinkedList<>();
 312
 313         DataChangeScope potentialScope = DataChangeScope.BASE;
 314         // We look at all children from before and compare it with after state.
 315         for (NormalizedNode<PathArgument, ?> beforeChild : beforeCont.getValue()) {
 316             PathArgument childId = beforeChild.getIdentifier();
 317             alreadyProcessed.add(childId);
 318             InstanceIdentifier childPath = path.node(childId);
 319             Collection<ListenerTree.Node> childListeners = getListenerChildrenWildcarded(listeners, childId);
 320             Optional<NormalizedNode<PathArgument, ?>> afterChild = afterCont.getChild(childId);
 321             DOMImmutableDataChangeEvent childChange = resolveNodeContainerChildUpdated(childPath, childListeners,
 322                     beforeChild, afterChild);
 323             // If change is empty (equals to NO_CHANGE)
 324             if (childChange != NO_CHANGE) {
 325                 childChanges.add(childChange);
 326             }
 327
 328         }
 329
 330         for (NormalizedNode<PathArgument, ?> afterChild : afterCont.getValue()) {
 331             PathArgument childId = afterChild.getIdentifier();
 332             if (!alreadyProcessed.contains(childId)) {
 333                 // We did not processed that child already
 334                 // and it was not present in previous loop, that means it is
 335                 // created.
 336                 Collection<ListenerTree.Node> childListeners = getListenerChildrenWildcarded(listeners, childId);
 337                 InstanceIdentifier childPath = path.node(childId);
 338                 childChanges.add(resolveSameEventRecursivelly(childPath , childListeners, afterChild,
 339                         DOMImmutableDataChangeEvent.getCreateEventFactory()));
 340             }
 341         }
 342         if (childChanges.isEmpty()) {
 343             return NO_CHANGE;
 344         }
 345
 346         Builder eventBuilder = builder(potentialScope) //
 347                 .setBefore(beforeCont) //
 348                 .setAfter(afterCont)
 349                 .addUpdated(path, beforeCont, afterCont);
 350         for (DOMImmutableDataChangeEvent childChange : childChanges) {
 351             eventBuilder.merge(childChange);
 352         }
 353
 354         DOMImmutableDataChangeEvent replaceEvent = eventBuilder.build();
 355         addPartialTask(listeners, replaceEvent);
 356         return replaceEvent;
 357     }
 358
 359     private DOMImmutableDataChangeEvent resolveNodeContainerChildUpdated(final InstanceIdentifier path,
 360             final Collection<Node> listeners, final NormalizedNode<PathArgument, ?> before,
 361             final Optional<NormalizedNode<PathArgument, ?>> after) {
 362
 363         if (after.isPresent()) {
 364             // REPLACE or SUBTREE Modified
 365             return resolveReplacedEvent(path, listeners, before, after.get());
 366
 367         } else {
 368             // AFTER state is not present - child was deleted.
 369             return resolveSameEventRecursivelly(path, listeners, before,
 370                     DOMImmutableDataChangeEvent.getRemoveEventFactory());
 371         }
 372     }
 373
 374     /**
 375      * Resolves create events deep down the interest listener tree.
 376      *
 377      *
 378      * @param path
 379      * @param listeners
 380      * @param afterState
 381      * @return
 382      */
 383     private DOMImmutableDataChangeEvent resolveCreateEvent(final InstanceIdentifier path,
 384             final Collection<ListenerTree.Node> listeners, final NormalizedNode<?, ?> afterState) {
 385         @SuppressWarnings({ "unchecked", "rawtypes" })
 386         final NormalizedNode<PathArgument, ?> node = (NormalizedNode) afterState;
 387         return resolveSameEventRecursivelly(path, listeners, node, DOMImmutableDataChangeEvent.getCreateEventFactory());
 388     }
 389
 390     private DOMImmutableDataChangeEvent resolveDeleteEvent(final InstanceIdentifier path,
 391             final Collection<ListenerTree.Node> listeners, final NormalizedNode<?, ?> beforeState) {
 392
 393         @SuppressWarnings({ "unchecked", "rawtypes" })
 394         final NormalizedNode<PathArgument, ?> node = (NormalizedNode) beforeState;
 395         return resolveSameEventRecursivelly(path, listeners, node, DOMImmutableDataChangeEvent.getRemoveEventFactory());
 396     }
 397
 398     private DOMImmutableDataChangeEvent resolveSameEventRecursivelly(final InstanceIdentifier path,
 399             final Collection<Node> listeners, final NormalizedNode<PathArgument, ?> node,
 400             final SimpleEventFactory eventFactory) {
 401         final DOMImmutableDataChangeEvent event = eventFactory.create(path, node);
 402         DOMImmutableDataChangeEvent propagateEvent = event;
 403         // We have listeners for this node or it's children, so we will try
 404         // to do additional processing
 405         if (node instanceof NormalizedNodeContainer<?, ?, ?>) {
 406             LOG.trace("Resolving subtree recursive event for {}, type {}", path, eventFactory);
 407
 408             Builder eventBuilder = builder(DataChangeScope.BASE);
 409             eventBuilder.merge(event);
 410             eventBuilder.setBefore(event.getOriginalSubtree());
 411             eventBuilder.setAfter(event.getUpdatedSubtree());
 412
 413             // Node has children, so we will try to resolve it's children
 414             // changes.
 415             @SuppressWarnings("unchecked")
 416             NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> container = (NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>>) node;
 417             for (NormalizedNode<PathArgument, ?> child : container.getValue()) {
 418                 PathArgument childId = child.getIdentifier();
 419                 LOG.trace("Resolving event for child {}", childId);
 420                 Collection<Node> childListeners = getListenerChildrenWildcarded(listeners, childId);
 421                 eventBuilder.merge(resolveSameEventRecursivelly(path.node(childId), childListeners, child, eventFactory));
 422             }
 423             propagateEvent = eventBuilder.build();
 424         } else {
 425             // We do not dispatch leaf events since Binding Aware components do not support them.
 426             propagateEvent = builder(DataChangeScope.BASE).build();
 427         }
 428         if (!listeners.isEmpty()) {
 429             addPartialTask(listeners, propagateEvent);
 430         }
 431         return propagateEvent;
 432     }
 433
 434     private DOMImmutableDataChangeEvent resolveSubtreeChangeEvent(final InstanceIdentifier path,
 435             final Collection<ListenerTree.Node> listeners, final DataTreeCandidateNode modification) {
 436
 437         Preconditions.checkArgument(modification.getDataBefore().isPresent(), "Subtree change with before-data not present at path %s", path);
 438         Preconditions.checkArgument(modification.getDataAfter().isPresent(), "Subtree change with after-data not present at path %s", path);
 439
 440         Builder one = builder(DataChangeScope.ONE).
 441                 setBefore(modification.getDataBefore().get()).
 442                 setAfter(modification.getDataAfter().get());
 443         Builder subtree = builder(DataChangeScope.SUBTREE).
 444                 setBefore(modification.getDataBefore().get()).
 445                 setAfter(modification.getDataAfter().get());
 446
 447         for (DataTreeCandidateNode childMod : modification.getChildNodes()) {
 448             PathArgument childId = childMod.getIdentifier();
 449             InstanceIdentifier childPath = path.node(childId);
 450             Collection<ListenerTree.Node> childListeners = getListenerChildrenWildcarded(listeners, childId);
 451
 452             switch (childMod.getModificationType()) {
 453             case WRITE:
 454             case MERGE:
 455             case DELETE:
 456                 one.merge(resolveAnyChangeEvent(childPath, childListeners, childMod));
 457                 break;
 458             case SUBTREE_MODIFIED:
 459                 subtree.merge(resolveSubtreeChangeEvent(childPath, childListeners, childMod));
 460                 break;
 461             case UNMODIFIED:
 462                 // no-op
 463                 break;
 464             }
 465         }
 466         DOMImmutableDataChangeEvent oneChangeEvent = one.build();
 467         subtree.merge(oneChangeEvent);
 468         DOMImmutableDataChangeEvent subtreeEvent = subtree.build();
 469         if (!listeners.isEmpty()) {
 470             addPartialTask(listeners, oneChangeEvent);
 471             addPartialTask(listeners, subtreeEvent);
 472         }
 473         return subtreeEvent;
 474     }
 475
 476     private DOMImmutableDataChangeEvent addPartialTask(final Collection<ListenerTree.Node> listeners,
 477             final DOMImmutableDataChangeEvent event) {
 478         for (ListenerTree.Node listenerNode : listeners) {
 479             if (!listenerNode.getListeners().isEmpty()) {
 480                 LOG.trace("Adding event {} for listeners {}",event,listenerNode);
 481                 events.put(listenerNode, event);
 482             }
 483         }
 484         return event;
 485     }
 486
 487     private static Collection<ListenerTree.Node> getListenerChildrenWildcarded(final Collection<ListenerTree.Node> parentNodes,
 488             final PathArgument child) {
 489         if (parentNodes.isEmpty()) {
 490             return Collections.emptyList();
 491         }
 492         com.google.common.collect.ImmutableList.Builder<ListenerTree.Node> result = ImmutableList.builder();
 493         if (child instanceof NodeWithValue || child instanceof NodeIdentifierWithPredicates) {
 494             NodeIdentifier wildcardedIdentifier = new NodeIdentifier(child.getNodeType());
 495             addChildrenNodesToBuilder(result, parentNodes, wildcardedIdentifier);
 496         }
 497         addChildrenNodesToBuilder(result, parentNodes, child);
 498         return result.build();
 499     }
 500
 501     private static void addChildrenNodesToBuilder(final ImmutableList.Builder<ListenerTree.Node> result,
 502             final Collection<ListenerTree.Node> parentNodes, final PathArgument childIdentifier) {
 503         for (ListenerTree.Node node : parentNodes) {
 504             Optional<ListenerTree.Node> child = node.getChild(childIdentifier);
 505             if (child.isPresent()) {
 506                 result.add(child.get());
 507             }
 508         }
 509     }
 510
 511     public static ResolveDataChangeEventsTask create(final DataTreeCandidate candidate, final ListenerTree listenerTree) {
 512         return new ResolveDataChangeEventsTask(candidate, listenerTree);
 513     }
 514 }