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

   1 package org.opendaylight.controller.md.sal.dom.store.impl;
   2
   3 import static org.opendaylight.controller.md.sal.dom.store.impl.DOMImmutableDataChangeEvent.builder;
   4 import static org.opendaylight.controller.md.sal.dom.store.impl.StoreUtils.append;
   5
   6 import java.util.Collection;
   7 import java.util.Collections;
   8 import java.util.HashSet;
   9 import java.util.LinkedList;
  10 import java.util.List;
  11 import java.util.Map.Entry;
  12 import java.util.Set;
  13 import java.util.concurrent.Callable;
  14
  15 import org.opendaylight.controller.md.sal.common.api.data.AsyncDataBroker.DataChangeScope;
  16 import org.opendaylight.controller.md.sal.dom.store.impl.DOMImmutableDataChangeEvent.Builder;
  17 import org.opendaylight.controller.md.sal.dom.store.impl.DOMImmutableDataChangeEvent.SimpleEventFactory;
  18 import org.opendaylight.controller.md.sal.dom.store.impl.tree.ListenerTree;
  19 import org.opendaylight.controller.md.sal.dom.store.impl.tree.ListenerTree.Node;
  20 import org.opendaylight.controller.md.sal.dom.store.impl.tree.ListenerTree.Walker;
  21 import org.opendaylight.controller.md.sal.dom.store.impl.tree.NodeModification;
  22 import org.opendaylight.controller.md.sal.dom.store.impl.tree.StoreMetadataNode;
  23 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier;
  24 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.NodeIdentifier;
  25 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.NodeIdentifierWithPredicates;
  26 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.NodeWithValue;
  27 import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier.PathArgument;
  28 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  29 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNodeContainer;
  30 import org.slf4j.Logger;
  31 import org.slf4j.LoggerFactory;
  32
  33 import com.google.common.base.Optional;
  34 import com.google.common.collect.HashMultimap;
  35 import com.google.common.collect.ImmutableList;
  36 import com.google.common.collect.Iterables;
  37 import com.google.common.collect.Multimap;
  38
  39 /**
  40  *
  41  * Resolve Data Change Events based on modifications and listeners
  42  *
  43  * Computes data change events for all affected registered listeners in data
  44  * tree.
  45  *
  46  * Prerequisites for computation is to set all parameters properly:
  47  * <ul>
  48  * <li>{@link #setRootPath(InstanceIdentifier)} - Root path of datastore
  49  * <li>{@link #setListenerRoot(ListenerTree)} - Root of listener registration
  50  * tree, which contains listeners to be notified
  51  * <li>{@link #setModificationRoot(NodeModification)} - Modification root, for
  52  * which events should be computed
  53  * <li>{@link #setBeforeRoot(Optional)} - State of before modification occurred
  54  * <li>{@link #setAfterRoot(Optional)} - State of after modification occurred
  55  * </ul>
  56  *
  57  */
  58 public class ResolveDataChangeEventsTask implements Callable<Iterable<ChangeListenerNotifyTask>> {
  59     private static final Logger LOG = LoggerFactory.getLogger(ResolveDataChangeEventsTask.class);
  60     private static final DOMImmutableDataChangeEvent NO_CHANGE = builder(DataChangeScope.BASE).build();
  61
  62     private InstanceIdentifier rootPath;
  63     private ListenerTree listenerRoot;
  64     private NodeModification modificationRoot;
  65     private Optional<StoreMetadataNode> beforeRoot;
  66     private Optional<StoreMetadataNode> afterRoot;
  67     private final Multimap<ListenerTree.Node, DOMImmutableDataChangeEvent> events = HashMultimap.create();
  68
  69     protected InstanceIdentifier getRootPath() {
  70         return rootPath;
  71     }
  72
  73     protected ResolveDataChangeEventsTask setRootPath(final InstanceIdentifier rootPath) {
  74         this.rootPath = rootPath;
  75         return this;
  76     }
  77
  78     protected ListenerTree getListenerRoot() {
  79         return listenerRoot;
  80     }
  81
  82     protected ResolveDataChangeEventsTask setListenerRoot(final ListenerTree listenerRoot) {
  83         this.listenerRoot = listenerRoot;
  84         return this;
  85     }
  86
  87     protected NodeModification getModificationRoot() {
  88         return modificationRoot;
  89     }
  90
  91     protected ResolveDataChangeEventsTask setModificationRoot(final NodeModification modificationRoot) {
  92         this.modificationRoot = modificationRoot;
  93         return this;
  94     }
  95
  96     protected Optional<StoreMetadataNode> getBeforeRoot() {
  97         return beforeRoot;
  98     }
  99
 100     protected ResolveDataChangeEventsTask setBeforeRoot(final Optional<StoreMetadataNode> beforeRoot) {
 101         this.beforeRoot = beforeRoot;
 102         return this;
 103     }
 104
 105     protected Optional<StoreMetadataNode> getAfterRoot() {
 106         return afterRoot;
 107     }
 108
 109     protected ResolveDataChangeEventsTask setAfterRoot(final Optional<StoreMetadataNode> afterRoot) {
 110         this.afterRoot = afterRoot;
 111         return this;
 112     }
 113
 114     /**
 115      * Resolves and creates Notification Tasks
 116      *
 117      * Implementation of done as Map-Reduce with two steps: 1. resolving events
 118      * and their mapping to listeners 2. merging events affecting same listener
 119      *
 120      * @return Iterable of Notification Tasks which needs to be executed in
 121      *         order to delivery data change events.
 122      */
 123     @Override
 124     public Iterable<ChangeListenerNotifyTask> call() {
 125         LOG.trace("Resolving events for {}", modificationRoot);
 126
 127         try (final Walker w = listenerRoot.getWalker()) {
 128             resolveAnyChangeEvent(rootPath, Collections.singleton(w.getRootNode()), modificationRoot, beforeRoot,
 129                     afterRoot);
 130             return createNotificationTasks();
 131         }
 132     }
 133
 134     /**
 135      *
 136      * Walks map of listeners to data change events, creates notification
 137      * delivery tasks.
 138      *
 139      * Walks map of registered and affected listeners and creates notification
 140      * tasks from set of listeners and events to be delivered.
 141      *
 142      * If set of listeners has more then one event (applicable to wildcarded
 143      * listeners), merges all data change events into one, final which contains
 144      * all separate updates.
 145      *
 146      * Dispatch between merge variant and reuse variant of notification task is
 147      * done in
 148      * {@link #addNotificationTask(com.google.common.collect.ImmutableList.Builder, Node, Collection)}
 149      *
 150      * @return Collection of notification tasks.
 151      */
 152     private Collection<ChangeListenerNotifyTask> createNotificationTasks() {
 153         ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder = ImmutableList.builder();
 154         for (Entry<ListenerTree.Node, Collection<DOMImmutableDataChangeEvent>> entry : events.asMap().entrySet()) {
 155             addNotificationTask(taskListBuilder, entry.getKey(), entry.getValue());
 156         }
 157         return taskListBuilder.build();
 158     }
 159
 160     /**
 161      * Adds notification task to task list.
 162      *
 163      * If entry collection contains one event, this event is reused and added to
 164      * notification tasks for listeners (see
 165      * {@link #addNotificationTaskByScope(com.google.common.collect.ImmutableList.Builder, Node, DOMImmutableDataChangeEvent)}
 166      * . Otherwise events are merged by scope and distributed between listeners
 167      * to particular scope. See
 168      * {@link #addNotificationTasksAndMergeEvents(com.google.common.collect.ImmutableList.Builder, Node, Collection)}
 169      * .
 170      *
 171      * @param taskListBuilder
 172      * @param listeners
 173      * @param entries
 174      */
 175     private static void addNotificationTask(final ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder,
 176             final ListenerTree.Node listeners, final Collection<DOMImmutableDataChangeEvent> entries) {
 177
 178         if (!entries.isEmpty()) {
 179             if (entries.size() == 1) {
 180                 addNotificationTaskByScope(taskListBuilder, listeners, Iterables.getOnlyElement(entries));
 181             } else {
 182                 addNotificationTasksAndMergeEvents(taskListBuilder, listeners, entries);
 183             }
 184         }
 185     }
 186
 187     /**
 188      *
 189      * Add notification deliveries task to the listener.
 190      *
 191      *
 192      * @param taskListBuilder
 193      * @param listeners
 194      * @param event
 195      */
 196     private static void addNotificationTaskByScope(
 197             final ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder, final ListenerTree.Node listeners,
 198             final DOMImmutableDataChangeEvent event) {
 199         DataChangeScope eventScope = event.getScope();
 200         for (DataChangeListenerRegistration<?> listenerReg : listeners.getListeners()) {
 201             DataChangeScope listenerScope = listenerReg.getScope();
 202             List<DataChangeListenerRegistration<?>> listenerSet = Collections
 203                     .<DataChangeListenerRegistration<?>> singletonList(listenerReg);
 204             if (eventScope == DataChangeScope.BASE) {
 205                 taskListBuilder.add(new ChangeListenerNotifyTask(listenerSet, event));
 206             } else if (eventScope == DataChangeScope.ONE && listenerScope != DataChangeScope.BASE) {
 207                 taskListBuilder.add(new ChangeListenerNotifyTask(listenerSet, event));
 208             } else if (eventScope == DataChangeScope.SUBTREE && listenerScope == DataChangeScope.SUBTREE) {
 209                 taskListBuilder.add(new ChangeListenerNotifyTask(listenerSet, event));
 210             }
 211         }
 212     }
 213
 214     /**
 215      *
 216      * Add notification tasks with merged event
 217      *
 218      * Separate Events by scope and creates merged notification tasks for each
 219      * and every scope which is present.
 220      *
 221      * Adds merged events to task list based on scope requested by client.
 222      *
 223      * @param taskListBuilder
 224      * @param listeners
 225      * @param entries
 226      */
 227     private static void addNotificationTasksAndMergeEvents(
 228             final ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder, final ListenerTree.Node listeners,
 229             final Collection<DOMImmutableDataChangeEvent> entries) {
 230
 231         final Builder baseBuilder = builder(DataChangeScope.BASE);
 232         final Builder oneBuilder = builder(DataChangeScope.ONE);
 233         final Builder subtreeBuilder = builder(DataChangeScope.SUBTREE);
 234
 235         boolean baseModified = false;
 236         boolean oneModified = false;
 237         boolean subtreeModified = false;
 238         for (final DOMImmutableDataChangeEvent entry : entries) {
 239             switch (entry.getScope()) {
 240             // Absence of breaks is intentional here. Subtree contains base and
 241             // one, one also contains base
 242             case BASE:
 243                 baseBuilder.merge(entry);
 244                 baseModified = true;
 245             case ONE:
 246                 oneBuilder.merge(entry);
 247                 oneModified = true;
 248             case SUBTREE:
 249                 subtreeBuilder.merge(entry);
 250                 subtreeModified = true;
 251             }
 252         }
 253
 254         if (baseModified) {
 255             addNotificationTaskExclusively(taskListBuilder, listeners, baseBuilder.build());
 256         }
 257         if (oneModified) {
 258             addNotificationTaskExclusively(taskListBuilder, listeners, oneBuilder.build());
 259         }
 260         if (subtreeModified) {
 261             addNotificationTaskExclusively(taskListBuilder, listeners, subtreeBuilder.build());
 262         }
 263     }
 264
 265     private static void addNotificationTaskExclusively(
 266             final ImmutableList.Builder<ChangeListenerNotifyTask> taskListBuilder, final Node listeners,
 267             final DOMImmutableDataChangeEvent event) {
 268         for (DataChangeListenerRegistration<?> listener : listeners.getListeners()) {
 269             if (listener.getScope() == event.getScope()) {
 270                 Set<DataChangeListenerRegistration<?>> listenerSet = Collections
 271                         .<DataChangeListenerRegistration<?>> singleton(listener);
 272                 taskListBuilder.add(new ChangeListenerNotifyTask(listenerSet, event));
 273             }
 274         }
 275     }
 276
 277     /**
 278      * Resolves data change event for supplied node
 279      *
 280      * @param path
 281      *            Path to current node in tree
 282      * @param listeners
 283      *            Collection of Listener registration nodes interested in
 284      *            subtree
 285      * @param modification
 286      *            Modification of current node
 287      * @param before
 288      *            - Original (before) state of current node
 289      * @param after
 290      *            - After state of current node
 291      * @return Data Change Event of this node and all it's children
 292      */
 293     private DOMImmutableDataChangeEvent resolveAnyChangeEvent(final InstanceIdentifier path,
 294             final Collection<ListenerTree.Node> listeners, final NodeModification modification,
 295             final Optional<StoreMetadataNode> before, final Optional<StoreMetadataNode> after) {
 296         // No listeners are present in listener registration subtree
 297         // no before and after state is present
 298         if (!before.isPresent() && !after.isPresent()) {
 299             return NO_CHANGE;
 300         }
 301         switch (modification.getModificationType()) {
 302         case SUBTREE_MODIFIED:
 303             return resolveSubtreeChangeEvent(path, listeners, modification, before.get(), after.get());
 304         case WRITE:
 305             if (before.isPresent()) {
 306                 return resolveReplacedEvent(path, listeners, before.get().getData(), after.get().getData());
 307             } else {
 308                 return resolveCreateEvent(path, listeners, after.get());
 309             }
 310         case DELETE:
 311             return resolveDeleteEvent(path, listeners, before.get());
 312         default:
 313             return NO_CHANGE;
 314         }
 315
 316     }
 317
 318     private DOMImmutableDataChangeEvent resolveReplacedEvent(final InstanceIdentifier path,
 319             final Collection<Node> listeners, final NormalizedNode<?, ?> beforeData,
 320             final NormalizedNode<?, ?> afterData) {
 321
 322         if (beforeData instanceof NormalizedNodeContainer<?, ?, ?> && !listeners.isEmpty()) {
 323             // Node is container (contains child) and we have interested
 324             // listeners registered for it, that means we need to do
 325             // resolution of changes on children level and can not
 326             // shortcut resolution.
 327
 328             @SuppressWarnings("unchecked")
 329             NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> beforeCont = (NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>>) beforeData;
 330             @SuppressWarnings("unchecked")
 331             NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> afterCont = (NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>>) afterData;
 332             return resolveNodeContainerReplaced(path, listeners, beforeCont, afterCont);
 333         } else if (!beforeData.equals(afterData)) {
 334             // Node is either of Leaf type (does not contain child nodes)
 335             // or we do not have listeners, so normal equals method is
 336             // sufficient for determining change.
 337
 338             DOMImmutableDataChangeEvent event = builder(DataChangeScope.BASE).setBefore(beforeData).setAfter(afterData)
 339                     .addUpdated(path, beforeData, afterData).build();
 340             addPartialTask(listeners, event);
 341             return event;
 342         } else {
 343             return NO_CHANGE;
 344         }
 345     }
 346
 347     private DOMImmutableDataChangeEvent resolveNodeContainerReplaced(final InstanceIdentifier path,
 348             final Collection<Node> listeners,
 349             final NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> beforeCont,
 350             final NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> afterCont) {
 351         final Set<PathArgument> alreadyProcessed = new HashSet<>();
 352         final List<DOMImmutableDataChangeEvent> childChanges = new LinkedList<>();
 353
 354         DataChangeScope potentialScope = DataChangeScope.BASE;
 355         // We look at all children from before and compare it with after state.
 356         for (NormalizedNode<PathArgument, ?> beforeChild : beforeCont.getValue()) {
 357             PathArgument childId = beforeChild.getIdentifier();
 358             alreadyProcessed.add(childId);
 359             InstanceIdentifier childPath = append(path, childId);
 360             Collection<ListenerTree.Node> childListeners = getListenerChildrenWildcarded(listeners, childId);
 361             Optional<NormalizedNode<PathArgument, ?>> afterChild = afterCont.getChild(childId);
 362             DOMImmutableDataChangeEvent childChange = resolveNodeContainerChildUpdated(childPath, childListeners,
 363                     beforeChild, afterChild);
 364             // If change is empty (equals to NO_CHANGE)
 365             if (childChange != NO_CHANGE) {
 366                 childChanges.add(childChange);
 367             }
 368
 369         }
 370
 371         for (NormalizedNode<PathArgument, ?> afterChild : afterCont.getValue()) {
 372             PathArgument childId = afterChild.getIdentifier();
 373             if (!alreadyProcessed.contains(childId)) {
 374                 // We did not processed that child already
 375                 // and it was not present in previous loop, that means it is
 376                 // created.
 377                 Collection<ListenerTree.Node> childListeners = getListenerChildrenWildcarded(listeners, childId);
 378                 InstanceIdentifier childPath = append(path,childId);
 379                 childChanges.add(resolveSameEventRecursivelly(childPath , childListeners, afterChild,
 380                         DOMImmutableDataChangeEvent.getCreateEventFactory()));
 381             }
 382         }
 383         if (childChanges.isEmpty()) {
 384             return NO_CHANGE;
 385         }
 386
 387         Builder eventBuilder = builder(potentialScope) //
 388                 .setBefore(beforeCont) //
 389                 .setAfter(afterCont);
 390         for (DOMImmutableDataChangeEvent childChange : childChanges) {
 391             eventBuilder.merge(childChange);
 392         }
 393
 394         DOMImmutableDataChangeEvent replaceEvent = eventBuilder.build();
 395         addPartialTask(listeners, replaceEvent);
 396         return replaceEvent;
 397     }
 398
 399     private DOMImmutableDataChangeEvent resolveNodeContainerChildUpdated(final InstanceIdentifier path,
 400             final Collection<Node> listeners, final NormalizedNode<PathArgument, ?> before,
 401             final Optional<NormalizedNode<PathArgument, ?>> after) {
 402
 403         if (after.isPresent()) {
 404             // REPLACE or SUBTREE Modified
 405             return resolveReplacedEvent(path, listeners, before, after.get());
 406
 407         } else {
 408             // AFTER state is not present - child was deleted.
 409             return resolveSameEventRecursivelly(path, listeners, before,
 410                     DOMImmutableDataChangeEvent.getRemoveEventFactory());
 411         }
 412     }
 413
 414     /**
 415      * Resolves create events deep down the interest listener tree.
 416      *
 417      *
 418      * @param path
 419      * @param listeners
 420      * @param afterState
 421      * @return
 422      */
 423     private DOMImmutableDataChangeEvent resolveCreateEvent(final InstanceIdentifier path,
 424             final Collection<ListenerTree.Node> listeners, final StoreMetadataNode afterState) {
 425         @SuppressWarnings({ "unchecked", "rawtypes" })
 426         final NormalizedNode<PathArgument, ?> node = (NormalizedNode) afterState.getData();
 427         return resolveSameEventRecursivelly(path, listeners, node, DOMImmutableDataChangeEvent.getCreateEventFactory());
 428     }
 429
 430     private DOMImmutableDataChangeEvent resolveDeleteEvent(final InstanceIdentifier path,
 431             final Collection<ListenerTree.Node> listeners, final StoreMetadataNode beforeState) {
 432
 433         @SuppressWarnings({ "unchecked", "rawtypes" })
 434         final NormalizedNode<PathArgument, ?> node = (NormalizedNode) beforeState.getData();
 435         return resolveSameEventRecursivelly(path, listeners, node, DOMImmutableDataChangeEvent.getRemoveEventFactory());
 436     }
 437
 438     private DOMImmutableDataChangeEvent resolveSameEventRecursivelly(final InstanceIdentifier path,
 439             final Collection<Node> listeners, final NormalizedNode<PathArgument, ?> node,
 440             final SimpleEventFactory eventFactory) {
 441
 442         DOMImmutableDataChangeEvent event = eventFactory.create(path, node);
 443
 444         if (!listeners.isEmpty()) {
 445             // We have listeners for this node or it's children, so we will try
 446             // to do additional processing
 447             if (node instanceof NormalizedNodeContainer<?, ?, ?>) {
 448                 // Node has children, so we will try to resolve it's children
 449                 // changes.
 450                 @SuppressWarnings("unchecked")
 451                 NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>> container = (NormalizedNodeContainer<?, PathArgument, NormalizedNode<PathArgument, ?>>) node;
 452                 for (NormalizedNode<PathArgument, ?> child : container.getValue()) {
 453                     PathArgument childId = child.getIdentifier();
 454                     Collection<Node> childListeners = getListenerChildrenWildcarded(listeners, childId);
 455                     if (!childListeners.isEmpty()) {
 456                         resolveSameEventRecursivelly(append(path, childId), childListeners, child, eventFactory);
 457                     }
 458                 }
 459             }
 460             addPartialTask(listeners, event);
 461         }
 462         return event;
 463     }
 464
 465     private DOMImmutableDataChangeEvent resolveSubtreeChangeEvent(final InstanceIdentifier path,
 466             final Collection<ListenerTree.Node> listeners, final NodeModification modification,
 467             final StoreMetadataNode before, final StoreMetadataNode after) {
 468
 469         Builder one = builder(DataChangeScope.ONE).setBefore(before.getData()).setAfter(after.getData());
 470
 471         Builder subtree = builder(DataChangeScope.SUBTREE);
 472
 473         for (NodeModification childMod : modification.getModifications()) {
 474             PathArgument childId = childMod.getIdentifier();
 475             InstanceIdentifier childPath = append(path, childId);
 476             Collection<ListenerTree.Node> childListeners = getListenerChildrenWildcarded(listeners, childId);
 477
 478             Optional<StoreMetadataNode> childBefore = before.getChild(childId);
 479             Optional<StoreMetadataNode> childAfter = after.getChild(childId);
 480
 481             switch (childMod.getModificationType()) {
 482             case WRITE:
 483             case DELETE:
 484                 one.merge(resolveAnyChangeEvent(childPath, childListeners, childMod, childBefore, childAfter));
 485                 break;
 486             case SUBTREE_MODIFIED:
 487                 subtree.merge(resolveSubtreeChangeEvent(childPath, childListeners, childMod, childBefore.get(),
 488                         childAfter.get()));
 489                 break;
 490             case UNMODIFIED:
 491                 // no-op
 492                 break;
 493             }
 494         }
 495         DOMImmutableDataChangeEvent oneChangeEvent = one.build();
 496         subtree.merge(oneChangeEvent);
 497         DOMImmutableDataChangeEvent subtreeEvent = subtree.build();
 498         if (!listeners.isEmpty()) {
 499             addPartialTask(listeners, oneChangeEvent);
 500             addPartialTask(listeners, subtreeEvent);
 501         }
 502         return subtreeEvent;
 503     }
 504
 505     private DOMImmutableDataChangeEvent addPartialTask(final Collection<ListenerTree.Node> listeners,
 506             final DOMImmutableDataChangeEvent event) {
 507
 508         for (ListenerTree.Node listenerNode : listeners) {
 509             if (!listenerNode.getListeners().isEmpty()) {
 510                 events.put(listenerNode, event);
 511             }
 512         }
 513         return event;
 514     }
 515
 516     private static Collection<ListenerTree.Node> getListenerChildrenWildcarded(final Collection<ListenerTree.Node> parentNodes,
 517             final PathArgument child) {
 518         if (parentNodes.isEmpty()) {
 519             return Collections.emptyList();
 520         }
 521         com.google.common.collect.ImmutableList.Builder<ListenerTree.Node> result = ImmutableList.builder();
 522         if (child instanceof NodeWithValue || child instanceof NodeIdentifierWithPredicates) {
 523             NodeIdentifier wildcardedIdentifier = new NodeIdentifier(child.getNodeType());
 524             addChildrenNodesToBuilder(result, parentNodes, wildcardedIdentifier);
 525         }
 526         addChildrenNodesToBuilder(result, parentNodes, child);
 527         return result.build();
 528     }
 529
 530     private static void addChildrenNodesToBuilder(final ImmutableList.Builder<ListenerTree.Node> result,
 531             final Collection<ListenerTree.Node> parentNodes, final PathArgument childIdentifier) {
 532         for (ListenerTree.Node node : parentNodes) {
 533             Optional<ListenerTree.Node> child = node.getChild(childIdentifier);
 534             if (child.isPresent()) {
 535                 result.add(child.get());
 536             }
 537         }
 538     }
 539
 540     public static ResolveDataChangeEventsTask create() {
 541         return new ResolveDataChangeEventsTask();
 542     }
 543 }