opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/entityownership/EntityOwnershipShard.java

   1 /*
   2  * Copyright (c) 2015 Brocade Communications 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.cluster.datastore.entityownership;
   9
  10 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.CANDIDATE_NAME_NODE_ID;
  11 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.CANDIDATE_NODE_ID;
  12 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_ID_NODE_ID;
  13 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_ID_QNAME;
  14 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_NODE_ID;
  15 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNERS_PATH;
  16 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNER_NODE_ID;
  17 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNER_QNAME;
  18 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPES_PATH;
  19 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPE_NODE_ID;
  20 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPE_QNAME;
  21 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidateMapEntry;
  22 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidateNodeKey;
  23 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidatePath;
  24 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.createEntity;
  25 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.entityOwnersWithCandidate;
  26 import akka.actor.ActorRef;
  27 import akka.actor.ActorSelection;
  28 import akka.actor.Props;
  29 import akka.pattern.Patterns;
  30 import com.google.common.base.Optional;
  31 import com.google.common.base.Strings;
  32 import java.util.ArrayList;
  33 import java.util.Collection;
  34 import java.util.HashMap;
  35 import java.util.HashSet;
  36 import java.util.Map;
  37 import java.util.Set;
  38 import java.util.concurrent.TimeUnit;
  39 import org.opendaylight.controller.cluster.datastore.DatastoreContext;
  40 import org.opendaylight.controller.cluster.datastore.Shard;
  41 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateAdded;
  42 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateRemoved;
  43 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterCandidateLocal;
  44 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterListenerLocal;
  45 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterCandidateLocal;
  46 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterListenerLocal;
  47 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategy;
  48 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.FirstCandidateSelectionStrategy;
  49 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
  50 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
  51 import org.opendaylight.controller.cluster.datastore.messages.PeerDown;
  52 import org.opendaylight.controller.cluster.datastore.messages.PeerUp;
  53 import org.opendaylight.controller.cluster.datastore.messages.SuccessReply;
  54 import org.opendaylight.controller.cluster.datastore.modification.DeleteModification;
  55 import org.opendaylight.controller.cluster.datastore.modification.MergeModification;
  56 import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
  57 import org.opendaylight.controller.md.sal.common.api.clustering.Entity;
  58 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  59 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
  60 import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
  61 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
  62 import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
  63 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  64 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeSnapshot;
  65 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  66 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
  67 import scala.concurrent.Future;
  68
  69 /**
  70  * Special Shard for EntityOwnership.
  71  *
  72  * @author Thomas Pantelis
  73  */
  74 class EntityOwnershipShard extends Shard {
  75
  76     private static final EntityOwnerSelectionStrategy DEFAULT_ENTITY_OWNER_SELECTION_STRATEGY
  77             = FirstCandidateSelectionStrategy.INSTANCE;
  78
  79     private final String localMemberName;
  80     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  81     private final EntityOwnershipListenerSupport listenerSupport;
  82     private final Set<String> downPeerMemberNames = new HashSet<>();
  83     private final Map<String, String> peerIdToMemberNames = new HashMap<>();
  84     private final Map<String, EntityOwnerSelectionStrategy> ownerSelectionStrategies = new HashMap<>();
  85
  86     private static DatastoreContext noPersistenceDatastoreContext(DatastoreContext datastoreContext) {
  87         return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
  88     }
  89
  90     protected EntityOwnershipShard(ShardIdentifier name, Map<String, String> peerAddresses,
  91             DatastoreContext datastoreContext, SchemaContext schemaContext, String localMemberName) {
  92         super(name, peerAddresses, noPersistenceDatastoreContext(datastoreContext), schemaContext);
  93         this.localMemberName = localMemberName;
  94         this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(localMemberName, LOG);
  95         this.listenerSupport = new EntityOwnershipListenerSupport(getContext(), persistenceId());
  96
  97         for(String peerId: peerAddresses.keySet()) {
  98             ShardIdentifier shardId = ShardIdentifier.builder().fromShardIdString(peerId).build();
  99             peerIdToMemberNames.put(peerId, shardId.getMemberName());
 100         }
 101     }
 102
 103     @Override
 104     protected void onDatastoreContext(DatastoreContext context) {
 105         super.onDatastoreContext(noPersistenceDatastoreContext(context));
 106     }
 107
 108     @Override
 109     protected void onRecoveryComplete() {
 110         super.onRecoveryComplete();
 111
 112         new CandidateListChangeListener(getSelf(), persistenceId()).init(getDataStore());
 113         new EntityOwnerChangeListener(localMemberName, listenerSupport).init(getDataStore());
 114     }
 115
 116     @Override
 117     public void onReceiveCommand(final Object message) throws Exception {
 118         if(message instanceof RegisterCandidateLocal) {
 119             onRegisterCandidateLocal((RegisterCandidateLocal)message);
 120         } else if(message instanceof UnregisterCandidateLocal) {
 121             onUnregisterCandidateLocal((UnregisterCandidateLocal)message);
 122         } else if(message instanceof CandidateAdded){
 123             onCandidateAdded((CandidateAdded) message);
 124         } else if(message instanceof CandidateRemoved){
 125             onCandidateRemoved((CandidateRemoved) message);
 126         } else if(message instanceof PeerDown) {
 127             onPeerDown((PeerDown) message);
 128         } else if(message instanceof PeerUp) {
 129             onPeerUp((PeerUp) message);
 130         } if(message instanceof RegisterListenerLocal) {
 131             onRegisterListenerLocal((RegisterListenerLocal)message);
 132         } if(message instanceof UnregisterListenerLocal) {
 133             onUnregisterListenerLocal((UnregisterListenerLocal)message);
 134         } else if(!commitCoordinator.handleMessage(message, this)) {
 135             super.onReceiveCommand(message);
 136         }
 137     }
 138
 139     private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
 140         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 141
 142         listenerSupport.setHasCandidateForEntity(registerCandidate.getEntity());
 143
 144         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 145                 registerCandidate.getEntity().getId(), localMemberName);
 146         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 147
 148         getSender().tell(SuccessReply.INSTANCE, getSelf());
 149     }
 150
 151     private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
 152         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 153
 154         Entity entity = unregisterCandidate.getEntity();
 155         listenerSupport.unsetHasCandidateForEntity(entity);
 156
 157         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
 158         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 159
 160         getSender().tell(SuccessReply.INSTANCE, getSelf());
 161     }
 162
 163     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 164         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 165
 166         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 167
 168         getSender().tell(SuccessReply.INSTANCE, getSelf());
 169
 170         searchForEntitiesOwnedBy(localMemberName, new EntityWalker() {
 171             @Override
 172             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 173                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleType =
 174                         entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 175                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 176                 if (registerListener.getEntityType().equals(entityType)) {
 177                     Entity entity = new Entity(entityType,
 178                             (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 179                     listenerSupport.notifyEntityOwnershipListener(entity, false, true, true, registerListener.getListener());
 180                 }
 181             }
 182         });
 183     }
 184
 185     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 186         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 187
 188         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 189
 190         getSender().tell(SuccessReply.INSTANCE, getSelf());
 191     }
 192
 193     void tryCommitModifications(final BatchedModifications modifications) {
 194         if(isLeader()) {
 195             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 196
 197             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 198             // to the state. However we don't need to retry it in that case b/c it will be committed to
 199             // the journal first and, once a majority of followers come back on line and it is replicated,
 200             // it will be applied at that point.
 201             handleBatchedModificationsLocal(modifications, self());
 202         } else {
 203             final ActorSelection leader = getLeader();
 204             if (leader != null) {
 205                 if(LOG.isDebugEnabled()) {
 206                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 207                             modifications.getTransactionID(), leader);
 208                 }
 209
 210                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 211                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 212
 213                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 214             }
 215         }
 216     }
 217
 218     boolean hasLeader() {
 219         return getLeader() != null && !isIsolatedLeader();
 220     }
 221
 222     @Override
 223     protected void onStateChanged() {
 224         super.onStateChanged();
 225
 226         commitCoordinator.onStateChanged(this, isLeader());
 227     }
 228
 229     @Override
 230     protected void onLeaderChanged(String oldLeader, String newLeader) {
 231         super.onLeaderChanged(oldLeader, newLeader);
 232
 233         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 234                 newLeader, isLeader());
 235
 236         if(isLeader()) {
 237             // We were just elected leader. If the old leader is down, select new owners for the entities
 238             // owned by the down leader.
 239
 240             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 241
 242             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 243
 244             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 245                 selectNewOwnerForEntitiesOwnedBy(oldLeaderMemberName);
 246             }
 247         }
 248     }
 249
 250     private void onCandidateRemoved(CandidateRemoved message) {
 251         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 252
 253         if(isLeader()) {
 254             String currentOwner = getCurrentOwner(message.getEntityPath());
 255             if(message.getRemovedCandidate().equals(currentOwner)){
 256                 writeNewOwner(message.getEntityPath(), newOwner(message.getRemainingCandidates(),
 257                         getEntityOwnerElectionStrategy(message.getEntityPath())));
 258             }
 259         } else {
 260             // We're not the leader. If the removed candidate is our local member then check if we actually
 261             // have a local candidate registered. If we do then we must have been partitioned from the leader
 262             // and the leader removed our candidate since the leader can't tell the difference between a
 263             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 264             // our candidate.
 265             if(localMemberName.equals(message.getRemovedCandidate()) &&
 266                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 267                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 268                     " - adding back local candidate", message.getEntityPath());
 269
 270                 commitCoordinator.commitModification(new MergeModification(
 271                         candidatePath(message.getEntityPath(), localMemberName),
 272                         candidateMapEntry(localMemberName)), this);
 273             }
 274         }
 275     }
 276
 277     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 278         String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 279         EntityOwnerSelectionStrategy entityOwnerSelectionStrategy = ownerSelectionStrategies.get(entityType);
 280
 281         if(entityOwnerSelectionStrategy == null){
 282             entityOwnerSelectionStrategy = DEFAULT_ENTITY_OWNER_SELECTION_STRATEGY;
 283             ownerSelectionStrategies.put(entityType, entityOwnerSelectionStrategy);
 284         }
 285
 286         return entityOwnerSelectionStrategy;
 287     }
 288
 289     private void onCandidateAdded(CandidateAdded message) {
 290         if(!isLeader()){
 291             return;
 292         }
 293
 294         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 295
 296         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 297         // remove it from the downPeerMemberNames.
 298         downPeerMemberNames.remove(message.getNewCandidate());
 299
 300         String currentOwner = getCurrentOwner(message.getEntityPath());
 301         if(Strings.isNullOrEmpty(currentOwner)){
 302             EntityOwnerSelectionStrategy entityOwnerSelectionStrategy
 303                     = getEntityOwnerElectionStrategy(message.getEntityPath());
 304             if(entityOwnerSelectionStrategy.selectionDelayInMillis() == 0L) {
 305                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(),
 306                         entityOwnerSelectionStrategy));
 307             } else {
 308                 throw new UnsupportedOperationException("Delayed selection not implemented yet");
 309             }
 310         }
 311     }
 312
 313     private void onPeerDown(PeerDown peerDown) {
 314         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 315
 316         String downMemberName = peerDown.getMemberName();
 317         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 318             // Remove the down peer as a candidate from all entities.
 319             removeCandidateFromEntities(downMemberName);
 320         }
 321     }
 322
 323     private void onPeerUp(PeerUp peerUp) {
 324         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 325
 326         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 327         downPeerMemberNames.remove(peerUp.getMemberName());
 328     }
 329
 330     private void selectNewOwnerForEntitiesOwnedBy(String owner) {
 331         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 332         searchForEntitiesOwnedBy(owner, new EntityWalker() {
 333             @Override
 334             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 335
 336                 YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH).
 337                         node(entityTypeNode.getIdentifier()).node(ENTITY_NODE_ID).node(entityNode.getIdentifier()).
 338                         node(ENTITY_OWNER_NODE_ID).build();
 339
 340                 Object newOwner = newOwner(getCandidateNames(entityNode), getEntityOwnerElectionStrategy(entityPath));
 341
 342                 LOG.debug("{}: Found entity {}, writing new owner {}", persistenceId(), entityPath, newOwner);
 343
 344                 modifications.addModification(new WriteModification(entityPath,
 345                         ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
 346             }
 347         });
 348
 349         commitCoordinator.commitModifications(modifications, this);
 350     }
 351
 352     private void removeCandidateFromEntities(final String owner) {
 353         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 354         searchForEntities(new EntityWalker() {
 355             @Override
 356             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 357                 if(hasCandidate(entityNode, owner)) {
 358                     YangInstanceIdentifier entityId =
 359                             (YangInstanceIdentifier)entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 360                     YangInstanceIdentifier candidatePath = candidatePath(
 361                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 362                             entityId, owner);
 363
 364                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 365                             owner, candidatePath);
 366
 367                     modifications.addModification(new DeleteModification(candidatePath));
 368                 }
 369             }
 370         });
 371
 372         commitCoordinator.commitModifications(modifications, this);
 373     }
 374
 375     private boolean hasCandidate(MapEntryNode entity, String candidateName) {
 376         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 377     }
 378
 379     private void searchForEntitiesOwnedBy(final String owner, final EntityWalker walker) {
 380         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 381         Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
 382         if(!possibleEntityTypes.isPresent()) {
 383             return;
 384         }
 385
 386         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);
 387
 388         searchForEntities(new EntityWalker() {
 389             @Override
 390             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 391                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 392                         entityNode.getChild(ENTITY_OWNER_NODE_ID);
 393                 if(possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
 394                     walker.onEntity(entityTypeNode, entityNode);
 395                 }
 396             }
 397         });
 398     }
 399
 400     private void searchForEntities(EntityWalker walker) {
 401         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 402         Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
 403         if(!possibleEntityTypes.isPresent()) {
 404             return;
 405         }
 406
 407         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 408             Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
 409                     entityType.getChild(ENTITY_NODE_ID);
 410             if(!possibleEntities.isPresent()) {
 411                 continue; // shouldn't happen but handle anyway
 412             }
 413
 414             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 415                 walker.onEntity(entityType, entity);
 416             }
 417         }
 418     }
 419
 420     private Collection<String> getCandidateNames(MapEntryNode entity) {
 421         Collection<MapEntryNode> candidates = ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getValue();
 422         Collection<String> candidateNames = new ArrayList<>(candidates.size());
 423         for(MapEntryNode candidate: candidates) {
 424             candidateNames.add(candidate.getChild(CANDIDATE_NAME_NODE_ID).get().getValue().toString());
 425         }
 426
 427         return candidateNames;
 428     }
 429
 430     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 431         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 432
 433         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 434                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 435     }
 436
 437     private String newOwner(Collection<String> candidates, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 438         Collection<String> viableCandidates = getViableCandidates(candidates);
 439         if(viableCandidates.size() == 0){
 440             return "";
 441         }
 442         return ownerSelectionStrategy.newOwner(viableCandidates);
 443     }
 444
 445     private Collection<String> getViableCandidates(Collection<String> candidates) {
 446         Collection<String> viableCandidates = new ArrayList<>();
 447
 448         for (String candidate : candidates) {
 449             if (!downPeerMemberNames.contains(candidate)) {
 450                 viableCandidates.add(candidate);
 451             }
 452         }
 453         return viableCandidates;
 454     }
 455
 456     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 457         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 458         Optional<NormalizedNode<?, ?>> optionalEntityOwner = snapshot.readNode(entityId.node(ENTITY_OWNER_QNAME));
 459         if(optionalEntityOwner.isPresent()){
 460             return optionalEntityOwner.get().getValue().toString();
 461         }
 462         return null;
 463     }
 464
 465     public static Props props(final ShardIdentifier name, final Map<String, String> peerAddresses,
 466             final DatastoreContext datastoreContext, final SchemaContext schemaContext, final String localMemberName) {
 467         return Props.create(new Creator(name, peerAddresses, datastoreContext, schemaContext, localMemberName));
 468     }
 469
 470     private static class Creator extends AbstractShardCreator {
 471         private static final long serialVersionUID = 1L;
 472
 473         private final String localMemberName;
 474
 475         Creator(final ShardIdentifier name, final Map<String, String> peerAddresses,
 476                 final DatastoreContext datastoreContext, final SchemaContext schemaContext,
 477                 final String localMemberName) {
 478             super(name, peerAddresses, datastoreContext, schemaContext);
 479             this.localMemberName = localMemberName;
 480         }
 481
 482         @Override
 483         public Shard create() throws Exception {
 484             return new EntityOwnershipShard(name, peerAddresses, datastoreContext, schemaContext, localMemberName);
 485         }
 486     }
 487
 488     private static interface EntityWalker {
 489         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 490     }
 491 }