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_NODE_ID;
  11 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_ID_NODE_ID;
  12 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_ID_QNAME;
  13 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_NODE_ID;
  14 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNERS_PATH;
  15 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNER_NODE_ID;
  16 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_OWNER_QNAME;
  17 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPES_PATH;
  18 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPE_NODE_ID;
  19 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.ENTITY_TYPE_QNAME;
  20 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidateMapEntry;
  21 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidateNodeKey;
  22 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.candidatePath;
  23 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.createEntity;
  24 import static org.opendaylight.controller.cluster.datastore.entityownership.EntityOwnersModel.entityOwnersWithCandidate;
  25 import akka.actor.ActorRef;
  26 import akka.actor.ActorSelection;
  27 import akka.actor.Cancellable;
  28 import akka.pattern.Patterns;
  29 import com.google.common.base.Optional;
  30 import com.google.common.base.Preconditions;
  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.SelectOwner;
  46 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterCandidateLocal;
  47 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterListenerLocal;
  48 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategy;
  49 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategyConfig;
  50 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
  51 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
  52 import org.opendaylight.controller.cluster.datastore.messages.PeerDown;
  53 import org.opendaylight.controller.cluster.datastore.messages.PeerUp;
  54 import org.opendaylight.controller.cluster.datastore.messages.SuccessReply;
  55 import org.opendaylight.controller.cluster.datastore.modification.DeleteModification;
  56 import org.opendaylight.controller.cluster.datastore.modification.MergeModification;
  57 import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
  58 import org.opendaylight.controller.md.sal.common.api.clustering.Entity;
  59 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  60 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
  61 import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
  62 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
  63 import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
  64 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  65 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  66 import scala.concurrent.Future;
  67 import scala.concurrent.duration.FiniteDuration;
  68
  69 /**
  70  * Special Shard for EntityOwnership.
  71  *
  72  * @author Thomas Pantelis
  73  */
  74 class EntityOwnershipShard extends Shard {
  75     private final String localMemberName;
  76     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  77     private final EntityOwnershipListenerSupport listenerSupport;
  78     private final Set<String> downPeerMemberNames = new HashSet<>();
  79     private final Map<String, String> peerIdToMemberNames = new HashMap<>();
  80     private final EntityOwnerSelectionStrategyConfig strategyConfig;
  81     private final Map<YangInstanceIdentifier, Cancellable> entityToScheduledOwnershipTask = new HashMap<>();
  82     private final EntityOwnershipStatistics entityOwnershipStatistics;
  83
  84     private static DatastoreContext noPersistenceDatastoreContext(DatastoreContext datastoreContext) {
  85         return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
  86     }
  87
  88     protected EntityOwnershipShard(Builder builder) {
  89         super(builder);
  90         this.localMemberName = builder.localMemberName;
  91         this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(builder.localMemberName, LOG);
  92         this.listenerSupport = new EntityOwnershipListenerSupport(getContext(), persistenceId());
  93         this.strategyConfig = builder.ownerSelectionStrategyConfig;
  94         this.entityOwnershipStatistics = new EntityOwnershipStatistics();
  95         this.entityOwnershipStatistics.init(getDataStore());
  96
  97         for(String peerId: getRaftActorContext().getPeerIds()) {
  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         } else if(message instanceof RegisterListenerLocal) {
 131             onRegisterListenerLocal((RegisterListenerLocal)message);
 132         } else if(message instanceof UnregisterListenerLocal) {
 133             onUnregisterListenerLocal((UnregisterListenerLocal) message);
 134         } else if(message instanceof SelectOwner) {
 135             onSelectOwner((SelectOwner) message);
 136         } else if(!commitCoordinator.handleMessage(message, this)) {
 137             super.onReceiveCommand(message);
 138         }
 139     }
 140
 141     private void onSelectOwner(SelectOwner selectOwner) {
 142         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 143         if(Strings.isNullOrEmpty(currentOwner)) {
 144             String entityType = EntityOwnersModel.entityTypeFromEntityPath(selectOwner.getEntityPath());
 145             writeNewOwner(selectOwner.getEntityPath(), newOwner(selectOwner.getAllCandidates(),
 146                     entityOwnershipStatistics.byEntityType(entityType),
 147                     selectOwner.getOwnerSelectionStrategy()));
 148
 149             Cancellable cancellable = entityToScheduledOwnershipTask.get(selectOwner.getEntityPath());
 150             if(cancellable != null){
 151                 if(!cancellable.isCancelled()){
 152                     cancellable.cancel();
 153                 }
 154                 entityToScheduledOwnershipTask.remove(selectOwner.getEntityPath());
 155             }
 156         }
 157     }
 158
 159     private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
 160         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 161
 162         listenerSupport.setHasCandidateForEntity(registerCandidate.getEntity());
 163
 164         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 165                 registerCandidate.getEntity().getId(), localMemberName);
 166         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 167
 168         getSender().tell(SuccessReply.INSTANCE, getSelf());
 169     }
 170
 171     private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
 172         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 173
 174         Entity entity = unregisterCandidate.getEntity();
 175         listenerSupport.unsetHasCandidateForEntity(entity);
 176
 177         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
 178         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 179
 180         getSender().tell(SuccessReply.INSTANCE, getSelf());
 181     }
 182
 183     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 184         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 185
 186         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 187
 188         getSender().tell(SuccessReply.INSTANCE, getSelf());
 189
 190         searchForEntitiesOwnedBy(localMemberName, new EntityWalker() {
 191             @Override
 192             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 193                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleType =
 194                         entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 195                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 196                 if (registerListener.getEntityType().equals(entityType)) {
 197                     Entity entity = new Entity(entityType,
 198                             (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 199                     listenerSupport.notifyEntityOwnershipListener(entity, false, true, true, registerListener.getListener());
 200                 }
 201             }
 202         });
 203     }
 204
 205     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 206         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 207
 208         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 209
 210         getSender().tell(SuccessReply.INSTANCE, getSelf());
 211     }
 212
 213     void tryCommitModifications(final BatchedModifications modifications) {
 214         if(isLeader()) {
 215             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 216
 217             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 218             // to the state. However we don't need to retry it in that case b/c it will be committed to
 219             // the journal first and, once a majority of followers come back on line and it is replicated,
 220             // it will be applied at that point.
 221             handleBatchedModificationsLocal(modifications, self());
 222         } else {
 223             final ActorSelection leader = getLeader();
 224             if (leader != null) {
 225                 if(LOG.isDebugEnabled()) {
 226                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 227                             modifications.getTransactionID(), leader);
 228                 }
 229
 230                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 231                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 232
 233                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 234             }
 235         }
 236     }
 237
 238     boolean hasLeader() {
 239         return getLeader() != null && !isIsolatedLeader();
 240     }
 241
 242     @Override
 243     protected void onStateChanged() {
 244         super.onStateChanged();
 245
 246         boolean isLeader = isLeader();
 247         if(LOG.isDebugEnabled()) {
 248             LOG.debug("{}: onStateChanged: isLeader: {}, hasLeader: {}", persistenceId(), isLeader, hasLeader());
 249         }
 250
 251         commitCoordinator.onStateChanged(this, isLeader);
 252     }
 253
 254     @Override
 255     protected void onLeaderChanged(String oldLeader, String newLeader) {
 256         super.onLeaderChanged(oldLeader, newLeader);
 257
 258         boolean isLeader = isLeader();
 259         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 260                 newLeader, isLeader);
 261
 262         if(isLeader) {
 263             // We were just elected leader. If the old leader is down, select new owners for the entities
 264             // owned by the down leader.
 265
 266             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 267
 268             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 269
 270             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 271                 removeCandidateFromEntities(oldLeaderMemberName);
 272             }
 273         } else {
 274             // The leader changed - notify the coordinator to check if pending modifications need to be sent.
 275             // While onStateChanged also does this, this method handles the case where the shard hears from a
 276             // leader and stays in the follower state. In that case no behavior state change occurs.
 277             commitCoordinator.onStateChanged(this, isLeader);
 278         }
 279     }
 280
 281     private void onCandidateRemoved(CandidateRemoved message) {
 282         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 283
 284         if(isLeader()) {
 285             String currentOwner = getCurrentOwner(message.getEntityPath());
 286             if(message.getRemovedCandidate().equals(currentOwner) || message.getRemainingCandidates().size() == 0){
 287                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 288                 writeNewOwner(message.getEntityPath(),
 289                         newOwner(message.getRemainingCandidates(), entityOwnershipStatistics.byEntityType(entityType),
 290                                 getEntityOwnerElectionStrategy(message.getEntityPath())));
 291             }
 292         } else {
 293             // We're not the leader. If the removed candidate is our local member then check if we actually
 294             // have a local candidate registered. If we do then we must have been partitioned from the leader
 295             // and the leader removed our candidate since the leader can't tell the difference between a
 296             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 297             // our candidate.
 298             if(localMemberName.equals(message.getRemovedCandidate()) &&
 299                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 300                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 301                     " - adding back local candidate", message.getEntityPath());
 302
 303                 commitCoordinator.commitModification(new MergeModification(
 304                         candidatePath(message.getEntityPath(), localMemberName),
 305                         candidateMapEntry(localMemberName)), this);
 306             }
 307         }
 308     }
 309
 310     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 311         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 312         return strategyConfig.createStrategy(entityType);
 313     }
 314
 315     private void onCandidateAdded(CandidateAdded message) {
 316         if(!isLeader()){
 317             return;
 318         }
 319
 320         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 321
 322         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 323         // remove it from the downPeerMemberNames.
 324         downPeerMemberNames.remove(message.getNewCandidate());
 325
 326         String currentOwner = getCurrentOwner(message.getEntityPath());
 327         EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 328         if(Strings.isNullOrEmpty(currentOwner)){
 329             if(strategy.getSelectionDelayInMillis() == 0L) {
 330                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 331                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(),
 332                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 333             } else {
 334                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 335             }
 336         }
 337     }
 338
 339     private void onPeerDown(PeerDown peerDown) {
 340         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 341
 342         String downMemberName = peerDown.getMemberName();
 343         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 344             // Remove the down peer as a candidate from all entities.
 345             removeCandidateFromEntities(downMemberName);
 346         }
 347     }
 348
 349     private void onPeerUp(PeerUp peerUp) {
 350         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 351
 352         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 353         downPeerMemberNames.remove(peerUp.getMemberName());
 354
 355         // Notify the coordinator to check if pending modifications need to be sent. We do this here
 356         // to handle the case where the leader's peer address isn't now yet when a prior state or
 357         // leader change occurred.
 358         commitCoordinator.onStateChanged(this, isLeader());
 359     }
 360
 361     private void removeCandidateFromEntities(final String owner) {
 362         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 363         searchForEntities(new EntityWalker() {
 364             @Override
 365             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 366                 if (hasCandidate(entityNode, owner)) {
 367                     YangInstanceIdentifier entityId =
 368                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 369                     YangInstanceIdentifier candidatePath = candidatePath(
 370                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 371                             entityId, owner);
 372
 373                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 374                             owner, candidatePath);
 375
 376                     modifications.addModification(new DeleteModification(candidatePath));
 377                 }
 378             }
 379         });
 380
 381         commitCoordinator.commitModifications(modifications, this);
 382     }
 383
 384     private static boolean hasCandidate(MapEntryNode entity, String candidateName) {
 385         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 386     }
 387
 388     private void searchForEntitiesOwnedBy(final String owner, final EntityWalker walker) {
 389         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 390         if(!possibleEntityTypes.isPresent()) {
 391             return;
 392         }
 393
 394         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);
 395
 396         searchForEntities(new EntityWalker() {
 397             @Override
 398             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 399                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 400                         entityNode.getChild(ENTITY_OWNER_NODE_ID);
 401                 if (possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
 402                     walker.onEntity(entityTypeNode, entityNode);
 403                 }
 404             }
 405         });
 406     }
 407
 408     private void searchForEntities(EntityWalker walker) {
 409         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 410         if(!possibleEntityTypes.isPresent()) {
 411             return;
 412         }
 413
 414         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 415             Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
 416                     entityType.getChild(ENTITY_NODE_ID);
 417             if(!possibleEntities.isPresent()) {
 418                 continue; // shouldn't happen but handle anyway
 419             }
 420
 421             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 422                 walker.onEntity(entityType, entity);
 423             }
 424         }
 425     }
 426
 427     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 428         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 429
 430         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 431                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 432     }
 433
 434     /**
 435      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 436      *
 437      * @param entityPath
 438      * @param allCandidates
 439      */
 440     public void scheduleOwnerSelection(YangInstanceIdentifier entityPath, Collection<String> allCandidates,
 441                                        EntityOwnerSelectionStrategy strategy){
 442         Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 443         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 444             lastScheduledTask.cancel();
 445         }
 446         lastScheduledTask = context().system().scheduler().scheduleOnce(
 447                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS)
 448                 , self(), new SelectOwner(entityPath, allCandidates, strategy)
 449                 , context().system().dispatcher(), self());
 450
 451         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 452     }
 453
 454     private String newOwner(Collection<String> candidates, Map<String, Long> statistics, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 455         Collection<String> viableCandidates = getViableCandidates(candidates);
 456         if(viableCandidates.size() == 0){
 457             return "";
 458         }
 459         return ownerSelectionStrategy.newOwner(viableCandidates, statistics);
 460     }
 461
 462     private Collection<String> getViableCandidates(Collection<String> candidates) {
 463         Collection<String> viableCandidates = new ArrayList<>();
 464
 465         for (String candidate : candidates) {
 466             if (!downPeerMemberNames.contains(candidate)) {
 467                 viableCandidates.add(candidate);
 468             }
 469         }
 470         return viableCandidates;
 471     }
 472
 473     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 474         Optional<NormalizedNode<?, ?>> optionalEntityOwner = getDataStore().readNode(entityId.node(ENTITY_OWNER_QNAME));
 475         if(optionalEntityOwner.isPresent()){
 476             return optionalEntityOwner.get().getValue().toString();
 477         }
 478         return null;
 479     }
 480
 481     private static interface EntityWalker {
 482         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 483     }
 484
 485     public static Builder newBuilder() {
 486         return new Builder();
 487     }
 488
 489     static class Builder extends Shard.AbstractBuilder<Builder, EntityOwnershipShard> {
 490         private String localMemberName;
 491         private EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig;
 492
 493         protected Builder() {
 494             super(EntityOwnershipShard.class);
 495         }
 496
 497         Builder localMemberName(String localMemberName) {
 498             checkSealed();
 499             this.localMemberName = localMemberName;
 500             return this;
 501         }
 502
 503         Builder ownerSelectionStrategyConfig(EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig){
 504             checkSealed();
 505             this.ownerSelectionStrategyConfig = ownerSelectionStrategyConfig;
 506             return this;
 507         }
 508
 509         @Override
 510         protected void verify() {
 511             super.verify();
 512             Preconditions.checkNotNull(localMemberName, "localMemberName should not be null");
 513             Preconditions.checkNotNull(ownerSelectionStrategyConfig, "ownerSelectionStrategyConfig should not be null");
 514         }
 515     }
 516 }