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.Cancellable;
  29 import akka.pattern.Patterns;
  30 import com.google.common.annotations.VisibleForTesting;
  31 import com.google.common.base.Optional;
  32 import com.google.common.base.Preconditions;
  33 import com.google.common.base.Strings;
  34 import java.util.ArrayList;
  35 import java.util.Collection;
  36 import java.util.HashMap;
  37 import java.util.HashSet;
  38 import java.util.Map;
  39 import java.util.Set;
  40 import java.util.concurrent.TimeUnit;
  41 import org.opendaylight.controller.cluster.datastore.DatastoreContext;
  42 import org.opendaylight.controller.cluster.datastore.Shard;
  43 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateAdded;
  44 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateRemoved;
  45 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterCandidateLocal;
  46 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterListenerLocal;
  47 import org.opendaylight.controller.cluster.datastore.entityownership.messages.SelectOwner;
  48 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterCandidateLocal;
  49 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterListenerLocal;
  50 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategy;
  51 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategyConfig;
  52 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
  53 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
  54 import org.opendaylight.controller.cluster.datastore.messages.PeerDown;
  55 import org.opendaylight.controller.cluster.datastore.messages.PeerUp;
  56 import org.opendaylight.controller.cluster.datastore.messages.SuccessReply;
  57 import org.opendaylight.controller.cluster.datastore.modification.DeleteModification;
  58 import org.opendaylight.controller.cluster.datastore.modification.MergeModification;
  59 import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
  60 import org.opendaylight.controller.md.sal.common.api.clustering.Entity;
  61 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  62 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
  63 import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
  64 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
  65 import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
  66 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  67 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  68 import scala.concurrent.Future;
  69 import scala.concurrent.duration.FiniteDuration;
  70
  71 /**
  72  * Special Shard for EntityOwnership.
  73  *
  74  * @author Thomas Pantelis
  75  */
  76 class EntityOwnershipShard extends Shard {
  77     private final String localMemberName;
  78     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  79     private final EntityOwnershipListenerSupport listenerSupport;
  80     private final Set<String> downPeerMemberNames = new HashSet<>();
  81     private final Map<String, String> peerIdToMemberNames = new HashMap<>();
  82     private EntityOwnerSelectionStrategyConfig strategyConfig;
  83     private Map<YangInstanceIdentifier, Cancellable> entityToScheduledOwnershipTask = new HashMap<>();
  84
  85     private static DatastoreContext noPersistenceDatastoreContext(DatastoreContext datastoreContext) {
  86         return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
  87     }
  88
  89     protected EntityOwnershipShard(Builder builder) {
  90         super(builder);
  91         this.localMemberName = builder.localMemberName;
  92         this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(builder.localMemberName, LOG);
  93         this.listenerSupport = new EntityOwnershipListenerSupport(getContext(), persistenceId());
  94         this.strategyConfig = EntityOwnerSelectionStrategyConfig.newBuilder().build();
  95
  96         for(String peerId: getRaftActorContext().getPeerIds()) {
  97             ShardIdentifier shardId = ShardIdentifier.builder().fromShardIdString(peerId).build();
  98             peerIdToMemberNames.put(peerId, shardId.getMemberName());
  99         }
 100     }
 101
 102     @Override
 103     protected void onDatastoreContext(DatastoreContext context) {
 104         super.onDatastoreContext(noPersistenceDatastoreContext(context));
 105     }
 106
 107     @Override
 108     protected void onRecoveryComplete() {
 109         super.onRecoveryComplete();
 110
 111         new CandidateListChangeListener(getSelf(), persistenceId()).init(getDataStore());
 112         new EntityOwnerChangeListener(localMemberName, listenerSupport).init(getDataStore());
 113     }
 114
 115     @Override
 116     public void onReceiveCommand(final Object message) throws Exception {
 117         if(message instanceof RegisterCandidateLocal) {
 118             onRegisterCandidateLocal((RegisterCandidateLocal) message);
 119         } else if(message instanceof UnregisterCandidateLocal) {
 120             onUnregisterCandidateLocal((UnregisterCandidateLocal)message);
 121         } else if(message instanceof CandidateAdded){
 122             onCandidateAdded((CandidateAdded) message);
 123         } else if(message instanceof CandidateRemoved){
 124             onCandidateRemoved((CandidateRemoved) message);
 125         } else if(message instanceof PeerDown) {
 126             onPeerDown((PeerDown) message);
 127         } else if(message instanceof PeerUp) {
 128             onPeerUp((PeerUp) message);
 129         } else if(message instanceof RegisterListenerLocal) {
 130             onRegisterListenerLocal((RegisterListenerLocal)message);
 131         } else if(message instanceof UnregisterListenerLocal) {
 132             onUnregisterListenerLocal((UnregisterListenerLocal) message);
 133         } else if(message instanceof SelectOwner) {
 134             onSelectOwner((SelectOwner) message);
 135         } else if(!commitCoordinator.handleMessage(message, this)) {
 136             super.onReceiveCommand(message);
 137         }
 138     }
 139
 140     private void onSelectOwner(SelectOwner selectOwner) {
 141         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 142         if(Strings.isNullOrEmpty(currentOwner)) {
 143             writeNewOwner(selectOwner.getEntityPath(), newOwner(selectOwner.getAllCandidates(),
 144                     selectOwner.getOwnerSelectionStrategy()));
 145
 146             Cancellable cancellable = entityToScheduledOwnershipTask.get(selectOwner.getEntityPath());
 147             if(cancellable != null){
 148                 if(!cancellable.isCancelled()){
 149                     cancellable.cancel();
 150                 }
 151                 entityToScheduledOwnershipTask.remove(selectOwner.getEntityPath());
 152             }
 153         }
 154     }
 155
 156     private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
 157         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 158
 159         listenerSupport.setHasCandidateForEntity(registerCandidate.getEntity());
 160
 161         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 162                 registerCandidate.getEntity().getId(), localMemberName);
 163         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 164
 165         getSender().tell(SuccessReply.INSTANCE, getSelf());
 166     }
 167
 168     private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
 169         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 170
 171         Entity entity = unregisterCandidate.getEntity();
 172         listenerSupport.unsetHasCandidateForEntity(entity);
 173
 174         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
 175         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 176
 177         getSender().tell(SuccessReply.INSTANCE, getSelf());
 178     }
 179
 180     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 181         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 182
 183         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 184
 185         getSender().tell(SuccessReply.INSTANCE, getSelf());
 186
 187         searchForEntitiesOwnedBy(localMemberName, new EntityWalker() {
 188             @Override
 189             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 190                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleType =
 191                         entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 192                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 193                 if (registerListener.getEntityType().equals(entityType)) {
 194                     Entity entity = new Entity(entityType,
 195                             (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 196                     listenerSupport.notifyEntityOwnershipListener(entity, false, true, true, registerListener.getListener());
 197                 }
 198             }
 199         });
 200     }
 201
 202     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 203         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 204
 205         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 206
 207         getSender().tell(SuccessReply.INSTANCE, getSelf());
 208     }
 209
 210     void tryCommitModifications(final BatchedModifications modifications) {
 211         if(isLeader()) {
 212             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 213
 214             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 215             // to the state. However we don't need to retry it in that case b/c it will be committed to
 216             // the journal first and, once a majority of followers come back on line and it is replicated,
 217             // it will be applied at that point.
 218             handleBatchedModificationsLocal(modifications, self());
 219         } else {
 220             final ActorSelection leader = getLeader();
 221             if (leader != null) {
 222                 if(LOG.isDebugEnabled()) {
 223                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 224                             modifications.getTransactionID(), leader);
 225                 }
 226
 227                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 228                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 229
 230                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 231             }
 232         }
 233     }
 234
 235     boolean hasLeader() {
 236         return getLeader() != null && !isIsolatedLeader();
 237     }
 238
 239     @Override
 240     protected void onStateChanged() {
 241         super.onStateChanged();
 242
 243         commitCoordinator.onStateChanged(this, isLeader());
 244     }
 245
 246     @Override
 247     protected void onLeaderChanged(String oldLeader, String newLeader) {
 248         super.onLeaderChanged(oldLeader, newLeader);
 249
 250         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 251                 newLeader, isLeader());
 252
 253         if(isLeader()) {
 254             // We were just elected leader. If the old leader is down, select new owners for the entities
 255             // owned by the down leader.
 256
 257             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 258
 259             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 260
 261             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 262                 selectNewOwnerForEntitiesOwnedBy(oldLeaderMemberName);
 263             }
 264         }
 265     }
 266
 267     private void onCandidateRemoved(CandidateRemoved message) {
 268         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 269
 270         if(isLeader()) {
 271             String currentOwner = getCurrentOwner(message.getEntityPath());
 272             if(message.getRemovedCandidate().equals(currentOwner)){
 273                 writeNewOwner(message.getEntityPath(),
 274                         newOwner(message.getRemainingCandidates(), getEntityOwnerElectionStrategy(message.getEntityPath())));
 275             }
 276         } else {
 277             // We're not the leader. If the removed candidate is our local member then check if we actually
 278             // have a local candidate registered. If we do then we must have been partitioned from the leader
 279             // and the leader removed our candidate since the leader can't tell the difference between a
 280             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 281             // our candidate.
 282             if(localMemberName.equals(message.getRemovedCandidate()) &&
 283                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 284                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 285                     " - adding back local candidate", message.getEntityPath());
 286
 287                 commitCoordinator.commitModification(new MergeModification(
 288                         candidatePath(message.getEntityPath(), localMemberName),
 289                         candidateMapEntry(localMemberName)), this);
 290             }
 291         }
 292     }
 293
 294     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 295         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 296         return strategyConfig.createStrategy(entityType);
 297     }
 298
 299     private void onCandidateAdded(CandidateAdded message) {
 300         if(!isLeader()){
 301             return;
 302         }
 303
 304         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 305
 306         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 307         // remove it from the downPeerMemberNames.
 308         downPeerMemberNames.remove(message.getNewCandidate());
 309
 310         String currentOwner = getCurrentOwner(message.getEntityPath());
 311         EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 312         if(Strings.isNullOrEmpty(currentOwner)){
 313             if(strategy.getSelectionDelayInMillis() == 0L) {
 314                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(), strategy));
 315             } else {
 316                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 317             }
 318         }
 319     }
 320
 321     private void onPeerDown(PeerDown peerDown) {
 322         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 323
 324         String downMemberName = peerDown.getMemberName();
 325         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 326             // Remove the down peer as a candidate from all entities.
 327             removeCandidateFromEntities(downMemberName);
 328         }
 329     }
 330
 331     private void onPeerUp(PeerUp peerUp) {
 332         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 333
 334         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 335         downPeerMemberNames.remove(peerUp.getMemberName());
 336     }
 337
 338     private void selectNewOwnerForEntitiesOwnedBy(String owner) {
 339         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 340         searchForEntitiesOwnedBy(owner, new EntityWalker() {
 341             @Override
 342             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 343
 344                 YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH).
 345                         node(entityTypeNode.getIdentifier()).node(ENTITY_NODE_ID).node(entityNode.getIdentifier()).
 346                         node(ENTITY_OWNER_NODE_ID).build();
 347
 348                 Object newOwner = newOwner(getCandidateNames(entityNode), getEntityOwnerElectionStrategy(entityPath));
 349
 350                 LOG.debug("{}: Found entity {}, writing new owner {}", persistenceId(), entityPath, newOwner);
 351
 352                 modifications.addModification(new WriteModification(entityPath,
 353                         ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
 354             }
 355         });
 356
 357         commitCoordinator.commitModifications(modifications, this);
 358     }
 359
 360     private void removeCandidateFromEntities(final String owner) {
 361         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 362         searchForEntities(new EntityWalker() {
 363             @Override
 364             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 365                 if (hasCandidate(entityNode, owner)) {
 366                     YangInstanceIdentifier entityId =
 367                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 368                     YangInstanceIdentifier candidatePath = candidatePath(
 369                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 370                             entityId, owner);
 371
 372                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 373                             owner, candidatePath);
 374
 375                     modifications.addModification(new DeleteModification(candidatePath));
 376                 }
 377             }
 378         });
 379
 380         commitCoordinator.commitModifications(modifications, this);
 381     }
 382
 383     private static boolean hasCandidate(MapEntryNode entity, String candidateName) {
 384         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 385     }
 386
 387     private void searchForEntitiesOwnedBy(final String owner, final EntityWalker walker) {
 388         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 389         if(!possibleEntityTypes.isPresent()) {
 390             return;
 391         }
 392
 393         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);
 394
 395         searchForEntities(new EntityWalker() {
 396             @Override
 397             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 398                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 399                         entityNode.getChild(ENTITY_OWNER_NODE_ID);
 400                 if(possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
 401                     walker.onEntity(entityTypeNode, entityNode);
 402                 }
 403             }
 404         });
 405     }
 406
 407     private void searchForEntities(EntityWalker walker) {
 408         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 409         if(!possibleEntityTypes.isPresent()) {
 410             return;
 411         }
 412
 413         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 414             Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
 415                     entityType.getChild(ENTITY_NODE_ID);
 416             if(!possibleEntities.isPresent()) {
 417                 continue; // shouldn't happen but handle anyway
 418             }
 419
 420             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 421                 walker.onEntity(entityType, entity);
 422             }
 423         }
 424     }
 425
 426     private Collection<String> getCandidateNames(MapEntryNode entity) {
 427         Collection<MapEntryNode> candidates = ((MapNode) entity.getChild(CANDIDATE_NODE_ID).get()).getValue();
 428         Collection<String> candidateNames = new ArrayList<>(candidates.size());
 429         for(MapEntryNode candidate: candidates) {
 430             candidateNames.add(candidate.getChild(CANDIDATE_NAME_NODE_ID).get().getValue().toString());
 431         }
 432
 433         return candidateNames;
 434     }
 435
 436     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 437         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 438
 439         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 440                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 441     }
 442
 443     /**
 444      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 445      *
 446      * @param entityPath
 447      * @param allCandidates
 448      */
 449     public void scheduleOwnerSelection(YangInstanceIdentifier entityPath, Collection<String> allCandidates,
 450                                        EntityOwnerSelectionStrategy strategy){
 451         Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 452         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 453             lastScheduledTask.cancel();
 454         }
 455         lastScheduledTask = context().system().scheduler().scheduleOnce(
 456                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS)
 457                 , self(), new SelectOwner(entityPath, allCandidates, strategy)
 458                 , context().system().dispatcher(), self());
 459
 460         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 461     }
 462
 463     private String newOwner(Collection<String> candidates, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 464         Collection<String> viableCandidates = getViableCandidates(candidates);
 465         if(viableCandidates.size() == 0){
 466             return "";
 467         }
 468         return ownerSelectionStrategy.newOwner(viableCandidates);
 469     }
 470
 471     private Collection<String> getViableCandidates(Collection<String> candidates) {
 472         Collection<String> viableCandidates = new ArrayList<>();
 473
 474         for (String candidate : candidates) {
 475             if (!downPeerMemberNames.contains(candidate)) {
 476                 viableCandidates.add(candidate);
 477             }
 478         }
 479         return viableCandidates;
 480     }
 481
 482     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 483         Optional<NormalizedNode<?, ?>> optionalEntityOwner = getDataStore().readNode(entityId.node(ENTITY_OWNER_QNAME));
 484         if(optionalEntityOwner.isPresent()){
 485             return optionalEntityOwner.get().getValue().toString();
 486         }
 487         return null;
 488     }
 489
 490     private static interface EntityWalker {
 491         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 492     }
 493
 494     @VisibleForTesting
 495     void addEntityOwnerSelectionStrategy(String entityType,
 496                                          Class<? extends EntityOwnerSelectionStrategy> clazz,
 497                                          long delay){
 498         EntityOwnerSelectionStrategyConfig config = EntityOwnerSelectionStrategyConfig.newBuilder()
 499                 .addStrategy(entityType, clazz, delay).build();
 500         this.strategyConfig = config;
 501     }
 502
 503     public static Builder newBuilder() {
 504         return new Builder();
 505     }
 506
 507     static class Builder extends Shard.AbstractBuilder<Builder, EntityOwnershipShard> {
 508         private String localMemberName;
 509
 510         protected Builder() {
 511             super(EntityOwnershipShard.class);
 512         }
 513
 514         Builder localMemberName(String localMemberName) {
 515             checkSealed();
 516             this.localMemberName = localMemberName;
 517             return this;
 518         }
 519
 520         @Override
 521         protected void verify() {
 522             super.verify();
 523             Preconditions.checkNotNull(localMemberName, "localMemberName should not be null");
 524         }
 525     }
 526 }