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.base.Optional;
  31 import com.google.common.base.Preconditions;
  32 import com.google.common.base.Strings;
  33 import java.util.ArrayList;
  34 import java.util.Collection;
  35 import java.util.HashMap;
  36 import java.util.HashSet;
  37 import java.util.Map;
  38 import java.util.Set;
  39 import java.util.concurrent.TimeUnit;
  40 import org.opendaylight.controller.cluster.datastore.DatastoreContext;
  41 import org.opendaylight.controller.cluster.datastore.Shard;
  42 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateAdded;
  43 import org.opendaylight.controller.cluster.datastore.entityownership.messages.CandidateRemoved;
  44 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterCandidateLocal;
  45 import org.opendaylight.controller.cluster.datastore.entityownership.messages.RegisterListenerLocal;
  46 import org.opendaylight.controller.cluster.datastore.entityownership.messages.SelectOwner;
  47 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterCandidateLocal;
  48 import org.opendaylight.controller.cluster.datastore.entityownership.messages.UnregisterListenerLocal;
  49 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategy;
  50 import org.opendaylight.controller.cluster.datastore.entityownership.selectionstrategy.EntityOwnerSelectionStrategyConfig;
  51 import org.opendaylight.controller.cluster.datastore.identifiers.ShardIdentifier;
  52 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
  53 import org.opendaylight.controller.cluster.datastore.messages.PeerDown;
  54 import org.opendaylight.controller.cluster.datastore.messages.PeerUp;
  55 import org.opendaylight.controller.cluster.datastore.messages.SuccessReply;
  56 import org.opendaylight.controller.cluster.datastore.modification.DeleteModification;
  57 import org.opendaylight.controller.cluster.datastore.modification.MergeModification;
  58 import org.opendaylight.controller.cluster.datastore.modification.WriteModification;
  59 import org.opendaylight.controller.md.sal.common.api.clustering.Entity;
  60 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  61 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
  62 import org.opendaylight.yangtools.yang.data.api.schema.DataContainerChild;
  63 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
  64 import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
  65 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  66 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  67 import scala.concurrent.Future;
  68 import scala.concurrent.duration.FiniteDuration;
  69
  70 /**
  71  * Special Shard for EntityOwnership.
  72  *
  73  * @author Thomas Pantelis
  74  */
  75 class EntityOwnershipShard extends Shard {
  76     private final String localMemberName;
  77     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  78     private final EntityOwnershipListenerSupport listenerSupport;
  79     private final Set<String> downPeerMemberNames = new HashSet<>();
  80     private final Map<String, String> peerIdToMemberNames = new HashMap<>();
  81     private final EntityOwnerSelectionStrategyConfig strategyConfig;
  82     private final Map<YangInstanceIdentifier, Cancellable> entityToScheduledOwnershipTask = new HashMap<>();
  83     private final EntityOwnershipStatistics entityOwnershipStatistics;
  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 = builder.ownerSelectionStrategyConfig;
  95         this.entityOwnershipStatistics = new EntityOwnershipStatistics();
  96         this.entityOwnershipStatistics.init(getDataStore());
  97
  98         for(String peerId: getRaftActorContext().getPeerIds()) {
  99             ShardIdentifier shardId = ShardIdentifier.builder().fromShardIdString(peerId).build();
 100             peerIdToMemberNames.put(peerId, shardId.getMemberName());
 101         }
 102     }
 103
 104     @Override
 105     protected void onDatastoreContext(DatastoreContext context) {
 106         super.onDatastoreContext(noPersistenceDatastoreContext(context));
 107     }
 108
 109     @Override
 110     protected void onRecoveryComplete() {
 111         super.onRecoveryComplete();
 112
 113         new CandidateListChangeListener(getSelf(), persistenceId()).init(getDataStore());
 114         new EntityOwnerChangeListener(localMemberName, listenerSupport).init(getDataStore());
 115     }
 116
 117     @Override
 118     public void onReceiveCommand(final Object message) throws Exception {
 119         if(message instanceof RegisterCandidateLocal) {
 120             onRegisterCandidateLocal((RegisterCandidateLocal) message);
 121         } else if(message instanceof UnregisterCandidateLocal) {
 122             onUnregisterCandidateLocal((UnregisterCandidateLocal)message);
 123         } else if(message instanceof CandidateAdded){
 124             onCandidateAdded((CandidateAdded) message);
 125         } else if(message instanceof CandidateRemoved){
 126             onCandidateRemoved((CandidateRemoved) message);
 127         } else if(message instanceof PeerDown) {
 128             onPeerDown((PeerDown) message);
 129         } else if(message instanceof PeerUp) {
 130             onPeerUp((PeerUp) message);
 131         } else if(message instanceof RegisterListenerLocal) {
 132             onRegisterListenerLocal((RegisterListenerLocal)message);
 133         } else if(message instanceof UnregisterListenerLocal) {
 134             onUnregisterListenerLocal((UnregisterListenerLocal) message);
 135         } else if(message instanceof SelectOwner) {
 136             onSelectOwner((SelectOwner) message);
 137         } else if(!commitCoordinator.handleMessage(message, this)) {
 138             super.onReceiveCommand(message);
 139         }
 140     }
 141
 142     private void onSelectOwner(SelectOwner selectOwner) {
 143         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 144         if(Strings.isNullOrEmpty(currentOwner)) {
 145             String entityType = EntityOwnersModel.entityTypeFromEntityPath(selectOwner.getEntityPath());
 146             writeNewOwner(selectOwner.getEntityPath(), newOwner(selectOwner.getAllCandidates(),
 147                     entityOwnershipStatistics.byEntityType(entityType),
 148                     selectOwner.getOwnerSelectionStrategy()));
 149
 150             Cancellable cancellable = entityToScheduledOwnershipTask.get(selectOwner.getEntityPath());
 151             if(cancellable != null){
 152                 if(!cancellable.isCancelled()){
 153                     cancellable.cancel();
 154                 }
 155                 entityToScheduledOwnershipTask.remove(selectOwner.getEntityPath());
 156             }
 157         }
 158     }
 159
 160     private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
 161         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 162
 163         listenerSupport.setHasCandidateForEntity(registerCandidate.getEntity());
 164
 165         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 166                 registerCandidate.getEntity().getId(), localMemberName);
 167         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 168
 169         getSender().tell(SuccessReply.INSTANCE, getSelf());
 170     }
 171
 172     private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
 173         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 174
 175         Entity entity = unregisterCandidate.getEntity();
 176         listenerSupport.unsetHasCandidateForEntity(entity);
 177
 178         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
 179         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 180
 181         getSender().tell(SuccessReply.INSTANCE, getSelf());
 182     }
 183
 184     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 185         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 186
 187         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 188
 189         getSender().tell(SuccessReply.INSTANCE, getSelf());
 190
 191         searchForEntitiesOwnedBy(localMemberName, new EntityWalker() {
 192             @Override
 193             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 194                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleType =
 195                         entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 196                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 197                 if (registerListener.getEntityType().equals(entityType)) {
 198                     Entity entity = new Entity(entityType,
 199                             (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 200                     listenerSupport.notifyEntityOwnershipListener(entity, false, true, true, registerListener.getListener());
 201                 }
 202             }
 203         });
 204     }
 205
 206     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 207         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 208
 209         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 210
 211         getSender().tell(SuccessReply.INSTANCE, getSelf());
 212     }
 213
 214     void tryCommitModifications(final BatchedModifications modifications) {
 215         if(isLeader()) {
 216             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 217
 218             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 219             // to the state. However we don't need to retry it in that case b/c it will be committed to
 220             // the journal first and, once a majority of followers come back on line and it is replicated,
 221             // it will be applied at that point.
 222             handleBatchedModificationsLocal(modifications, self());
 223         } else {
 224             final ActorSelection leader = getLeader();
 225             if (leader != null) {
 226                 if(LOG.isDebugEnabled()) {
 227                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 228                             modifications.getTransactionID(), leader);
 229                 }
 230
 231                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 232                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 233
 234                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 235             }
 236         }
 237     }
 238
 239     boolean hasLeader() {
 240         return getLeader() != null && !isIsolatedLeader();
 241     }
 242
 243     @Override
 244     protected void onStateChanged() {
 245         super.onStateChanged();
 246
 247         commitCoordinator.onStateChanged(this, isLeader());
 248     }
 249
 250     @Override
 251     protected void onLeaderChanged(String oldLeader, String newLeader) {
 252         super.onLeaderChanged(oldLeader, newLeader);
 253
 254         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 255                 newLeader, isLeader());
 256
 257         if(isLeader()) {
 258             // We were just elected leader. If the old leader is down, select new owners for the entities
 259             // owned by the down leader.
 260
 261             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 262
 263             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 264
 265             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 266                 selectNewOwnerForEntitiesOwnedBy(oldLeaderMemberName);
 267             }
 268         }
 269     }
 270
 271     private void onCandidateRemoved(CandidateRemoved message) {
 272         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 273
 274         if(isLeader()) {
 275             String currentOwner = getCurrentOwner(message.getEntityPath());
 276             if(message.getRemovedCandidate().equals(currentOwner) || message.getRemainingCandidates().size() == 0){
 277                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 278                 writeNewOwner(message.getEntityPath(),
 279                         newOwner(message.getRemainingCandidates(), entityOwnershipStatistics.byEntityType(entityType),
 280                                 getEntityOwnerElectionStrategy(message.getEntityPath())));
 281             }
 282         } else {
 283             // We're not the leader. If the removed candidate is our local member then check if we actually
 284             // have a local candidate registered. If we do then we must have been partitioned from the leader
 285             // and the leader removed our candidate since the leader can't tell the difference between a
 286             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 287             // our candidate.
 288             if(localMemberName.equals(message.getRemovedCandidate()) &&
 289                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 290                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 291                     " - adding back local candidate", message.getEntityPath());
 292
 293                 commitCoordinator.commitModification(new MergeModification(
 294                         candidatePath(message.getEntityPath(), localMemberName),
 295                         candidateMapEntry(localMemberName)), this);
 296             }
 297         }
 298     }
 299
 300     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 301         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 302         return strategyConfig.createStrategy(entityType);
 303     }
 304
 305     private void onCandidateAdded(CandidateAdded message) {
 306         if(!isLeader()){
 307             return;
 308         }
 309
 310         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 311
 312         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 313         // remove it from the downPeerMemberNames.
 314         downPeerMemberNames.remove(message.getNewCandidate());
 315
 316         String currentOwner = getCurrentOwner(message.getEntityPath());
 317         EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 318         if(Strings.isNullOrEmpty(currentOwner)){
 319             if(strategy.getSelectionDelayInMillis() == 0L) {
 320                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 321                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(),
 322                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 323             } else {
 324                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 325             }
 326         }
 327     }
 328
 329     private void onPeerDown(PeerDown peerDown) {
 330         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 331
 332         String downMemberName = peerDown.getMemberName();
 333         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 334             // Remove the down peer as a candidate from all entities.
 335             removeCandidateFromEntities(downMemberName);
 336         }
 337     }
 338
 339     private void onPeerUp(PeerUp peerUp) {
 340         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 341
 342         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 343         downPeerMemberNames.remove(peerUp.getMemberName());
 344     }
 345
 346     private void selectNewOwnerForEntitiesOwnedBy(String owner) {
 347         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 348         searchForEntitiesOwnedBy(owner, new EntityWalker() {
 349             @Override
 350             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 351
 352                 YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH).
 353                         node(entityTypeNode.getIdentifier()).node(ENTITY_NODE_ID).node(entityNode.getIdentifier()).
 354                         node(ENTITY_OWNER_NODE_ID).build();
 355
 356                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 357
 358                 Object newOwner = newOwner(getCandidateNames(entityNode),
 359                         entityOwnershipStatistics.byEntityType(entityType),
 360                         getEntityOwnerElectionStrategy(entityPath));
 361
 362                 LOG.debug("{}: Found entity {}, writing new owner {}", persistenceId(), entityPath, newOwner);
 363
 364                 modifications.addModification(new WriteModification(entityPath,
 365                         ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
 366             }
 367         });
 368
 369         commitCoordinator.commitModifications(modifications, this);
 370     }
 371
 372     private void removeCandidateFromEntities(final String owner) {
 373         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 374         searchForEntities(new EntityWalker() {
 375             @Override
 376             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 377                 if (hasCandidate(entityNode, owner)) {
 378                     YangInstanceIdentifier entityId =
 379                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 380                     YangInstanceIdentifier candidatePath = candidatePath(
 381                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 382                             entityId, owner);
 383
 384                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 385                             owner, candidatePath);
 386
 387                     modifications.addModification(new DeleteModification(candidatePath));
 388                 }
 389             }
 390         });
 391
 392         commitCoordinator.commitModifications(modifications, this);
 393     }
 394
 395     private static boolean hasCandidate(MapEntryNode entity, String candidateName) {
 396         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 397     }
 398
 399     private void searchForEntitiesOwnedBy(final String owner, final EntityWalker walker) {
 400         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 401         if(!possibleEntityTypes.isPresent()) {
 402             return;
 403         }
 404
 405         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);
 406
 407         searchForEntities(new EntityWalker() {
 408             @Override
 409             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 410                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 411                         entityNode.getChild(ENTITY_OWNER_NODE_ID);
 412                 if (possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
 413                     walker.onEntity(entityTypeNode, entityNode);
 414                 }
 415             }
 416         });
 417     }
 418
 419     private void searchForEntities(EntityWalker walker) {
 420         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 421         if(!possibleEntityTypes.isPresent()) {
 422             return;
 423         }
 424
 425         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 426             Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
 427                     entityType.getChild(ENTITY_NODE_ID);
 428             if(!possibleEntities.isPresent()) {
 429                 continue; // shouldn't happen but handle anyway
 430             }
 431
 432             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 433                 walker.onEntity(entityType, entity);
 434             }
 435         }
 436     }
 437
 438     private Collection<String> getCandidateNames(MapEntryNode entity) {
 439         Collection<MapEntryNode> candidates = ((MapNode) entity.getChild(CANDIDATE_NODE_ID).get()).getValue();
 440         Collection<String> candidateNames = new ArrayList<>(candidates.size());
 441         for(MapEntryNode candidate: candidates) {
 442             candidateNames.add(candidate.getChild(CANDIDATE_NAME_NODE_ID).get().getValue().toString());
 443         }
 444
 445         return candidateNames;
 446     }
 447
 448     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 449         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 450
 451         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 452                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 453     }
 454
 455     /**
 456      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 457      *
 458      * @param entityPath
 459      * @param allCandidates
 460      */
 461     public void scheduleOwnerSelection(YangInstanceIdentifier entityPath, Collection<String> allCandidates,
 462                                        EntityOwnerSelectionStrategy strategy){
 463         Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 464         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 465             lastScheduledTask.cancel();
 466         }
 467         lastScheduledTask = context().system().scheduler().scheduleOnce(
 468                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS)
 469                 , self(), new SelectOwner(entityPath, allCandidates, strategy)
 470                 , context().system().dispatcher(), self());
 471
 472         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 473     }
 474
 475     private String newOwner(Collection<String> candidates, Map<String, Long> statistics, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 476         Collection<String> viableCandidates = getViableCandidates(candidates);
 477         if(viableCandidates.size() == 0){
 478             return "";
 479         }
 480         return ownerSelectionStrategy.newOwner(viableCandidates, statistics);
 481     }
 482
 483     private Collection<String> getViableCandidates(Collection<String> candidates) {
 484         Collection<String> viableCandidates = new ArrayList<>();
 485
 486         for (String candidate : candidates) {
 487             if (!downPeerMemberNames.contains(candidate)) {
 488                 viableCandidates.add(candidate);
 489             }
 490         }
 491         return viableCandidates;
 492     }
 493
 494     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 495         Optional<NormalizedNode<?, ?>> optionalEntityOwner = getDataStore().readNode(entityId.node(ENTITY_OWNER_QNAME));
 496         if(optionalEntityOwner.isPresent()){
 497             return optionalEntityOwner.get().getValue().toString();
 498         }
 499         return null;
 500     }
 501
 502     private static interface EntityWalker {
 503         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 504     }
 505
 506     public static Builder newBuilder() {
 507         return new Builder();
 508     }
 509
 510     static class Builder extends Shard.AbstractBuilder<Builder, EntityOwnershipShard> {
 511         private String localMemberName;
 512         private EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig;
 513
 514         protected Builder() {
 515             super(EntityOwnershipShard.class);
 516         }
 517
 518         Builder localMemberName(String localMemberName) {
 519             checkSealed();
 520             this.localMemberName = localMemberName;
 521             return this;
 522         }
 523
 524         Builder ownerSelectionStrategyConfig(EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig){
 525             checkSealed();
 526             this.ownerSelectionStrategyConfig = ownerSelectionStrategyConfig;
 527             return this;
 528         }
 529
 530         @Override
 531         protected void verify() {
 532             super.verify();
 533             Preconditions.checkNotNull(localMemberName, "localMemberName should not be null");
 534             Preconditions.checkNotNull(ownerSelectionStrategyConfig, "ownerSelectionStrategyConfig should not be null");
 535         }
 536     }
 537 }