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         LOG.debug("{}: onSelectOwner: {}", persistenceId(), selectOwner);
 143
 144         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 145         if(Strings.isNullOrEmpty(currentOwner)) {
 146             String entityType = EntityOwnersModel.entityTypeFromEntityPath(selectOwner.getEntityPath());
 147             writeNewOwner(selectOwner.getEntityPath(), newOwner(selectOwner.getAllCandidates(),
 148                     entityOwnershipStatistics.byEntityType(entityType),
 149                     selectOwner.getOwnerSelectionStrategy()));
 150
 151             Cancellable cancellable = entityToScheduledOwnershipTask.get(selectOwner.getEntityPath());
 152             if(cancellable != null){
 153                 if(!cancellable.isCancelled()){
 154                     cancellable.cancel();
 155                 }
 156                 entityToScheduledOwnershipTask.remove(selectOwner.getEntityPath());
 157             }
 158         }
 159     }
 160
 161     private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
 162         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 163
 164         listenerSupport.setHasCandidateForEntity(registerCandidate.getEntity());
 165
 166         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 167                 registerCandidate.getEntity().getId(), localMemberName);
 168         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 169
 170         getSender().tell(SuccessReply.INSTANCE, getSelf());
 171     }
 172
 173     private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
 174         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 175
 176         Entity entity = unregisterCandidate.getEntity();
 177         listenerSupport.unsetHasCandidateForEntity(entity);
 178
 179         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
 180         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 181
 182         getSender().tell(SuccessReply.INSTANCE, getSelf());
 183     }
 184
 185     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 186         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 187
 188         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 189
 190         getSender().tell(SuccessReply.INSTANCE, getSelf());
 191
 192         searchForEntitiesOwnedBy(localMemberName, new EntityWalker() {
 193             @Override
 194             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 195                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleType =
 196                         entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 197                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 198                 if (registerListener.getEntityType().equals(entityType)) {
 199                     Entity entity = new Entity(entityType,
 200                             (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 201                     listenerSupport.notifyEntityOwnershipListener(entity, false, true, true, registerListener.getListener());
 202                 }
 203             }
 204         });
 205     }
 206
 207     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 208         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 209
 210         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 211
 212         getSender().tell(SuccessReply.INSTANCE, getSelf());
 213     }
 214
 215     void tryCommitModifications(final BatchedModifications modifications) {
 216         if(isLeader()) {
 217             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 218
 219             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 220             // to the state. However we don't need to retry it in that case b/c it will be committed to
 221             // the journal first and, once a majority of followers come back on line and it is replicated,
 222             // it will be applied at that point.
 223             handleBatchedModificationsLocal(modifications, self());
 224         } else {
 225             final ActorSelection leader = getLeader();
 226             if (leader != null) {
 227                 if(LOG.isDebugEnabled()) {
 228                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 229                             modifications.getTransactionID(), leader);
 230                 }
 231
 232                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 233                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 234
 235                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 236             }
 237         }
 238     }
 239
 240     boolean hasLeader() {
 241         return getLeader() != null && !isIsolatedLeader();
 242     }
 243
 244     @Override
 245     protected void onStateChanged() {
 246         super.onStateChanged();
 247
 248         boolean isLeader = isLeader();
 249         if(LOG.isDebugEnabled()) {
 250             LOG.debug("{}: onStateChanged: isLeader: {}, hasLeader: {}", persistenceId(), isLeader, hasLeader());
 251         }
 252
 253         commitCoordinator.onStateChanged(this, isLeader);
 254     }
 255
 256     @Override
 257     protected void onLeaderChanged(String oldLeader, String newLeader) {
 258         super.onLeaderChanged(oldLeader, newLeader);
 259
 260         boolean isLeader = isLeader();
 261         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 262                 newLeader, isLeader);
 263
 264         if(isLeader) {
 265             // We were just elected leader. If the old leader is down, select new owners for the entities
 266             // owned by the down leader.
 267
 268             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 269
 270             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 271
 272             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 273                 removeCandidateFromEntities(oldLeaderMemberName);
 274             }
 275         } else {
 276             // The leader changed - notify the coordinator to check if pending modifications need to be sent.
 277             // While onStateChanged also does this, this method handles the case where the shard hears from a
 278             // leader and stays in the follower state. In that case no behavior state change occurs.
 279             commitCoordinator.onStateChanged(this, isLeader);
 280         }
 281     }
 282
 283     private void onCandidateRemoved(CandidateRemoved message) {
 284         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 285
 286         if(isLeader()) {
 287             String currentOwner = getCurrentOwner(message.getEntityPath());
 288             if(message.getRemovedCandidate().equals(currentOwner) || message.getRemainingCandidates().size() == 0){
 289                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 290                 writeNewOwner(message.getEntityPath(),
 291                         newOwner(message.getRemainingCandidates(), entityOwnershipStatistics.byEntityType(entityType),
 292                                 getEntityOwnerElectionStrategy(message.getEntityPath())));
 293             }
 294         } else {
 295             // We're not the leader. If the removed candidate is our local member then check if we actually
 296             // have a local candidate registered. If we do then we must have been partitioned from the leader
 297             // and the leader removed our candidate since the leader can't tell the difference between a
 298             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 299             // our candidate.
 300             if(localMemberName.equals(message.getRemovedCandidate()) &&
 301                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 302                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 303                     " - adding back local candidate", message.getEntityPath());
 304
 305                 commitCoordinator.commitModification(new MergeModification(
 306                         candidatePath(message.getEntityPath(), localMemberName),
 307                         candidateMapEntry(localMemberName)), this);
 308             }
 309         }
 310     }
 311
 312     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 313         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 314         return strategyConfig.createStrategy(entityType);
 315     }
 316
 317     private void onCandidateAdded(CandidateAdded message) {
 318         if(!isLeader()){
 319             return;
 320         }
 321
 322         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 323
 324         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 325         // remove it from the downPeerMemberNames.
 326         downPeerMemberNames.remove(message.getNewCandidate());
 327
 328         final String currentOwner = getCurrentOwner(message.getEntityPath());
 329         final EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 330         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 331
 332         // Available members is all the known peers - the number of peers that are down + self
 333         // So if there are 2 peers and 1 is down then availableMembers will be 2
 334         final int availableMembers = (peerIdToMemberNames.size() - downPeerMemberNames.size()) + 1;
 335
 336         LOG.debug("{}: Using strategy {} to select owner", persistenceId(), strategy);
 337         if(Strings.isNullOrEmpty(currentOwner)){
 338             if(strategy.getSelectionDelayInMillis() == 0L) {
 339                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(),
 340                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 341             } else if(message.getAllCandidates().size() == availableMembers) {
 342                 LOG.debug("{}: Received the maximum candidates requests : {} writing new owner",
 343                         persistenceId(), availableMembers);
 344                 cancelOwnerSelectionTask(message.getEntityPath());
 345                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(),
 346                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 347             } else {
 348                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 349             }
 350         }
 351     }
 352
 353     private void onPeerDown(PeerDown peerDown) {
 354         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 355
 356         String downMemberName = peerDown.getMemberName();
 357         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 358             // Remove the down peer as a candidate from all entities.
 359             removeCandidateFromEntities(downMemberName);
 360         }
 361     }
 362
 363     private void onPeerUp(PeerUp peerUp) {
 364         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 365
 366         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 367         downPeerMemberNames.remove(peerUp.getMemberName());
 368
 369         // Notify the coordinator to check if pending modifications need to be sent. We do this here
 370         // to handle the case where the leader's peer address isn't now yet when a prior state or
 371         // leader change occurred.
 372         commitCoordinator.onStateChanged(this, isLeader());
 373     }
 374
 375     private void removeCandidateFromEntities(final String owner) {
 376         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 377         searchForEntities(new EntityWalker() {
 378             @Override
 379             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 380                 if (hasCandidate(entityNode, owner)) {
 381                     YangInstanceIdentifier entityId =
 382                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 383                     YangInstanceIdentifier candidatePath = candidatePath(
 384                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 385                             entityId, owner);
 386
 387                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 388                             owner, candidatePath);
 389
 390                     modifications.addModification(new DeleteModification(candidatePath));
 391                 }
 392             }
 393         });
 394
 395         commitCoordinator.commitModifications(modifications, this);
 396     }
 397
 398     private static boolean hasCandidate(MapEntryNode entity, String candidateName) {
 399         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 400     }
 401
 402     private void searchForEntitiesOwnedBy(final String owner, final EntityWalker walker) {
 403         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 404         if(!possibleEntityTypes.isPresent()) {
 405             return;
 406         }
 407
 408         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);
 409
 410         searchForEntities(new EntityWalker() {
 411             @Override
 412             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 413                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 414                         entityNode.getChild(ENTITY_OWNER_NODE_ID);
 415                 if (possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
 416                     walker.onEntity(entityTypeNode, entityNode);
 417                 }
 418             }
 419         });
 420     }
 421
 422     private void searchForEntities(EntityWalker walker) {
 423         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 424         if(!possibleEntityTypes.isPresent()) {
 425             return;
 426         }
 427
 428         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 429             Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
 430                     entityType.getChild(ENTITY_NODE_ID);
 431             if(!possibleEntities.isPresent()) {
 432                 continue; // shouldn't happen but handle anyway
 433             }
 434
 435             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 436                 walker.onEntity(entityType, entity);
 437             }
 438         }
 439     }
 440
 441     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 442         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 443
 444         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 445                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 446     }
 447
 448     /**
 449      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 450      *
 451      * @param entityPath
 452      * @param allCandidates
 453      */
 454     public void scheduleOwnerSelection(YangInstanceIdentifier entityPath, Collection<String> allCandidates,
 455                                        EntityOwnerSelectionStrategy strategy){
 456         cancelOwnerSelectionTask(entityPath);
 457
 458         LOG.debug("{}: Scheduling owner selection after {} ms", persistenceId(), strategy.getSelectionDelayInMillis());
 459
 460         final Cancellable lastScheduledTask = context().system().scheduler().scheduleOnce(
 461                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS)
 462                 , self(), new SelectOwner(entityPath, allCandidates, strategy)
 463                 , context().system().dispatcher(), self());
 464
 465         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 466     }
 467
 468     private void cancelOwnerSelectionTask(YangInstanceIdentifier entityPath){
 469         final Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 470         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 471             lastScheduledTask.cancel();
 472         }
 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 }