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.schema.DataContainerChild;
  61 import org.opendaylight.yangtools.yang.data.api.schema.MapEntryNode;
  62 import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
  63 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  64 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  65 import scala.concurrent.Future;
  66 import scala.concurrent.duration.FiniteDuration;
  67
  68 /**
  69  * Special Shard for EntityOwnership.
  70  *
  71  * @author Thomas Pantelis
  72  */
  73 class EntityOwnershipShard extends Shard {
  74     private final String localMemberName;
  75     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  76     private final EntityOwnershipListenerSupport listenerSupport;
  77     private final Set<String> downPeerMemberNames = new HashSet<>();
  78     private final Map<String, String> peerIdToMemberNames = new HashMap<>();
  79     private final EntityOwnerSelectionStrategyConfig strategyConfig;
  80     private final Map<YangInstanceIdentifier, Cancellable> entityToScheduledOwnershipTask = new HashMap<>();
  81     private final EntityOwnershipStatistics entityOwnershipStatistics;
  82
  83     private static DatastoreContext noPersistenceDatastoreContext(DatastoreContext datastoreContext) {
  84         return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
  85     }
  86
  87     protected EntityOwnershipShard(Builder builder) {
  88         super(builder);
  89         this.localMemberName = builder.localMemberName;
  90         this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(builder.localMemberName, LOG);
  91         this.listenerSupport = new EntityOwnershipListenerSupport(getContext(), persistenceId());
  92         this.strategyConfig = builder.ownerSelectionStrategyConfig;
  93         this.entityOwnershipStatistics = new EntityOwnershipStatistics();
  94         this.entityOwnershipStatistics.init(getDataStore());
  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 handleNonRaftCommand(final Object message) {
 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.handleNonRaftCommand(message);
 137         }
 138     }
 139
 140     private void onSelectOwner(SelectOwner selectOwner) {
 141         LOG.debug("{}: onSelectOwner: {}", persistenceId(), selectOwner);
 142
 143         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 144         if(Strings.isNullOrEmpty(currentOwner)) {
 145             String entityType = EntityOwnersModel.entityTypeFromEntityPath(selectOwner.getEntityPath());
 146             writeNewOwner(selectOwner.getEntityPath(), newOwner(currentOwner, 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         searchForEntities(new EntityWalker() {
 192             @Override
 193             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 194                 Optional<DataContainerChild<?, ?>> possibleType = entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 195                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 196                 if (registerListener.getEntityType().equals(entityType)) {
 197                     final boolean hasOwner;
 198                     final boolean isOwner;
 199
 200                     Optional<DataContainerChild<?, ?>> possibleOwner = entityNode.getChild(ENTITY_OWNER_NODE_ID);
 201                     if (possibleOwner.isPresent()) {
 202                         isOwner = localMemberName.equals(possibleOwner.get().getValue().toString());
 203                         hasOwner = true;
 204                     } else {
 205                         isOwner = false;
 206                         hasOwner = false;
 207                     }
 208
 209                     Entity entity = new Entity(entityType,
 210                         (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 211
 212                     listenerSupport.notifyEntityOwnershipListener(entity, false, isOwner, hasOwner,
 213                         registerListener.getListener());
 214                 }
 215             }
 216         });
 217     }
 218
 219     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 220         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 221
 222         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 223
 224         getSender().tell(SuccessReply.INSTANCE, getSelf());
 225     }
 226
 227     void tryCommitModifications(final BatchedModifications modifications) {
 228         if(isLeader()) {
 229             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 230
 231             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 232             // to the state. However we don't need to retry it in that case b/c it will be committed to
 233             // the journal first and, once a majority of followers come back on line and it is replicated,
 234             // it will be applied at that point.
 235             handleBatchedModificationsLocal(modifications, self());
 236         } else {
 237             final ActorSelection leader = getLeader();
 238             if (leader != null) {
 239                 if(LOG.isDebugEnabled()) {
 240                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 241                             modifications.getTransactionID(), leader);
 242                 }
 243
 244                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 245                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 246
 247                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 248             }
 249         }
 250     }
 251
 252     boolean hasLeader() {
 253         return getLeader() != null && !isIsolatedLeader();
 254     }
 255
 256     @Override
 257     protected void onStateChanged() {
 258         super.onStateChanged();
 259
 260         boolean isLeader = isLeader();
 261         if(LOG.isDebugEnabled()) {
 262             LOG.debug("{}: onStateChanged: isLeader: {}, hasLeader: {}", persistenceId(), isLeader, hasLeader());
 263         }
 264
 265         commitCoordinator.onStateChanged(this, isLeader);
 266     }
 267
 268     @Override
 269     protected void onLeaderChanged(String oldLeader, String newLeader) {
 270         super.onLeaderChanged(oldLeader, newLeader);
 271
 272         boolean isLeader = isLeader();
 273         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 274                 newLeader, isLeader);
 275
 276         if(isLeader) {
 277
 278             // Clear all existing strategies so that they get re-created when we call createStrategy again
 279             // This allows the strategies to be re-initialized with existing statistics maintained by
 280             // EntityOwnershipStatistics
 281             strategyConfig.clearStrategies();
 282
 283             // Remove the candidates for all members that are known to be down. In a cluster which has greater than
 284             // 3 nodes it is possible for a some node beside the leader being down when the leadership transitions
 285             // it makes sense to use this event to remove all the candidates for those downed nodes
 286             for(String downPeerName : downPeerMemberNames){
 287                 removeCandidateFromEntities(downPeerName);
 288             }
 289         } else {
 290             // The leader changed - notify the coordinator to check if pending modifications need to be sent.
 291             // While onStateChanged also does this, this method handles the case where the shard hears from a
 292             // leader and stays in the follower state. In that case no behavior state change occurs.
 293             commitCoordinator.onStateChanged(this, isLeader);
 294         }
 295     }
 296
 297     private void onCandidateRemoved(CandidateRemoved message) {
 298         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 299
 300         if(isLeader()) {
 301             String currentOwner = getCurrentOwner(message.getEntityPath());
 302             if(message.getRemovedCandidate().equals(currentOwner) || message.getRemainingCandidates().size() == 0){
 303                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 304                 writeNewOwner(message.getEntityPath(),
 305                         newOwner(currentOwner, message.getRemainingCandidates(), entityOwnershipStatistics.byEntityType(entityType),
 306                                 getEntityOwnerElectionStrategy(message.getEntityPath())));
 307             }
 308         } else {
 309             // We're not the leader. If the removed candidate is our local member then check if we actually
 310             // have a local candidate registered. If we do then we must have been partitioned from the leader
 311             // and the leader removed our candidate since the leader can't tell the difference between a
 312             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 313             // our candidate.
 314             if(localMemberName.equals(message.getRemovedCandidate()) &&
 315                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 316                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 317                     " - adding back local candidate", message.getEntityPath());
 318
 319                 commitCoordinator.commitModification(new MergeModification(
 320                         candidatePath(message.getEntityPath(), localMemberName),
 321                         candidateMapEntry(localMemberName)), this);
 322             }
 323         }
 324     }
 325
 326     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 327         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 328         return strategyConfig.createStrategy(entityType, entityOwnershipStatistics.byEntityType(entityType));
 329     }
 330
 331     private void onCandidateAdded(CandidateAdded message) {
 332         if(!isLeader()){
 333             return;
 334         }
 335
 336         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 337
 338         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 339         // remove it from the downPeerMemberNames.
 340         downPeerMemberNames.remove(message.getNewCandidate());
 341
 342         final String currentOwner = getCurrentOwner(message.getEntityPath());
 343         final EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 344         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 345
 346         // Available members is all the known peers - the number of peers that are down + self
 347         // So if there are 2 peers and 1 is down then availableMembers will be 2
 348         final int availableMembers = (peerIdToMemberNames.size() - downPeerMemberNames.size()) + 1;
 349
 350         LOG.debug("{}: Using strategy {} to select owner, currentOwner = {}", persistenceId(), strategy, currentOwner);
 351
 352         if(!message.getAllCandidates().contains(currentOwner)){
 353             if(strategy.getSelectionDelayInMillis() == 0L) {
 354                 writeNewOwner(message.getEntityPath(), newOwner(currentOwner, message.getAllCandidates(),
 355                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 356             } else if(message.getAllCandidates().size() == availableMembers) {
 357                 LOG.debug("{}: Received the maximum candidates requests : {} writing new owner",
 358                         persistenceId(), availableMembers);
 359                 cancelOwnerSelectionTask(message.getEntityPath());
 360                 writeNewOwner(message.getEntityPath(), newOwner(currentOwner, message.getAllCandidates(),
 361                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 362             } else {
 363                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 364             }
 365         }
 366     }
 367
 368     private void onPeerDown(PeerDown peerDown) {
 369         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 370
 371         String downMemberName = peerDown.getMemberName();
 372         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 373             // Remove the down peer as a candidate from all entities.
 374             removeCandidateFromEntities(downMemberName);
 375         }
 376     }
 377
 378     private void onPeerUp(PeerUp peerUp) {
 379         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 380
 381         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 382         downPeerMemberNames.remove(peerUp.getMemberName());
 383
 384         // Notify the coordinator to check if pending modifications need to be sent. We do this here
 385         // to handle the case where the leader's peer address isn't now yet when a prior state or
 386         // leader change occurred.
 387         commitCoordinator.onStateChanged(this, isLeader());
 388     }
 389
 390     private void removeCandidateFromEntities(final String owner) {
 391         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 392         searchForEntities(new EntityWalker() {
 393             @Override
 394             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 395                 if (hasCandidate(entityNode, owner)) {
 396                     YangInstanceIdentifier entityId =
 397                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 398                     YangInstanceIdentifier candidatePath = candidatePath(
 399                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 400                             entityId, owner);
 401
 402                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 403                             owner, candidatePath);
 404
 405                     modifications.addModification(new DeleteModification(candidatePath));
 406                 }
 407             }
 408         });
 409
 410         commitCoordinator.commitModifications(modifications, this);
 411     }
 412
 413     private static boolean hasCandidate(MapEntryNode entity, String candidateName) {
 414         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 415     }
 416
 417     private void searchForEntities(EntityWalker walker) {
 418         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 419         if(!possibleEntityTypes.isPresent()) {
 420             return;
 421         }
 422
 423         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 424             Optional<DataContainerChild<?, ?>> possibleEntities = entityType.getChild(ENTITY_NODE_ID);
 425             if(!possibleEntities.isPresent()) {
 426                 // shouldn't happen but handle anyway
 427                 continue;
 428             }
 429
 430             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 431                 walker.onEntity(entityType, entity);
 432             }
 433         }
 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         cancelOwnerSelectionTask(entityPath);
 452
 453         LOG.debug("{}: Scheduling owner selection after {} ms", persistenceId(), strategy.getSelectionDelayInMillis());
 454
 455         final Cancellable 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 void cancelOwnerSelectionTask(YangInstanceIdentifier entityPath){
 464         final Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 465         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 466             lastScheduledTask.cancel();
 467         }
 468     }
 469
 470     private String newOwner(String currentOwner, Collection<String> candidates, Map<String, Long> statistics, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 471         Collection<String> viableCandidates = getViableCandidates(candidates);
 472         if(viableCandidates.size() == 0){
 473             return "";
 474         }
 475         return ownerSelectionStrategy.newOwner(currentOwner, viableCandidates);
 476     }
 477
 478     private Collection<String> getViableCandidates(Collection<String> candidates) {
 479         Collection<String> viableCandidates = new ArrayList<>();
 480
 481         for (String candidate : candidates) {
 482             if (!downPeerMemberNames.contains(candidate)) {
 483                 viableCandidates.add(candidate);
 484             }
 485         }
 486         return viableCandidates;
 487     }
 488
 489     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 490         Optional<NormalizedNode<?, ?>> optionalEntityOwner = getDataStore().readNode(entityId.node(ENTITY_OWNER_QNAME));
 491         if(optionalEntityOwner.isPresent()){
 492             return optionalEntityOwner.get().getValue().toString();
 493         }
 494         return null;
 495     }
 496
 497     private static interface EntityWalker {
 498         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 499     }
 500
 501     public static Builder newBuilder() {
 502         return new Builder();
 503     }
 504
 505     static class Builder extends Shard.AbstractBuilder<Builder, EntityOwnershipShard> {
 506         private String localMemberName;
 507         private EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig;
 508
 509         protected Builder() {
 510             super(EntityOwnershipShard.class);
 511         }
 512
 513         Builder localMemberName(String localMemberName) {
 514             checkSealed();
 515             this.localMemberName = localMemberName;
 516             return this;
 517         }
 518
 519         Builder ownerSelectionStrategyConfig(EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig){
 520             checkSealed();
 521             this.ownerSelectionStrategyConfig = ownerSelectionStrategyConfig;
 522             return this;
 523         }
 524
 525         @Override
 526         protected void verify() {
 527             super.verify();
 528             Preconditions.checkNotNull(localMemberName, "localMemberName should not be null");
 529             Preconditions.checkNotNull(ownerSelectionStrategyConfig, "ownerSelectionStrategyConfig should not be null");
 530         }
 531     }
 532 }