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 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         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(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             // We were just elected leader. If the old leader is down, select new owners for the entities
 278             // owned by the down leader.
 279
 280             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 281
 282             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 283
 284             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 285                 removeCandidateFromEntities(oldLeaderMemberName);
 286             }
 287         } else {
 288             // The leader changed - notify the coordinator to check if pending modifications need to be sent.
 289             // While onStateChanged also does this, this method handles the case where the shard hears from a
 290             // leader and stays in the follower state. In that case no behavior state change occurs.
 291             commitCoordinator.onStateChanged(this, isLeader);
 292         }
 293     }
 294
 295     private void onCandidateRemoved(CandidateRemoved message) {
 296         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 297
 298         if(isLeader()) {
 299             String currentOwner = getCurrentOwner(message.getEntityPath());
 300             if(message.getRemovedCandidate().equals(currentOwner) || message.getRemainingCandidates().size() == 0){
 301                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 302                 writeNewOwner(message.getEntityPath(),
 303                         newOwner(message.getRemainingCandidates(), entityOwnershipStatistics.byEntityType(entityType),
 304                                 getEntityOwnerElectionStrategy(message.getEntityPath())));
 305             }
 306         } else {
 307             // We're not the leader. If the removed candidate is our local member then check if we actually
 308             // have a local candidate registered. If we do then we must have been partitioned from the leader
 309             // and the leader removed our candidate since the leader can't tell the difference between a
 310             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 311             // our candidate.
 312             if(localMemberName.equals(message.getRemovedCandidate()) &&
 313                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 314                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 315                     " - adding back local candidate", message.getEntityPath());
 316
 317                 commitCoordinator.commitModification(new MergeModification(
 318                         candidatePath(message.getEntityPath(), localMemberName),
 319                         candidateMapEntry(localMemberName)), this);
 320             }
 321         }
 322     }
 323
 324     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 325         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 326         return strategyConfig.createStrategy(entityType);
 327     }
 328
 329     private void onCandidateAdded(CandidateAdded message) {
 330         if(!isLeader()){
 331             return;
 332         }
 333
 334         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 335
 336         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 337         // remove it from the downPeerMemberNames.
 338         downPeerMemberNames.remove(message.getNewCandidate());
 339
 340         final String currentOwner = getCurrentOwner(message.getEntityPath());
 341         final EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 342         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 343
 344         // Available members is all the known peers - the number of peers that are down + self
 345         // So if there are 2 peers and 1 is down then availableMembers will be 2
 346         final int availableMembers = (peerIdToMemberNames.size() - downPeerMemberNames.size()) + 1;
 347
 348         LOG.debug("{}: Using strategy {} to select owner", persistenceId(), strategy);
 349         if(Strings.isNullOrEmpty(currentOwner)){
 350             if(strategy.getSelectionDelayInMillis() == 0L) {
 351                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(),
 352                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 353             } else if(message.getAllCandidates().size() == availableMembers) {
 354                 LOG.debug("{}: Received the maximum candidates requests : {} writing new owner",
 355                         persistenceId(), availableMembers);
 356                 cancelOwnerSelectionTask(message.getEntityPath());
 357                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(),
 358                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 359             } else {
 360                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 361             }
 362         }
 363     }
 364
 365     private void onPeerDown(PeerDown peerDown) {
 366         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 367
 368         String downMemberName = peerDown.getMemberName();
 369         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 370             // Remove the down peer as a candidate from all entities.
 371             removeCandidateFromEntities(downMemberName);
 372         }
 373     }
 374
 375     private void onPeerUp(PeerUp peerUp) {
 376         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 377
 378         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 379         downPeerMemberNames.remove(peerUp.getMemberName());
 380
 381         // Notify the coordinator to check if pending modifications need to be sent. We do this here
 382         // to handle the case where the leader's peer address isn't now yet when a prior state or
 383         // leader change occurred.
 384         commitCoordinator.onStateChanged(this, isLeader());
 385     }
 386
 387     private void removeCandidateFromEntities(final String owner) {
 388         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 389         searchForEntities(new EntityWalker() {
 390             @Override
 391             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 392                 if (hasCandidate(entityNode, owner)) {
 393                     YangInstanceIdentifier entityId =
 394                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 395                     YangInstanceIdentifier candidatePath = candidatePath(
 396                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 397                             entityId, owner);
 398
 399                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 400                             owner, candidatePath);
 401
 402                     modifications.addModification(new DeleteModification(candidatePath));
 403                 }
 404             }
 405         });
 406
 407         commitCoordinator.commitModifications(modifications, this);
 408     }
 409
 410     private static boolean hasCandidate(MapEntryNode entity, String candidateName) {
 411         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 412     }
 413
 414     private void searchForEntities(EntityWalker walker) {
 415         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 416         if(!possibleEntityTypes.isPresent()) {
 417             return;
 418         }
 419
 420         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 421             Optional<DataContainerChild<?, ?>> possibleEntities = entityType.getChild(ENTITY_NODE_ID);
 422             if(!possibleEntities.isPresent()) {
 423                 // shouldn't happen but handle anyway
 424                 continue;
 425             }
 426
 427             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 428                 walker.onEntity(entityType, entity);
 429             }
 430         }
 431     }
 432
 433     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 434         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 435
 436         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 437                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 438     }
 439
 440     /**
 441      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 442      *
 443      * @param entityPath
 444      * @param allCandidates
 445      */
 446     public void scheduleOwnerSelection(YangInstanceIdentifier entityPath, Collection<String> allCandidates,
 447                                        EntityOwnerSelectionStrategy strategy){
 448         cancelOwnerSelectionTask(entityPath);
 449
 450         LOG.debug("{}: Scheduling owner selection after {} ms", persistenceId(), strategy.getSelectionDelayInMillis());
 451
 452         final Cancellable lastScheduledTask = context().system().scheduler().scheduleOnce(
 453                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS)
 454                 , self(), new SelectOwner(entityPath, allCandidates, strategy)
 455                 , context().system().dispatcher(), self());
 456
 457         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 458     }
 459
 460     private void cancelOwnerSelectionTask(YangInstanceIdentifier entityPath){
 461         final Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 462         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 463             lastScheduledTask.cancel();
 464         }
 465     }
 466
 467     private String newOwner(Collection<String> candidates, Map<String, Long> statistics, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 468         Collection<String> viableCandidates = getViableCandidates(candidates);
 469         if(viableCandidates.size() == 0){
 470             return "";
 471         }
 472         return ownerSelectionStrategy.newOwner(viableCandidates, statistics);
 473     }
 474
 475     private Collection<String> getViableCandidates(Collection<String> candidates) {
 476         Collection<String> viableCandidates = new ArrayList<>();
 477
 478         for (String candidate : candidates) {
 479             if (!downPeerMemberNames.contains(candidate)) {
 480                 viableCandidates.add(candidate);
 481             }
 482         }
 483         return viableCandidates;
 484     }
 485
 486     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 487         Optional<NormalizedNode<?, ?>> optionalEntityOwner = getDataStore().readNode(entityId.node(ENTITY_OWNER_QNAME));
 488         if(optionalEntityOwner.isPresent()){
 489             return optionalEntityOwner.get().getValue().toString();
 490         }
 491         return null;
 492     }
 493
 494     private static interface EntityWalker {
 495         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 496     }
 497
 498     public static Builder newBuilder() {
 499         return new Builder();
 500     }
 501
 502     static class Builder extends Shard.AbstractBuilder<Builder, EntityOwnershipShard> {
 503         private String localMemberName;
 504         private EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig;
 505
 506         protected Builder() {
 507             super(EntityOwnershipShard.class);
 508         }
 509
 510         Builder localMemberName(String localMemberName) {
 511             checkSealed();
 512             this.localMemberName = localMemberName;
 513             return this;
 514         }
 515
 516         Builder ownerSelectionStrategyConfig(EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig){
 517             checkSealed();
 518             this.ownerSelectionStrategyConfig = ownerSelectionStrategyConfig;
 519             return this;
 520         }
 521
 522         @Override
 523         protected void verify() {
 524             super.verify();
 525             Preconditions.checkNotNull(localMemberName, "localMemberName should not be null");
 526             Preconditions.checkNotNull(ownerSelectionStrategyConfig, "ownerSelectionStrategyConfig should not be null");
 527         }
 528     }
 529 }