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