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.actor.Props;
  30 import akka.pattern.Patterns;
  31 import com.google.common.base.Optional;
  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.api.schema.tree.DataTreeSnapshot;
  67 import org.opendaylight.yangtools.yang.data.impl.schema.ImmutableNodes;
  68 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
  69 import scala.concurrent.Future;
  70 import scala.concurrent.duration.FiniteDuration;
  71
  72 /**
  73  * Special Shard for EntityOwnership.
  74  *
  75  * @author Thomas Pantelis
  76  */
  77 class EntityOwnershipShard extends Shard {
  78     private final String localMemberName;
  79     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  80     private final EntityOwnershipListenerSupport listenerSupport;
  81     private final Set<String> downPeerMemberNames = new HashSet<>();
  82     private final Map<String, String> peerIdToMemberNames = new HashMap<>();
  83     private EntityOwnerSelectionStrategyConfig strategyConfig;
  84     private Map<YangInstanceIdentifier, Cancellable> entityToScheduledOwnershipTask = new HashMap<>();
  85     private final EntityOwnershipStatistics entityOwnershipStatistics;
  86
  87     private static DatastoreContext noPersistenceDatastoreContext(DatastoreContext datastoreContext) {
  88         return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
  89     }
  90
  91     protected EntityOwnershipShard(ShardIdentifier name, Map<String, String> peerAddresses,
  92                                    DatastoreContext datastoreContext, SchemaContext schemaContext, String localMemberName,
  93                                    EntityOwnerSelectionStrategyConfig strategyConfig) {
  94         super(name, peerAddresses, noPersistenceDatastoreContext(datastoreContext), schemaContext);
  95         this.localMemberName = localMemberName;
  96         this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(localMemberName, LOG);
  97         this.listenerSupport = new EntityOwnershipListenerSupport(getContext(), persistenceId());
  98         this.strategyConfig = strategyConfig;
  99         this.entityOwnershipStatistics = new EntityOwnershipStatistics();
 100         this.entityOwnershipStatistics.init(getDataStore());
 101
 102         for(String peerId: peerAddresses.keySet()) {
 103             ShardIdentifier shardId = ShardIdentifier.builder().fromShardIdString(peerId).build();
 104             peerIdToMemberNames.put(peerId, shardId.getMemberName());
 105         }
 106     }
 107
 108     @Override
 109     protected void onDatastoreContext(DatastoreContext context) {
 110         super.onDatastoreContext(noPersistenceDatastoreContext(context));
 111     }
 112
 113     @Override
 114     protected void onRecoveryComplete() {
 115         super.onRecoveryComplete();
 116
 117         new CandidateListChangeListener(getSelf(), persistenceId()).init(getDataStore());
 118         new EntityOwnerChangeListener(localMemberName, listenerSupport).init(getDataStore());
 119     }
 120
 121     @Override
 122     public void onReceiveCommand(final Object message) throws Exception {
 123         if(message instanceof RegisterCandidateLocal) {
 124             onRegisterCandidateLocal((RegisterCandidateLocal) message);
 125         } else if(message instanceof UnregisterCandidateLocal) {
 126             onUnregisterCandidateLocal((UnregisterCandidateLocal)message);
 127         } else if(message instanceof CandidateAdded){
 128             onCandidateAdded((CandidateAdded) message);
 129         } else if(message instanceof CandidateRemoved){
 130             onCandidateRemoved((CandidateRemoved) message);
 131         } else if(message instanceof PeerDown) {
 132             onPeerDown((PeerDown) message);
 133         } else if(message instanceof PeerUp) {
 134             onPeerUp((PeerUp) message);
 135         } else if(message instanceof RegisterListenerLocal) {
 136             onRegisterListenerLocal((RegisterListenerLocal)message);
 137         } else if(message instanceof UnregisterListenerLocal) {
 138             onUnregisterListenerLocal((UnregisterListenerLocal) message);
 139         } else if(message instanceof SelectOwner) {
 140             onSelectOwner((SelectOwner) message);
 141         } else if(!commitCoordinator.handleMessage(message, this)) {
 142             super.onReceiveCommand(message);
 143         }
 144     }
 145
 146     private void onSelectOwner(SelectOwner selectOwner) {
 147         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 148         if(Strings.isNullOrEmpty(currentOwner)) {
 149             writeNewOwner(selectOwner.getEntityPath(), newOwner(selectOwner.getAllCandidates(),
 150                     selectOwner.getOwnerSelectionStrategy()));
 151
 152             Cancellable cancellable = entityToScheduledOwnershipTask.get(selectOwner.getEntityPath());
 153             if(cancellable != null){
 154                 if(!cancellable.isCancelled()){
 155                     cancellable.cancel();
 156                 }
 157                 entityToScheduledOwnershipTask.remove(selectOwner.getEntityPath());
 158             }
 159         }
 160     }
 161
 162     private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
 163         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 164
 165         listenerSupport.setHasCandidateForEntity(registerCandidate.getEntity());
 166
 167         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 168                 registerCandidate.getEntity().getId(), localMemberName);
 169         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 170
 171         getSender().tell(SuccessReply.INSTANCE, getSelf());
 172     }
 173
 174     private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
 175         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 176
 177         Entity entity = unregisterCandidate.getEntity();
 178         listenerSupport.unsetHasCandidateForEntity(entity);
 179
 180         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
 181         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 182
 183         getSender().tell(SuccessReply.INSTANCE, getSelf());
 184     }
 185
 186     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 187         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 188
 189         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 190
 191         getSender().tell(SuccessReply.INSTANCE, getSelf());
 192
 193         searchForEntitiesOwnedBy(localMemberName, new EntityWalker() {
 194             @Override
 195             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 196                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleType =
 197                         entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 198                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 199                 if (registerListener.getEntityType().equals(entityType)) {
 200                     Entity entity = new Entity(entityType,
 201                             (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 202                     listenerSupport.notifyEntityOwnershipListener(entity, false, true, true, registerListener.getListener());
 203                 }
 204             }
 205         });
 206     }
 207
 208     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 209         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 210
 211         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 212
 213         getSender().tell(SuccessReply.INSTANCE, getSelf());
 214     }
 215
 216     void tryCommitModifications(final BatchedModifications modifications) {
 217         if(isLeader()) {
 218             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 219
 220             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 221             // to the state. However we don't need to retry it in that case b/c it will be committed to
 222             // the journal first and, once a majority of followers come back on line and it is replicated,
 223             // it will be applied at that point.
 224             handleBatchedModificationsLocal(modifications, self());
 225         } else {
 226             final ActorSelection leader = getLeader();
 227             if (leader != null) {
 228                 if(LOG.isDebugEnabled()) {
 229                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 230                             modifications.getTransactionID(), leader);
 231                 }
 232
 233                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 234                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 235
 236                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 237             }
 238         }
 239     }
 240
 241     boolean hasLeader() {
 242         return getLeader() != null && !isIsolatedLeader();
 243     }
 244
 245     @Override
 246     protected void onStateChanged() {
 247         super.onStateChanged();
 248
 249         commitCoordinator.onStateChanged(this, isLeader());
 250     }
 251
 252     @Override
 253     protected void onLeaderChanged(String oldLeader, String newLeader) {
 254         super.onLeaderChanged(oldLeader, newLeader);
 255
 256         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 257                 newLeader, isLeader());
 258
 259         if(isLeader()) {
 260             // We were just elected leader. If the old leader is down, select new owners for the entities
 261             // owned by the down leader.
 262
 263             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 264
 265             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 266
 267             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 268                 selectNewOwnerForEntitiesOwnedBy(oldLeaderMemberName);
 269             }
 270         }
 271     }
 272
 273     private void onCandidateRemoved(CandidateRemoved message) {
 274         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 275
 276         if(isLeader()) {
 277             String currentOwner = getCurrentOwner(message.getEntityPath());
 278             if(message.getRemovedCandidate().equals(currentOwner)){
 279                 writeNewOwner(message.getEntityPath(),
 280                         newOwner(message.getRemainingCandidates(), getEntityOwnerElectionStrategy(message.getEntityPath())));
 281             }
 282         } else {
 283             // We're not the leader. If the removed candidate is our local member then check if we actually
 284             // have a local candidate registered. If we do then we must have been partitioned from the leader
 285             // and the leader removed our candidate since the leader can't tell the difference between a
 286             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 287             // our candidate.
 288             if(localMemberName.equals(message.getRemovedCandidate()) &&
 289                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 290                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 291                     " - adding back local candidate", message.getEntityPath());
 292
 293                 commitCoordinator.commitModification(new MergeModification(
 294                         candidatePath(message.getEntityPath(), localMemberName),
 295                         candidateMapEntry(localMemberName)), this);
 296             }
 297         }
 298     }
 299
 300     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 301         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 302         return strategyConfig.createStrategy(entityType);
 303     }
 304
 305     private void onCandidateAdded(CandidateAdded message) {
 306         if(!isLeader()){
 307             return;
 308         }
 309
 310         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 311
 312         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 313         // remove it from the downPeerMemberNames.
 314         downPeerMemberNames.remove(message.getNewCandidate());
 315
 316         String currentOwner = getCurrentOwner(message.getEntityPath());
 317         EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 318         if(Strings.isNullOrEmpty(currentOwner)){
 319             if(strategy.getSelectionDelayInMillis() == 0L) {
 320                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(), strategy));
 321             } else {
 322                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 323             }
 324         }
 325     }
 326
 327     private void onPeerDown(PeerDown peerDown) {
 328         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 329
 330         String downMemberName = peerDown.getMemberName();
 331         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 332             // Remove the down peer as a candidate from all entities.
 333             removeCandidateFromEntities(downMemberName);
 334         }
 335     }
 336
 337     private void onPeerUp(PeerUp peerUp) {
 338         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 339
 340         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 341         downPeerMemberNames.remove(peerUp.getMemberName());
 342     }
 343
 344     private void selectNewOwnerForEntitiesOwnedBy(String owner) {
 345         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 346         searchForEntitiesOwnedBy(owner, new EntityWalker() {
 347             @Override
 348             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 349
 350                 YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH).
 351                         node(entityTypeNode.getIdentifier()).node(ENTITY_NODE_ID).node(entityNode.getIdentifier()).
 352                         node(ENTITY_OWNER_NODE_ID).build();
 353
 354                 Object newOwner = newOwner(getCandidateNames(entityNode), getEntityOwnerElectionStrategy(entityPath));
 355
 356                 LOG.debug("{}: Found entity {}, writing new owner {}", persistenceId(), entityPath, newOwner);
 357
 358                 modifications.addModification(new WriteModification(entityPath,
 359                         ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
 360             }
 361         });
 362
 363         commitCoordinator.commitModifications(modifications, this);
 364     }
 365
 366     private void removeCandidateFromEntities(final String owner) {
 367         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 368         searchForEntities(new EntityWalker() {
 369             @Override
 370             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 371                 if (hasCandidate(entityNode, owner)) {
 372                     YangInstanceIdentifier entityId =
 373                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 374                     YangInstanceIdentifier candidatePath = candidatePath(
 375                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 376                             entityId, owner);
 377
 378                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 379                             owner, candidatePath);
 380
 381                     modifications.addModification(new DeleteModification(candidatePath));
 382                 }
 383             }
 384         });
 385
 386         commitCoordinator.commitModifications(modifications, this);
 387     }
 388
 389     private boolean hasCandidate(MapEntryNode entity, String candidateName) {
 390         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 391     }
 392
 393     private void searchForEntitiesOwnedBy(final String owner, final EntityWalker walker) {
 394         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 395         Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
 396         if(!possibleEntityTypes.isPresent()) {
 397             return;
 398         }
 399
 400         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);
 401
 402         searchForEntities(new EntityWalker() {
 403             @Override
 404             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 405                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 406                         entityNode.getChild(ENTITY_OWNER_NODE_ID);
 407                 if(possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
 408                     walker.onEntity(entityTypeNode, entityNode);
 409                 }
 410             }
 411         });
 412     }
 413
 414     private void searchForEntities(EntityWalker walker) {
 415         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 416         Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
 417         if(!possibleEntityTypes.isPresent()) {
 418             return;
 419         }
 420
 421         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 422             Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
 423                     entityType.getChild(ENTITY_NODE_ID);
 424             if(!possibleEntities.isPresent()) {
 425                 continue; // shouldn't happen but handle anyway
 426             }
 427
 428             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 429                 walker.onEntity(entityType, entity);
 430             }
 431         }
 432     }
 433
 434     private Collection<String> getCandidateNames(MapEntryNode entity) {
 435         Collection<MapEntryNode> candidates = ((MapNode) entity.getChild(CANDIDATE_NODE_ID).get()).getValue();
 436         Collection<String> candidateNames = new ArrayList<>(candidates.size());
 437         for(MapEntryNode candidate: candidates) {
 438             candidateNames.add(candidate.getChild(CANDIDATE_NAME_NODE_ID).get().getValue().toString());
 439         }
 440
 441         return candidateNames;
 442     }
 443
 444     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 445         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 446
 447         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 448                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 449     }
 450
 451     /**
 452      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 453      *
 454      * @param entityPath
 455      * @param allCandidates
 456      */
 457     public void scheduleOwnerSelection(YangInstanceIdentifier entityPath, Collection<String> allCandidates,
 458                                        EntityOwnerSelectionStrategy strategy){
 459         Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 460         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 461             lastScheduledTask.cancel();
 462         }
 463         lastScheduledTask = context().system().scheduler().scheduleOnce(
 464                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS)
 465                 , self(), new SelectOwner(entityPath, allCandidates, strategy)
 466                 , context().system().dispatcher(), self());
 467
 468         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 469     }
 470
 471     private String newOwner(Collection<String> candidates, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 472         Collection<String> viableCandidates = getViableCandidates(candidates);
 473         if(viableCandidates.size() == 0){
 474             return "";
 475         }
 476         return ownerSelectionStrategy.newOwner(viableCandidates);
 477     }
 478
 479     private Collection<String> getViableCandidates(Collection<String> candidates) {
 480         Collection<String> viableCandidates = new ArrayList<>();
 481
 482         for (String candidate : candidates) {
 483             if (!downPeerMemberNames.contains(candidate)) {
 484                 viableCandidates.add(candidate);
 485             }
 486         }
 487         return viableCandidates;
 488     }
 489
 490     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 491         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 492         Optional<NormalizedNode<?, ?>> optionalEntityOwner = snapshot.readNode(entityId.node(ENTITY_OWNER_QNAME));
 493         if(optionalEntityOwner.isPresent()){
 494             return optionalEntityOwner.get().getValue().toString();
 495         }
 496         return null;
 497     }
 498
 499     public static Props props(final ShardIdentifier name, final Map<String, String> peerAddresses,
 500                               final DatastoreContext datastoreContext, final SchemaContext schemaContext,
 501                               final String localMemberName, final EntityOwnerSelectionStrategyConfig strategyConfig) {
 502         return Props.create(new Creator(name, peerAddresses, datastoreContext, schemaContext, localMemberName, strategyConfig));
 503     }
 504
 505     private static class Creator extends AbstractShardCreator {
 506         private static final long serialVersionUID = 1L;
 507
 508         private final String localMemberName;
 509         private final EntityOwnerSelectionStrategyConfig strategyConfig;
 510
 511         Creator(final ShardIdentifier name, final Map<String, String> peerAddresses,
 512                 final DatastoreContext datastoreContext, final SchemaContext schemaContext,
 513                 final String localMemberName, EntityOwnerSelectionStrategyConfig strategyConfig) {
 514             super(name, peerAddresses, datastoreContext, schemaContext);
 515             this.localMemberName = localMemberName;
 516             this.strategyConfig = strategyConfig;
 517         }
 518
 519         @Override
 520         public Shard create() throws Exception {
 521             return new EntityOwnershipShard(name, peerAddresses, datastoreContext, schemaContext, localMemberName, strategyConfig);
 522         }
 523     }
 524
 525     private static interface EntityWalker {
 526         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 527     }
 528 }