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             String entityType = EntityOwnersModel.entityTypeFromEntityPath(selectOwner.getEntityPath());
 150             writeNewOwner(selectOwner.getEntityPath(), newOwner(selectOwner.getAllCandidates(),
 151                     entityOwnershipStatistics.byEntityType(entityType),
 152                     selectOwner.getOwnerSelectionStrategy()));
 153
 154             Cancellable cancellable = entityToScheduledOwnershipTask.get(selectOwner.getEntityPath());
 155             if(cancellable != null){
 156                 if(!cancellable.isCancelled()){
 157                     cancellable.cancel();
 158                 }
 159                 entityToScheduledOwnershipTask.remove(selectOwner.getEntityPath());
 160             }
 161         }
 162     }
 163
 164     private void onRegisterCandidateLocal(RegisterCandidateLocal registerCandidate) {
 165         LOG.debug("{}: onRegisterCandidateLocal: {}", persistenceId(), registerCandidate);
 166
 167         listenerSupport.setHasCandidateForEntity(registerCandidate.getEntity());
 168
 169         NormalizedNode<?, ?> entityOwners = entityOwnersWithCandidate(registerCandidate.getEntity().getType(),
 170                 registerCandidate.getEntity().getId(), localMemberName);
 171         commitCoordinator.commitModification(new MergeModification(ENTITY_OWNERS_PATH, entityOwners), this);
 172
 173         getSender().tell(SuccessReply.INSTANCE, getSelf());
 174     }
 175
 176     private void onUnregisterCandidateLocal(UnregisterCandidateLocal unregisterCandidate) {
 177         LOG.debug("{}: onUnregisterCandidateLocal: {}", persistenceId(), unregisterCandidate);
 178
 179         Entity entity = unregisterCandidate.getEntity();
 180         listenerSupport.unsetHasCandidateForEntity(entity);
 181
 182         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getId(), localMemberName);
 183         commitCoordinator.commitModification(new DeleteModification(candidatePath), this);
 184
 185         getSender().tell(SuccessReply.INSTANCE, getSelf());
 186     }
 187
 188     private void onRegisterListenerLocal(final RegisterListenerLocal registerListener) {
 189         LOG.debug("{}: onRegisterListenerLocal: {}", persistenceId(), registerListener);
 190
 191         listenerSupport.addEntityOwnershipListener(registerListener.getEntityType(), registerListener.getListener());
 192
 193         getSender().tell(SuccessReply.INSTANCE, getSelf());
 194
 195         searchForEntitiesOwnedBy(localMemberName, new EntityWalker() {
 196             @Override
 197             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 198                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleType =
 199                         entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 200                 String entityType = possibleType.isPresent() ? possibleType.get().getValue().toString() : null;
 201                 if (registerListener.getEntityType().equals(entityType)) {
 202                     Entity entity = new Entity(entityType,
 203                             (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 204                     listenerSupport.notifyEntityOwnershipListener(entity, false, true, true, registerListener.getListener());
 205                 }
 206             }
 207         });
 208     }
 209
 210     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 211         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 212
 213         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 214
 215         getSender().tell(SuccessReply.INSTANCE, getSelf());
 216     }
 217
 218     void tryCommitModifications(final BatchedModifications modifications) {
 219         if(isLeader()) {
 220             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 221
 222             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 223             // to the state. However we don't need to retry it in that case b/c it will be committed to
 224             // the journal first and, once a majority of followers come back on line and it is replicated,
 225             // it will be applied at that point.
 226             handleBatchedModificationsLocal(modifications, self());
 227         } else {
 228             final ActorSelection leader = getLeader();
 229             if (leader != null) {
 230                 if(LOG.isDebugEnabled()) {
 231                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 232                             modifications.getTransactionID(), leader);
 233                 }
 234
 235                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 236                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 237
 238                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 239             }
 240         }
 241     }
 242
 243     boolean hasLeader() {
 244         return getLeader() != null && !isIsolatedLeader();
 245     }
 246
 247     @Override
 248     protected void onStateChanged() {
 249         super.onStateChanged();
 250
 251         commitCoordinator.onStateChanged(this, isLeader());
 252     }
 253
 254     @Override
 255     protected void onLeaderChanged(String oldLeader, String newLeader) {
 256         super.onLeaderChanged(oldLeader, newLeader);
 257
 258         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 259                 newLeader, isLeader());
 260
 261         if(isLeader()) {
 262             // We were just elected leader. If the old leader is down, select new owners for the entities
 263             // owned by the down leader.
 264
 265             String oldLeaderMemberName = peerIdToMemberNames.get(oldLeader);
 266
 267             LOG.debug("{}: oldLeaderMemberName: {}", persistenceId(), oldLeaderMemberName);
 268
 269             if(downPeerMemberNames.contains(oldLeaderMemberName)) {
 270                 selectNewOwnerForEntitiesOwnedBy(oldLeaderMemberName);
 271             }
 272         }
 273     }
 274
 275     private void onCandidateRemoved(CandidateRemoved message) {
 276         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 277
 278         if(isLeader()) {
 279             String currentOwner = getCurrentOwner(message.getEntityPath());
 280             if(message.getRemovedCandidate().equals(currentOwner)){
 281                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 282                 writeNewOwner(message.getEntityPath(),
 283                         newOwner(message.getRemainingCandidates(), entityOwnershipStatistics.byEntityType(entityType),
 284                                 getEntityOwnerElectionStrategy(message.getEntityPath())));
 285             }
 286         } else {
 287             // We're not the leader. If the removed candidate is our local member then check if we actually
 288             // have a local candidate registered. If we do then we must have been partitioned from the leader
 289             // and the leader removed our candidate since the leader can't tell the difference between a
 290             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 291             // our candidate.
 292             if(localMemberName.equals(message.getRemovedCandidate()) &&
 293                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 294                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 295                     " - adding back local candidate", message.getEntityPath());
 296
 297                 commitCoordinator.commitModification(new MergeModification(
 298                         candidatePath(message.getEntityPath(), localMemberName),
 299                         candidateMapEntry(localMemberName)), this);
 300             }
 301         }
 302     }
 303
 304     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 305         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 306         return strategyConfig.createStrategy(entityType);
 307     }
 308
 309     private void onCandidateAdded(CandidateAdded message) {
 310         if(!isLeader()){
 311             return;
 312         }
 313
 314         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 315
 316         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 317         // remove it from the downPeerMemberNames.
 318         downPeerMemberNames.remove(message.getNewCandidate());
 319
 320         String currentOwner = getCurrentOwner(message.getEntityPath());
 321         EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 322         if(Strings.isNullOrEmpty(currentOwner)){
 323             if(strategy.getSelectionDelayInMillis() == 0L) {
 324                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 325                 writeNewOwner(message.getEntityPath(), newOwner(message.getAllCandidates(),
 326                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 327             } else {
 328                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 329             }
 330         }
 331     }
 332
 333     private void onPeerDown(PeerDown peerDown) {
 334         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 335
 336         String downMemberName = peerDown.getMemberName();
 337         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 338             // Remove the down peer as a candidate from all entities.
 339             removeCandidateFromEntities(downMemberName);
 340         }
 341     }
 342
 343     private void onPeerUp(PeerUp peerUp) {
 344         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 345
 346         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 347         downPeerMemberNames.remove(peerUp.getMemberName());
 348     }
 349
 350     private void selectNewOwnerForEntitiesOwnedBy(String owner) {
 351         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 352         searchForEntitiesOwnedBy(owner, new EntityWalker() {
 353             @Override
 354             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 355
 356                 YangInstanceIdentifier entityPath = YangInstanceIdentifier.builder(ENTITY_TYPES_PATH).
 357                         node(entityTypeNode.getIdentifier()).node(ENTITY_NODE_ID).node(entityNode.getIdentifier()).
 358                         node(ENTITY_OWNER_NODE_ID).build();
 359
 360                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 361
 362                 Object newOwner = newOwner(getCandidateNames(entityNode),
 363                         entityOwnershipStatistics.byEntityType(entityType),
 364                         getEntityOwnerElectionStrategy(entityPath));
 365
 366                 LOG.debug("{}: Found entity {}, writing new owner {}", persistenceId(), entityPath, newOwner);
 367
 368                 modifications.addModification(new WriteModification(entityPath,
 369                         ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)));
 370             }
 371         });
 372
 373         commitCoordinator.commitModifications(modifications, this);
 374     }
 375
 376     private void removeCandidateFromEntities(final String owner) {
 377         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 378         searchForEntities(new EntityWalker() {
 379             @Override
 380             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 381                 if (hasCandidate(entityNode, owner)) {
 382                     YangInstanceIdentifier entityId =
 383                             (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 384                     YangInstanceIdentifier candidatePath = candidatePath(
 385                             entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 386                             entityId, owner);
 387
 388                     LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 389                             owner, candidatePath);
 390
 391                     modifications.addModification(new DeleteModification(candidatePath));
 392                 }
 393             }
 394         });
 395
 396         commitCoordinator.commitModifications(modifications, this);
 397     }
 398
 399     private boolean hasCandidate(MapEntryNode entity, String candidateName) {
 400         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName)).isPresent();
 401     }
 402
 403     private void searchForEntitiesOwnedBy(final String owner, final EntityWalker walker) {
 404         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 405         Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
 406         if(!possibleEntityTypes.isPresent()) {
 407             return;
 408         }
 409
 410         LOG.debug("{}: Searching for entities owned by {}", persistenceId(), owner);
 411
 412         searchForEntities(new EntityWalker() {
 413             @Override
 414             public void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode) {
 415                 Optional<DataContainerChild<? extends PathArgument, ?>> possibleOwner =
 416                         entityNode.getChild(ENTITY_OWNER_NODE_ID);
 417                 if(possibleOwner.isPresent() && owner.equals(possibleOwner.get().getValue().toString())) {
 418                     walker.onEntity(entityTypeNode, entityNode);
 419                 }
 420             }
 421         });
 422     }
 423
 424     private void searchForEntities(EntityWalker walker) {
 425         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 426         Optional<NormalizedNode<?, ?>> possibleEntityTypes = snapshot.readNode(ENTITY_TYPES_PATH);
 427         if(!possibleEntityTypes.isPresent()) {
 428             return;
 429         }
 430
 431         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 432             Optional<DataContainerChild<? extends PathArgument, ?>> possibleEntities =
 433                     entityType.getChild(ENTITY_NODE_ID);
 434             if(!possibleEntities.isPresent()) {
 435                 continue; // shouldn't happen but handle anyway
 436             }
 437
 438             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 439                 walker.onEntity(entityType, entity);
 440             }
 441         }
 442     }
 443
 444     private Collection<String> getCandidateNames(MapEntryNode entity) {
 445         Collection<MapEntryNode> candidates = ((MapNode) entity.getChild(CANDIDATE_NODE_ID).get()).getValue();
 446         Collection<String> candidateNames = new ArrayList<>(candidates.size());
 447         for(MapEntryNode candidate: candidates) {
 448             candidateNames.add(candidate.getChild(CANDIDATE_NAME_NODE_ID).get().getValue().toString());
 449         }
 450
 451         return candidateNames;
 452     }
 453
 454     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 455         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 456
 457         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 458                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 459     }
 460
 461     /**
 462      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 463      *
 464      * @param entityPath
 465      * @param allCandidates
 466      */
 467     public void scheduleOwnerSelection(YangInstanceIdentifier entityPath, Collection<String> allCandidates,
 468                                        EntityOwnerSelectionStrategy strategy){
 469         Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 470         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 471             lastScheduledTask.cancel();
 472         }
 473         lastScheduledTask = context().system().scheduler().scheduleOnce(
 474                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS)
 475                 , self(), new SelectOwner(entityPath, allCandidates, strategy)
 476                 , context().system().dispatcher(), self());
 477
 478         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 479     }
 480
 481     private String newOwner(Collection<String> candidates, Map<String, Long> statistics, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 482         Collection<String> viableCandidates = getViableCandidates(candidates);
 483         if(viableCandidates.size() == 0){
 484             return "";
 485         }
 486         return ownerSelectionStrategy.newOwner(viableCandidates, statistics);
 487     }
 488
 489     private Collection<String> getViableCandidates(Collection<String> candidates) {
 490         Collection<String> viableCandidates = new ArrayList<>();
 491
 492         for (String candidate : candidates) {
 493             if (!downPeerMemberNames.contains(candidate)) {
 494                 viableCandidates.add(candidate);
 495             }
 496         }
 497         return viableCandidates;
 498     }
 499
 500     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 501         DataTreeSnapshot snapshot = getDataStore().getDataTree().takeSnapshot();
 502         Optional<NormalizedNode<?, ?>> optionalEntityOwner = snapshot.readNode(entityId.node(ENTITY_OWNER_QNAME));
 503         if(optionalEntityOwner.isPresent()){
 504             return optionalEntityOwner.get().getValue().toString();
 505         }
 506         return null;
 507     }
 508
 509     public static Props props(final ShardIdentifier name, final Map<String, String> peerAddresses,
 510                               final DatastoreContext datastoreContext, final SchemaContext schemaContext,
 511                               final String localMemberName, final EntityOwnerSelectionStrategyConfig strategyConfig) {
 512         return Props.create(new Creator(name, peerAddresses, datastoreContext, schemaContext, localMemberName, strategyConfig));
 513     }
 514
 515     private static class Creator extends AbstractShardCreator {
 516         private static final long serialVersionUID = 1L;
 517
 518         private final String localMemberName;
 519         private final EntityOwnerSelectionStrategyConfig strategyConfig;
 520
 521         Creator(final ShardIdentifier name, final Map<String, String> peerAddresses,
 522                 final DatastoreContext datastoreContext, final SchemaContext schemaContext,
 523                 final String localMemberName, EntityOwnerSelectionStrategyConfig strategyConfig) {
 524             super(name, peerAddresses, datastoreContext, schemaContext);
 525             this.localMemberName = localMemberName;
 526             this.strategyConfig = strategyConfig;
 527         }
 528
 529         @Override
 530         public Shard create() throws Exception {
 531             return new EntityOwnershipShard(name, peerAddresses, datastoreContext, schemaContext, localMemberName, strategyConfig);
 532         }
 533     }
 534
 535     private static interface EntityWalker {
 536         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 537     }
 538 }