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.access.concepts.MemberName;
  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.cluster.raft.RaftState;
  60 import org.opendaylight.mdsal.eos.dom.api.DOMEntity;
  61 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  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 MemberName localMemberName;
  77     private final EntityOwnershipShardCommitCoordinator commitCoordinator;
  78     private final EntityOwnershipListenerSupport listenerSupport;
  79     private final Set<MemberName> downPeerMemberNames = new HashSet<>();
  80     private final Map<String, MemberName> peerIdToMemberNames = new HashMap<>();
  81     private final EntityOwnerSelectionStrategyConfig strategyConfig;
  82     private final Map<YangInstanceIdentifier, Cancellable> entityToScheduledOwnershipTask = new HashMap<>();
  83     private final EntityOwnershipStatistics entityOwnershipStatistics;
  84
  85     private static DatastoreContext noPersistenceDatastoreContext(DatastoreContext datastoreContext) {
  86         return DatastoreContext.newBuilderFrom(datastoreContext).persistent(false).build();
  87     }
  88
  89     protected EntityOwnershipShard(Builder builder) {
  90         super(builder);
  91         this.localMemberName = builder.localMemberName;
  92         this.commitCoordinator = new EntityOwnershipShardCommitCoordinator(builder.localMemberName, LOG);
  93         this.listenerSupport = new EntityOwnershipListenerSupport(getContext(), persistenceId());
  94         this.strategyConfig = builder.ownerSelectionStrategyConfig;
  95         this.entityOwnershipStatistics = new EntityOwnershipStatistics();
  96         this.entityOwnershipStatistics.init(getDataStore());
  97
  98         for(String peerId: getRaftActorContext().getPeerIds()) {
  99             ShardIdentifier shardId = ShardIdentifier.fromShardIdString(peerId);
 100             peerIdToMemberNames.put(peerId, shardId.getMemberName());
 101         }
 102     }
 103
 104     @Override
 105     protected void onDatastoreContext(DatastoreContext context) {
 106         super.onDatastoreContext(noPersistenceDatastoreContext(context));
 107     }
 108
 109     @Override
 110     protected void onRecoveryComplete() {
 111         super.onRecoveryComplete();
 112
 113         new CandidateListChangeListener(getSelf(), persistenceId()).init(getDataStore());
 114         new EntityOwnerChangeListener(localMemberName, listenerSupport).init(getDataStore());
 115     }
 116
 117     @Override
 118     public void handleNonRaftCommand(final Object message) {
 119         if(message instanceof RegisterCandidateLocal) {
 120             onRegisterCandidateLocal((RegisterCandidateLocal) message);
 121         } else if(message instanceof UnregisterCandidateLocal) {
 122             onUnregisterCandidateLocal((UnregisterCandidateLocal)message);
 123         } else if(message instanceof CandidateAdded){
 124             onCandidateAdded((CandidateAdded) message);
 125         } else if(message instanceof CandidateRemoved){
 126             onCandidateRemoved((CandidateRemoved) message);
 127         } else if(message instanceof PeerDown) {
 128             onPeerDown((PeerDown) message);
 129         } else if(message instanceof PeerUp) {
 130             onPeerUp((PeerUp) message);
 131         } else if(message instanceof RegisterListenerLocal) {
 132             onRegisterListenerLocal((RegisterListenerLocal)message);
 133         } else if(message instanceof UnregisterListenerLocal) {
 134             onUnregisterListenerLocal((UnregisterListenerLocal) message);
 135         } else if(message instanceof SelectOwner) {
 136             onSelectOwner((SelectOwner) message);
 137         } else if(!commitCoordinator.handleMessage(message, this)) {
 138             super.handleNonRaftCommand(message);
 139         }
 140     }
 141
 142     private void onSelectOwner(SelectOwner selectOwner) {
 143         LOG.debug("{}: onSelectOwner: {}", persistenceId(), selectOwner);
 144
 145         String currentOwner = getCurrentOwner(selectOwner.getEntityPath());
 146         if(Strings.isNullOrEmpty(currentOwner)) {
 147             String entityType = EntityOwnersModel.entityTypeFromEntityPath(selectOwner.getEntityPath());
 148             writeNewOwner(selectOwner.getEntityPath(), newOwner(currentOwner, selectOwner.getAllCandidates(),
 149                     entityOwnershipStatistics.byEntityType(entityType),
 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().getIdentifier(), localMemberName.getName());
 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         DOMEntity entity = unregisterCandidate.getEntity();
 178         listenerSupport.unsetHasCandidateForEntity(entity);
 179
 180         YangInstanceIdentifier candidatePath = candidatePath(entity.getType(), entity.getIdentifier(), localMemberName.getName());
 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         searchForEntities((entityTypeNode, 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.getName().equals(possibleOwner.get().getValue().toString());
 203                     hasOwner = true;
 204                 } else {
 205                     isOwner = false;
 206                     hasOwner = false;
 207                 }
 208
 209                 DOMEntity entity = new DOMEntity(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     private void onUnregisterListenerLocal(UnregisterListenerLocal unregisterListener) {
 219         LOG.debug("{}: onUnregisterListenerLocal: {}", persistenceId(), unregisterListener);
 220
 221         listenerSupport.removeEntityOwnershipListener(unregisterListener.getEntityType(), unregisterListener.getListener());
 222
 223         getSender().tell(SuccessReply.INSTANCE, getSelf());
 224     }
 225
 226     void tryCommitModifications(final BatchedModifications modifications) {
 227         if(isLeader()) {
 228             LOG.debug("{}: Committing BatchedModifications {} locally", persistenceId(), modifications.getTransactionID());
 229
 230             // Note that it's possible the commit won't get consensus and will timeout and not be applied
 231             // to the state. However we don't need to retry it in that case b/c it will be committed to
 232             // the journal first and, once a majority of followers come back on line and it is replicated,
 233             // it will be applied at that point.
 234             handleBatchedModificationsLocal(modifications, self());
 235         } else {
 236             final ActorSelection leader = getLeader();
 237             if (leader != null) {
 238                 if(LOG.isDebugEnabled()) {
 239                     LOG.debug("{}: Sending BatchedModifications {} to leader {}", persistenceId(),
 240                             modifications.getTransactionID(), leader);
 241                 }
 242
 243                 Future<Object> future = Patterns.ask(leader, modifications, TimeUnit.SECONDS.toMillis(
 244                         getDatastoreContext().getShardTransactionCommitTimeoutInSeconds()));
 245
 246                 Patterns.pipe(future, getContext().dispatcher()).pipeTo(getSelf(), ActorRef.noSender());
 247             }
 248         }
 249     }
 250
 251     boolean hasLeader() {
 252         return getLeader() != null && !isIsolatedLeader();
 253     }
 254
 255     /**
 256      * Determine if we are in jeopardy based on observed RAFT state.
 257      */
 258     private static boolean inJeopardy(final RaftState state) {
 259         switch (state) {
 260             case Candidate:
 261             case Follower:
 262             case Leader:
 263             case PreLeader:
 264                 return false;
 265             case IsolatedLeader:
 266                 return true;
 267         }
 268         throw new IllegalStateException("Unsupported RAFT state " + state);
 269     }
 270
 271     private void notifyAllListeners() {
 272         searchForEntities((entityTypeNode, entityNode) -> {
 273             Optional<DataContainerChild<?, ?>> possibleType = entityTypeNode.getChild(ENTITY_TYPE_NODE_ID);
 274             if (possibleType.isPresent()) {
 275                 final boolean hasOwner;
 276                 final boolean isOwner;
 277
 278                 Optional<DataContainerChild<?, ?>> possibleOwner = entityNode.getChild(ENTITY_OWNER_NODE_ID);
 279                 if (possibleOwner.isPresent()) {
 280                     isOwner = localMemberName.getName().equals(possibleOwner.get().getValue().toString());
 281                     hasOwner = true;
 282                 } else {
 283                     isOwner = false;
 284                     hasOwner = false;
 285                 }
 286
 287                 DOMEntity entity = new DOMEntity(possibleType.get().getValue().toString(),
 288                     (YangInstanceIdentifier) entityNode.getChild(ENTITY_ID_NODE_ID).get().getValue());
 289
 290                 listenerSupport.notifyEntityOwnershipListeners(entity, isOwner, isOwner, hasOwner);
 291             }
 292         });
 293     }
 294
 295     @Override
 296     protected void onStateChanged() {
 297         super.onStateChanged();
 298
 299         boolean isLeader = isLeader();
 300         LOG.debug("{}: onStateChanged: isLeader: {}, hasLeader: {}", persistenceId(), isLeader, hasLeader());
 301
 302         // Examine current RAFT state to see if we are in jeopardy, potentially notifying all listeners
 303         final boolean inJeopardy = inJeopardy(getRaftState());
 304         final boolean wasInJeopardy = listenerSupport.setInJeopardy(inJeopardy);
 305         if (inJeopardy != wasInJeopardy) {
 306             LOG.debug("{}: {} jeopardy state, notifying all listeners", persistenceId(),
 307                 inJeopardy ? "entered" : "left");
 308             notifyAllListeners();
 309         }
 310
 311         commitCoordinator.onStateChanged(this, isLeader);
 312     }
 313
 314     @Override
 315     protected void onLeaderChanged(String oldLeader, String newLeader) {
 316         super.onLeaderChanged(oldLeader, newLeader);
 317
 318         boolean isLeader = isLeader();
 319         LOG.debug("{}: onLeaderChanged: oldLeader: {}, newLeader: {}, isLeader: {}", persistenceId(), oldLeader,
 320                 newLeader, isLeader);
 321
 322         if (isLeader) {
 323
 324             // Clear all existing strategies so that they get re-created when we call createStrategy again
 325             // This allows the strategies to be re-initialized with existing statistics maintained by
 326             // EntityOwnershipStatistics
 327             strategyConfig.clearStrategies();
 328
 329             // Remove the candidates for all members that are known to be down. In a cluster which has greater than
 330             // 3 nodes it is possible for a some node beside the leader being down when the leadership transitions
 331             // it makes sense to use this event to remove all the candidates for those downed nodes
 332             for (MemberName downPeerName : downPeerMemberNames) {
 333                 removeCandidateFromEntities(downPeerName);
 334             }
 335         } else {
 336             // The leader changed - notify the coordinator to check if pending modifications need to be sent.
 337             // While onStateChanged also does this, this method handles the case where the shard hears from a
 338             // leader and stays in the follower state. In that case no behavior state change occurs.
 339             commitCoordinator.onStateChanged(this, isLeader);
 340         }
 341     }
 342
 343     private void onCandidateRemoved(CandidateRemoved message) {
 344         LOG.debug("{}: onCandidateRemoved: {}", persistenceId(), message);
 345
 346         if(isLeader()) {
 347             String currentOwner = getCurrentOwner(message.getEntityPath());
 348             if(message.getRemovedCandidate().equals(currentOwner) || message.getRemainingCandidates().size() == 0){
 349                 String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 350                 writeNewOwner(message.getEntityPath(),
 351                         newOwner(currentOwner, message.getRemainingCandidates(), entityOwnershipStatistics.byEntityType(entityType),
 352                                 getEntityOwnerElectionStrategy(message.getEntityPath())));
 353             }
 354         } else {
 355             // We're not the leader. If the removed candidate is our local member then check if we actually
 356             // have a local candidate registered. If we do then we must have been partitioned from the leader
 357             // and the leader removed our candidate since the leader can't tell the difference between a
 358             // temporary network partition and a node's process actually restarted. So, in that case, re-add
 359             // our candidate.
 360             if(localMemberName.getName().equals(message.getRemovedCandidate()) &&
 361                     listenerSupport.hasCandidateForEntity(createEntity(message.getEntityPath()))) {
 362                 LOG.debug("Local candidate member was removed but a local candidate is registered for {}" +
 363                     " - adding back local candidate", message.getEntityPath());
 364
 365                 commitCoordinator.commitModification(new MergeModification(
 366                         candidatePath(message.getEntityPath(), localMemberName.getName()),
 367                         candidateMapEntry(localMemberName.getName())), this);
 368             }
 369         }
 370     }
 371
 372     private EntityOwnerSelectionStrategy getEntityOwnerElectionStrategy(YangInstanceIdentifier entityPath) {
 373         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(entityPath);
 374         return strategyConfig.createStrategy(entityType, entityOwnershipStatistics.byEntityType(entityType));
 375     }
 376
 377     private void onCandidateAdded(CandidateAdded message) {
 378         if(!isLeader()){
 379             return;
 380         }
 381
 382         LOG.debug("{}: onCandidateAdded: {}", persistenceId(), message);
 383
 384         // Since a node's candidate member is only added by the node itself, we can assume the node is up so
 385         // remove it from the downPeerMemberNames.
 386         downPeerMemberNames.remove(message.getNewCandidate());
 387
 388         final String currentOwner = getCurrentOwner(message.getEntityPath());
 389         final EntityOwnerSelectionStrategy strategy = getEntityOwnerElectionStrategy(message.getEntityPath());
 390         final String entityType = EntityOwnersModel.entityTypeFromEntityPath(message.getEntityPath());
 391
 392         // Available members is all the known peers - the number of peers that are down + self
 393         // So if there are 2 peers and 1 is down then availableMembers will be 2
 394         final int availableMembers = (peerIdToMemberNames.size() - downPeerMemberNames.size()) + 1;
 395
 396         LOG.debug("{}: Using strategy {} to select owner, currentOwner = {}", persistenceId(), strategy, currentOwner);
 397
 398         if(!message.getAllCandidates().contains(currentOwner)){
 399             if(strategy.getSelectionDelayInMillis() == 0L) {
 400                 writeNewOwner(message.getEntityPath(), newOwner(currentOwner, message.getAllCandidates(),
 401                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 402             } else if(message.getAllCandidates().size() == availableMembers) {
 403                 LOG.debug("{}: Received the maximum candidates requests : {} writing new owner",
 404                         persistenceId(), availableMembers);
 405                 cancelOwnerSelectionTask(message.getEntityPath());
 406                 writeNewOwner(message.getEntityPath(), newOwner(currentOwner, message.getAllCandidates(),
 407                         entityOwnershipStatistics.byEntityType(entityType), strategy));
 408             } else {
 409                 scheduleOwnerSelection(message.getEntityPath(), message.getAllCandidates(), strategy);
 410             }
 411         }
 412     }
 413
 414     private void onPeerDown(PeerDown peerDown) {
 415         LOG.info("{}: onPeerDown: {}", persistenceId(), peerDown);
 416
 417         MemberName downMemberName = peerDown.getMemberName();
 418         if(downPeerMemberNames.add(downMemberName) && isLeader()) {
 419             // Remove the down peer as a candidate from all entities.
 420             removeCandidateFromEntities(downMemberName);
 421         }
 422     }
 423
 424     private void onPeerUp(PeerUp peerUp) {
 425         LOG.debug("{}: onPeerUp: {}", persistenceId(), peerUp);
 426
 427         peerIdToMemberNames.put(peerUp.getPeerId(), peerUp.getMemberName());
 428         downPeerMemberNames.remove(peerUp.getMemberName());
 429
 430         // Notify the coordinator to check if pending modifications need to be sent. We do this here
 431         // to handle the case where the leader's peer address isn't now yet when a prior state or
 432         // leader change occurred.
 433         commitCoordinator.onStateChanged(this, isLeader());
 434     }
 435
 436     private void removeCandidateFromEntities(final MemberName owner) {
 437         final BatchedModifications modifications = commitCoordinator.newBatchedModifications();
 438         searchForEntities((entityTypeNode, entityNode) -> {
 439             if (hasCandidate(entityNode, owner)) {
 440                 YangInstanceIdentifier entityId =
 441                         (YangInstanceIdentifier) entityNode.getIdentifier().getKeyValues().get(ENTITY_ID_QNAME);
 442                 YangInstanceIdentifier candidatePath = candidatePath(
 443                         entityTypeNode.getIdentifier().getKeyValues().get(ENTITY_TYPE_QNAME).toString(),
 444                         entityId, owner.getName());
 445
 446                 LOG.info("{}: Found entity {}, removing candidate {}, path {}", persistenceId(), entityId,
 447                         owner, candidatePath);
 448
 449                 modifications.addModification(new DeleteModification(candidatePath));
 450             }
 451         });
 452
 453         commitCoordinator.commitModifications(modifications, this);
 454     }
 455
 456     private static boolean hasCandidate(MapEntryNode entity, MemberName candidateName) {
 457         return ((MapNode)entity.getChild(CANDIDATE_NODE_ID).get()).getChild(candidateNodeKey(candidateName.getName()))
 458                 .isPresent();
 459     }
 460
 461     private void searchForEntities(EntityWalker walker) {
 462         Optional<NormalizedNode<?, ?>> possibleEntityTypes = getDataStore().readNode(ENTITY_TYPES_PATH);
 463         if(!possibleEntityTypes.isPresent()) {
 464             return;
 465         }
 466
 467         for(MapEntryNode entityType:  ((MapNode) possibleEntityTypes.get()).getValue()) {
 468             Optional<DataContainerChild<?, ?>> possibleEntities = entityType.getChild(ENTITY_NODE_ID);
 469             if(!possibleEntities.isPresent()) {
 470                 // shouldn't happen but handle anyway
 471                 continue;
 472             }
 473
 474             for(MapEntryNode entity:  ((MapNode) possibleEntities.get()).getValue()) {
 475                 walker.onEntity(entityType, entity);
 476             }
 477         }
 478     }
 479
 480     private void writeNewOwner(YangInstanceIdentifier entityPath, String newOwner) {
 481         LOG.debug("{}: Writing new owner {} for entity {}", persistenceId(), newOwner, entityPath);
 482
 483         commitCoordinator.commitModification(new WriteModification(entityPath.node(ENTITY_OWNER_QNAME),
 484                 ImmutableNodes.leafNode(ENTITY_OWNER_NODE_ID, newOwner)), this);
 485     }
 486
 487     /**
 488      * Schedule a new owner selection job. Cancelling any outstanding job if it has not been cancelled.
 489      *
 490      * @param entityPath
 491      * @param allCandidates
 492      */
 493     public void scheduleOwnerSelection(YangInstanceIdentifier entityPath, Collection<String> allCandidates,
 494                                        EntityOwnerSelectionStrategy strategy){
 495         cancelOwnerSelectionTask(entityPath);
 496
 497         LOG.debug("{}: Scheduling owner selection after {} ms", persistenceId(), strategy.getSelectionDelayInMillis());
 498
 499         final Cancellable lastScheduledTask = context().system().scheduler().scheduleOnce(
 500                 FiniteDuration.apply(strategy.getSelectionDelayInMillis(), TimeUnit.MILLISECONDS)
 501                 , self(), new SelectOwner(entityPath, allCandidates, strategy)
 502                 , context().system().dispatcher(), self());
 503
 504         entityToScheduledOwnershipTask.put(entityPath, lastScheduledTask);
 505     }
 506
 507     private void cancelOwnerSelectionTask(YangInstanceIdentifier entityPath){
 508         final Cancellable lastScheduledTask = entityToScheduledOwnershipTask.get(entityPath);
 509         if(lastScheduledTask != null && !lastScheduledTask.isCancelled()){
 510             lastScheduledTask.cancel();
 511         }
 512     }
 513
 514     private String newOwner(String currentOwner, Collection<String> candidates, Map<String, Long> statistics, EntityOwnerSelectionStrategy ownerSelectionStrategy) {
 515         Collection<String> viableCandidates = getViableCandidates(candidates);
 516         if(viableCandidates.size() == 0){
 517             return "";
 518         }
 519         return ownerSelectionStrategy.newOwner(currentOwner, viableCandidates);
 520     }
 521
 522     private Collection<String> getViableCandidates(Collection<String> candidates) {
 523         Collection<String> viableCandidates = new ArrayList<>();
 524
 525         for (String candidate : candidates) {
 526             if (!downPeerMemberNames.contains(candidate)) {
 527                 viableCandidates.add(candidate);
 528             }
 529         }
 530         return viableCandidates;
 531     }
 532
 533     private String getCurrentOwner(YangInstanceIdentifier entityId) {
 534         Optional<NormalizedNode<?, ?>> optionalEntityOwner = getDataStore().readNode(entityId.node(ENTITY_OWNER_QNAME));
 535         if(optionalEntityOwner.isPresent()){
 536             return optionalEntityOwner.get().getValue().toString();
 537         }
 538         return null;
 539     }
 540
 541     private static interface EntityWalker {
 542         void onEntity(MapEntryNode entityTypeNode, MapEntryNode entityNode);
 543     }
 544
 545     public static Builder newBuilder() {
 546         return new Builder();
 547     }
 548
 549     static class Builder extends Shard.AbstractBuilder<Builder, EntityOwnershipShard> {
 550         private MemberName localMemberName;
 551         private EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig;
 552
 553         protected Builder() {
 554             super(EntityOwnershipShard.class);
 555         }
 556
 557         Builder localMemberName(MemberName localMemberName) {
 558             checkSealed();
 559             this.localMemberName = localMemberName;
 560             return this;
 561         }
 562
 563         Builder ownerSelectionStrategyConfig(EntityOwnerSelectionStrategyConfig ownerSelectionStrategyConfig){
 564             checkSealed();
 565             this.ownerSelectionStrategyConfig = ownerSelectionStrategyConfig;
 566             return this;
 567         }
 568
 569         @Override
 570         protected void verify() {
 571             super.verify();
 572             Preconditions.checkNotNull(localMemberName, "localMemberName should not be null");
 573             Preconditions.checkNotNull(ownerSelectionStrategyConfig, "ownerSelectionStrategyConfig should not be null");
 574         }
 575     }
 576 }