opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/RaftActor.java

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  * Copyright (c) 2015 Brocade Communications Systems, Inc. and others.  All rights reserved.
   4  *
   5  * This program and the accompanying materials are made available under the
   6  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   7  * and is available at http://www.eclipse.org/legal/epl-v10.html
   8  */
   9
  10 package org.opendaylight.controller.cluster.raft;
  11
  12 import akka.actor.ActorRef;
  13 import akka.actor.ActorSelection;
  14 import akka.japi.Procedure;
  15 import akka.persistence.SnapshotSelectionCriteria;
  16 import com.google.common.annotations.VisibleForTesting;
  17 import com.google.common.base.Objects;
  18 import com.google.common.base.Optional;
  19 import com.google.common.collect.ImmutableMap;
  20 import com.google.common.collect.Lists;
  21 import java.io.Serializable;
  22 import java.util.Collection;
  23 import java.util.List;
  24 import java.util.Map;
  25 import java.util.concurrent.TimeUnit;
  26 import javax.annotation.Nonnull;
  27 import org.apache.commons.lang3.time.DurationFormatUtils;
  28 import org.opendaylight.controller.cluster.DataPersistenceProvider;
  29 import org.opendaylight.controller.cluster.DelegatingPersistentDataProvider;
  30 import org.opendaylight.controller.cluster.NonPersistentDataProvider;
  31 import org.opendaylight.controller.cluster.PersistentDataProvider;
  32 import org.opendaylight.controller.cluster.common.actor.AbstractUntypedPersistentActor;
  33 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
  34 import org.opendaylight.controller.cluster.notifications.RoleChanged;
  35 import org.opendaylight.controller.cluster.raft.base.messages.ApplyJournalEntries;
  36 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  37 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  38 import org.opendaylight.controller.cluster.raft.behaviors.AbstractLeader;
  39 import org.opendaylight.controller.cluster.raft.behaviors.DelegatingRaftActorBehavior;
  40 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
  41 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  42 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
  43 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
  44 import org.opendaylight.controller.cluster.raft.client.messages.FollowerInfo;
  45 import org.opendaylight.controller.cluster.raft.client.messages.GetOnDemandRaftState;
  46 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
  47 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
  48 import org.slf4j.Logger;
  49 import org.slf4j.LoggerFactory;
  50
  51 /**
  52  * RaftActor encapsulates a state machine that needs to be kept synchronized
  53  * in a cluster. It implements the RAFT algorithm as described in the paper
  54  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
  55  * In Search of an Understandable Consensus Algorithm</a>
  56  * <p/>
  57  * RaftActor has 3 states and each state has a certain behavior associated
  58  * with it. A Raft actor can behave as,
  59  * <ul>
  60  * <li> A Leader </li>
  61  * <li> A Follower (or) </li>
  62  * <li> A Candidate </li>
  63  * </ul>
  64  * <p/>
  65  * <p/>
  66  * A RaftActor MUST be a Leader in order to accept requests from clients to
  67  * change the state of it's encapsulated state machine. Once a RaftActor becomes
  68  * a Leader it is also responsible for ensuring that all followers ultimately
  69  * have the same log and therefore the same state machine as itself.
  70  * <p/>
  71  * <p/>
  72  * The current behavior of a RaftActor determines how election for leadership
  73  * is initiated and how peer RaftActors react to request for votes.
  74  * <p/>
  75  * <p/>
  76  * Each RaftActor also needs to know the current election term. It uses this
  77  * information for a couple of things. One is to simply figure out who it
  78  * voted for in the last election. Another is to figure out if the message
  79  * it received to update it's state is stale.
  80  * <p/>
  81  * <p/>
  82  * The RaftActor uses akka-persistence to store it's replicated log.
  83  * Furthermore through it's behaviors a Raft Actor determines
  84  * <p/>
  85  * <ul>
  86  * <li> when a log entry should be persisted </li>
  87  * <li> when a log entry should be applied to the state machine (and) </li>
  88  * <li> when a snapshot should be saved </li>
  89  * </ul>
  90  */
  91 public abstract class RaftActor extends AbstractUntypedPersistentActor {
  92
  93     private static final long APPLY_STATE_DELAY_THRESHOLD_IN_NANOS = TimeUnit.MILLISECONDS.toNanos(50L); // 50 millis
  94
  95     protected final Logger LOG = LoggerFactory.getLogger(getClass());
  96
  97     /**
  98      * The current state determines the current behavior of a RaftActor
  99      * A Raft Actor always starts off in the Follower State
 100      */
 101     private final DelegatingRaftActorBehavior currentBehavior = new DelegatingRaftActorBehavior();
 102
 103     /**
 104      * This context should NOT be passed directly to any other actor it is
 105      * only to be consumed by the RaftActorBehaviors
 106      */
 107     private final RaftActorContextImpl context;
 108
 109     private final DelegatingPersistentDataProvider delegatingPersistenceProvider = new DelegatingPersistentDataProvider(null);
 110
 111     private RaftActorRecoverySupport raftRecovery;
 112
 113     private RaftActorSnapshotMessageSupport snapshotSupport;
 114
 115     private final BehaviorStateHolder reusableBehaviorStateHolder = new BehaviorStateHolder();
 116
 117     public RaftActor(String id, Map<String, String> peerAddresses) {
 118         this(id, peerAddresses, Optional.<ConfigParams>absent());
 119     }
 120
 121     public RaftActor(String id, Map<String, String> peerAddresses,
 122          Optional<ConfigParams> configParams) {
 123
 124         context = new RaftActorContextImpl(this.getSelf(),
 125             this.getContext(), id, new ElectionTermImpl(delegatingPersistenceProvider, id, LOG),
 126             -1, -1, peerAddresses,
 127             (configParams.isPresent() ? configParams.get(): new DefaultConfigParamsImpl()),
 128             delegatingPersistenceProvider, LOG);
 129
 130         context.setReplicatedLog(ReplicatedLogImpl.newInstance(context, delegatingPersistenceProvider, currentBehavior));
 131     }
 132
 133     @Override
 134     public void preStart() throws Exception {
 135         LOG.info("Starting recovery for {} with journal batch size {}", persistenceId(),
 136                 context.getConfigParams().getJournalRecoveryLogBatchSize());
 137
 138         super.preStart();
 139     }
 140
 141     @Override
 142     public void postStop() {
 143         if(currentBehavior.getDelegate() != null) {
 144             try {
 145                 currentBehavior.close();
 146             } catch (Exception e) {
 147                 LOG.debug("{}: Error closing behavior {}", persistenceId(), currentBehavior.state());
 148             }
 149         }
 150
 151         super.postStop();
 152     }
 153
 154     @Override
 155     public void handleRecover(Object message) {
 156         if(raftRecovery == null) {
 157             raftRecovery = newRaftActorRecoverySupport();
 158         }
 159
 160         boolean recoveryComplete = raftRecovery.handleRecoveryMessage(message);
 161         if(recoveryComplete) {
 162             if(!persistence().isRecoveryApplicable()) {
 163                 // Delete all the messages from the akka journal so that we do not end up with consistency issues
 164                 // Note I am not using the dataPersistenceProvider and directly using the akka api here
 165                 deleteMessages(lastSequenceNr());
 166
 167                 // Delete all the akka snapshots as they will not be needed
 168                 deleteSnapshots(new SnapshotSelectionCriteria(scala.Long.MaxValue(), scala.Long.MaxValue()));
 169             }
 170
 171             onRecoveryComplete();
 172
 173             initializeBehavior();
 174
 175             raftRecovery = null;
 176         }
 177     }
 178
 179     protected RaftActorRecoverySupport newRaftActorRecoverySupport() {
 180         return new RaftActorRecoverySupport(delegatingPersistenceProvider, context, currentBehavior,
 181                 getRaftActorRecoveryCohort());
 182     }
 183
 184     protected void initializeBehavior(){
 185         changeCurrentBehavior(new Follower(context));
 186     }
 187
 188     protected void changeCurrentBehavior(RaftActorBehavior newBehavior){
 189         reusableBehaviorStateHolder.init(getCurrentBehavior());
 190         setCurrentBehavior(newBehavior);
 191         handleBehaviorChange(reusableBehaviorStateHolder, getCurrentBehavior());
 192     }
 193
 194     @Override
 195     public void handleCommand(Object message) {
 196         if(snapshotSupport == null) {
 197             snapshotSupport = newRaftActorSnapshotMessageSupport();
 198         }
 199
 200         boolean handled = snapshotSupport.handleSnapshotMessage(message);
 201         if(handled) {
 202             return;
 203         }
 204
 205         if (message instanceof ApplyState){
 206             ApplyState applyState = (ApplyState) message;
 207
 208             long elapsedTime = (System.nanoTime() - applyState.getStartTime());
 209             if(elapsedTime >= APPLY_STATE_DELAY_THRESHOLD_IN_NANOS){
 210                 LOG.warn("ApplyState took more time than expected. Elapsed Time = {} ms ApplyState = {}",
 211                         TimeUnit.NANOSECONDS.toMillis(elapsedTime), applyState);
 212             }
 213
 214             if(LOG.isDebugEnabled()) {
 215                 LOG.debug("{}: Applying state for log index {} data {}",
 216                     persistenceId(), applyState.getReplicatedLogEntry().getIndex(),
 217                     applyState.getReplicatedLogEntry().getData());
 218             }
 219
 220             applyState(applyState.getClientActor(), applyState.getIdentifier(),
 221                 applyState.getReplicatedLogEntry().getData());
 222
 223         } else if (message instanceof ApplyJournalEntries){
 224             ApplyJournalEntries applyEntries = (ApplyJournalEntries) message;
 225             if(LOG.isDebugEnabled()) {
 226                 LOG.debug("{}: Persisting ApplyLogEntries with index={}", persistenceId(), applyEntries.getToIndex());
 227             }
 228
 229             persistence().persist(applyEntries, NoopProcedure.instance());
 230
 231         } else if (message instanceof FindLeader) {
 232             getSender().tell(
 233                 new FindLeaderReply(getLeaderAddress()),
 234                 getSelf()
 235             );
 236         } else if(message instanceof GetOnDemandRaftState) {
 237             onGetOnDemandRaftStats();
 238         } else {
 239             reusableBehaviorStateHolder.init(getCurrentBehavior());
 240
 241             setCurrentBehavior(currentBehavior.handleMessage(getSender(), message));
 242
 243             handleBehaviorChange(reusableBehaviorStateHolder, getCurrentBehavior());
 244         }
 245     }
 246
 247     protected RaftActorSnapshotMessageSupport newRaftActorSnapshotMessageSupport() {
 248         return new RaftActorSnapshotMessageSupport(delegatingPersistenceProvider, context,
 249                 currentBehavior, getRaftActorSnapshotCohort());
 250     }
 251
 252     private void onGetOnDemandRaftStats() {
 253         // Debugging message to retrieve raft stats.
 254
 255         OnDemandRaftState.Builder builder = OnDemandRaftState.builder()
 256                 .commitIndex(context.getCommitIndex())
 257                 .currentTerm(context.getTermInformation().getCurrentTerm())
 258                 .inMemoryJournalDataSize(replicatedLog().dataSize())
 259                 .inMemoryJournalLogSize(replicatedLog().size())
 260                 .isSnapshotCaptureInitiated(context.getSnapshotManager().isCapturing())
 261                 .lastApplied(context.getLastApplied())
 262                 .lastIndex(replicatedLog().lastIndex())
 263                 .lastTerm(replicatedLog().lastTerm())
 264                 .leader(getLeaderId())
 265                 .raftState(currentBehavior.state().toString())
 266                 .replicatedToAllIndex(currentBehavior.getReplicatedToAllIndex())
 267                 .snapshotIndex(replicatedLog().getSnapshotIndex())
 268                 .snapshotTerm(replicatedLog().getSnapshotTerm())
 269                 .votedFor(context.getTermInformation().getVotedFor())
 270                 .peerAddresses(ImmutableMap.copyOf(context.getPeerAddresses()));
 271
 272         ReplicatedLogEntry lastLogEntry = getLastLogEntry();
 273         if (lastLogEntry != null) {
 274             builder.lastLogIndex(lastLogEntry.getIndex());
 275             builder.lastLogTerm(lastLogEntry.getTerm());
 276         }
 277
 278         if(getCurrentBehavior() instanceof AbstractLeader) {
 279             AbstractLeader leader = (AbstractLeader)getCurrentBehavior();
 280             Collection<String> followerIds = leader.getFollowerIds();
 281             List<FollowerInfo> followerInfoList = Lists.newArrayListWithCapacity(followerIds.size());
 282             for(String id: followerIds) {
 283                 final FollowerLogInformation info = leader.getFollower(id);
 284                 followerInfoList.add(new FollowerInfo(id, info.getNextIndex(), info.getMatchIndex(),
 285                         info.isFollowerActive(), DurationFormatUtils.formatDurationHMS(info.timeSinceLastActivity())));
 286             }
 287
 288             builder.followerInfoList(followerInfoList);
 289         }
 290
 291         sender().tell(builder.build(), self());
 292
 293     }
 294
 295     private void handleBehaviorChange(BehaviorStateHolder oldBehaviorState, RaftActorBehavior currentBehavior) {
 296         RaftActorBehavior oldBehavior = oldBehaviorState.getBehavior();
 297
 298         if (oldBehavior != currentBehavior){
 299             onStateChanged();
 300         }
 301
 302         String oldBehaviorLeaderId = oldBehavior == null ? null : oldBehaviorState.getLeaderId();
 303         String oldBehaviorStateName = oldBehavior == null ? null : oldBehavior.state().name();
 304
 305         // it can happen that the state has not changed but the leader has changed.
 306         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 307         if(!Objects.equal(oldBehaviorLeaderId, currentBehavior.getLeaderId())) {
 308             if(roleChangeNotifier.isPresent()) {
 309                 roleChangeNotifier.get().tell(new LeaderStateChanged(getId(), currentBehavior.getLeaderId()), getSelf());
 310             }
 311
 312             onLeaderChanged(oldBehaviorLeaderId, currentBehavior.getLeaderId());
 313         }
 314
 315         if (roleChangeNotifier.isPresent() &&
 316                 (oldBehavior == null || (oldBehavior.state() != currentBehavior.state()))) {
 317             roleChangeNotifier.get().tell(new RoleChanged(getId(), oldBehaviorStateName ,
 318                     currentBehavior.state().name()), getSelf());
 319         }
 320     }
 321
 322     /**
 323      * When a derived RaftActor needs to persist something it must call
 324      * persistData.
 325      *
 326      * @param clientActor
 327      * @param identifier
 328      * @param data
 329      */
 330     protected void persistData(final ActorRef clientActor, final String identifier,
 331         final Payload data) {
 332
 333         ReplicatedLogEntry replicatedLogEntry = new ReplicatedLogImplEntry(
 334             context.getReplicatedLog().lastIndex() + 1,
 335             context.getTermInformation().getCurrentTerm(), data);
 336
 337         if(LOG.isDebugEnabled()) {
 338             LOG.debug("{}: Persist data {}", persistenceId(), replicatedLogEntry);
 339         }
 340
 341         final RaftActorContext raftContext = getRaftActorContext();
 342
 343         replicatedLog().appendAndPersist(replicatedLogEntry, new Procedure<ReplicatedLogEntry>() {
 344             @Override
 345             public void apply(ReplicatedLogEntry replicatedLogEntry) throws Exception {
 346                 if(!hasFollowers()){
 347                     // Increment the Commit Index and the Last Applied values
 348                     raftContext.setCommitIndex(replicatedLogEntry.getIndex());
 349                     raftContext.setLastApplied(replicatedLogEntry.getIndex());
 350
 351                     // Apply the state immediately
 352                     applyState(clientActor, identifier, data);
 353
 354                     // Send a ApplyJournalEntries message so that we write the fact that we applied
 355                     // the state to durable storage
 356                     self().tell(new ApplyJournalEntries(replicatedLogEntry.getIndex()), self());
 357
 358                     context.getSnapshotManager().trimLog(context.getLastApplied(), currentBehavior);
 359
 360                 } else if (clientActor != null) {
 361                     // Send message for replication
 362                     currentBehavior.handleMessage(getSelf(),
 363                             new Replicate(clientActor, identifier, replicatedLogEntry));
 364                 }
 365             }
 366         });
 367     }
 368
 369     private ReplicatedLog replicatedLog() {
 370         return context.getReplicatedLog();
 371     }
 372
 373     protected String getId() {
 374         return context.getId();
 375     }
 376
 377     @VisibleForTesting
 378     void setCurrentBehavior(RaftActorBehavior behavior) {
 379         currentBehavior.setDelegate(behavior);
 380     }
 381
 382     protected RaftActorBehavior getCurrentBehavior() {
 383         return currentBehavior.getDelegate();
 384     }
 385
 386     /**
 387      * Derived actors can call the isLeader method to check if the current
 388      * RaftActor is the Leader or not
 389      *
 390      * @return true it this RaftActor is a Leader false otherwise
 391      */
 392     protected boolean isLeader() {
 393         return context.getId().equals(currentBehavior.getLeaderId());
 394     }
 395
 396     /**
 397      * Derived actor can call getLeader if they need a reference to the Leader.
 398      * This would be useful for example in forwarding a request to an actor
 399      * which is the leader
 400      *
 401      * @return A reference to the leader if known, null otherwise
 402      */
 403     protected ActorSelection getLeader(){
 404         String leaderAddress = getLeaderAddress();
 405
 406         if(leaderAddress == null){
 407             return null;
 408         }
 409
 410         return context.actorSelection(leaderAddress);
 411     }
 412
 413     /**
 414      *
 415      * @return the current leader's id
 416      */
 417     protected String getLeaderId(){
 418         return currentBehavior.getLeaderId();
 419     }
 420
 421     protected RaftState getRaftState() {
 422         return currentBehavior.state();
 423     }
 424
 425     protected ReplicatedLogEntry getLastLogEntry() {
 426         return replicatedLog().last();
 427     }
 428
 429     protected Long getCurrentTerm(){
 430         return context.getTermInformation().getCurrentTerm();
 431     }
 432
 433     protected Long getCommitIndex(){
 434         return context.getCommitIndex();
 435     }
 436
 437     protected Long getLastApplied(){
 438         return context.getLastApplied();
 439     }
 440
 441     protected RaftActorContext getRaftActorContext() {
 442         return context;
 443     }
 444
 445     protected void updateConfigParams(ConfigParams configParams) {
 446         context.setConfigParams(configParams);
 447     }
 448
 449     public final DataPersistenceProvider persistence() {
 450         return delegatingPersistenceProvider.getDelegate();
 451     }
 452
 453     public void setPersistence(DataPersistenceProvider provider) {
 454         delegatingPersistenceProvider.setDelegate(provider);
 455     }
 456
 457     protected void setPersistence(boolean persistent) {
 458         if(persistent) {
 459             setPersistence(new PersistentDataProvider(this));
 460         } else {
 461             setPersistence(new NonPersistentDataProvider() {
 462                 /**
 463                  * The way snapshotting works is,
 464                  * <ol>
 465                  * <li> RaftActor calls createSnapshot on the Shard
 466                  * <li> Shard sends a CaptureSnapshotReply and RaftActor then calls saveSnapshot
 467                  * <li> When saveSnapshot is invoked on the akka-persistence API it uses the SnapshotStore to save
 468                  * the snapshot. The SnapshotStore sends SaveSnapshotSuccess or SaveSnapshotFailure. When the
 469                  * RaftActor gets SaveSnapshot success it commits the snapshot to the in-memory journal. This
 470                  * commitSnapshot is mimicking what is done in SaveSnapshotSuccess.
 471                  * </ol>
 472                  */
 473                 @Override
 474                 public void saveSnapshot(Object o) {
 475                     // Make saving Snapshot successful
 476                     // Committing the snapshot here would end up calling commit in the creating state which would
 477                     // be a state violation. That's why now we send a message to commit the snapshot.
 478                     self().tell(RaftActorSnapshotMessageSupport.COMMIT_SNAPSHOT, self());
 479                 }
 480             });
 481         }
 482     }
 483
 484     /**
 485      * setPeerAddress sets the address of a known peer at a later time.
 486      * <p>
 487      * This is to account for situations where a we know that a peer
 488      * exists but we do not know an address up-front. This may also be used in
 489      * situations where a known peer starts off in a different location and we
 490      * need to change it's address
 491      * <p>
 492      * Note that if the peerId does not match the list of peers passed to
 493      * this actor during construction an IllegalStateException will be thrown.
 494      *
 495      * @param peerId
 496      * @param peerAddress
 497      */
 498     protected void setPeerAddress(String peerId, String peerAddress){
 499         context.setPeerAddress(peerId, peerAddress);
 500     }
 501
 502     /**
 503      * The applyState method will be called by the RaftActor when some data
 504      * needs to be applied to the actor's state
 505      *
 506      * @param clientActor A reference to the client who sent this message. This
 507      *                    is the same reference that was passed to persistData
 508      *                    by the derived actor. clientActor may be null when
 509      *                    the RaftActor is behaving as a follower or during
 510      *                    recovery.
 511      * @param identifier  The identifier of the persisted data. This is also
 512      *                    the same identifier that was passed to persistData by
 513      *                    the derived actor. identifier may be null when
 514      *                    the RaftActor is behaving as a follower or during
 515      *                    recovery
 516      * @param data        A piece of data that was persisted by the persistData call.
 517      *                    This should NEVER be null.
 518      */
 519     protected abstract void applyState(ActorRef clientActor, String identifier,
 520         Object data);
 521
 522     /**
 523      * Returns the RaftActorRecoveryCohort to participate in persistence recovery.
 524      */
 525     @Nonnull
 526     protected abstract RaftActorRecoveryCohort getRaftActorRecoveryCohort();
 527
 528     /**
 529      * This method is called when recovery is complete.
 530      */
 531     protected abstract void onRecoveryComplete();
 532
 533     /**
 534      * Returns the RaftActorSnapshotCohort to participate in persistence recovery.
 535      */
 536     @Nonnull
 537     protected abstract RaftActorSnapshotCohort getRaftActorSnapshotCohort();
 538
 539     /**
 540      * This method will be called by the RaftActor when the state of the
 541      * RaftActor changes. The derived actor can then use methods like
 542      * isLeader or getLeader to do something useful
 543      */
 544     protected abstract void onStateChanged();
 545
 546     /**
 547      * Notifier Actor for this RaftActor to notify when a role change happens
 548      * @return ActorRef - ActorRef of the notifier or Optional.absent if none.
 549      */
 550     protected abstract Optional<ActorRef> getRoleChangeNotifier();
 551
 552     protected void onLeaderChanged(String oldLeader, String newLeader){};
 553
 554     private String getLeaderAddress(){
 555         if(isLeader()){
 556             return getSelf().path().toString();
 557         }
 558         String leaderId = currentBehavior.getLeaderId();
 559         if (leaderId == null) {
 560             return null;
 561         }
 562         String peerAddress = context.getPeerAddress(leaderId);
 563         if(LOG.isDebugEnabled()) {
 564             LOG.debug("{}: getLeaderAddress leaderId = {} peerAddress = {}",
 565                     persistenceId(), leaderId, peerAddress);
 566         }
 567
 568         return peerAddress;
 569     }
 570
 571     protected boolean hasFollowers(){
 572         return getRaftActorContext().hasFollowers();
 573     }
 574
 575     /**
 576      * @deprecated Deprecated in favor of {@link org.opendaylight.controller.cluster.raft.base.messages.DeleteEntriesTest}
 577      *             whose type for fromIndex is long instead of int. This class was kept for backwards
 578      *             compatibility with Helium.
 579      */
 580     @Deprecated
 581     static class DeleteEntries implements Serializable {
 582         private static final long serialVersionUID = 1L;
 583         private final int fromIndex;
 584
 585         public DeleteEntries(int fromIndex) {
 586             this.fromIndex = fromIndex;
 587         }
 588
 589         public int getFromIndex() {
 590             return fromIndex;
 591         }
 592     }
 593
 594     static class UpdateElectionTerm implements Serializable {
 595         private static final long serialVersionUID = 1L;
 596         private final long currentTerm;
 597         private final String votedFor;
 598
 599         public UpdateElectionTerm(long currentTerm, String votedFor) {
 600             this.currentTerm = currentTerm;
 601             this.votedFor = votedFor;
 602         }
 603
 604         public long getCurrentTerm() {
 605             return currentTerm;
 606         }
 607
 608         public String getVotedFor() {
 609             return votedFor;
 610         }
 611     }
 612
 613     private static class BehaviorStateHolder {
 614         private RaftActorBehavior behavior;
 615         private String leaderId;
 616
 617         void init(RaftActorBehavior behavior) {
 618             this.behavior = behavior;
 619             this.leaderId = behavior != null ? behavior.getLeaderId() : null;
 620         }
 621
 622         RaftActorBehavior getBehavior() {
 623             return behavior;
 624         }
 625
 626         String getLeaderId() {
 627             return leaderId;
 628         }
 629     }
 630 }