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         snapshotSupport = newRaftActorSnapshotMessageSupport();
 141     }
 142
 143     @Override
 144     public void postStop() {
 145         if(currentBehavior.getDelegate() != null) {
 146             try {
 147                 currentBehavior.close();
 148             } catch (Exception e) {
 149                 LOG.debug("{}: Error closing behavior {}", persistenceId(), currentBehavior.state());
 150             }
 151         }
 152
 153         super.postStop();
 154     }
 155
 156     @Override
 157     public void handleRecover(Object message) {
 158         if(raftRecovery == null) {
 159             raftRecovery = newRaftActorRecoverySupport();
 160         }
 161
 162         boolean recoveryComplete = raftRecovery.handleRecoveryMessage(message);
 163         if(recoveryComplete) {
 164             if(!persistence().isRecoveryApplicable()) {
 165                 // Delete all the messages from the akka journal so that we do not end up with consistency issues
 166                 // Note I am not using the dataPersistenceProvider and directly using the akka api here
 167                 deleteMessages(lastSequenceNr());
 168
 169                 // Delete all the akka snapshots as they will not be needed
 170                 deleteSnapshots(new SnapshotSelectionCriteria(scala.Long.MaxValue(), scala.Long.MaxValue()));
 171             }
 172
 173             onRecoveryComplete();
 174
 175             initializeBehavior();
 176
 177             raftRecovery = null;
 178         }
 179     }
 180
 181     protected RaftActorRecoverySupport newRaftActorRecoverySupport() {
 182         return new RaftActorRecoverySupport(delegatingPersistenceProvider, context, currentBehavior,
 183                 getRaftActorRecoveryCohort());
 184     }
 185
 186     protected void initializeBehavior(){
 187         changeCurrentBehavior(new Follower(context));
 188     }
 189
 190     protected void changeCurrentBehavior(RaftActorBehavior newBehavior){
 191         reusableBehaviorStateHolder.init(getCurrentBehavior());
 192         setCurrentBehavior(newBehavior);
 193         handleBehaviorChange(reusableBehaviorStateHolder, getCurrentBehavior());
 194     }
 195
 196     @Override
 197     public void handleCommand(Object message) {
 198         boolean handled = snapshotSupport.handleSnapshotMessage(message);
 199         if(handled) {
 200             return;
 201         }
 202
 203         if (message instanceof ApplyState){
 204             ApplyState applyState = (ApplyState) message;
 205
 206             long elapsedTime = (System.nanoTime() - applyState.getStartTime());
 207             if(elapsedTime >= APPLY_STATE_DELAY_THRESHOLD_IN_NANOS){
 208                 LOG.warn("ApplyState took more time than expected. Elapsed Time = {} ms ApplyState = {}",
 209                         TimeUnit.NANOSECONDS.toMillis(elapsedTime), applyState);
 210             }
 211
 212             if(LOG.isDebugEnabled()) {
 213                 LOG.debug("{}: Applying state for log index {} data {}",
 214                     persistenceId(), applyState.getReplicatedLogEntry().getIndex(),
 215                     applyState.getReplicatedLogEntry().getData());
 216             }
 217
 218             applyState(applyState.getClientActor(), applyState.getIdentifier(),
 219                 applyState.getReplicatedLogEntry().getData());
 220
 221         } else if (message instanceof ApplyJournalEntries){
 222             ApplyJournalEntries applyEntries = (ApplyJournalEntries) message;
 223             if(LOG.isDebugEnabled()) {
 224                 LOG.debug("{}: Persisting ApplyLogEntries with index={}", persistenceId(), applyEntries.getToIndex());
 225             }
 226
 227             persistence().persist(applyEntries, NoopProcedure.instance());
 228
 229         } else if (message instanceof FindLeader) {
 230             getSender().tell(
 231                 new FindLeaderReply(getLeaderAddress()),
 232                 getSelf()
 233             );
 234         } else if(message instanceof GetOnDemandRaftState) {
 235             onGetOnDemandRaftStats();
 236         } else {
 237             reusableBehaviorStateHolder.init(getCurrentBehavior());
 238
 239             setCurrentBehavior(currentBehavior.handleMessage(getSender(), message));
 240
 241             handleBehaviorChange(reusableBehaviorStateHolder, getCurrentBehavior());
 242         }
 243     }
 244
 245     protected RaftActorSnapshotMessageSupport newRaftActorSnapshotMessageSupport() {
 246         return new RaftActorSnapshotMessageSupport(delegatingPersistenceProvider, context,
 247                 currentBehavior, getRaftActorSnapshotCohort());
 248     }
 249
 250     private void onGetOnDemandRaftStats() {
 251         // Debugging message to retrieve raft stats.
 252
 253         OnDemandRaftState.Builder builder = OnDemandRaftState.builder()
 254                 .commitIndex(context.getCommitIndex())
 255                 .currentTerm(context.getTermInformation().getCurrentTerm())
 256                 .inMemoryJournalDataSize(replicatedLog().dataSize())
 257                 .inMemoryJournalLogSize(replicatedLog().size())
 258                 .isSnapshotCaptureInitiated(context.getSnapshotManager().isCapturing())
 259                 .lastApplied(context.getLastApplied())
 260                 .lastIndex(replicatedLog().lastIndex())
 261                 .lastTerm(replicatedLog().lastTerm())
 262                 .leader(getLeaderId())
 263                 .raftState(currentBehavior.state().toString())
 264                 .replicatedToAllIndex(currentBehavior.getReplicatedToAllIndex())
 265                 .snapshotIndex(replicatedLog().getSnapshotIndex())
 266                 .snapshotTerm(replicatedLog().getSnapshotTerm())
 267                 .votedFor(context.getTermInformation().getVotedFor())
 268                 .peerAddresses(ImmutableMap.copyOf(context.getPeerAddresses()));
 269
 270         ReplicatedLogEntry lastLogEntry = getLastLogEntry();
 271         if (lastLogEntry != null) {
 272             builder.lastLogIndex(lastLogEntry.getIndex());
 273             builder.lastLogTerm(lastLogEntry.getTerm());
 274         }
 275
 276         if(getCurrentBehavior() instanceof AbstractLeader) {
 277             AbstractLeader leader = (AbstractLeader)getCurrentBehavior();
 278             Collection<String> followerIds = leader.getFollowerIds();
 279             List<FollowerInfo> followerInfoList = Lists.newArrayListWithCapacity(followerIds.size());
 280             for(String id: followerIds) {
 281                 final FollowerLogInformation info = leader.getFollower(id);
 282                 followerInfoList.add(new FollowerInfo(id, info.getNextIndex(), info.getMatchIndex(),
 283                         info.isFollowerActive(), DurationFormatUtils.formatDurationHMS(info.timeSinceLastActivity())));
 284             }
 285
 286             builder.followerInfoList(followerInfoList);
 287         }
 288
 289         sender().tell(builder.build(), self());
 290
 291     }
 292
 293     private void handleBehaviorChange(BehaviorStateHolder oldBehaviorState, RaftActorBehavior currentBehavior) {
 294         RaftActorBehavior oldBehavior = oldBehaviorState.getBehavior();
 295
 296         if (oldBehavior != currentBehavior){
 297             onStateChanged();
 298         }
 299
 300         String oldBehaviorLeaderId = oldBehavior == null ? null : oldBehaviorState.getLeaderId();
 301         String oldBehaviorStateName = oldBehavior == null ? null : oldBehavior.state().name();
 302
 303         // it can happen that the state has not changed but the leader has changed.
 304         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 305         if(!Objects.equal(oldBehaviorLeaderId, currentBehavior.getLeaderId())) {
 306             if(roleChangeNotifier.isPresent()) {
 307                 roleChangeNotifier.get().tell(new LeaderStateChanged(getId(), currentBehavior.getLeaderId()), getSelf());
 308             }
 309
 310             onLeaderChanged(oldBehaviorLeaderId, currentBehavior.getLeaderId());
 311         }
 312
 313         if (roleChangeNotifier.isPresent() &&
 314                 (oldBehavior == null || (oldBehavior.state() != currentBehavior.state()))) {
 315             roleChangeNotifier.get().tell(new RoleChanged(getId(), oldBehaviorStateName ,
 316                     currentBehavior.state().name()), getSelf());
 317         }
 318     }
 319
 320     /**
 321      * When a derived RaftActor needs to persist something it must call
 322      * persistData.
 323      *
 324      * @param clientActor
 325      * @param identifier
 326      * @param data
 327      */
 328     protected void persistData(final ActorRef clientActor, final String identifier,
 329         final Payload data) {
 330
 331         ReplicatedLogEntry replicatedLogEntry = new ReplicatedLogImplEntry(
 332             context.getReplicatedLog().lastIndex() + 1,
 333             context.getTermInformation().getCurrentTerm(), data);
 334
 335         if(LOG.isDebugEnabled()) {
 336             LOG.debug("{}: Persist data {}", persistenceId(), replicatedLogEntry);
 337         }
 338
 339         final RaftActorContext raftContext = getRaftActorContext();
 340
 341         replicatedLog().appendAndPersist(replicatedLogEntry, new Procedure<ReplicatedLogEntry>() {
 342             @Override
 343             public void apply(ReplicatedLogEntry replicatedLogEntry) throws Exception {
 344                 if(!hasFollowers()){
 345                     // Increment the Commit Index and the Last Applied values
 346                     raftContext.setCommitIndex(replicatedLogEntry.getIndex());
 347                     raftContext.setLastApplied(replicatedLogEntry.getIndex());
 348
 349                     // Apply the state immediately
 350                     applyState(clientActor, identifier, data);
 351
 352                     // Send a ApplyJournalEntries message so that we write the fact that we applied
 353                     // the state to durable storage
 354                     self().tell(new ApplyJournalEntries(replicatedLogEntry.getIndex()), self());
 355
 356                     context.getSnapshotManager().trimLog(context.getLastApplied(), currentBehavior);
 357
 358                 } else if (clientActor != null) {
 359                     // Send message for replication
 360                     currentBehavior.handleMessage(getSelf(),
 361                             new Replicate(clientActor, identifier, replicatedLogEntry));
 362                 }
 363             }
 364         });
 365     }
 366
 367     private ReplicatedLog replicatedLog() {
 368         return context.getReplicatedLog();
 369     }
 370
 371     protected String getId() {
 372         return context.getId();
 373     }
 374
 375     @VisibleForTesting
 376     void setCurrentBehavior(RaftActorBehavior behavior) {
 377         currentBehavior.setDelegate(behavior);
 378     }
 379
 380     protected RaftActorBehavior getCurrentBehavior() {
 381         return currentBehavior.getDelegate();
 382     }
 383
 384     /**
 385      * Derived actors can call the isLeader method to check if the current
 386      * RaftActor is the Leader or not
 387      *
 388      * @return true it this RaftActor is a Leader false otherwise
 389      */
 390     protected boolean isLeader() {
 391         return context.getId().equals(currentBehavior.getLeaderId());
 392     }
 393
 394     /**
 395      * Derived actor can call getLeader if they need a reference to the Leader.
 396      * This would be useful for example in forwarding a request to an actor
 397      * which is the leader
 398      *
 399      * @return A reference to the leader if known, null otherwise
 400      */
 401     protected ActorSelection getLeader(){
 402         String leaderAddress = getLeaderAddress();
 403
 404         if(leaderAddress == null){
 405             return null;
 406         }
 407
 408         return context.actorSelection(leaderAddress);
 409     }
 410
 411     /**
 412      *
 413      * @return the current leader's id
 414      */
 415     protected String getLeaderId(){
 416         return currentBehavior.getLeaderId();
 417     }
 418
 419     protected RaftState getRaftState() {
 420         return currentBehavior.state();
 421     }
 422
 423     protected ReplicatedLogEntry getLastLogEntry() {
 424         return replicatedLog().last();
 425     }
 426
 427     protected Long getCurrentTerm(){
 428         return context.getTermInformation().getCurrentTerm();
 429     }
 430
 431     protected Long getCommitIndex(){
 432         return context.getCommitIndex();
 433     }
 434
 435     protected Long getLastApplied(){
 436         return context.getLastApplied();
 437     }
 438
 439     protected RaftActorContext getRaftActorContext() {
 440         return context;
 441     }
 442
 443     protected void updateConfigParams(ConfigParams configParams) {
 444         context.setConfigParams(configParams);
 445     }
 446
 447     public final DataPersistenceProvider persistence() {
 448         return delegatingPersistenceProvider.getDelegate();
 449     }
 450
 451     public void setPersistence(DataPersistenceProvider provider) {
 452         delegatingPersistenceProvider.setDelegate(provider);
 453     }
 454
 455     protected void setPersistence(boolean persistent) {
 456         if(persistent) {
 457             setPersistence(new PersistentDataProvider(this));
 458         } else {
 459             setPersistence(new NonPersistentDataProvider() {
 460                 /**
 461                  * The way snapshotting works is,
 462                  * <ol>
 463                  * <li> RaftActor calls createSnapshot on the Shard
 464                  * <li> Shard sends a CaptureSnapshotReply and RaftActor then calls saveSnapshot
 465                  * <li> When saveSnapshot is invoked on the akka-persistence API it uses the SnapshotStore to save
 466                  * the snapshot. The SnapshotStore sends SaveSnapshotSuccess or SaveSnapshotFailure. When the
 467                  * RaftActor gets SaveSnapshot success it commits the snapshot to the in-memory journal. This
 468                  * commitSnapshot is mimicking what is done in SaveSnapshotSuccess.
 469                  * </ol>
 470                  */
 471                 @Override
 472                 public void saveSnapshot(Object o) {
 473                     // Make saving Snapshot successful
 474                     // Committing the snapshot here would end up calling commit in the creating state which would
 475                     // be a state violation. That's why now we send a message to commit the snapshot.
 476                     self().tell(RaftActorSnapshotMessageSupport.COMMIT_SNAPSHOT, self());
 477                 }
 478             });
 479         }
 480     }
 481
 482     /**
 483      * setPeerAddress sets the address of a known peer at a later time.
 484      * <p>
 485      * This is to account for situations where a we know that a peer
 486      * exists but we do not know an address up-front. This may also be used in
 487      * situations where a known peer starts off in a different location and we
 488      * need to change it's address
 489      * <p>
 490      * Note that if the peerId does not match the list of peers passed to
 491      * this actor during construction an IllegalStateException will be thrown.
 492      *
 493      * @param peerId
 494      * @param peerAddress
 495      */
 496     protected void setPeerAddress(String peerId, String peerAddress){
 497         context.setPeerAddress(peerId, peerAddress);
 498     }
 499
 500     /**
 501      * The applyState method will be called by the RaftActor when some data
 502      * needs to be applied to the actor's state
 503      *
 504      * @param clientActor A reference to the client who sent this message. This
 505      *                    is the same reference that was passed to persistData
 506      *                    by the derived actor. clientActor may be null when
 507      *                    the RaftActor is behaving as a follower or during
 508      *                    recovery.
 509      * @param identifier  The identifier of the persisted data. This is also
 510      *                    the same identifier that was passed to persistData by
 511      *                    the derived actor. identifier may be null when
 512      *                    the RaftActor is behaving as a follower or during
 513      *                    recovery
 514      * @param data        A piece of data that was persisted by the persistData call.
 515      *                    This should NEVER be null.
 516      */
 517     protected abstract void applyState(ActorRef clientActor, String identifier,
 518         Object data);
 519
 520     /**
 521      * Returns the RaftActorRecoveryCohort to participate in persistence recovery.
 522      */
 523     @Nonnull
 524     protected abstract RaftActorRecoveryCohort getRaftActorRecoveryCohort();
 525
 526     /**
 527      * This method is called when recovery is complete.
 528      */
 529     protected abstract void onRecoveryComplete();
 530
 531     /**
 532      * Returns the RaftActorSnapshotCohort to participate in persistence recovery.
 533      */
 534     @Nonnull
 535     protected abstract RaftActorSnapshotCohort getRaftActorSnapshotCohort();
 536
 537     /**
 538      * This method will be called by the RaftActor when the state of the
 539      * RaftActor changes. The derived actor can then use methods like
 540      * isLeader or getLeader to do something useful
 541      */
 542     protected abstract void onStateChanged();
 543
 544     /**
 545      * Notifier Actor for this RaftActor to notify when a role change happens
 546      * @return ActorRef - ActorRef of the notifier or Optional.absent if none.
 547      */
 548     protected abstract Optional<ActorRef> getRoleChangeNotifier();
 549
 550     protected void onLeaderChanged(String oldLeader, String newLeader){};
 551
 552     private String getLeaderAddress(){
 553         if(isLeader()){
 554             return getSelf().path().toString();
 555         }
 556         String leaderId = currentBehavior.getLeaderId();
 557         if (leaderId == null) {
 558             return null;
 559         }
 560         String peerAddress = context.getPeerAddress(leaderId);
 561         if(LOG.isDebugEnabled()) {
 562             LOG.debug("{}: getLeaderAddress leaderId = {} peerAddress = {}",
 563                     persistenceId(), leaderId, peerAddress);
 564         }
 565
 566         return peerAddress;
 567     }
 568
 569     protected boolean hasFollowers(){
 570         return getRaftActorContext().hasFollowers();
 571     }
 572
 573     /**
 574      * @deprecated Deprecated in favor of {@link org.opendaylight.controller.cluster.raft.base.messages.DeleteEntriesTest}
 575      *             whose type for fromIndex is long instead of int. This class was kept for backwards
 576      *             compatibility with Helium.
 577      */
 578     @Deprecated
 579     static class DeleteEntries implements Serializable {
 580         private static final long serialVersionUID = 1L;
 581         private final int fromIndex;
 582
 583         public DeleteEntries(int fromIndex) {
 584             this.fromIndex = fromIndex;
 585         }
 586
 587         public int getFromIndex() {
 588             return fromIndex;
 589         }
 590     }
 591
 592     static class UpdateElectionTerm implements Serializable {
 593         private static final long serialVersionUID = 1L;
 594         private final long currentTerm;
 595         private final String votedFor;
 596
 597         public UpdateElectionTerm(long currentTerm, String votedFor) {
 598             this.currentTerm = currentTerm;
 599             this.votedFor = votedFor;
 600         }
 601
 602         public long getCurrentTerm() {
 603             return currentTerm;
 604         }
 605
 606         public String getVotedFor() {
 607             return votedFor;
 608         }
 609     }
 610
 611     private static class BehaviorStateHolder {
 612         private RaftActorBehavior behavior;
 613         private String leaderId;
 614
 615         void init(RaftActorBehavior behavior) {
 616             this.behavior = behavior;
 617             this.leaderId = behavior != null ? behavior.getLeaderId() : null;
 618         }
 619
 620         RaftActorBehavior getBehavior() {
 621             return behavior;
 622         }
 623
 624         String getLeaderId() {
 625             return leaderId;
 626         }
 627     }
 628 }