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  *
   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
   9 package org.opendaylight.controller.cluster.raft;
  10
  11 import akka.actor.ActorRef;
  12 import akka.actor.ActorSelection;
  13 import akka.event.Logging;
  14 import akka.event.LoggingAdapter;
  15 import akka.japi.Procedure;
  16 import akka.persistence.RecoveryCompleted;
  17 import akka.persistence.SaveSnapshotFailure;
  18 import akka.persistence.SaveSnapshotSuccess;
  19 import akka.persistence.SnapshotOffer;
  20 import akka.persistence.SnapshotSelectionCriteria;
  21 import akka.persistence.UntypedPersistentActor;
  22 import com.google.common.base.Optional;
  23 import com.google.protobuf.ByteString;
  24 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  25 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  26 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshot;
  27 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshotReply;
  28 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  29 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
  30 import org.opendaylight.controller.cluster.raft.behaviors.Candidate;
  31 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
  32 import org.opendaylight.controller.cluster.raft.behaviors.Leader;
  33 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  34 import org.opendaylight.controller.cluster.raft.client.messages.AddRaftPeer;
  35 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
  36 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
  37 import org.opendaylight.controller.cluster.raft.client.messages.RemoveRaftPeer;
  38 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  39 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
  40 import org.opendaylight.controller.protobuff.messages.cluster.raft.AppendEntriesMessages;
  41
  42 import java.io.Serializable;
  43 import java.util.Map;
  44
  45 /**
  46  * RaftActor encapsulates a state machine that needs to be kept synchronized
  47  * in a cluster. It implements the RAFT algorithm as described in the paper
  48  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
  49  * In Search of an Understandable Consensus Algorithm</a>
  50  * <p/>
  51  * RaftActor has 3 states and each state has a certain behavior associated
  52  * with it. A Raft actor can behave as,
  53  * <ul>
  54  * <li> A Leader </li>
  55  * <li> A Follower (or) </li>
  56  * <li> A Candidate </li>
  57  * </ul>
  58  * <p/>
  59  * <p/>
  60  * A RaftActor MUST be a Leader in order to accept requests from clients to
  61  * change the state of it's encapsulated state machine. Once a RaftActor becomes
  62  * a Leader it is also responsible for ensuring that all followers ultimately
  63  * have the same log and therefore the same state machine as itself.
  64  * <p/>
  65  * <p/>
  66  * The current behavior of a RaftActor determines how election for leadership
  67  * is initiated and how peer RaftActors react to request for votes.
  68  * <p/>
  69  * <p/>
  70  * Each RaftActor also needs to know the current election term. It uses this
  71  * information for a couple of things. One is to simply figure out who it
  72  * voted for in the last election. Another is to figure out if the message
  73  * it received to update it's state is stale.
  74  * <p/>
  75  * <p/>
  76  * The RaftActor uses akka-persistence to store it's replicated log.
  77  * Furthermore through it's behaviors a Raft Actor determines
  78  * <p/>
  79  * <ul>
  80  * <li> when a log entry should be persisted </li>
  81  * <li> when a log entry should be applied to the state machine (and) </li>
  82  * <li> when a snapshot should be saved </li>
  83  * </ul>
  84  */
  85 public abstract class RaftActor extends UntypedPersistentActor {
  86     protected final LoggingAdapter LOG =
  87         Logging.getLogger(getContext().system(), this);
  88
  89     /**
  90      * The current state determines the current behavior of a RaftActor
  91      * A Raft Actor always starts off in the Follower State
  92      */
  93     private RaftActorBehavior currentBehavior;
  94
  95     /**
  96      * This context should NOT be passed directly to any other actor it is
  97      * only to be consumed by the RaftActorBehaviors
  98      */
  99     private RaftActorContext context;
 100
 101     /**
 102      * The in-memory journal
 103      */
 104     private ReplicatedLogImpl replicatedLog = new ReplicatedLogImpl();
 105
 106     private CaptureSnapshot captureSnapshot = null;
 107
 108     private volatile boolean hasSnapshotCaptureInitiated = false;
 109
 110     public RaftActor(String id, Map<String, String> peerAddresses) {
 111         this(id, peerAddresses, Optional.<ConfigParams>absent());
 112     }
 113
 114     public RaftActor(String id, Map<String, String> peerAddresses,
 115          Optional<ConfigParams> configParams) {
 116
 117         context = new RaftActorContextImpl(this.getSelf(),
 118             this.getContext(), id, new ElectionTermImpl(),
 119             -1, -1, replicatedLog, peerAddresses,
 120             (configParams.isPresent() ? configParams.get(): new DefaultConfigParamsImpl()),
 121             LOG);
 122     }
 123
 124     @Override public void onReceiveRecover(Object message) {
 125         if (message instanceof SnapshotOffer) {
 126             LOG.info("SnapshotOffer called..");
 127             SnapshotOffer offer = (SnapshotOffer) message;
 128             Snapshot snapshot = (Snapshot) offer.snapshot();
 129
 130             // Create a replicated log with the snapshot information
 131             // The replicated log can be used later on to retrieve this snapshot
 132             // when we need to install it on a peer
 133             replicatedLog = new ReplicatedLogImpl(snapshot);
 134
 135             context.setReplicatedLog(replicatedLog);
 136             context.setLastApplied(snapshot.getLastAppliedIndex());
 137
 138             LOG.info("Applied snapshot to replicatedLog. " +
 139                     "snapshotIndex={}, snapshotTerm={}, journal-size={}",
 140                 replicatedLog.snapshotIndex, replicatedLog.snapshotTerm,
 141                 replicatedLog.size()
 142             );
 143
 144             // Apply the snapshot to the actors state
 145             applySnapshot(ByteString.copyFrom(snapshot.getState()));
 146
 147         } else if (message instanceof ReplicatedLogEntry) {
 148             ReplicatedLogEntry logEntry = (ReplicatedLogEntry) message;
 149
 150             // Apply State immediately
 151             replicatedLog.append(logEntry);
 152             applyState(null, "recovery", logEntry.getData());
 153             context.setLastApplied(logEntry.getIndex());
 154             context.setCommitIndex(logEntry.getIndex());
 155         } else if (message instanceof DeleteEntries) {
 156             replicatedLog.removeFrom(((DeleteEntries) message).getFromIndex());
 157         } else if (message instanceof UpdateElectionTerm) {
 158             context.getTermInformation().update(((UpdateElectionTerm) message).getCurrentTerm(), ((UpdateElectionTerm) message).getVotedFor());
 159         } else if (message instanceof RecoveryCompleted) {
 160             LOG.debug(
 161                 "RecoveryCompleted - Switching actor to Follower - " +
 162                     "Persistence Id =  " + persistenceId() +
 163                     " Last index in log:{}, snapshotIndex={}, snapshotTerm={}, " +
 164                     "journal-size={}",
 165                 replicatedLog.lastIndex(), replicatedLog.snapshotIndex,
 166                 replicatedLog.snapshotTerm, replicatedLog.size());
 167             currentBehavior = switchBehavior(RaftState.Follower);
 168             onStateChanged();
 169         }
 170     }
 171
 172     @Override public void onReceiveCommand(Object message) {
 173         if (message instanceof ApplyState){
 174             ApplyState applyState = (ApplyState) message;
 175
 176             LOG.debug("Applying state for log index {} data {}",
 177                 applyState.getReplicatedLogEntry().getIndex(),
 178                 applyState.getReplicatedLogEntry().getData());
 179
 180             applyState(applyState.getClientActor(), applyState.getIdentifier(),
 181                 applyState.getReplicatedLogEntry().getData());
 182
 183         } else if(message instanceof ApplySnapshot ) {
 184             Snapshot snapshot = ((ApplySnapshot) message).getSnapshot();
 185
 186             LOG.debug("ApplySnapshot called on Follower Actor " +
 187                 "snapshotIndex:{}, snapshotTerm:{}", snapshot.getLastAppliedIndex(),
 188                 snapshot.getLastAppliedTerm());
 189             applySnapshot(ByteString.copyFrom(snapshot.getState()));
 190
 191             //clears the followers log, sets the snapshot index to ensure adjusted-index works
 192             replicatedLog = new ReplicatedLogImpl(snapshot);
 193             context.setReplicatedLog(replicatedLog);
 194             context.setLastApplied(snapshot.getLastAppliedIndex());
 195
 196         } else if (message instanceof FindLeader) {
 197             getSender().tell(
 198                 new FindLeaderReply(getLeaderAddress()),
 199                 getSelf()
 200             );
 201
 202         } else if (message instanceof SaveSnapshotSuccess) {
 203             SaveSnapshotSuccess success = (SaveSnapshotSuccess) message;
 204             LOG.info("SaveSnapshotSuccess received for snapshot");
 205
 206             context.getReplicatedLog().snapshotCommit();
 207
 208             // TODO: Not sure if we want to be this aggressive with trimming stuff
 209             trimPersistentData(success.metadata().sequenceNr());
 210
 211         } else if (message instanceof SaveSnapshotFailure) {
 212             SaveSnapshotFailure saveSnapshotFailure = (SaveSnapshotFailure) message;
 213
 214             LOG.info("saveSnapshotFailure.metadata():{}", saveSnapshotFailure.metadata().toString());
 215             LOG.error(saveSnapshotFailure.cause(), "SaveSnapshotFailure received for snapshot Cause:");
 216
 217             context.getReplicatedLog().snapshotRollback();
 218
 219             LOG.info("Replicated Log rollbacked. Snapshot will be attempted in the next cycle." +
 220                 "snapshotIndex:{}, snapshotTerm:{}, log-size:{}",
 221                 context.getReplicatedLog().getSnapshotIndex(),
 222                 context.getReplicatedLog().getSnapshotTerm(),
 223                 context.getReplicatedLog().size());
 224
 225         } else if (message instanceof AddRaftPeer){
 226
 227             // FIXME : Do not add raft peers like this.
 228             // When adding a new Peer we have to ensure that the a majority of
 229             // the peers know about the new Peer. Doing it this way may cause
 230             // a situation where multiple Leaders may emerge
 231             AddRaftPeer arp = (AddRaftPeer)message;
 232            context.addToPeers(arp.getName(), arp.getAddress());
 233
 234         } else if (message instanceof RemoveRaftPeer){
 235
 236             RemoveRaftPeer rrp = (RemoveRaftPeer)message;
 237             context.removePeer(rrp.getName());
 238
 239         } else if (message instanceof CaptureSnapshot) {
 240             LOG.info("CaptureSnapshot received by actor");
 241             CaptureSnapshot cs = (CaptureSnapshot)message;
 242             captureSnapshot = cs;
 243             createSnapshot();
 244
 245         } else if (message instanceof CaptureSnapshotReply){
 246             LOG.info("CaptureSnapshotReply received by actor");
 247             CaptureSnapshotReply csr = (CaptureSnapshotReply) message;
 248
 249             ByteString stateInBytes = csr.getSnapshot();
 250             LOG.info("CaptureSnapshotReply stateInBytes size:{}", stateInBytes.size());
 251             handleCaptureSnapshotReply(stateInBytes);
 252
 253         } else {
 254             if (!(message instanceof AppendEntriesMessages.AppendEntries)
 255                 && !(message instanceof AppendEntriesReply) && !(message instanceof SendHeartBeat)) {
 256                 LOG.debug("onReceiveCommand: message:" + message.getClass());
 257             }
 258
 259             RaftState state =
 260                 currentBehavior.handleMessage(getSender(), message);
 261             RaftActorBehavior oldBehavior = currentBehavior;
 262             currentBehavior = switchBehavior(state);
 263             if(oldBehavior != currentBehavior){
 264                 onStateChanged();
 265             }
 266
 267             onLeaderChanged(oldBehavior.getLeaderId(), currentBehavior.getLeaderId());
 268         }
 269     }
 270
 271     public java.util.Set<String> getPeers() {
 272         return context.getPeerAddresses().keySet();
 273     }
 274
 275     protected String getReplicatedLogState() {
 276         return "snapshotIndex=" + context.getReplicatedLog().getSnapshotIndex()
 277             + ", snapshotTerm=" + context.getReplicatedLog().getSnapshotTerm()
 278             + ", im-mem journal size=" + context.getReplicatedLog().size();
 279     }
 280
 281
 282     /**
 283      * When a derived RaftActor needs to persist something it must call
 284      * persistData.
 285      *
 286      * @param clientActor
 287      * @param identifier
 288      * @param data
 289      */
 290     protected void persistData(ActorRef clientActor, String identifier,
 291         Payload data) {
 292
 293         ReplicatedLogEntry replicatedLogEntry = new ReplicatedLogImplEntry(
 294             context.getReplicatedLog().lastIndex() + 1,
 295             context.getTermInformation().getCurrentTerm(), data);
 296
 297         LOG.debug("Persist data {}", replicatedLogEntry);
 298
 299         replicatedLog
 300             .appendAndPersist(clientActor, identifier, replicatedLogEntry);
 301     }
 302
 303     protected String getId() {
 304         return context.getId();
 305     }
 306
 307     /**
 308      * Derived actors can call the isLeader method to check if the current
 309      * RaftActor is the Leader or not
 310      *
 311      * @return true it this RaftActor is a Leader false otherwise
 312      */
 313     protected boolean isLeader() {
 314         return context.getId().equals(currentBehavior.getLeaderId());
 315     }
 316
 317     /**
 318      * Derived actor can call getLeader if they need a reference to the Leader.
 319      * This would be useful for example in forwarding a request to an actor
 320      * which is the leader
 321      *
 322      * @return A reference to the leader if known, null otherwise
 323      */
 324     protected ActorSelection getLeader(){
 325         String leaderAddress = getLeaderAddress();
 326
 327         if(leaderAddress == null){
 328             return null;
 329         }
 330
 331         return context.actorSelection(leaderAddress);
 332     }
 333
 334     /**
 335      *
 336      * @return the current leader's id
 337      */
 338     protected String getLeaderId(){
 339         return currentBehavior.getLeaderId();
 340     }
 341
 342     protected RaftState getRaftState() {
 343         return currentBehavior.state();
 344     }
 345
 346     protected ReplicatedLogEntry getLastLogEntry() {
 347         return replicatedLog.last();
 348     }
 349
 350     protected Long getCurrentTerm(){
 351         return context.getTermInformation().getCurrentTerm();
 352     }
 353
 354     protected Long getCommitIndex(){
 355         return context.getCommitIndex();
 356     }
 357
 358     protected Long getLastApplied(){
 359         return context.getLastApplied();
 360     }
 361
 362     /**
 363      * setPeerAddress sets the address of a known peer at a later time.
 364      * <p>
 365      * This is to account for situations where a we know that a peer
 366      * exists but we do not know an address up-front. This may also be used in
 367      * situations where a known peer starts off in a different location and we
 368      * need to change it's address
 369      * <p>
 370      * Note that if the peerId does not match the list of peers passed to
 371      * this actor during construction an IllegalStateException will be thrown.
 372      *
 373      * @param peerId
 374      * @param peerAddress
 375      */
 376     protected void setPeerAddress(String peerId, String peerAddress){
 377         context.setPeerAddress(peerId, peerAddress);
 378     }
 379
 380
 381
 382     /**
 383      * The applyState method will be called by the RaftActor when some data
 384      * needs to be applied to the actor's state
 385      *
 386      * @param clientActor A reference to the client who sent this message. This
 387      *                    is the same reference that was passed to persistData
 388      *                    by the derived actor. clientActor may be null when
 389      *                    the RaftActor is behaving as a follower or during
 390      *                    recovery.
 391      * @param identifier  The identifier of the persisted data. This is also
 392      *                    the same identifier that was passed to persistData by
 393      *                    the derived actor. identifier may be null when
 394      *                    the RaftActor is behaving as a follower or during
 395      *                    recovery
 396      * @param data        A piece of data that was persisted by the persistData call.
 397      *                    This should NEVER be null.
 398      */
 399     protected abstract void applyState(ActorRef clientActor, String identifier,
 400         Object data);
 401
 402     /**
 403      * This method will be called by the RaftActor when a snapshot needs to be
 404      * created. The derived actor should respond with its current state.
 405      * <p/>
 406      * During recovery the state that is returned by the derived actor will
 407      * be passed back to it by calling the applySnapshot  method
 408      *
 409      * @return The current state of the actor
 410      */
 411     protected abstract void createSnapshot();
 412
 413     /**
 414      * This method will be called by the RaftActor during recovery to
 415      * reconstruct the state of the actor.
 416      * <p/>
 417      * This method may also be called at any other point during normal
 418      * operations when the derived actor is out of sync with it's peers
 419      * and the only way to bring it in sync is by applying a snapshot
 420      *
 421      * @param snapshot A snapshot of the state of the actor
 422      */
 423     protected abstract void applySnapshot(ByteString snapshot);
 424
 425     /**
 426      * This method will be called by the RaftActor when the state of the
 427      * RaftActor changes. The derived actor can then use methods like
 428      * isLeader or getLeader to do something useful
 429      */
 430     protected abstract void onStateChanged();
 431
 432     protected void onLeaderChanged(String oldLeader, String newLeader){};
 433
 434     private RaftActorBehavior switchBehavior(RaftState state) {
 435         if (currentBehavior != null) {
 436             if (currentBehavior.state() == state) {
 437                 return currentBehavior;
 438             }
 439             LOG.info("Switching from state " + currentBehavior.state() + " to "
 440                 + state);
 441
 442             try {
 443                 currentBehavior.close();
 444             } catch (Exception e) {
 445                 LOG.error(e,
 446                     "Failed to close behavior : " + currentBehavior.state());
 447             }
 448
 449         } else {
 450             LOG.info("Switching behavior to " + state);
 451         }
 452         RaftActorBehavior behavior = null;
 453         if (state == RaftState.Candidate) {
 454             behavior = new Candidate(context);
 455         } else if (state == RaftState.Follower) {
 456             behavior = new Follower(context);
 457         } else {
 458             behavior = new Leader(context);
 459         }
 460
 461
 462
 463         return behavior;
 464     }
 465
 466     private void trimPersistentData(long sequenceNumber) {
 467         // Trim akka snapshots
 468         // FIXME : Not sure how exactly the SnapshotSelectionCriteria is applied
 469         // For now guessing that it is ANDed.
 470         deleteSnapshots(new SnapshotSelectionCriteria(
 471             sequenceNumber - context.getConfigParams().getSnapshotBatchCount(), 43200000));
 472
 473         // Trim akka journal
 474         deleteMessages(sequenceNumber);
 475     }
 476
 477     private String getLeaderAddress(){
 478         if(isLeader()){
 479             return getSelf().path().toString();
 480         }
 481         String leaderId = currentBehavior.getLeaderId();
 482         if (leaderId == null) {
 483             return null;
 484         }
 485         String peerAddress = context.getPeerAddress(leaderId);
 486         LOG.debug("getLeaderAddress leaderId = " + leaderId + " peerAddress = "
 487             + peerAddress);
 488
 489         return peerAddress;
 490     }
 491
 492     private void handleCaptureSnapshotReply(ByteString stateInBytes) {
 493         // create a snapshot object from the state provided and save it
 494         // when snapshot is saved async, SaveSnapshotSuccess is raised.
 495
 496         Snapshot sn = Snapshot.create(stateInBytes.toByteArray(),
 497             context.getReplicatedLog().getFrom(captureSnapshot.getLastAppliedIndex() + 1),
 498             captureSnapshot.getLastIndex(), captureSnapshot.getLastTerm(),
 499             captureSnapshot.getLastAppliedIndex(), captureSnapshot.getLastAppliedTerm());
 500
 501         saveSnapshot(sn);
 502
 503         LOG.info("Persisting of snapshot done:{}", sn.getLogMessage());
 504
 505         //be greedy and remove entries from in-mem journal which are in the snapshot
 506         // and update snapshotIndex and snapshotTerm without waiting for the success,
 507
 508         context.getReplicatedLog().snapshotPreCommit(stateInBytes,
 509             captureSnapshot.getLastAppliedIndex(),
 510             captureSnapshot.getLastAppliedTerm());
 511
 512         LOG.info("Removed in-memory snapshotted entries, adjusted snaphsotIndex:{} " +
 513             "and term:{}", captureSnapshot.getLastAppliedIndex(),
 514             captureSnapshot.getLastAppliedTerm());
 515
 516         captureSnapshot = null;
 517         hasSnapshotCaptureInitiated = false;
 518     }
 519
 520
 521     private class ReplicatedLogImpl extends AbstractReplicatedLogImpl {
 522
 523         public ReplicatedLogImpl(Snapshot snapshot) {
 524             super(ByteString.copyFrom(snapshot.getState()),
 525                 snapshot.getLastAppliedIndex(), snapshot.getLastAppliedTerm(),
 526                 snapshot.getUnAppliedEntries());
 527         }
 528
 529         public ReplicatedLogImpl() {
 530             super();
 531         }
 532
 533         @Override public void removeFromAndPersist(long logEntryIndex) {
 534             int adjustedIndex = adjustedIndex(logEntryIndex);
 535
 536             if (adjustedIndex < 0) {
 537                 return;
 538             }
 539
 540             // FIXME: Maybe this should be done after the command is saved
 541             journal.subList(adjustedIndex , journal.size()).clear();
 542
 543             persist(new DeleteEntries(adjustedIndex), new Procedure<DeleteEntries>(){
 544
 545                 @Override public void apply(DeleteEntries param)
 546                     throws Exception {
 547                     //FIXME : Doing nothing for now
 548                 }
 549             });
 550         }
 551
 552         @Override public void appendAndPersist(
 553             final ReplicatedLogEntry replicatedLogEntry) {
 554             appendAndPersist(null, null, replicatedLogEntry);
 555         }
 556
 557         public void appendAndPersist(final ActorRef clientActor,
 558             final String identifier,
 559             final ReplicatedLogEntry replicatedLogEntry) {
 560             context.getLogger().debug(
 561                 "Append log entry and persist {} ", replicatedLogEntry);
 562             // FIXME : By adding the replicated log entry to the in-memory journal we are not truly ensuring durability of the logs
 563             journal.add(replicatedLogEntry);
 564
 565             // When persisting events with persist it is guaranteed that the
 566             // persistent actor will not receive further commands between the
 567             // persist call and the execution(s) of the associated event
 568             // handler. This also holds for multiple persist calls in context
 569             // of a single command.
 570             persist(replicatedLogEntry,
 571                 new Procedure<ReplicatedLogEntry>() {
 572                     public void apply(ReplicatedLogEntry evt) throws Exception {
 573                         // when a snaphsot is being taken, captureSnapshot != null
 574                         if (hasSnapshotCaptureInitiated == false &&
 575                             journal.size() % context.getConfigParams().getSnapshotBatchCount() == 0) {
 576
 577                             LOG.info("Initiating Snapshot Capture..");
 578                             long lastAppliedIndex = -1;
 579                             long lastAppliedTerm = -1;
 580
 581                             ReplicatedLogEntry lastAppliedEntry = get(context.getLastApplied());
 582                             if (lastAppliedEntry != null) {
 583                                 lastAppliedIndex = lastAppliedEntry.getIndex();
 584                                 lastAppliedTerm = lastAppliedEntry.getTerm();
 585                             }
 586
 587                             LOG.debug("Snapshot Capture logSize: {}", journal.size());
 588                             LOG.debug("Snapshot Capture lastApplied:{} ", context.getLastApplied());
 589                             LOG.debug("Snapshot Capture lastAppliedIndex:{}", lastAppliedIndex);
 590                             LOG.debug("Snapshot Capture lastAppliedTerm:{}", lastAppliedTerm);
 591
 592                             // send a CaptureSnapshot to self to make the expensive operation async.
 593                             getSelf().tell(new CaptureSnapshot(
 594                                 lastIndex(), lastTerm(), lastAppliedIndex, lastAppliedTerm),
 595                                 null);
 596                             hasSnapshotCaptureInitiated = true;
 597                         }
 598                         // Send message for replication
 599                         if (clientActor != null) {
 600                             currentBehavior.handleMessage(getSelf(),
 601                                 new Replicate(clientActor, identifier,
 602                                     replicatedLogEntry)
 603                             );
 604                         }
 605                     }
 606                 }
 607             );
 608         }
 609
 610     }
 611
 612     private static class DeleteEntries implements Serializable {
 613         private final int fromIndex;
 614
 615
 616         public DeleteEntries(int fromIndex) {
 617             this.fromIndex = fromIndex;
 618         }
 619
 620         public int getFromIndex() {
 621             return fromIndex;
 622         }
 623     }
 624
 625
 626     private class ElectionTermImpl implements ElectionTerm {
 627         /**
 628          * Identifier of the actor whose election term information this is
 629          */
 630         private long currentTerm = 0;
 631         private String votedFor = null;
 632
 633         public long getCurrentTerm() {
 634             return currentTerm;
 635         }
 636
 637         public String getVotedFor() {
 638             return votedFor;
 639         }
 640
 641         @Override public void update(long currentTerm, String votedFor) {
 642             LOG.debug("Set currentTerm={}, votedFor={}", currentTerm, votedFor);
 643
 644             this.currentTerm = currentTerm;
 645             this.votedFor = votedFor;
 646         }
 647
 648         @Override
 649         public void updateAndPersist(long currentTerm, String votedFor){
 650             update(currentTerm, votedFor);
 651             // FIXME : Maybe first persist then update the state
 652             persist(new UpdateElectionTerm(this.currentTerm, this.votedFor), new Procedure<UpdateElectionTerm>(){
 653
 654                 @Override public void apply(UpdateElectionTerm param)
 655                     throws Exception {
 656
 657                 }
 658             });
 659         }
 660     }
 661
 662     private static class UpdateElectionTerm implements Serializable {
 663         private final long currentTerm;
 664         private final String votedFor;
 665
 666         public UpdateElectionTerm(long currentTerm, String votedFor) {
 667             this.currentTerm = currentTerm;
 668             this.votedFor = votedFor;
 669         }
 670
 671         public long getCurrentTerm() {
 672             return currentTerm;
 673         }
 674
 675         public String getVotedFor() {
 676             return votedFor;
 677         }
 678     }
 679
 680 }