08907e3fd25449d0208d9efcba84acba02624bfb
[controller.git] / 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.actor.PoisonPill;
15 import com.google.common.annotations.VisibleForTesting;
16 import com.google.common.base.Optional;
17 import com.google.common.base.Preconditions;
18 import com.google.common.base.Verify;
19 import com.google.common.collect.Lists;
20 import java.util.Collection;
21 import java.util.HashMap;
22 import java.util.List;
23 import java.util.Map;
24 import java.util.Objects;
25 import java.util.concurrent.TimeUnit;
26 import javax.annotation.Nonnull;
27 import javax.annotation.Nullable;
28 import org.apache.commons.lang3.time.DurationFormatUtils;
29 import org.opendaylight.controller.cluster.DataPersistenceProvider;
30 import org.opendaylight.controller.cluster.DelegatingPersistentDataProvider;
31 import org.opendaylight.controller.cluster.NonPersistentDataProvider;
32 import org.opendaylight.controller.cluster.PersistentDataProvider;
33 import org.opendaylight.controller.cluster.common.actor.AbstractUntypedPersistentActor;
34 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
35 import org.opendaylight.controller.cluster.notifications.RoleChanged;
36 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
37 import org.opendaylight.controller.cluster.raft.base.messages.CheckConsensusReached;
38 import org.opendaylight.controller.cluster.raft.base.messages.InitiateCaptureSnapshot;
39 import org.opendaylight.controller.cluster.raft.base.messages.LeaderTransitioning;
40 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
41 import org.opendaylight.controller.cluster.raft.base.messages.SwitchBehavior;
42 import org.opendaylight.controller.cluster.raft.behaviors.AbstractLeader;
43 import org.opendaylight.controller.cluster.raft.behaviors.AbstractRaftActorBehavior;
44 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
45 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
46 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
47 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
48 import org.opendaylight.controller.cluster.raft.client.messages.FollowerInfo;
49 import org.opendaylight.controller.cluster.raft.client.messages.GetOnDemandRaftState;
50 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
51 import org.opendaylight.controller.cluster.raft.client.messages.Shutdown;
52 import org.opendaylight.controller.cluster.raft.persisted.ApplyJournalEntries;
53 import org.opendaylight.controller.cluster.raft.persisted.NoopPayload;
54 import org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
55 import org.opendaylight.controller.cluster.raft.persisted.SimpleReplicatedLogEntry;
56 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
57 import org.opendaylight.yangtools.concepts.Identifier;
58 import org.opendaylight.yangtools.concepts.Immutable;
59
60 /**
61  * RaftActor encapsulates a state machine that needs to be kept synchronized
62  * in a cluster. It implements the RAFT algorithm as described in the paper
63  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
64  * In Search of an Understandable Consensus Algorithm</a>
65  *
66  * <p>
67  * RaftActor has 3 states and each state has a certain behavior associated
68  * with it. A Raft actor can behave as,
69  * <ul>
70  * <li> A Leader </li>
71  * <li> A Follower (or) </li>
72  * <li> A Candidate </li>
73  * </ul>
74  *
75  * <p>
76  * A RaftActor MUST be a Leader in order to accept requests from clients to
77  * change the state of it's encapsulated state machine. Once a RaftActor becomes
78  * a Leader it is also responsible for ensuring that all followers ultimately
79  * have the same log and therefore the same state machine as itself.
80  *
81  * <p>
82  * The current behavior of a RaftActor determines how election for leadership
83  * is initiated and how peer RaftActors react to request for votes.
84  *
85  * <p>
86  * Each RaftActor also needs to know the current election term. It uses this
87  * information for a couple of things. One is to simply figure out who it
88  * voted for in the last election. Another is to figure out if the message
89  * it received to update it's state is stale.
90  *
91  * <p>
92  * The RaftActor uses akka-persistence to store it's replicated log.
93  * Furthermore through it's behaviors a Raft Actor determines
94  * <ul>
95  * <li> when a log entry should be persisted </li>
96  * <li> when a log entry should be applied to the state machine (and) </li>
97  * <li> when a snapshot should be saved </li>
98  * </ul>
99  */
100 public abstract class RaftActor extends AbstractUntypedPersistentActor {
101
102     private static final long APPLY_STATE_DELAY_THRESHOLD_IN_NANOS = TimeUnit.MILLISECONDS.toNanos(50L); // 50 millis
103
104     /**
105      * This context should NOT be passed directly to any other actor it is
106      * only to be consumed by the RaftActorBehaviors.
107      */
108     private final RaftActorContextImpl context;
109
110     private final DelegatingPersistentDataProvider delegatingPersistenceProvider;
111
112     private final PersistentDataProvider persistentProvider;
113
114     private final BehaviorStateTracker behaviorStateTracker = new BehaviorStateTracker();
115
116     private RaftActorRecoverySupport raftRecovery;
117
118     private RaftActorSnapshotMessageSupport snapshotSupport;
119
120     private RaftActorServerConfigurationSupport serverConfigurationSupport;
121
122     private RaftActorLeadershipTransferCohort leadershipTransferInProgress;
123
124     private boolean shuttingDown;
125
126     protected RaftActor(String id, Map<String, String> peerAddresses,
127          Optional<ConfigParams> configParams, short payloadVersion) {
128
129         persistentProvider = new PersistentDataProvider(this);
130         delegatingPersistenceProvider = new RaftActorDelegatingPersistentDataProvider(null, persistentProvider);
131
132         context = new RaftActorContextImpl(this.getSelf(),
133             this.getContext(), id, new ElectionTermImpl(persistentProvider, id, LOG),
134             -1, -1, peerAddresses,
135             configParams.isPresent() ? configParams.get() : new DefaultConfigParamsImpl(),
136             delegatingPersistenceProvider, this::handleApplyState, LOG);
137
138         context.setPayloadVersion(payloadVersion);
139         context.setReplicatedLog(ReplicatedLogImpl.newInstance(context));
140     }
141
142     @Override
143     public void preStart() throws Exception {
144         LOG.info("Starting recovery for {} with journal batch size {}", persistenceId(),
145                 context.getConfigParams().getJournalRecoveryLogBatchSize());
146
147         super.preStart();
148
149         snapshotSupport = newRaftActorSnapshotMessageSupport();
150         serverConfigurationSupport = new RaftActorServerConfigurationSupport(this);
151     }
152
153     @Override
154     public void postStop() {
155         context.close();
156         super.postStop();
157     }
158
159     @Override
160     protected void handleRecover(Object message) {
161         if (raftRecovery == null) {
162             raftRecovery = newRaftActorRecoverySupport();
163         }
164
165         boolean recoveryComplete = raftRecovery.handleRecoveryMessage(message, persistentProvider);
166         if (recoveryComplete) {
167             onRecoveryComplete();
168
169             initializeBehavior();
170
171             raftRecovery = null;
172         }
173     }
174
175     protected RaftActorRecoverySupport newRaftActorRecoverySupport() {
176         return new RaftActorRecoverySupport(context, getRaftActorRecoveryCohort());
177     }
178
179     @VisibleForTesting
180     void initializeBehavior() {
181         changeCurrentBehavior(new Follower(context));
182     }
183
184     @VisibleForTesting
185     @SuppressWarnings("checkstyle:IllegalCatch")
186     protected void changeCurrentBehavior(RaftActorBehavior newBehavior) {
187         final RaftActorBehavior currentBehavior = getCurrentBehavior();
188         if (currentBehavior != null) {
189             try {
190                 currentBehavior.close();
191             } catch (Exception e) {
192                 LOG.warn("{}: Error closing behavior {}", persistence(), currentBehavior, e);
193             }
194         }
195
196         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
197         setCurrentBehavior(newBehavior);
198         handleBehaviorChange(state, newBehavior);
199     }
200
201     /**
202      * Method exposed for subclasses to plug-in their logic. This method is invoked by {@link #handleCommand(Object)}
203      * for messages which are not handled by this class. Subclasses overriding this class should fall back to this
204      * implementation for messages which they do not handle
205      *
206      * @param message Incoming command message
207      */
208     protected void handleNonRaftCommand(final Object message) {
209         unhandled(message);
210     }
211
212     /**
213      * Handles a message.
214      *
215      * @deprecated This method is not final for testing purposes. DO NOT OVERRIDE IT, override
216      * {@link #handleNonRaftCommand(Object)} instead.
217      */
218     @Deprecated
219     @Override
220     // FIXME: make this method final once our unit tests do not need to override it
221     protected void handleCommand(final Object message) {
222         if (serverConfigurationSupport.handleMessage(message, getSender())) {
223             return;
224         }
225         if (snapshotSupport.handleSnapshotMessage(message, getSender())) {
226             return;
227         }
228         if (message instanceof ApplyState) {
229             ApplyState applyState = (ApplyState) message;
230
231             if (!hasFollowers()) {
232                 // for single node, the capture should happen after the apply state
233                 // as we delete messages from the persistent journal which have made it to the snapshot
234                 // capturing the snapshot before applying makes the persistent journal and snapshot out of sync
235                 // and recovery shows data missing
236                 context.getReplicatedLog().captureSnapshotIfReady(applyState.getReplicatedLogEntry());
237
238                 context.getSnapshotManager().trimLog(context.getLastApplied());
239             }
240
241             possiblyHandleBehaviorMessage(message);
242         } else if (message instanceof ApplyJournalEntries) {
243             ApplyJournalEntries applyEntries = (ApplyJournalEntries) message;
244             LOG.debug("{}: Persisting ApplyJournalEntries with index={}", persistenceId(), applyEntries.getToIndex());
245
246             persistence().persistAsync(applyEntries, NoopProcedure.instance());
247
248         } else if (message instanceof FindLeader) {
249             getSender().tell(
250                 new FindLeaderReply(getLeaderAddress()),
251                 getSelf()
252             );
253         } else if (message instanceof GetOnDemandRaftState) {
254             onGetOnDemandRaftStats();
255         } else if (message instanceof InitiateCaptureSnapshot) {
256             captureSnapshot();
257         } else if (message instanceof SwitchBehavior) {
258             switchBehavior((SwitchBehavior) message);
259         } else if (message instanceof LeaderTransitioning) {
260             onLeaderTransitioning((LeaderTransitioning)message);
261         } else if (message instanceof Shutdown) {
262             onShutDown();
263         } else if (message instanceof Runnable) {
264             ((Runnable)message).run();
265         } else if (message instanceof NoopPayload) {
266             persistData(null, null, (NoopPayload)message, false);
267         } else if (!possiblyHandleBehaviorMessage(message)) {
268             handleNonRaftCommand(message);
269         }
270     }
271
272     private boolean possiblyHandleBehaviorMessage(final Object message) {
273         final RaftActorBehavior currentBehavior = getCurrentBehavior();
274         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
275
276         // A behavior indicates that it processed the change by returning a reference to the next behavior
277         // to be used. A null return indicates it has not processed the message and we should be passing it to
278         // the subclass for handling.
279         final RaftActorBehavior nextBehavior = currentBehavior.handleMessage(getSender(), message);
280         if (nextBehavior != null) {
281             switchBehavior(state, nextBehavior);
282             return true;
283         }
284
285         return false;
286     }
287
288     private void initiateLeadershipTransfer(final RaftActorLeadershipTransferCohort.OnComplete onComplete) {
289         LOG.debug("{}: Initiating leader transfer", persistenceId());
290
291         if (leadershipTransferInProgress == null) {
292             leadershipTransferInProgress = new RaftActorLeadershipTransferCohort(this);
293             leadershipTransferInProgress.addOnComplete(new RaftActorLeadershipTransferCohort.OnComplete() {
294                 @Override
295                 public void onSuccess(ActorRef raftActorRef) {
296                     leadershipTransferInProgress = null;
297                 }
298
299                 @Override
300                 public void onFailure(ActorRef raftActorRef) {
301                     leadershipTransferInProgress = null;
302                 }
303             });
304
305             leadershipTransferInProgress.addOnComplete(onComplete);
306             leadershipTransferInProgress.init();
307         } else {
308             LOG.debug("{}: prior leader transfer in progress - adding callback", persistenceId());
309             leadershipTransferInProgress.addOnComplete(onComplete);
310         }
311     }
312
313     private void onShutDown() {
314         LOG.debug("{}: onShutDown", persistenceId());
315
316         if (shuttingDown) {
317             return;
318         }
319
320         shuttingDown = true;
321
322         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
323         if (currentBehavior.state() != RaftState.Leader) {
324             // For non-leaders shutdown is a no-op
325             self().tell(PoisonPill.getInstance(), self());
326             return;
327         }
328
329         if (context.hasFollowers()) {
330             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
331                 @Override
332                 public void onSuccess(ActorRef raftActorRef) {
333                     LOG.debug("{}: leader transfer succeeded - sending PoisonPill", persistenceId());
334                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
335                 }
336
337                 @Override
338                 public void onFailure(ActorRef raftActorRef) {
339                     LOG.debug("{}: leader transfer failed - sending PoisonPill", persistenceId());
340                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
341                 }
342             });
343         } else {
344             pauseLeader(new TimedRunnable(context.getConfigParams().getElectionTimeOutInterval(), this) {
345                 @Override
346                 protected void doRun() {
347                     self().tell(PoisonPill.getInstance(), self());
348                 }
349
350                 @Override
351                 protected void doCancel() {
352                     self().tell(PoisonPill.getInstance(), self());
353                 }
354             });
355         }
356     }
357
358     private void onLeaderTransitioning(final LeaderTransitioning leaderTransitioning) {
359         LOG.debug("{}: onLeaderTransitioning: {}", persistenceId(), leaderTransitioning);
360         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
361         if (getRaftState() == RaftState.Follower && roleChangeNotifier.isPresent()
362                 && leaderTransitioning.getLeaderId().equals(getCurrentBehavior().getLeaderId())) {
363             roleChangeNotifier.get().tell(newLeaderStateChanged(getId(), null,
364                 getCurrentBehavior().getLeaderPayloadVersion()), getSelf());
365         }
366     }
367
368     private void switchBehavior(SwitchBehavior message) {
369         if (!getRaftActorContext().getRaftPolicy().automaticElectionsEnabled()) {
370             RaftState newState = message.getNewState();
371             if (newState == RaftState.Leader || newState == RaftState.Follower) {
372                 switchBehavior(behaviorStateTracker.capture(getCurrentBehavior()),
373                     AbstractRaftActorBehavior.createBehavior(context, message.getNewState()));
374                 getRaftActorContext().getTermInformation().updateAndPersist(message.getNewTerm(), "");
375             } else {
376                 LOG.warn("Switching to behavior : {} - not supported", newState);
377             }
378         }
379     }
380
381     private void switchBehavior(final BehaviorState oldBehaviorState, final RaftActorBehavior nextBehavior) {
382         setCurrentBehavior(nextBehavior);
383         handleBehaviorChange(oldBehaviorState, nextBehavior);
384     }
385
386     @VisibleForTesting
387     RaftActorSnapshotMessageSupport newRaftActorSnapshotMessageSupport() {
388         return new RaftActorSnapshotMessageSupport(context, getRaftActorSnapshotCohort());
389     }
390
391     private void onGetOnDemandRaftStats() {
392         // Debugging message to retrieve raft stats.
393
394         Map<String, String> peerAddresses = new HashMap<>();
395         Map<String, Boolean> peerVotingStates = new HashMap<>();
396         for (PeerInfo info: context.getPeers()) {
397             peerVotingStates.put(info.getId(), info.isVoting());
398             peerAddresses.put(info.getId(), info.getAddress() != null ? info.getAddress() : "");
399         }
400
401         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
402         OnDemandRaftState.Builder builder = OnDemandRaftState.builder()
403                 .commitIndex(context.getCommitIndex())
404                 .currentTerm(context.getTermInformation().getCurrentTerm())
405                 .inMemoryJournalDataSize(replicatedLog().dataSize())
406                 .inMemoryJournalLogSize(replicatedLog().size())
407                 .isSnapshotCaptureInitiated(context.getSnapshotManager().isCapturing())
408                 .lastApplied(context.getLastApplied())
409                 .lastIndex(replicatedLog().lastIndex())
410                 .lastTerm(replicatedLog().lastTerm())
411                 .leader(getLeaderId())
412                 .raftState(currentBehavior.state().toString())
413                 .replicatedToAllIndex(currentBehavior.getReplicatedToAllIndex())
414                 .snapshotIndex(replicatedLog().getSnapshotIndex())
415                 .snapshotTerm(replicatedLog().getSnapshotTerm())
416                 .votedFor(context.getTermInformation().getVotedFor())
417                 .isVoting(context.isVotingMember())
418                 .peerAddresses(peerAddresses)
419                 .peerVotingStates(peerVotingStates)
420                 .customRaftPolicyClassName(context.getConfigParams().getCustomRaftPolicyImplementationClass());
421
422         ReplicatedLogEntry lastLogEntry = replicatedLog().last();
423         if (lastLogEntry != null) {
424             builder.lastLogIndex(lastLogEntry.getIndex());
425             builder.lastLogTerm(lastLogEntry.getTerm());
426         }
427
428         if (getCurrentBehavior() instanceof AbstractLeader) {
429             AbstractLeader leader = (AbstractLeader)getCurrentBehavior();
430             Collection<String> followerIds = leader.getFollowerIds();
431             List<FollowerInfo> followerInfoList = Lists.newArrayListWithCapacity(followerIds.size());
432             for (String id: followerIds) {
433                 final FollowerLogInformation info = leader.getFollower(id);
434                 followerInfoList.add(new FollowerInfo(id, info.getNextIndex(), info.getMatchIndex(),
435                         info.isFollowerActive(), DurationFormatUtils.formatDurationHMS(info.timeSinceLastActivity()),
436                         context.getPeerInfo(info.getId()).isVoting()));
437             }
438
439             builder.followerInfoList(followerInfoList);
440         }
441
442         sender().tell(builder.build(), self());
443
444     }
445
446     private void handleBehaviorChange(BehaviorState oldBehaviorState, RaftActorBehavior currentBehavior) {
447         RaftActorBehavior oldBehavior = oldBehaviorState.getBehavior();
448
449         if (oldBehavior != currentBehavior) {
450             onStateChanged();
451         }
452
453         String lastLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastLeaderId();
454         String lastValidLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastValidLeaderId();
455         String oldBehaviorStateName = oldBehavior == null ? null : oldBehavior.state().name();
456
457         // it can happen that the state has not changed but the leader has changed.
458         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
459         if (!Objects.equals(lastLeaderId, currentBehavior.getLeaderId())
460                 || oldBehaviorState.getLeaderPayloadVersion() != currentBehavior.getLeaderPayloadVersion()) {
461             if (roleChangeNotifier.isPresent()) {
462                 roleChangeNotifier.get().tell(newLeaderStateChanged(getId(), currentBehavior.getLeaderId(),
463                         currentBehavior.getLeaderPayloadVersion()), getSelf());
464             }
465
466             onLeaderChanged(lastValidLeaderId, currentBehavior.getLeaderId());
467
468             if (leadershipTransferInProgress != null) {
469                 leadershipTransferInProgress.onNewLeader(currentBehavior.getLeaderId());
470             }
471
472             serverConfigurationSupport.onNewLeader(currentBehavior.getLeaderId());
473         }
474
475         if (roleChangeNotifier.isPresent()
476                 && (oldBehavior == null || oldBehavior.state() != currentBehavior.state())) {
477             roleChangeNotifier.get().tell(new RoleChanged(getId(), oldBehaviorStateName ,
478                     currentBehavior.state().name()), getSelf());
479         }
480     }
481
482     private void handleApplyState(ApplyState applyState) {
483         long startTime = System.nanoTime();
484
485         Payload payload = applyState.getReplicatedLogEntry().getData();
486         if (LOG.isDebugEnabled()) {
487             LOG.debug("{}: Applying state for log index {} data {}",
488                 persistenceId(), applyState.getReplicatedLogEntry().getIndex(), payload);
489         }
490
491         if (!(payload instanceof NoopPayload) && !(payload instanceof ServerConfigurationPayload)) {
492             applyState(applyState.getClientActor(), applyState.getIdentifier(), payload);
493         }
494
495         long elapsedTime = System.nanoTime() - startTime;
496         if (elapsedTime >= APPLY_STATE_DELAY_THRESHOLD_IN_NANOS) {
497             LOG.debug("ApplyState took more time than expected. Elapsed Time = {} ms ApplyState = {}",
498                     TimeUnit.NANOSECONDS.toMillis(elapsedTime), applyState);
499         }
500
501         // Send the ApplyState message back to self to handle further processing asynchronously.
502         self().tell(applyState, self());
503     }
504
505     protected LeaderStateChanged newLeaderStateChanged(String memberId, String leaderId, short leaderPayloadVersion) {
506         return new LeaderStateChanged(memberId, leaderId, leaderPayloadVersion);
507     }
508
509     @Override
510     public long snapshotSequenceNr() {
511         // When we do a snapshot capture, we also capture and save the sequence-number of the persistent journal,
512         // so that we can delete the persistent journal based on the saved sequence-number
513         // However , when akka replays the journal during recovery, it replays it from the sequence number when the
514         // snapshot was saved and not the number we saved. We would want to override it , by asking akka to use the
515         // last-sequence number known to us.
516         return context.getSnapshotManager().getLastSequenceNumber();
517     }
518
519     /**
520      * Persists the given Payload in the journal and replicates to any followers. After successful completion,
521      * {@link #applyState(ActorRef, Identifier, Object)} is notified.
522      *
523      * @param clientActor optional ActorRef that is provided via the applyState callback
524      * @param identifier the payload identifier
525      * @param data the payload data to persist
526      * @param batchHint if true, an attempt is made to delay immediate replication and batch the payload with
527      *        subsequent payloads for efficiency. Otherwise the payload is immediately replicated.
528      */
529     protected final void persistData(final ActorRef clientActor, final Identifier identifier, final Payload data,
530             final boolean batchHint) {
531         ReplicatedLogEntry replicatedLogEntry = new SimpleReplicatedLogEntry(
532             context.getReplicatedLog().lastIndex() + 1,
533             context.getTermInformation().getCurrentTerm(), data);
534         replicatedLogEntry.setPersistencePending(true);
535
536         LOG.debug("{}: Persist data {}", persistenceId(), replicatedLogEntry);
537
538         final RaftActorContext raftContext = getRaftActorContext();
539
540         boolean wasAppended = replicatedLog().appendAndPersist(replicatedLogEntry, persistedLogEntry -> {
541             // Clear the persistence pending flag in the log entry.
542             persistedLogEntry.setPersistencePending(false);
543
544             if (!hasFollowers()) {
545                 // Increment the Commit Index and the Last Applied values
546                 raftContext.setCommitIndex(persistedLogEntry.getIndex());
547                 raftContext.setLastApplied(persistedLogEntry.getIndex());
548
549                 // Apply the state immediately.
550                 handleApplyState(new ApplyState(clientActor, identifier, persistedLogEntry));
551
552                 // Send a ApplyJournalEntries message so that we write the fact that we applied
553                 // the state to durable storage
554                 self().tell(new ApplyJournalEntries(persistedLogEntry.getIndex()), self());
555
556             } else {
557                 context.getReplicatedLog().captureSnapshotIfReady(replicatedLogEntry);
558
559                 // Local persistence is complete so send the CheckConsensusReached message to the behavior (which
560                 // normally should still be the leader) to check if consensus has now been reached in conjunction with
561                 // follower replication.
562                 getCurrentBehavior().handleMessage(getSelf(), CheckConsensusReached.INSTANCE);
563             }
564         }, true);
565
566         if (wasAppended && hasFollowers()) {
567             // Send log entry for replication.
568             getCurrentBehavior().handleMessage(getSelf(), new Replicate(clientActor, identifier, replicatedLogEntry,
569                     !batchHint));
570         }
571     }
572
573     private ReplicatedLog replicatedLog() {
574         return context.getReplicatedLog();
575     }
576
577     protected String getId() {
578         return context.getId();
579     }
580
581     @VisibleForTesting
582     void setCurrentBehavior(RaftActorBehavior behavior) {
583         context.setCurrentBehavior(behavior);
584     }
585
586     protected RaftActorBehavior getCurrentBehavior() {
587         return context.getCurrentBehavior();
588     }
589
590     /**
591      * Derived actors can call the isLeader method to check if the current
592      * RaftActor is the Leader or not.
593      *
594      * @return true it this RaftActor is a Leader false otherwise
595      */
596     protected boolean isLeader() {
597         return context.getId().equals(getCurrentBehavior().getLeaderId());
598     }
599
600     protected final boolean isLeaderActive() {
601         return getRaftState() != RaftState.IsolatedLeader && getRaftState() != RaftState.PreLeader
602                 && !shuttingDown && !isLeadershipTransferInProgress();
603     }
604
605     private boolean isLeadershipTransferInProgress() {
606         return leadershipTransferInProgress != null && leadershipTransferInProgress.isTransferring();
607     }
608
609     /**
610      * Derived actor can call getLeader if they need a reference to the Leader.
611      * This would be useful for example in forwarding a request to an actor
612      * which is the leader
613      *
614      * @return A reference to the leader if known, null otherwise
615      */
616     public ActorSelection getLeader() {
617         String leaderAddress = getLeaderAddress();
618
619         if (leaderAddress == null) {
620             return null;
621         }
622
623         return context.actorSelection(leaderAddress);
624     }
625
626     /**
627      * Returns the id of the current leader.
628      *
629      * @return the current leader's id
630      */
631     protected final String getLeaderId() {
632         return getCurrentBehavior().getLeaderId();
633     }
634
635     @VisibleForTesting
636     protected final RaftState getRaftState() {
637         return getCurrentBehavior().state();
638     }
639
640     protected Long getCurrentTerm() {
641         return context.getTermInformation().getCurrentTerm();
642     }
643
644     protected RaftActorContext getRaftActorContext() {
645         return context;
646     }
647
648     protected void updateConfigParams(ConfigParams configParams) {
649
650         // obtain the RaftPolicy for oldConfigParams and the updated one.
651         String oldRaftPolicy = context.getConfigParams().getCustomRaftPolicyImplementationClass();
652         String newRaftPolicy = configParams.getCustomRaftPolicyImplementationClass();
653
654         LOG.debug("{}: RaftPolicy used with prev.config {}, RaftPolicy used with newConfig {}", persistenceId(),
655             oldRaftPolicy, newRaftPolicy);
656         context.setConfigParams(configParams);
657         if (!Objects.equals(oldRaftPolicy, newRaftPolicy)) {
658             // The RaftPolicy was modified. If the current behavior is Follower then re-initialize to Follower
659             // but transfer the previous leaderId so it doesn't immediately try to schedule an election. This
660             // avoids potential disruption. Otherwise, switch to Follower normally.
661             RaftActorBehavior behavior = getCurrentBehavior();
662             if (behavior != null && behavior.state() == RaftState.Follower) {
663                 String previousLeaderId = behavior.getLeaderId();
664                 short previousLeaderPayloadVersion = behavior.getLeaderPayloadVersion();
665
666                 LOG.debug("{}: Re-initializing to Follower with previous leaderId {}", persistenceId(),
667                         previousLeaderId);
668
669                 changeCurrentBehavior(new Follower(context, previousLeaderId, previousLeaderPayloadVersion));
670             } else {
671                 initializeBehavior();
672             }
673         }
674     }
675
676     public final DataPersistenceProvider persistence() {
677         return delegatingPersistenceProvider.getDelegate();
678     }
679
680     public void setPersistence(DataPersistenceProvider provider) {
681         delegatingPersistenceProvider.setDelegate(provider);
682     }
683
684     protected void setPersistence(boolean persistent) {
685         DataPersistenceProvider currentPersistence = persistence();
686         if (persistent && (currentPersistence == null || !currentPersistence.isRecoveryApplicable())) {
687             setPersistence(new PersistentDataProvider(this));
688
689             if (getCurrentBehavior() != null) {
690                 LOG.info("{}: Persistence has been enabled - capturing snapshot", persistenceId());
691                 captureSnapshot();
692             }
693         } else if (!persistent && (currentPersistence == null || currentPersistence.isRecoveryApplicable())) {
694             setPersistence(new NonPersistentDataProvider() {
695                 /**
696                  * The way snapshotting works is,
697                  * <ol>
698                  * <li> RaftActor calls createSnapshot on the Shard
699                  * <li> Shard sends a CaptureSnapshotReply and RaftActor then calls saveSnapshot
700                  * <li> When saveSnapshot is invoked on the akka-persistence API it uses the SnapshotStore to save
701                  * the snapshot. The SnapshotStore sends SaveSnapshotSuccess or SaveSnapshotFailure. When the
702                  * RaftActor gets SaveSnapshot success it commits the snapshot to the in-memory journal. This
703                  * commitSnapshot is mimicking what is done in SaveSnapshotSuccess.
704                  * </ol>
705                  */
706                 @Override
707                 public void saveSnapshot(Object object) {
708                     // Make saving Snapshot successful
709                     // Committing the snapshot here would end up calling commit in the creating state which would
710                     // be a state violation. That's why now we send a message to commit the snapshot.
711                     self().tell(RaftActorSnapshotMessageSupport.COMMIT_SNAPSHOT, self());
712                 }
713             });
714         }
715     }
716
717     /**
718      * setPeerAddress sets the address of a known peer at a later time.
719      *
720      * <p>
721      * This is to account for situations where a we know that a peer
722      * exists but we do not know an address up-front. This may also be used in
723      * situations where a known peer starts off in a different location and we
724      * need to change it's address
725      *
726      * <p>
727      * Note that if the peerId does not match the list of peers passed to
728      * this actor during construction an IllegalStateException will be thrown.
729      */
730     protected void setPeerAddress(String peerId, String peerAddress) {
731         context.setPeerAddress(peerId, peerAddress);
732     }
733
734     /**
735      * The applyState method will be called by the RaftActor when some data
736      * needs to be applied to the actor's state.
737      *
738      * @param clientActor A reference to the client who sent this message. This
739      *                    is the same reference that was passed to persistData
740      *                    by the derived actor. clientActor may be null when
741      *                    the RaftActor is behaving as a follower or during
742      *                    recovery.
743      * @param identifier  The identifier of the persisted data. This is also
744      *                    the same identifier that was passed to persistData by
745      *                    the derived actor. identifier may be null when
746      *                    the RaftActor is behaving as a follower or during
747      *                    recovery
748      * @param data        A piece of data that was persisted by the persistData call.
749      *                    This should NEVER be null.
750      */
751     protected abstract void applyState(ActorRef clientActor, Identifier identifier, Object data);
752
753     /**
754      * Returns the RaftActorRecoveryCohort to participate in persistence recovery.
755      */
756     @Nonnull
757     protected abstract RaftActorRecoveryCohort getRaftActorRecoveryCohort();
758
759     /**
760      * This method is called when recovery is complete.
761      */
762     protected abstract void onRecoveryComplete();
763
764     /**
765      * Returns the RaftActorSnapshotCohort to participate in snapshot captures.
766      */
767     @Nonnull
768     protected abstract RaftActorSnapshotCohort getRaftActorSnapshotCohort();
769
770     /**
771      * This method will be called by the RaftActor when the state of the
772      * RaftActor changes. The derived actor can then use methods like
773      * isLeader or getLeader to do something useful
774      */
775     protected abstract void onStateChanged();
776
777     /**
778      * Notifier Actor for this RaftActor to notify when a role change happens.
779      *
780      * @return ActorRef - ActorRef of the notifier or Optional.absent if none.
781      */
782     protected abstract Optional<ActorRef> getRoleChangeNotifier();
783
784     /**
785      * This method is called prior to operations such as leadership transfer and actor shutdown when the leader
786      * must pause or stop its duties. This method allows derived classes to gracefully pause or finish current
787      * work prior to performing the operation. On completion of any work, the run method must be called on the
788      * given Runnable to proceed with the given operation. <b>Important:</b> the run method must be called on
789      * this actor's thread dispatcher as as it modifies internal state.
790      *
791      * <p>
792      * The default implementation immediately runs the operation.
793      *
794      * @param operation the operation to run
795      */
796     protected void pauseLeader(Runnable operation) {
797         operation.run();
798     }
799
800     protected void onLeaderChanged(String oldLeader, String newLeader) {
801     }
802
803     private String getLeaderAddress() {
804         if (isLeader()) {
805             return getSelf().path().toString();
806         }
807         String leaderId = getLeaderId();
808         if (leaderId == null) {
809             return null;
810         }
811         String peerAddress = context.getPeerAddress(leaderId);
812         LOG.debug("{}: getLeaderAddress leaderId = {} peerAddress = {}", persistenceId(), leaderId, peerAddress);
813
814         return peerAddress;
815     }
816
817     protected boolean hasFollowers() {
818         return getRaftActorContext().hasFollowers();
819     }
820
821     private void captureSnapshot() {
822         SnapshotManager snapshotManager = context.getSnapshotManager();
823
824         if (!snapshotManager.isCapturing()) {
825             final long idx = getCurrentBehavior().getReplicatedToAllIndex();
826             LOG.debug("Take a snapshot of current state. lastReplicatedLog is {} and replicatedToAllIndex is {}",
827                 replicatedLog().last(), idx);
828
829             snapshotManager.capture(replicatedLog().last(), idx);
830         }
831     }
832
833     /**
834      * Switch this member to non-voting status. This is a no-op for all behaviors except when we are the leader,
835      * in which case we need to step down.
836      */
837     void becomeNonVoting() {
838         if (isLeader()) {
839             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
840                 @Override
841                 public void onSuccess(ActorRef raftActorRef) {
842                     LOG.debug("{}: leader transfer succeeded after change to non-voting", persistenceId());
843                     ensureFollowerState();
844                 }
845
846                 @Override
847                 public void onFailure(ActorRef raftActorRef) {
848                     LOG.debug("{}: leader transfer failed after change to non-voting", persistenceId());
849                     ensureFollowerState();
850                 }
851
852                 private void ensureFollowerState() {
853                     // Whether or not leadership transfer succeeded, we have to step down as leader and
854                     // switch to Follower so ensure that.
855                     if (getRaftState() != RaftState.Follower) {
856                         initializeBehavior();
857                     }
858                 }
859             });
860         }
861     }
862
863     /**
864      * A point-in-time capture of {@link RaftActorBehavior} state critical for transitioning between behaviors.
865      */
866     private abstract static class BehaviorState implements Immutable {
867         @Nullable abstract RaftActorBehavior getBehavior();
868
869         @Nullable abstract String getLastValidLeaderId();
870
871         @Nullable abstract String getLastLeaderId();
872
873         @Nullable abstract short getLeaderPayloadVersion();
874     }
875
876     /**
877      * A {@link BehaviorState} corresponding to non-null {@link RaftActorBehavior} state.
878      */
879     private static final class SimpleBehaviorState extends BehaviorState {
880         private final RaftActorBehavior behavior;
881         private final String lastValidLeaderId;
882         private final String lastLeaderId;
883         private final short leaderPayloadVersion;
884
885         SimpleBehaviorState(final String lastValidLeaderId, final String lastLeaderId,
886                 final RaftActorBehavior behavior) {
887             this.lastValidLeaderId = lastValidLeaderId;
888             this.lastLeaderId = lastLeaderId;
889             this.behavior = Preconditions.checkNotNull(behavior);
890             this.leaderPayloadVersion = behavior.getLeaderPayloadVersion();
891         }
892
893         @Override
894         RaftActorBehavior getBehavior() {
895             return behavior;
896         }
897
898         @Override
899         String getLastValidLeaderId() {
900             return lastValidLeaderId;
901         }
902
903         @Override
904         short getLeaderPayloadVersion() {
905             return leaderPayloadVersion;
906         }
907
908         @Override
909         String getLastLeaderId() {
910             return lastLeaderId;
911         }
912     }
913
914     /**
915      * Class tracking behavior-related information, which we need to keep around and pass across behavior switches.
916      * An instance is created for each RaftActor. It has two functions:
917      * - it keeps track of the last leader ID we have encountered since we have been created
918      * - it creates state capture needed to transition from one behavior to the next
919      */
920     private static final class BehaviorStateTracker {
921         /**
922          * A {@link BehaviorState} corresponding to null {@link RaftActorBehavior} state. Since null behavior is only
923          * allowed before we receive the first message, we know the leader ID to be null.
924          */
925         private static final BehaviorState NULL_BEHAVIOR_STATE = new BehaviorState() {
926             @Override
927             RaftActorBehavior getBehavior() {
928                 return null;
929             }
930
931             @Override
932             String getLastValidLeaderId() {
933                 return null;
934             }
935
936             @Override
937             short getLeaderPayloadVersion() {
938                 return -1;
939             }
940
941             @Override
942             String getLastLeaderId() {
943                 return null;
944             }
945         };
946
947         private String lastValidLeaderId;
948         private String lastLeaderId;
949
950         BehaviorState capture(final RaftActorBehavior behavior) {
951             if (behavior == null) {
952                 Verify.verify(lastValidLeaderId == null, "Null behavior with non-null last leader");
953                 return NULL_BEHAVIOR_STATE;
954             }
955
956             lastLeaderId = behavior.getLeaderId();
957             if (lastLeaderId != null) {
958                 lastValidLeaderId = lastLeaderId;
959             }
960
961             return new SimpleBehaviorState(lastValidLeaderId, lastLeaderId, behavior);
962         }
963     }
964
965 }

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