/*
* Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0 which accompanies this distribution,
* and is available at http://www.eclipse.org/legal/epl-v10.html
*/
package org.opendaylight.controller.cluster.raft.behaviors;
import akka.actor.ActorRef;
import akka.actor.Cancellable;
import com.google.common.base.Preconditions;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import org.opendaylight.controller.cluster.raft.ClientRequestTracker;
import org.opendaylight.controller.cluster.raft.RaftActorContext;
import org.opendaylight.controller.cluster.raft.RaftState;
import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
import org.opendaylight.controller.cluster.raft.messages.RequestVote;
import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
import org.opendaylight.controller.cluster.raft.persisted.ApplyJournalEntries;
import org.slf4j.Logger;
import scala.concurrent.duration.FiniteDuration;
/**
* Abstract class that provides common code for a RaftActor behavior.
*/
public abstract class AbstractRaftActorBehavior implements RaftActorBehavior {
/**
* Information about the RaftActor whose behavior this class represents.
*/
protected final RaftActorContext context;
/**
* Used for message logging.
*/
protected final Logger log;
/**
* Prepended to log messages to provide appropriate context.
*/
private final String logName;
/**
* The RaftState corresponding to his behavior.
*/
private final RaftState state;
/**
* Used to cancel a scheduled election.
*/
private Cancellable electionCancel = null;
/**
* The index of the last log entry that has been replicated to all raft peers.
*/
private long replicatedToAllIndex = -1;
AbstractRaftActorBehavior(final RaftActorContext context, final RaftState state) {
this.context = Preconditions.checkNotNull(context);
this.state = Preconditions.checkNotNull(state);
this.log = context.getLogger();
logName = String.format("%s (%s)", context.getId(), state);
}
public static RaftActorBehavior createBehavior(final RaftActorContext context, final RaftState state) {
switch (state) {
case Candidate:
return new Candidate(context);
case Follower:
return new Follower(context);
case IsolatedLeader:
return new IsolatedLeader(context);
case Leader:
return new Leader(context);
case PreLeader:
return new PreLeader(context);
default:
throw new IllegalArgumentException("Unhandled state " + state);
}
}
@Override
public final RaftState state() {
return state;
}
protected final String logName() {
return logName;
}
@Override
public void setReplicatedToAllIndex(long replicatedToAllIndex) {
this.replicatedToAllIndex = replicatedToAllIndex;
}
@Override
public long getReplicatedToAllIndex() {
return replicatedToAllIndex;
}
/**
* Derived classes should not directly handle AppendEntries messages it
* should let the base class handle it first. Once the base class handles
* the AppendEntries message and does the common actions that are applicable
* in all RaftState's it will delegate the handling of the AppendEntries
* message to the derived class to do more state specific handling by calling
* this method
*
* @param sender The actor that sent this message
* @param appendEntries The AppendEntries message
* @return a new behavior if it was changed or the current behavior
*/
protected abstract RaftActorBehavior handleAppendEntries(ActorRef sender,
AppendEntries appendEntries);
/**
* Handles the common logic for the AppendEntries message and delegates handling to the derived class.
*
* @param sender the ActorRef that sent the message
* @param appendEntries the message
* @return a new behavior if it was changed or the current behavior
*/
protected RaftActorBehavior appendEntries(ActorRef sender, AppendEntries appendEntries) {
// 1. Reply false if term < currentTerm (§5.1)
if (appendEntries.getTerm() < currentTerm()) {
log.info("{}: Cannot append entries because sender's term {} is less than {}", logName(),
appendEntries.getTerm(), currentTerm());
sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex(), lastTerm(),
context.getPayloadVersion()), actor());
return this;
}
return handleAppendEntries(sender, appendEntries);
}
/**
* Derived classes should not directly handle AppendEntriesReply messages it
* should let the base class handle it first. Once the base class handles
* the AppendEntriesReply message and does the common actions that are
* applicable in all RaftState's it will delegate the handling of the
* AppendEntriesReply message to the derived class to do more state specific
* handling by calling this method
*
* @param sender The actor that sent this message
* @param appendEntriesReply The AppendEntriesReply message
* @return a new behavior if it was changed or the current behavior
*/
protected abstract RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
AppendEntriesReply appendEntriesReply);
/**
* Handles the logic for the RequestVote message that is common for all behaviors.
*
* @param sender the ActorRef that sent the message
* @param requestVote the message
* @return a new behavior if it was changed or the current behavior
*/
protected RaftActorBehavior requestVote(ActorRef sender, RequestVote requestVote) {
log.debug("{}: In requestVote: {} - currentTerm: {}, votedFor: {}, lastIndex: {}, lastTerm: {}", logName(),
requestVote, currentTerm(), votedFor(), lastIndex(), lastTerm());
boolean grantVote = canGrantVote(requestVote);
if (grantVote) {
context.getTermInformation().updateAndPersist(requestVote.getTerm(), requestVote.getCandidateId());
}
RequestVoteReply reply = new RequestVoteReply(currentTerm(), grantVote);
log.debug("{}: requestVote returning: {}", logName(), reply);
sender.tell(reply, actor());
return this;
}
protected boolean canGrantVote(RequestVote requestVote) {
boolean grantVote = false;
// Reply false if term < currentTerm (§5.1)
if (requestVote.getTerm() < currentTerm()) {
grantVote = false;
// If votedFor is null or candidateId, and candidate’s log is at
// least as up-to-date as receiver’s log, grant vote (§5.2, §5.4)
} else if (votedFor() == null || votedFor()
.equals(requestVote.getCandidateId())) {
boolean candidateLatest = false;
// From §5.4.1
// Raft determines which of two logs is more up-to-date
// by comparing the index and term of the last entries in the
// logs. If the logs have last entries with different terms, then
// the log with the later term is more up-to-date. If the logs
// end with the same term, then whichever log is longer is
// more up-to-date.
if (requestVote.getLastLogTerm() > lastTerm()) {
candidateLatest = true;
} else if (requestVote.getLastLogTerm() == lastTerm()
&& requestVote.getLastLogIndex() >= lastIndex()) {
candidateLatest = true;
}
if (candidateLatest) {
grantVote = true;
}
}
return grantVote;
}
/**
* Derived classes should not directly handle RequestVoteReply messages it
* should let the base class handle it first. Once the base class handles
* the RequestVoteReply message and does the common actions that are
* applicable in all RaftState's it will delegate the handling of the
* RequestVoteReply message to the derived class to do more state specific
* handling by calling this method
*
* @param sender The actor that sent this message
* @param requestVoteReply The RequestVoteReply message
* @return a new behavior if it was changed or the current behavior
*/
protected abstract RaftActorBehavior handleRequestVoteReply(ActorRef sender,
RequestVoteReply requestVoteReply);
/**
* Returns a duration for election with an additional variance for randomness.
*
* @return a random election duration
*/
protected FiniteDuration electionDuration() {
long variance = new Random().nextInt(context.getConfigParams().getElectionTimeVariance());
return context.getConfigParams().getElectionTimeOutInterval().$plus(
new FiniteDuration(variance, TimeUnit.MILLISECONDS));
}
/**
* Stops the currently scheduled election.
*/
protected void stopElection() {
if (electionCancel != null && !electionCancel.isCancelled()) {
electionCancel.cancel();
}
}
protected boolean canStartElection() {
return context.getRaftPolicy().automaticElectionsEnabled() && context.isVotingMember();
}
/**
* Schedule a new election.
*
* @param interval the duration after which we should trigger a new election
*/
protected void scheduleElection(FiniteDuration interval) {
stopElection();
// Schedule an election. When the scheduler triggers an ElectionTimeout message is sent to itself
electionCancel = context.getActorSystem().scheduler().scheduleOnce(interval, context.getActor(),
ElectionTimeout.INSTANCE, context.getActorSystem().dispatcher(), context.getActor());
}
/**
* Returns the current election term.
*
* @return the current term
*/
protected long currentTerm() {
return context.getTermInformation().getCurrentTerm();
}
/**
* Returns the id of the candidate that this server voted for in current term.
*
* @return the candidate for whom we voted in the current term
*/
protected String votedFor() {
return context.getTermInformation().getVotedFor();
}
/**
* Returns the actor associated with this behavior.
*
* @return the actor
*/
protected ActorRef actor() {
return context.getActor();
}
/**
* Returns the term of the last entry in the log.
*
* @return the term
*/
protected long lastTerm() {
return context.getReplicatedLog().lastTerm();
}
/**
* Returns the index of the last entry in the log.
*
* @return the index
*/
protected long lastIndex() {
return context.getReplicatedLog().lastIndex();
}
/**
* Removes and returns the ClientRequestTracker for the specified log index.
* @param logIndex the log index
* @return the ClientRequestTracker or null if none available
*/
protected ClientRequestTracker removeClientRequestTracker(long logIndex) {
return null;
}
/**
* Returns the actual index of the entry in replicated log for the given index or -1 if not found.
*
* @return the log entry index or -1 if not found
*/
protected long getLogEntryIndex(long index) {
if (index == context.getReplicatedLog().getSnapshotIndex()) {
return context.getReplicatedLog().getSnapshotIndex();
}
ReplicatedLogEntry entry = context.getReplicatedLog().get(index);
if (entry != null) {
return entry.getIndex();
}
return -1;
}
/**
* Returns the actual term of the entry in replicated log for the given index or -1 if not found.
*
* @return the log entry term or -1 if not found
*/
protected long getLogEntryTerm(long index) {
if (index == context.getReplicatedLog().getSnapshotIndex()) {
return context.getReplicatedLog().getSnapshotTerm();
}
ReplicatedLogEntry entry = context.getReplicatedLog().get(index);
if (entry != null) {
return entry.getTerm();
}
return -1;
}
/**
* Applies the log entries up to the specified index that is known to be committed to the state machine.
*
* @param index the log index
*/
protected void applyLogToStateMachine(final long index) {
// Now maybe we apply to the state machine
for (long i = context.getLastApplied() + 1; i < index + 1; i++) {
ReplicatedLogEntry replicatedLogEntry = context.getReplicatedLog().get(i);
if (replicatedLogEntry != null) {
// Send a local message to the local RaftActor (it's derived class to be
// specific to apply the log to it's index)
final ApplyState applyState;
final ClientRequestTracker tracker = removeClientRequestTracker(i);
if (tracker != null) {
applyState = new ApplyState(tracker.getClientActor(), tracker.getIdentifier(), replicatedLogEntry);
} else {
applyState = new ApplyState(null, null, replicatedLogEntry);
}
log.debug("{}: Setting last applied to {}", logName(), i);
context.setLastApplied(i);
context.getApplyStateConsumer().accept(applyState);
} else {
//if one index is not present in the log, no point in looping
// around as the rest wont be present either
log.warn("{}: Missing index {} from log. Cannot apply state. Ignoring {} to {}",
logName(), i, i, index);
break;
}
}
// send a message to persist a ApplyLogEntries marker message into akka's persistent journal
// will be used during recovery
//in case if the above code throws an error and this message is not sent, it would be fine
// as the append entries received later would initiate add this message to the journal
actor().tell(new ApplyJournalEntries(context.getLastApplied()), actor());
}
@Override
public RaftActorBehavior handleMessage(ActorRef sender, Object message) {
if (message instanceof AppendEntries) {
return appendEntries(sender, (AppendEntries) message);
} else if (message instanceof AppendEntriesReply) {
return handleAppendEntriesReply(sender, (AppendEntriesReply) message);
} else if (message instanceof RequestVote) {
return requestVote(sender, (RequestVote) message);
} else if (message instanceof RequestVoteReply) {
return handleRequestVoteReply(sender, (RequestVoteReply) message);
} else {
return null;
}
}
@Override
public RaftActorBehavior switchBehavior(RaftActorBehavior behavior) {
return internalSwitchBehavior(behavior);
}
protected RaftActorBehavior internalSwitchBehavior(RaftState newState) {
return internalSwitchBehavior(createBehavior(context, newState));
}
@SuppressWarnings("checkstyle:IllegalCatch")
protected RaftActorBehavior internalSwitchBehavior(RaftActorBehavior newBehavior) {
if (!context.getRaftPolicy().automaticElectionsEnabled()) {
return this;
}
log.info("{} :- Switching from behavior {} to {}, election term: {}", logName(), this.state(),
newBehavior.state(), context.getTermInformation().getCurrentTerm());
try {
close();
} catch (RuntimeException e) {
log.error("{}: Failed to close behavior : {}", logName(), this.state(), e);
}
return newBehavior;
}
protected int getMajorityVoteCount(int numPeers) {
// Votes are required from a majority of the peers including self.
// The numMajority field therefore stores a calculated value
// of the number of votes required for this candidate to win an
// election based on it's known peers.
// If a peer was added during normal operation and raft replicas
// came to know about them then the new peer would also need to be
// taken into consideration when calculating this value.
// Here are some examples for what the numMajority would be for n
// peers
// 0 peers = 1 numMajority -: (0 + 1) / 2 + 1 = 1
// 2 peers = 2 numMajority -: (2 + 1) / 2 + 1 = 2
// 4 peers = 3 numMajority -: (4 + 1) / 2 + 1 = 3
int numMajority = 0;
if (numPeers > 0) {
int self = 1;
numMajority = (numPeers + self) / 2 + 1;
}
return numMajority;
}
/**
* Performs a snapshot with no capture on the replicated log. It clears the log from the supplied index or
* lastApplied-1 which ever is minimum.
*
* @param snapshotCapturedIndex the index from which to clear
*/
protected void performSnapshotWithoutCapture(final long snapshotCapturedIndex) {
long actualIndex = context.getSnapshotManager().trimLog(snapshotCapturedIndex);
if (actualIndex != -1) {
setReplicatedToAllIndex(actualIndex);
}
}
protected String getId() {
return context.getId();
}
}