/*
* 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 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.internal.messages.ApplySnapshot;
import org.opendaylight.controller.cluster.raft.internal.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.InstallSnapshot;
import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
/**
* The behavior of a RaftActor in the Follower state
*
*
* - Respond to RPCs from candidates and leaders
*
- If election timeout elapses without receiving AppendEntries
* RPC from current leader or granting vote to candidate:
* convert to candidate
*
*/
public class Follower extends AbstractRaftActorBehavior {
public Follower(RaftActorContext context) {
super(context);
scheduleElection(electionDuration());
}
@Override protected RaftState handleAppendEntries(ActorRef sender,
AppendEntries appendEntries) {
// TODO : Refactor this method into a bunch of smaller methods
// to make it easier to read. Before refactoring ensure tests
// cover the code properly
// 1. Reply false if term < currentTerm (§5.1)
// This is handled in the appendEntries method of the base class
// If we got here then we do appear to be talking to the leader
leaderId = appendEntries.getLeaderId();
// 2. Reply false if log doesn’t contain an entry at prevLogIndex
// whose term matches prevLogTerm (§5.3)
ReplicatedLogEntry previousEntry = context.getReplicatedLog()
.get(appendEntries.getPrevLogIndex());
boolean outOfSync = true;
// First check if the logs are in sync or not
if (lastIndex() == -1
&& appendEntries.getPrevLogIndex() != -1) {
// The follower's log is out of sync because the leader does have
// an entry at prevLogIndex and this follower has no entries in
// it's log.
context.getLogger().debug(
"The followers log is empty and the senders prevLogIndex is {}",
appendEntries.getPrevLogIndex());
} else if (lastIndex() > -1
&& appendEntries.getPrevLogIndex() != -1
&& previousEntry == null) {
// The follower's log is out of sync because the Leader's
// prevLogIndex entry was not found in it's log
context.getLogger().debug(
"The log is not empty but the prevLogIndex {} was not found in it",
appendEntries.getPrevLogIndex());
} else if (lastIndex() > -1
&& previousEntry != null
&& previousEntry.getTerm()!= appendEntries.getPrevLogTerm()) {
// The follower's log is out of sync because the Leader's
// prevLogIndex entry does exist in the follower's log but it has
// a different term in it
context.getLogger().debug(
"Cannot append entries because previous entry term {} is not equal to append entries prevLogTerm {}"
, previousEntry.getTerm()
, appendEntries.getPrevLogTerm());
} else {
outOfSync = false;
}
if (outOfSync) {
// We found that the log was out of sync so just send a negative
// reply and return
sender.tell(
new AppendEntriesReply(context.getId(), currentTerm(), false,
lastIndex(), lastTerm()), actor()
);
return state();
}
if (appendEntries.getEntries() != null
&& appendEntries.getEntries().size() > 0) {
context.getLogger().debug(
"Number of entries to be appended = " + appendEntries
.getEntries().size()
);
// 3. If an existing entry conflicts with a new one (same index
// but different terms), delete the existing entry and all that
// follow it (§5.3)
int addEntriesFrom = 0;
if (context.getReplicatedLog().size() > 0) {
// Find the entry up until which the one that is not in the
// follower's log
for (int i = 0;
i < appendEntries.getEntries()
.size(); i++, addEntriesFrom++) {
ReplicatedLogEntry matchEntry =
appendEntries.getEntries().get(i);
ReplicatedLogEntry newEntry = context.getReplicatedLog()
.get(matchEntry.getIndex());
if (newEntry == null) {
//newEntry not found in the log
break;
}
if (newEntry.getTerm() == matchEntry
.getTerm()) {
continue;
}
context.getLogger().debug(
"Removing entries from log starting at "
+ matchEntry.getIndex()
);
// Entries do not match so remove all subsequent entries
context.getReplicatedLog()
.removeFromAndPersist(matchEntry.getIndex());
break;
}
}
context.getLogger().debug(
"After cleanup entries to be added from = " + (addEntriesFrom
+ lastIndex())
);
// 4. Append any new entries not already in the log
for (int i = addEntriesFrom;
i < appendEntries.getEntries().size(); i++) {
context.getLogger().debug(
"Append entry to log " + appendEntries.getEntries().get(i).getData()
.toString()
);
context.getReplicatedLog()
.appendAndPersist(appendEntries.getEntries().get(i));
}
context.getLogger().debug(
"Log size is now " + context.getReplicatedLog().size());
}
// 5. If leaderCommit > commitIndex, set commitIndex =
// min(leaderCommit, index of last new entry)
long prevCommitIndex = context.getCommitIndex();
context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(),
context.getReplicatedLog().lastIndex()));
if (prevCommitIndex != context.getCommitIndex()) {
context.getLogger()
.debug("Commit index set to " + context.getCommitIndex());
}
// If commitIndex > lastApplied: increment lastApplied, apply
// log[lastApplied] to state machine (§5.3)
if (appendEntries.getLeaderCommit() > context.getLastApplied()) {
applyLogToStateMachine(appendEntries.getLeaderCommit());
}
sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), true,
lastIndex(), lastTerm()), actor());
return state();
}
@Override protected RaftState handleAppendEntriesReply(ActorRef sender,
AppendEntriesReply appendEntriesReply) {
return state();
}
@Override protected RaftState handleRequestVoteReply(ActorRef sender,
RequestVoteReply requestVoteReply) {
return state();
}
@Override public RaftState state() {
return RaftState.Follower;
}
@Override public RaftState handleMessage(ActorRef sender, Object originalMessage) {
Object message = fromSerializableMessage(originalMessage);
if (message instanceof RaftRPC) {
RaftRPC rpc = (RaftRPC) message;
// If RPC request or response contains term T > currentTerm:
// set currentTerm = T, convert to follower (§5.1)
// This applies to all RPC messages and responses
if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
}
}
if (message instanceof ElectionTimeout) {
return RaftState.Candidate;
} else if (message instanceof InstallSnapshot) {
InstallSnapshot installSnapshot = (InstallSnapshot) message;
actor().tell(new ApplySnapshot(installSnapshot.getData()), actor());
}
scheduleElection(electionDuration());
return super.handleMessage(sender, message);
}
@Override public void close() throws Exception {
stopElection();
}
}