opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Candidate.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.behaviors;
  10
  11 import akka.actor.ActorRef;
  12 import akka.actor.ActorSelection;
  13 import java.util.ArrayList;
  14 import java.util.Collection;
  15 import org.opendaylight.controller.cluster.raft.PeerInfo;
  16 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  17 import org.opendaylight.controller.cluster.raft.RaftState;
  18 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  19 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  20 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  21 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  22 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
  23 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  24
  25 /**
  26  * The behavior of a RaftActor when it is in the CandidateState
  27  * <p/>
  28  * Candidates (§5.2):
  29  * <ul>
  30  * <li> On conversion to candidate, start election:
  31  * <ul>
  32  * <li> Increment currentTerm
  33  * <li> Vote for self
  34  * <li> Reset election timer
  35  * <li> Send RequestVote RPCs to all other servers
  36  * </ul>
  37  * <li> If votes received from majority of servers: become leader
  38  * <li> If AppendEntries RPC received from new leader: convert to
  39  * follower
  40  * <li> If election timeout elapses: start new election
  41  * </ul>
  42  */
  43 public class Candidate extends AbstractRaftActorBehavior {
  44
  45     private int voteCount;
  46
  47     private final int votesRequired;
  48
  49     private final Collection<String> votingPeers = new ArrayList<>();
  50
  51     public Candidate(RaftActorContext context) {
  52         super(context, RaftState.Candidate);
  53
  54         for(PeerInfo peer: context.getPeers()) {
  55             if(peer.isVoting()) {
  56                 votingPeers.add(peer.getId());
  57             }
  58         }
  59
  60         if(LOG.isDebugEnabled()) {
  61             LOG.debug("{}: Election: Candidate has following voting peers: {}", logName(), votingPeers);
  62         }
  63
  64         votesRequired = getMajorityVoteCount(votingPeers.size());
  65
  66         startNewTerm();
  67
  68         if(votingPeers.isEmpty()){
  69             actor().tell(ElectionTimeout.INSTANCE, actor());
  70         } else {
  71             scheduleElection(electionDuration());
  72         }
  73
  74
  75     }
  76
  77     @Override protected RaftActorBehavior handleAppendEntries(ActorRef sender,
  78         AppendEntries appendEntries) {
  79
  80         if(LOG.isDebugEnabled()) {
  81             LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
  82         }
  83
  84         // Some other candidate for the same term became a leader and sent us an append entry
  85         if(currentTerm() == appendEntries.getTerm()){
  86             LOG.debug("{}: New Leader sent an append entry to Candidate for term {} will switch to Follower",
  87                     logName(), currentTerm());
  88
  89             return switchBehavior(new Follower(context));
  90         }
  91
  92         return this;
  93     }
  94
  95     @Override protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
  96         AppendEntriesReply appendEntriesReply) {
  97
  98         return this;
  99     }
 100
 101     @Override protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 102             RequestVoteReply requestVoteReply) {
 103
 104         LOG.debug("{}: handleRequestVoteReply: {}, current voteCount: {}", logName(), requestVoteReply,
 105                 voteCount);
 106
 107         if (requestVoteReply.isVoteGranted()) {
 108             voteCount++;
 109         }
 110
 111         if (voteCount >= votesRequired) {
 112             return internalSwitchBehavior(RaftState.Leader);
 113         }
 114
 115         return this;
 116     }
 117
 118     @Override
 119     public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 120
 121         Object message = fromSerializableMessage(originalMessage);
 122
 123         if (message instanceof RaftRPC) {
 124
 125             RaftRPC rpc = (RaftRPC) message;
 126
 127             if(LOG.isDebugEnabled()) {
 128                 LOG.debug("{}: RaftRPC message received {}, my term is {}", logName(), rpc,
 129                         context.getTermInformation().getCurrentTerm());
 130             }
 131
 132             // If RPC request or response contains term T > currentTerm:
 133             // set currentTerm = T, convert to follower (§5.1)
 134             // This applies to all RPC messages and responses
 135             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 136                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 137
 138                 return internalSwitchBehavior(RaftState.Follower);
 139             }
 140         }
 141
 142         if (message instanceof ElectionTimeout) {
 143             LOG.debug("{}: Received ElectionTimeout", logName());
 144
 145             if (votesRequired == 0) {
 146                 // If there are no peers then we should be a Leader
 147                 // We wait for the election timeout to occur before declare
 148                 // ourselves the leader. This gives enough time for a leader
 149                 // who we do not know about (as a peer)
 150                 // to send a message to the candidate
 151
 152                 return internalSwitchBehavior(RaftState.Leader);
 153             }
 154             startNewTerm();
 155             scheduleElection(electionDuration());
 156             return this;
 157         }
 158
 159         return super.handleMessage(sender, message);
 160     }
 161
 162
 163     private void startNewTerm() {
 164
 165
 166         // set voteCount back to 1 (that is voting for self)
 167         voteCount = 1;
 168
 169         // Increment the election term and vote for self
 170         long currentTerm = context.getTermInformation().getCurrentTerm();
 171         long newTerm = currentTerm + 1;
 172         context.getTermInformation().updateAndPersist(newTerm, context.getId());
 173
 174         LOG.debug("{}: Starting new term {}", logName(), newTerm);
 175
 176         // Request for a vote
 177         // TODO: Retry request for vote if replies do not arrive in a reasonable
 178         // amount of time TBD
 179         for (String peerId : votingPeers) {
 180             ActorSelection peerActor = context.getPeerActorSelection(peerId);
 181             if(peerActor != null) {
 182                 RequestVote requestVote = new RequestVote(
 183                         context.getTermInformation().getCurrentTerm(),
 184                         context.getId(),
 185                         context.getReplicatedLog().lastIndex(),
 186                         context.getReplicatedLog().lastTerm());
 187
 188                 LOG.debug("{}: Sending {} to peer {}", logName(), requestVote, peerId);
 189
 190                 peerActor.tell(requestVote, context.getActor());
 191             }
 192         }
 193     }
 194
 195     @Override
 196     public void close() {
 197         stopElection();
 198     }
 199 }