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