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 org.opendaylight.controller.cluster.raft.RaftActorContext;
  14 import org.opendaylight.controller.cluster.raft.RaftState;
  15 import org.opendaylight.controller.cluster.raft.internal.messages.ElectionTimeout;
  16 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  17 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  18 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
  19 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  20
  21 import java.util.Collection;
  22 import java.util.HashMap;
  23 import java.util.Map;
  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 final Map<String, ActorSelection> peerToActor = new HashMap<>();
  46
  47     private int voteCount;
  48
  49     private final int votesRequired;
  50
  51     public Candidate(RaftActorContext context) {
  52         super(context);
  53
  54         Collection<String> peerPaths = context.getPeerAddresses().values();
  55
  56         for (String peerPath : peerPaths) {
  57             peerToActor.put(peerPath,
  58                 context.actorSelection(peerPath));
  59         }
  60
  61         if(peerPaths.size() > 0) {
  62             // Votes are required from a majority of the peers including self.
  63             // The votesRequired field therefore stores a calculated value
  64             // of the number of votes required for this candidate to win an
  65             // election based on it's known peers.
  66             // If a peer was added during normal operation and raft replicas
  67             // came to know about them then the new peer would also need to be
  68             // taken into consideration when calculating this value.
  69             // Here are some examples for what the votesRequired would be for n
  70             // peers
  71             // 0 peers = 1 votesRequired (0 + 1) / 2 + 1 = 1
  72             // 2 peers = 2 votesRequired (2 + 1) / 2 + 1 = 2
  73             // 4 peers = 3 votesRequired (4 + 1) / 2 + 1 = 3
  74             int noOfPeers = peerPaths.size();
  75             int self = 1;
  76             votesRequired = (noOfPeers + self) / 2 + 1;
  77         } else {
  78             votesRequired = 0;
  79         }
  80
  81         startNewTerm();
  82         scheduleElection(electionDuration());
  83     }
  84
  85     @Override protected RaftState handleAppendEntries(ActorRef sender,
  86         AppendEntries appendEntries, RaftState suggestedState) {
  87
  88         context.getLogger().error("An unexpected AppendEntries received in state " + state());
  89
  90         return suggestedState;
  91     }
  92
  93     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
  94         AppendEntriesReply appendEntriesReply, RaftState suggestedState) {
  95
  96         // Some peer thinks I was a leader and sent me a reply
  97
  98         return suggestedState;
  99     }
 100
 101     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 102         RequestVoteReply requestVoteReply, RaftState suggestedState) {
 103         if (suggestedState == RaftState.Follower) {
 104             // If base class thinks I should be follower then I am
 105             return suggestedState;
 106         }
 107
 108         if (requestVoteReply.isVoteGranted()) {
 109             voteCount++;
 110         }
 111
 112         if (voteCount >= votesRequired) {
 113             return RaftState.Leader;
 114         }
 115
 116         return state();
 117     }
 118
 119     @Override public RaftState state() {
 120         return RaftState.Candidate;
 121     }
 122
 123     @Override
 124     public RaftState handleMessage(ActorRef sender, Object message) {
 125         if (message instanceof ElectionTimeout) {
 126             if (votesRequired == 0) {
 127                 // If there are no peers then we should be a Leader
 128                 // We wait for the election timeout to occur before declare
 129                 // ourselves the leader. This gives enough time for a leader
 130                 // who we do not know about (as a peer)
 131                 // to send a message to the candidate
 132                 return RaftState.Leader;
 133             }
 134             startNewTerm();
 135             scheduleElection(electionDuration());
 136             return state();
 137         }
 138         return super.handleMessage(sender, message);
 139     }
 140
 141
 142     private void startNewTerm() {
 143
 144
 145         // set voteCount back to 1 (that is voting for self)
 146         voteCount = 1;
 147
 148         // Increment the election term and vote for self
 149         long currentTerm = context.getTermInformation().getCurrentTerm();
 150         context.getTermInformation().update(currentTerm + 1, context.getId());
 151
 152         context.getLogger().debug("Starting new term " + (currentTerm+1));
 153
 154         // Request for a vote
 155         for (ActorSelection peerActor : peerToActor.values()) {
 156             peerActor.tell(new RequestVote(
 157                     context.getTermInformation().getCurrentTerm(),
 158                     context.getId(),
 159                     context.getReplicatedLog().lastIndex(),
 160                     context.getReplicatedLog().lastTerm()),
 161                 context.getActor()
 162             );
 163         }
 164
 165
 166     }
 167
 168     @Override public void close() throws Exception {
 169         stopElection();
 170     }
 171 }