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.RaftRPC;
  19 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
  20 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  21
  22 import java.util.Collection;
  23 import java.util.HashMap;
  24 import java.util.Map;
  25
  26 /**
  27  * The behavior of a RaftActor when it is in the CandidateState
  28  * <p/>
  29  * Candidates (§5.2):
  30  * <ul>
  31  * <li> On conversion to candidate, start election:
  32  * <ul>
  33  * <li> Increment currentTerm
  34  * <li> Vote for self
  35  * <li> Reset election timer
  36  * <li> Send RequestVote RPCs to all other servers
  37  * </ul>
  38  * <li> If votes received from majority of servers: become leader
  39  * <li> If AppendEntries RPC received from new leader: convert to
  40  * follower
  41  * <li> If election timeout elapses: start new election
  42  * </ul>
  43  */
  44 public class Candidate extends AbstractRaftActorBehavior {
  45
  46     private final Map<String, ActorSelection> peerToActor = new HashMap<>();
  47
  48     private int voteCount;
  49
  50     private final int votesRequired;
  51
  52     public Candidate(RaftActorContext context) {
  53         super(context);
  54
  55         Collection<String> peerPaths = context.getPeerAddresses().values();
  56
  57         for (String peerPath : peerPaths) {
  58             peerToActor.put(peerPath,
  59                 context.actorSelection(peerPath));
  60         }
  61
  62         context.getLogger().debug("Election:Candidate has following peers:"+peerToActor.keySet());
  63         if(peerPaths.size() > 0) {
  64             // Votes are required from a majority of the peers including self.
  65             // The votesRequired field therefore stores a calculated value
  66             // of the number of votes required for this candidate to win an
  67             // election based on it's known peers.
  68             // If a peer was added during normal operation and raft replicas
  69             // came to know about them then the new peer would also need to be
  70             // taken into consideration when calculating this value.
  71             // Here are some examples for what the votesRequired would be for n
  72             // peers
  73             // 0 peers = 1 votesRequired (0 + 1) / 2 + 1 = 1
  74             // 2 peers = 2 votesRequired (2 + 1) / 2 + 1 = 2
  75             // 4 peers = 3 votesRequired (4 + 1) / 2 + 1 = 3
  76             int noOfPeers = peerPaths.size();
  77             int self = 1;
  78             votesRequired = (noOfPeers + self) / 2 + 1;
  79         } else {
  80             votesRequired = 0;
  81         }
  82
  83         startNewTerm();
  84         scheduleElection(electionDuration());
  85     }
  86
  87     @Override protected RaftState handleAppendEntries(ActorRef sender,
  88         AppendEntries appendEntries) {
  89
  90         return state();
  91     }
  92
  93     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
  94         AppendEntriesReply appendEntriesReply) {
  95
  96         return state();
  97     }
  98
  99     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 100         RequestVoteReply requestVoteReply) {
 101
 102         if (requestVoteReply.isVoteGranted()) {
 103             voteCount++;
 104         }
 105
 106         if (voteCount >= votesRequired) {
 107             return RaftState.Leader;
 108         }
 109
 110         return state();
 111     }
 112
 113     @Override public RaftState state() {
 114         return RaftState.Candidate;
 115     }
 116
 117     @Override
 118     public RaftState handleMessage(ActorRef sender, Object message) {
 119
 120         if (message instanceof RaftRPC) {
 121             RaftRPC rpc = (RaftRPC) message;
 122             // If RPC request or response contains term T > currentTerm:
 123             // set currentTerm = T, convert to follower (§5.1)
 124             // This applies to all RPC messages and responses
 125             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 126                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 127                 return RaftState.Follower;
 128             }
 129         }
 130
 131         if (message instanceof ElectionTimeout) {
 132             if (votesRequired == 0) {
 133                 // If there are no peers then we should be a Leader
 134                 // We wait for the election timeout to occur before declare
 135                 // ourselves the leader. This gives enough time for a leader
 136                 // who we do not know about (as a peer)
 137                 // to send a message to the candidate
 138                 return RaftState.Leader;
 139             }
 140             startNewTerm();
 141             scheduleElection(electionDuration());
 142             return state();
 143         }
 144         return super.handleMessage(sender, message);
 145     }
 146
 147
 148     private void startNewTerm() {
 149
 150
 151         // set voteCount back to 1 (that is voting for self)
 152         voteCount = 1;
 153
 154         // Increment the election term and vote for self
 155         long currentTerm = context.getTermInformation().getCurrentTerm();
 156         context.getTermInformation().updateAndPersist(currentTerm + 1, context.getId());
 157
 158         context.getLogger().debug("Starting new term " + (currentTerm+1));
 159
 160         // Request for a vote
 161         for (ActorSelection peerActor : peerToActor.values()) {
 162             peerActor.tell(new RequestVote(
 163                     context.getTermInformation().getCurrentTerm(),
 164                     context.getId(),
 165                     context.getReplicatedLog().lastIndex(),
 166                     context.getReplicatedLog().lastTerm()),
 167                 context.getActor()
 168             );
 169         }
 170
 171
 172     }
 173
 174     @Override public void close() throws Exception {
 175         stopElection();
 176     }
 177 }