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         scheduleElection(electionDuration());
  62     }
  63
  64     @Override protected RaftActorBehavior handleAppendEntries(ActorRef sender,
  65         AppendEntries appendEntries) {
  66
  67         if(LOG.isDebugEnabled()) {
  68             LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
  69         }
  70
  71         return this;
  72     }
  73
  74     @Override protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
  75         AppendEntriesReply appendEntriesReply) {
  76
  77         return this;
  78     }
  79
  80     @Override protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
  81             RequestVoteReply requestVoteReply) {
  82
  83         LOG.debug("{}: handleRequestVoteReply: {}, current voteCount: {}", logName(), requestVoteReply,
  84                 voteCount);
  85
  86         if (requestVoteReply.isVoteGranted()) {
  87             voteCount++;
  88         }
  89
  90         if (voteCount >= votesRequired) {
  91             return switchBehavior(new Leader(context));
  92         }
  93
  94         return this;
  95     }
  96
  97     @Override
  98     public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
  99
 100         Object message = fromSerializableMessage(originalMessage);
 101
 102         if (message instanceof RaftRPC) {
 103
 104             RaftRPC rpc = (RaftRPC) message;
 105
 106             if(LOG.isDebugEnabled()) {
 107                 LOG.debug("{}: RaftRPC message received {}, my term is {}", logName(), rpc,
 108                         context.getTermInformation().getCurrentTerm());
 109             }
 110
 111             // If RPC request or response contains term T > currentTerm:
 112             // set currentTerm = T, convert to follower (§5.1)
 113             // This applies to all RPC messages and responses
 114             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 115                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 116
 117                 return switchBehavior(new Follower(context));
 118             }
 119         }
 120
 121         if (message instanceof ElectionTimeout) {
 122             LOG.debug("{}: Received ElectionTimeout", logName());
 123
 124             if (votesRequired == 0) {
 125                 // If there are no peers then we should be a Leader
 126                 // We wait for the election timeout to occur before declare
 127                 // ourselves the leader. This gives enough time for a leader
 128                 // who we do not know about (as a peer)
 129                 // to send a message to the candidate
 130
 131                 return switchBehavior(new Leader(context));
 132             }
 133             startNewTerm();
 134             scheduleElection(electionDuration());
 135             return this;
 136         }
 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         long newTerm = currentTerm + 1;
 151         context.getTermInformation().updateAndPersist(newTerm, context.getId());
 152
 153         LOG.debug("{}: Starting new term {}", logName(), newTerm);
 154
 155         // Request for a vote
 156         // TODO: Retry request for vote if replies do not arrive in a reasonable
 157         // amount of time TBD
 158         for (String peerId : peers) {
 159             ActorSelection peerActor = context.getPeerActorSelection(peerId);
 160             if(peerActor != null) {
 161                 RequestVote requestVote = new RequestVote(
 162                         context.getTermInformation().getCurrentTerm(),
 163                         context.getId(),
 164                         context.getReplicatedLog().lastIndex(),
 165                         context.getReplicatedLog().lastTerm());
 166
 167                 LOG.debug("{}: Sending {} to peer {}", logName(), requestVote, peerId);
 168
 169                 peerActor.tell(requestVote, context.getActor());
 170             }
 171         }
 172     }
 173
 174     @Override public void close() throws Exception {
 175         stopElection();
 176     }
 177 }