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         // Some other candidate for the same term became a leader and sent us an append entry
  79         if(currentTerm() == appendEntries.getTerm()){
  80             LOG.debug("{}: New Leader sent an append entry to Candidate for term {} will switch to Follower",
  81                     logName(), currentTerm());
  82
  83             return switchBehavior(new Follower(context));
  84         }
  85
  86         return this;
  87     }
  88
  89     @Override protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
  90         AppendEntriesReply appendEntriesReply) {
  91
  92         return this;
  93     }
  94
  95     @Override protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
  96             RequestVoteReply requestVoteReply) {
  97
  98         LOG.debug("{}: handleRequestVoteReply: {}, current voteCount: {}", logName(), requestVoteReply,
  99                 voteCount);
 100
 101         if (requestVoteReply.isVoteGranted()) {
 102             voteCount++;
 103         }
 104
 105         if (voteCount >= votesRequired) {
 106             return switchBehavior(new Leader(context));
 107         }
 108
 109         return this;
 110     }
 111
 112     @Override
 113     public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 114
 115         Object message = fromSerializableMessage(originalMessage);
 116
 117         if (message instanceof RaftRPC) {
 118
 119             RaftRPC rpc = (RaftRPC) message;
 120
 121             if(LOG.isDebugEnabled()) {
 122                 LOG.debug("{}: RaftRPC message received {}, my term is {}", logName(), rpc,
 123                         context.getTermInformation().getCurrentTerm());
 124             }
 125
 126             // If RPC request or response contains term T > currentTerm:
 127             // set currentTerm = T, convert to follower (§5.1)
 128             // This applies to all RPC messages and responses
 129             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 130                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 131
 132                 return switchBehavior(new Follower(context));
 133             }
 134         }
 135
 136         if (message instanceof ElectionTimeout) {
 137             LOG.debug("{}: Received ElectionTimeout", logName());
 138
 139             if (votesRequired == 0) {
 140                 // If there are no peers then we should be a Leader
 141                 // We wait for the election timeout to occur before declare
 142                 // ourselves the leader. This gives enough time for a leader
 143                 // who we do not know about (as a peer)
 144                 // to send a message to the candidate
 145
 146                 return switchBehavior(new Leader(context));
 147             }
 148             startNewTerm();
 149             scheduleElection(electionDuration());
 150             return this;
 151         }
 152
 153         return super.handleMessage(sender, message);
 154     }
 155
 156
 157     private void startNewTerm() {
 158
 159
 160         // set voteCount back to 1 (that is voting for self)
 161         voteCount = 1;
 162
 163         // Increment the election term and vote for self
 164         long currentTerm = context.getTermInformation().getCurrentTerm();
 165         long newTerm = currentTerm + 1;
 166         context.getTermInformation().updateAndPersist(newTerm, context.getId());
 167
 168         LOG.debug("{}: Starting new term {}", logName(), newTerm);
 169
 170         // Request for a vote
 171         // TODO: Retry request for vote if replies do not arrive in a reasonable
 172         // amount of time TBD
 173         for (String peerId : peers) {
 174             ActorSelection peerActor = context.getPeerActorSelection(peerId);
 175             if(peerActor != null) {
 176                 RequestVote requestVote = new RequestVote(
 177                         context.getTermInformation().getCurrentTerm(),
 178                         context.getId(),
 179                         context.getReplicatedLog().lastIndex(),
 180                         context.getReplicatedLog().lastTerm());
 181
 182                 LOG.debug("{}: Sending {} to peer {}", logName(), requestVote, peerId);
 183
 184                 peerActor.tell(requestVote, context.getActor());
 185             }
 186         }
 187     }
 188
 189     @Override public void close() throws Exception {
 190         stopElection();
 191     }
 192 }