opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Follower.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 org.opendaylight.controller.cluster.raft.RaftActorContext;
  13 import org.opendaylight.controller.cluster.raft.RaftState;
  14 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  15 import org.opendaylight.controller.cluster.raft.internal.messages.ApplySnapshot;
  16 import org.opendaylight.controller.cluster.raft.internal.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.InstallSnapshot;
  20 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  21
  22 /**
  23  * The behavior of a RaftActor in the Follower state
  24  * <p/>
  25  * <ul>
  26  * <li> Respond to RPCs from candidates and leaders
  27  * <li> If election timeout elapses without receiving AppendEntries
  28  * RPC from current leader or granting vote to candidate:
  29  * convert to candidate
  30  * </ul>
  31  */
  32 public class Follower extends AbstractRaftActorBehavior {
  33     public Follower(RaftActorContext context) {
  34         super(context);
  35
  36         scheduleElection(electionDuration());
  37     }
  38
  39     @Override protected RaftState handleAppendEntries(ActorRef sender,
  40         AppendEntries appendEntries, RaftState suggestedState) {
  41
  42         // If we got here then we do appear to be talking to the leader
  43         leaderId = appendEntries.getLeaderId();
  44
  45         // 2. Reply false if log doesn’t contain an entry at prevLogIndex
  46         // whose term matches prevLogTerm (§5.3)
  47         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  48             .get(appendEntries.getPrevLogIndex());
  49
  50
  51         boolean noMatchingTerms = true;
  52
  53         if (lastIndex() == -1
  54             && appendEntries.getPrevLogIndex() != -1) {
  55
  56             context.getLogger().debug(
  57                 "The followers log is empty and the senders prevLogIndex is {}",
  58                 appendEntries.getPrevLogIndex());
  59
  60         } else if (lastIndex() > -1
  61             && appendEntries.getPrevLogIndex() != -1
  62             && previousEntry == null) {
  63
  64             context.getLogger().debug(
  65                 "The log is not empty but the prevLogIndex {} was not found in it",
  66                 appendEntries.getPrevLogIndex());
  67
  68         } else if (lastIndex() > -1
  69             && previousEntry != null
  70             && previousEntry.getTerm()!= appendEntries.getPrevLogTerm()) {
  71
  72             context.getLogger().debug(
  73                 "Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}"
  74                 , previousEntry.getTerm()
  75                 , appendEntries.getPrevLogTerm());
  76         } else {
  77             noMatchingTerms = false;
  78         }
  79
  80         if (noMatchingTerms) {
  81             sender.tell(
  82                 new AppendEntriesReply(context.getId(), currentTerm(), false,
  83                     lastIndex(), lastTerm()), actor()
  84             );
  85             return state();
  86         }
  87
  88         if (appendEntries.getEntries() != null
  89             && appendEntries.getEntries().size() > 0) {
  90             context.getLogger().debug(
  91                 "Number of entries to be appended = " + appendEntries
  92                     .getEntries().size()
  93             );
  94
  95             // 3. If an existing entry conflicts with a new one (same index
  96             // but different terms), delete the existing entry and all that
  97             // follow it (§5.3)
  98             int addEntriesFrom = 0;
  99             if (context.getReplicatedLog().size() > 0) {
 100                 for (int i = 0;
 101                      i < appendEntries.getEntries()
 102                          .size(); i++, addEntriesFrom++) {
 103                     ReplicatedLogEntry matchEntry =
 104                         appendEntries.getEntries().get(i);
 105                     ReplicatedLogEntry newEntry = context.getReplicatedLog()
 106                         .get(matchEntry.getIndex());
 107
 108                     if (newEntry == null) {
 109                         //newEntry not found in the log
 110                         break;
 111                     }
 112
 113                     if (newEntry != null && newEntry.getTerm() == matchEntry
 114                         .getTerm()) {
 115                         continue;
 116                     }
 117                     if (newEntry != null && newEntry.getTerm() != matchEntry
 118                         .getTerm()) {
 119                         context.getLogger().debug(
 120                             "Removing entries from log starting at "
 121                                 + matchEntry.getIndex()
 122                         );
 123                         context.getReplicatedLog()
 124                             .removeFrom(matchEntry.getIndex());
 125                         break;
 126                     }
 127                 }
 128             }
 129
 130             context.getLogger().debug(
 131                 "After cleanup entries to be added from = " + (addEntriesFrom
 132                     + lastIndex())
 133             );
 134
 135             // 4. Append any new entries not already in the log
 136             for (int i = addEntriesFrom;
 137                  i < appendEntries.getEntries().size(); i++) {
 138                 context.getLogger().debug(
 139                     "Append entry to log " + appendEntries.getEntries().get(i).getData()
 140                         .toString()
 141                 );
 142                 context.getReplicatedLog()
 143                     .appendAndPersist(appendEntries.getEntries().get(i));
 144             }
 145
 146             context.getLogger().debug(
 147                 "Log size is now " + context.getReplicatedLog().size());
 148         }
 149
 150
 151         // 5. If leaderCommit > commitIndex, set commitIndex =
 152         // min(leaderCommit, index of last new entry)
 153
 154         long prevCommitIndex = context.getCommitIndex();
 155
 156         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(),
 157             context.getReplicatedLog().lastIndex()));
 158
 159         if (prevCommitIndex != context.getCommitIndex()) {
 160             context.getLogger()
 161                 .debug("Commit index set to " + context.getCommitIndex());
 162         }
 163
 164         // If commitIndex > lastApplied: increment lastApplied, apply
 165         // log[lastApplied] to state machine (§5.3)
 166         if (appendEntries.getLeaderCommit() > context.getLastApplied()) {
 167             applyLogToStateMachine(appendEntries.getLeaderCommit());
 168         }
 169
 170         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), true,
 171             lastIndex(), lastTerm()), actor());
 172
 173         return suggestedState;
 174     }
 175
 176     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
 177         AppendEntriesReply appendEntriesReply, RaftState suggestedState) {
 178         return suggestedState;
 179     }
 180
 181     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 182         RequestVoteReply requestVoteReply, RaftState suggestedState) {
 183         return suggestedState;
 184     }
 185
 186     @Override public RaftState state() {
 187         return RaftState.Follower;
 188     }
 189
 190     @Override public RaftState handleMessage(ActorRef sender, Object message) {
 191         if (message instanceof ElectionTimeout) {
 192             return RaftState.Candidate;
 193         } else if (message instanceof InstallSnapshot) {
 194             InstallSnapshot snapshot = (InstallSnapshot) message;
 195             actor().tell(new ApplySnapshot(snapshot), actor());
 196         }
 197
 198         scheduleElection(electionDuration());
 199
 200         return super.handleMessage(sender, message);
 201     }
 202
 203     @Override public void close() throws Exception {
 204         stopElection();
 205     }
 206 }