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.RaftRPC;
  21 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  22
  23 /**
  24  * The behavior of a RaftActor in the Follower state
  25  * <p/>
  26  * <ul>
  27  * <li> Respond to RPCs from candidates and leaders
  28  * <li> If election timeout elapses without receiving AppendEntries
  29  * RPC from current leader or granting vote to candidate:
  30  * convert to candidate
  31  * </ul>
  32  */
  33 public class Follower extends AbstractRaftActorBehavior {
  34     public Follower(RaftActorContext context) {
  35         super(context);
  36
  37         scheduleElection(electionDuration());
  38     }
  39
  40     @Override protected RaftState handleAppendEntries(ActorRef sender,
  41         AppendEntries appendEntries) {
  42
  43         // If we got here then we do appear to be talking to the leader
  44         leaderId = appendEntries.getLeaderId();
  45
  46         // 2. Reply false if log doesn’t contain an entry at prevLogIndex
  47         // whose term matches prevLogTerm (§5.3)
  48         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  49             .get(appendEntries.getPrevLogIndex());
  50
  51
  52         boolean noMatchingTerms = true;
  53
  54         if (lastIndex() == -1
  55             && appendEntries.getPrevLogIndex() != -1) {
  56
  57             context.getLogger().debug(
  58                 "The followers log is empty and the senders prevLogIndex is {}",
  59                 appendEntries.getPrevLogIndex());
  60
  61         } else if (lastIndex() > -1
  62             && appendEntries.getPrevLogIndex() != -1
  63             && previousEntry == null) {
  64
  65             context.getLogger().debug(
  66                 "The log is not empty but the prevLogIndex {} was not found in it",
  67                 appendEntries.getPrevLogIndex());
  68
  69         } else if (lastIndex() > -1
  70             && previousEntry != null
  71             && previousEntry.getTerm()!= appendEntries.getPrevLogTerm()) {
  72
  73             context.getLogger().debug(
  74                 "Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}"
  75                 , previousEntry.getTerm()
  76                 , appendEntries.getPrevLogTerm());
  77         } else {
  78             noMatchingTerms = false;
  79         }
  80
  81         if (noMatchingTerms) {
  82             sender.tell(
  83                 new AppendEntriesReply(context.getId(), currentTerm(), false,
  84                     lastIndex(), lastTerm()), actor()
  85             );
  86             return state();
  87         }
  88
  89         if (appendEntries.getEntries() != null
  90             && appendEntries.getEntries().size() > 0) {
  91             context.getLogger().debug(
  92                 "Number of entries to be appended = " + appendEntries
  93                     .getEntries().size()
  94             );
  95
  96             // 3. If an existing entry conflicts with a new one (same index
  97             // but different terms), delete the existing entry and all that
  98             // follow it (§5.3)
  99             int addEntriesFrom = 0;
 100             if (context.getReplicatedLog().size() > 0) {
 101                 for (int i = 0;
 102                      i < appendEntries.getEntries()
 103                          .size(); i++, addEntriesFrom++) {
 104                     ReplicatedLogEntry matchEntry =
 105                         appendEntries.getEntries().get(i);
 106                     ReplicatedLogEntry newEntry = context.getReplicatedLog()
 107                         .get(matchEntry.getIndex());
 108
 109                     if (newEntry == null) {
 110                         //newEntry not found in the log
 111                         break;
 112                     }
 113
 114                     if (newEntry != null && newEntry.getTerm() == matchEntry
 115                         .getTerm()) {
 116                         continue;
 117                     }
 118                     if (newEntry != null && newEntry.getTerm() != matchEntry
 119                         .getTerm()) {
 120                         context.getLogger().debug(
 121                             "Removing entries from log starting at "
 122                                 + matchEntry.getIndex()
 123                         );
 124                         context.getReplicatedLog()
 125                             .removeFrom(matchEntry.getIndex());
 126                         break;
 127                     }
 128                 }
 129             }
 130
 131             context.getLogger().debug(
 132                 "After cleanup entries to be added from = " + (addEntriesFrom
 133                     + lastIndex())
 134             );
 135
 136             // 4. Append any new entries not already in the log
 137             for (int i = addEntriesFrom;
 138                  i < appendEntries.getEntries().size(); i++) {
 139                 context.getLogger().debug(
 140                     "Append entry to log " + appendEntries.getEntries().get(i).getData()
 141                         .toString()
 142                 );
 143                 context.getReplicatedLog()
 144                     .appendAndPersist(appendEntries.getEntries().get(i));
 145             }
 146
 147             context.getLogger().debug(
 148                 "Log size is now " + context.getReplicatedLog().size());
 149         }
 150
 151
 152         // 5. If leaderCommit > commitIndex, set commitIndex =
 153         // min(leaderCommit, index of last new entry)
 154
 155         long prevCommitIndex = context.getCommitIndex();
 156
 157         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(),
 158             context.getReplicatedLog().lastIndex()));
 159
 160         if (prevCommitIndex != context.getCommitIndex()) {
 161             context.getLogger()
 162                 .debug("Commit index set to " + context.getCommitIndex());
 163         }
 164
 165         // If commitIndex > lastApplied: increment lastApplied, apply
 166         // log[lastApplied] to state machine (§5.3)
 167         if (appendEntries.getLeaderCommit() > context.getLastApplied()) {
 168             applyLogToStateMachine(appendEntries.getLeaderCommit());
 169         }
 170
 171         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), true,
 172             lastIndex(), lastTerm()), actor());
 173
 174         return state();
 175     }
 176
 177     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
 178         AppendEntriesReply appendEntriesReply) {
 179         return state();
 180     }
 181
 182     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 183         RequestVoteReply requestVoteReply) {
 184         return state();
 185     }
 186
 187     @Override public RaftState state() {
 188         return RaftState.Follower;
 189     }
 190
 191     @Override public RaftState handleMessage(ActorRef sender, Object message) {
 192         if (message instanceof RaftRPC) {
 193             RaftRPC rpc = (RaftRPC) message;
 194             // If RPC request or response contains term T > currentTerm:
 195             // set currentTerm = T, convert to follower (§5.1)
 196             // This applies to all RPC messages and responses
 197             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 198                 context.getTermInformation().update(rpc.getTerm(), null);
 199             }
 200         }
 201
 202         if (message instanceof ElectionTimeout) {
 203             return RaftState.Candidate;
 204         } else if (message instanceof InstallSnapshot) {
 205             InstallSnapshot snapshot = (InstallSnapshot) message;
 206             actor().tell(new ApplySnapshot(snapshot), actor());
 207         }
 208
 209         scheduleElection(electionDuration());
 210
 211         return super.handleMessage(sender, message);
 212     }
 213
 214     @Override public void close() throws Exception {
 215         stopElection();
 216     }
 217 }