opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Leader.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 akka.actor.Cancellable;
  14 import com.google.common.base.Preconditions;
  15 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
  16 import org.opendaylight.controller.cluster.raft.FollowerLogInformationImpl;
  17 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  18 import org.opendaylight.controller.cluster.raft.RaftState;
  19 import org.opendaylight.controller.cluster.raft.internal.messages.SendHeartBeat;
  20 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  21 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  22 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  23 import scala.concurrent.duration.FiniteDuration;
  24
  25 import java.util.Collections;
  26 import java.util.HashMap;
  27 import java.util.List;
  28 import java.util.Map;
  29 import java.util.concurrent.TimeUnit;
  30 import java.util.concurrent.atomic.AtomicLong;
  31
  32 /**
  33  * The behavior of a RaftActor when it is in the Leader state
  34  * <p/>
  35  * Leaders:
  36  * <ul>
  37  * <li> Upon election: send initial empty AppendEntries RPCs
  38  * (heartbeat) to each server; repeat during idle periods to
  39  * prevent election timeouts (§5.2)
  40  * <li> If command received from client: append entry to local log,
  41  * respond after entry applied to state machine (§5.3)
  42  * <li> If last log index ≥ nextIndex for a follower: send
  43  * AppendEntries RPC with log entries starting at nextIndex
  44  * <ul>
  45  * <li> If successful: update nextIndex and matchIndex for
  46  * follower (§5.3)
  47  * <li> If AppendEntries fails because of log inconsistency:
  48  * decrement nextIndex and retry (§5.3)
  49  * </ul>
  50  * <li> If there exists an N such that N > commitIndex, a majority
  51  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  52  * set commitIndex = N (§5.3, §5.4).
  53  */
  54 public class Leader extends AbstractRaftActorBehavior {
  55
  56     /**
  57      * The interval at which a heart beat message will be sent to the remote
  58      * RaftActor
  59      * <p/>
  60      * Since this is set to 100 milliseconds the Election timeout should be
  61      * at least 200 milliseconds
  62      */
  63     public static final FiniteDuration HEART_BEAT_INTERVAL =
  64         new FiniteDuration(100, TimeUnit.MILLISECONDS);
  65
  66     private final Map<String, FollowerLogInformation> followerToLog =
  67         new HashMap();
  68
  69     private final Map<String, ActorSelection> followerToActor = new HashMap<>();
  70
  71     private Cancellable heartbeatCancel = null;
  72
  73     public Leader(RaftActorContext context, List<String> followePaths) {
  74         super(context);
  75
  76         for (String followerPath : followePaths) {
  77             FollowerLogInformation followerLogInformation =
  78                 new FollowerLogInformationImpl(followerPath,
  79                     new AtomicLong(0),
  80                     new AtomicLong(0));
  81
  82             followerToActor.put(followerPath,
  83                 context.actorSelection(followerLogInformation.getId()));
  84             followerToLog.put(followerPath, followerLogInformation);
  85
  86         }
  87
  88         // Immediately schedule a heartbeat
  89         // Upon election: send initial empty AppendEntries RPCs
  90         // (heartbeat) to each server; repeat during idle periods to
  91         // prevent election timeouts (§5.2)
  92         scheduleHeartBeat(new FiniteDuration(0, TimeUnit.SECONDS));
  93
  94
  95     }
  96
  97     @Override protected RaftState handleAppendEntries(ActorRef sender,
  98         AppendEntries appendEntries, RaftState suggestedState) {
  99         return suggestedState;
 100     }
 101
 102     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
 103         AppendEntriesReply appendEntriesReply, RaftState suggestedState) {
 104         return suggestedState;
 105     }
 106
 107     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 108         RequestVoteReply requestVoteReply, RaftState suggestedState) {
 109         return suggestedState;
 110     }
 111
 112     @Override protected RaftState state() {
 113         return RaftState.Leader;
 114     }
 115
 116     @Override public RaftState handleMessage(ActorRef sender, Object message) {
 117         Preconditions.checkNotNull(sender, "sender should not be null");
 118
 119         scheduleHeartBeat(HEART_BEAT_INTERVAL);
 120
 121         if (message instanceof SendHeartBeat) {
 122             for (ActorSelection follower : followerToActor.values()) {
 123                 follower.tell(new AppendEntries(
 124                     context.getTermInformation().getCurrentTerm(),
 125                     context.getId(),
 126                     context.getReplicatedLog().last().getIndex(),
 127                     context.getReplicatedLog().last().getTerm(),
 128                     Collections.EMPTY_LIST, context.getCommitIndex()),
 129                     context.getActor());
 130             }
 131             return state();
 132         }
 133         return super.handleMessage(sender, message);
 134     }
 135
 136     private void scheduleHeartBeat(FiniteDuration interval) {
 137         if (heartbeatCancel != null && !heartbeatCancel.isCancelled()) {
 138             heartbeatCancel.cancel();
 139         }
 140
 141         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 142         // message is sent to itself.
 143         // Scheduling the heartbeat only once here because heartbeats do not
 144         // need to be sent if there are other messages being sent to the remote
 145         // actor.
 146         heartbeatCancel =
 147             context.getActorSystem().scheduler().scheduleOnce(interval,
 148                 context.getActor(), new SendHeartBeat(),
 149                 context.getActorSystem().dispatcher(), context.getActor());
 150     }
 151
 152 }