Further Guava Optional cleanups
[controller.git] / opendaylight / md-sal / sal-akka-raft / src / main / java / org / opendaylight / controller / cluster / raft / behaviors / Leader.java
index ee3cc65..3534ac5 100644 (file)
@@ -7,18 +7,27 @@
  */
 package org.opendaylight.controller.cluster.raft.behaviors;
 
+import static java.util.Objects.requireNonNull;
+
 import akka.actor.ActorRef;
-import akka.actor.Cancellable;
+import akka.actor.ActorSelection;
 import com.google.common.annotations.VisibleForTesting;
-import com.google.common.base.Preconditions;
+import com.google.common.base.Stopwatch;
+import java.util.Optional;
+import java.util.concurrent.TimeUnit;
+import org.eclipse.jdt.annotation.NonNull;
+import org.eclipse.jdt.annotation.Nullable;
+import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
 import org.opendaylight.controller.cluster.raft.RaftActorContext;
-import org.opendaylight.controller.cluster.raft.base.messages.InitiateInstallSnapshot;
-import org.opendaylight.controller.cluster.raft.base.messages.IsolatedLeaderCheck;
-import scala.concurrent.duration.FiniteDuration;
+import org.opendaylight.controller.cluster.raft.RaftActorLeadershipTransferCohort;
+import org.opendaylight.controller.cluster.raft.RaftState;
+import org.opendaylight.controller.cluster.raft.base.messages.TimeoutNow;
+import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
 
 /**
- * The behavior of a RaftActor when it is in the Leader state
- * <p/>
+ * The behavior of a RaftActor when it is in the Leader state.
+ *
+ * <p>
  * Leaders:
  * <ul>
  * <li> Upon election: send initial empty AppendEntries RPCs
@@ -28,94 +37,178 @@ import scala.concurrent.duration.FiniteDuration;
  * respond after entry applied to state machine (§5.3)
  * <li> If last log index ≥ nextIndex for a follower: send
  * AppendEntries RPC with log entries starting at nextIndex
- * <ul>
  * <li> If successful: update nextIndex and matchIndex for
  * follower (§5.3)
  * <li> If AppendEntries fails because of log inconsistency:
  * decrement nextIndex and retry (§5.3)
- * </ul>
- * <li> If there exists an N such that N > commitIndex, a majority
+ * <li> If there exists an N such that N &gt; commitIndex, a majority
  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  * set commitIndex = N (§5.3, §5.4).
+ * </ul>
  */
 public class Leader extends AbstractLeader {
-    private Cancellable installSnapshotSchedule = null;
-    private Cancellable isolatedLeaderCheckSchedule = null;
+    /**
+     * Internal message sent to periodically check if this leader has become isolated and should transition
+     * to {@link IsolatedLeader}.
+     */
+    @VisibleForTesting
+    static final Object ISOLATED_LEADER_CHECK = new Object();
 
-    public Leader(RaftActorContext context) {
-        super(context);
+    private final Stopwatch isolatedLeaderCheck = Stopwatch.createStarted();
+    private @Nullable LeadershipTransferContext leadershipTransferContext;
 
-        scheduleInstallSnapshotCheck(context.getConfigParams().getIsolatedCheckInterval());
+    Leader(final RaftActorContext context, @Nullable final AbstractLeader initializeFromLeader) {
+        super(context, RaftState.Leader, initializeFromLeader);
+    }
 
-        scheduleIsolatedLeaderCheck(
-            new FiniteDuration(context.getConfigParams().getHeartBeatInterval().length() * 10,
-                context.getConfigParams().getHeartBeatInterval().unit()));
+    public Leader(final RaftActorContext context) {
+        this(context, null);
     }
 
-    @Override public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
-        Preconditions.checkNotNull(sender, "sender should not be null");
+    @Override
+    public RaftActorBehavior handleMessage(final ActorRef sender, final Object originalMessage) {
+        requireNonNull(sender, "sender should not be null");
 
-        if (originalMessage instanceof IsolatedLeaderCheck) {
+        if (ISOLATED_LEADER_CHECK.equals(originalMessage)) {
             if (isLeaderIsolated()) {
-                LOG.info("At least {} followers need to be active, Switching {} from Leader to IsolatedLeader",
-                    minIsolatedLeaderPeerCount, leaderId);
-                return switchBehavior(new IsolatedLeader(context));
+                log.warn("{}: At least {} followers need to be active, Switching {} from Leader to IsolatedLeader",
+                    context.getId(), getMinIsolatedLeaderPeerCount(), getLeaderId());
+                return internalSwitchBehavior(new IsolatedLeader(context, this));
+            } else {
+                return this;
             }
+        } else {
+            return super.handleMessage(sender, originalMessage);
         }
-
-        return super.handleMessage(sender, originalMessage);
     }
 
-    protected void stopInstallSnapshotSchedule() {
-        if (installSnapshotSchedule != null && !installSnapshotSchedule.isCancelled()) {
-            installSnapshotSchedule.cancel();
+    @Override
+    protected void beforeSendHeartbeat() {
+        if (isolatedLeaderCheck.elapsed(TimeUnit.MILLISECONDS)
+                > context.getConfigParams().getIsolatedCheckIntervalInMillis()) {
+            context.getActor().tell(ISOLATED_LEADER_CHECK, context.getActor());
+            isolatedLeaderCheck.reset().start();
         }
-    }
 
-    protected void scheduleInstallSnapshotCheck(FiniteDuration interval) {
-        if (getFollowerIds().isEmpty()) {
-            // Optimization - do not bother scheduling a heartbeat as there are
-            // no followers
-            return;
+        if (leadershipTransferContext != null && leadershipTransferContext.isExpired(
+                context.getConfigParams().getElectionTimeOutInterval().toMillis())) {
+            log.debug("{}: Leadership transfer expired", logName());
+            leadershipTransferContext = null;
         }
+    }
 
-        stopInstallSnapshotSchedule();
+    @Override
+    protected RaftActorBehavior handleAppendEntriesReply(final ActorRef sender,
+            final AppendEntriesReply appendEntriesReply) {
+        RaftActorBehavior returnBehavior = super.handleAppendEntriesReply(sender, appendEntriesReply);
+        tryToCompleteLeadershipTransfer(appendEntriesReply.getFollowerId());
+        return returnBehavior;
+    }
 
-        // Schedule a message to send append entries to followers that can
-        // accept an append entries with some data in it
-        installSnapshotSchedule =
-            context.getActorSystem().scheduler().scheduleOnce(
-                interval,
-                context.getActor(), new InitiateInstallSnapshot(),
-                context.getActorSystem().dispatcher(), context.getActor());
+    /**
+     * Attempts to transfer leadership to a follower as per the raft paper (§3.10) as follows:
+     * <ul>
+     * <li>Start a timer (Stopwatch).</li>
+     * <li>Send an initial AppendEntries heartbeat to all followers.</li>
+     * <li>On AppendEntriesReply, check if the follower's new match Index matches the leader's last index</li>
+     * <li>If it matches,
+     *   <ul>
+     *   <li>Send an additional AppendEntries to ensure the follower has applied all its log entries to its state.</li>
+     *   <li>Send an ElectionTimeout to the follower to immediately start an election.</li>
+     *   <li>Notify {@link RaftActorLeadershipTransferCohort#transferComplete}.</li>
+     *   </ul></li>
+     * <li>Otherwise if the election time out period elapses, notify
+     *     {@link RaftActorLeadershipTransferCohort#abortTransfer}.</li>
+     * </ul>
+     *
+     * @param leadershipTransferCohort the cohort participating in the leadership transfer
+     */
+    public void transferLeadership(@NonNull final RaftActorLeadershipTransferCohort leadershipTransferCohort) {
+        log.debug("{}: Attempting to transfer leadership", logName());
+
+        leadershipTransferContext = new LeadershipTransferContext(leadershipTransferCohort);
+
+        // Send an immediate heart beat to the followers.
+        sendAppendEntries(0, false);
     }
 
-    protected void stopIsolatedLeaderCheckSchedule() {
-        if (isolatedLeaderCheckSchedule != null && !isolatedLeaderCheckSchedule.isCancelled()) {
-            isolatedLeaderCheckSchedule.cancel();
+    private void tryToCompleteLeadershipTransfer(final String followerId) {
+        if (leadershipTransferContext == null) {
+            return;
+        }
+
+        final Optional<String> requestedFollowerIdOptional
+                = leadershipTransferContext.transferCohort.getRequestedFollowerId();
+        if (requestedFollowerIdOptional.isPresent() && !requestedFollowerIdOptional.get().equals(followerId)) {
+            // we want to transfer leadership to specific follower
+            return;
         }
-    }
 
-    protected void scheduleIsolatedLeaderCheck(FiniteDuration isolatedCheckInterval) {
-        isolatedLeaderCheckSchedule = context.getActorSystem().scheduler().schedule(isolatedCheckInterval, isolatedCheckInterval,
-            context.getActor(), new IsolatedLeaderCheck(),
-            context.getActorSystem().dispatcher(), context.getActor());
+        FollowerLogInformation followerInfo = getFollower(followerId);
+        if (followerInfo == null) {
+            return;
+        }
+
+        long lastIndex = context.getReplicatedLog().lastIndex();
+        boolean isVoting = context.getPeerInfo(followerId).isVoting();
+
+        log.debug("{}: tryToCompleteLeadershipTransfer: followerId: {}, matchIndex: {}, lastIndex: {}, isVoting: {}",
+                logName(), followerId, followerInfo.getMatchIndex(), lastIndex, isVoting);
+
+        if (isVoting && followerInfo.getMatchIndex() == lastIndex) {
+            log.debug("{}: Follower's log matches - sending ElectionTimeout", logName());
+
+            // We can't be sure if the follower has applied all its log entries to its state so send an
+            // additional AppendEntries with the latest commit index.
+            sendAppendEntries(0, false);
+
+            // Now send a TimeoutNow message to the matching follower to immediately start an election.
+            ActorSelection followerActor = context.getPeerActorSelection(followerId);
+            followerActor.tell(TimeoutNow.INSTANCE, context.getActor());
+
+            log.debug("{}: Leader transfer complete", logName());
+
+            leadershipTransferContext.transferCohort.transferComplete();
+            leadershipTransferContext = null;
+        }
     }
 
     @Override
-    public void close() throws Exception {
-        stopInstallSnapshotSchedule();
-        stopIsolatedLeaderCheckSchedule();
+    public void close() {
+        if (leadershipTransferContext != null) {
+            LeadershipTransferContext localLeadershipTransferContext = leadershipTransferContext;
+            leadershipTransferContext = null;
+            localLeadershipTransferContext.transferCohort.abortTransfer();
+        }
+
         super.close();
     }
 
     @VisibleForTesting
-    void markFollowerActive(String followerId) {
+    void markFollowerActive(final String followerId) {
         getFollower(followerId).markFollowerActive();
     }
 
     @VisibleForTesting
-    void markFollowerInActive(String followerId) {
+    void markFollowerInActive(final String followerId) {
         getFollower(followerId).markFollowerInActive();
     }
+
+    private static class LeadershipTransferContext {
+        RaftActorLeadershipTransferCohort transferCohort;
+        Stopwatch timer = Stopwatch.createStarted();
+
+        LeadershipTransferContext(final RaftActorLeadershipTransferCohort transferCohort) {
+            this.transferCohort = transferCohort;
+        }
+
+        boolean isExpired(final long timeout) {
+            if (timer.elapsed(TimeUnit.MILLISECONDS) >= timeout) {
+                transferCohort.abortTransfer();
+                return true;
+            }
+
+            return false;
+        }
+    }
 }

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