Bug 5504: Add PreLeader raft state

[controller.git] / opendaylight / md-sal / sal-akka-raft / src / main / java / org / opendaylight / controller / cluster / raft / behaviors / PreLeader.java

diff --git a/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/PreLeader.java b/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/PreLeader.java
new file mode 100644 (file)
index 0000000..e3ae4f4
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+++ b/opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/PreLeader.java
@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2016 Brocade Communications Systems, Inc. and others.  All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.opendaylight.controller.cluster.raft.behaviors;
+
+import akka.actor.ActorRef;
+import org.opendaylight.controller.cluster.raft.RaftActorContext;
+import org.opendaylight.controller.cluster.raft.RaftState;
+import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
+import org.opendaylight.controller.cluster.raft.persisted.NoopPayload;
+
+/**
+ * The behavior of a RaftActor when it is in the PreLeader state. This state performs all the duties of
+ * Leader with the added behavior of attempting to commit all uncommitted entries from the previous leader's
+ * term. Raft does not allow a leader to commit entries from a previous term by simply counting replicas -
+ * only entries from the leader's current term can be committed (§5.4.2). Rather then waiting for a client
+ * interaction to commit a new entry, the PreLeader state immediately appends a no-op entry (NoopPayload) to
+ * the log with the leader's current term. Once the no-op entry is committed, all prior entries are committed
+ * indirectly. Once all entries are committed, ie commitIndex matches the last log index, it switches to the
+ * normal Leader state.
+ * <p>
+ * The use of a no-op entry in this manner is outlined in the last paragraph in §8 of the
+ * <a href="https://raft.github.io/raft.pdf">extended raft version</a>.
+ *
+ * @author Thomas Pantelis
+ */
+public class PreLeader extends AbstractLeader {
+
+    public PreLeader(RaftActorContext context) {
+        super(context, RaftState.PreLeader);
+
+        context.getActor().tell(NoopPayload.INSTANCE, context.getActor());
+    }
+
+    @Override
+    protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
+        RaftActorBehavior returnBehavior = super.handleAppendEntriesReply(sender, appendEntriesReply);
+
+        if(context.getCommitIndex() >= context.getReplicatedLog().lastIndex()) {
+            // We've committed all entries - we can switch to Leader.
+            returnBehavior = internalSwitchBehavior(new Leader(context, this));
+        }
+
+        return returnBehavior;
+    }
+}