Implement anti-entropy for the EventuallyConsistentMap.

ONOS-857. 

Change-Id: Ife2070142d3c165c2a0035c3011c05b426c8baa4

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.store.impl;
+
+import org.onosproject.cluster.NodeId;
+import org.onosproject.store.Timestamp;
+
+import java.util.Map;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Anti-entropy advertisement message for eventually consistent map.
+ */
+public class AntiEntropyAdvertisement<K> {
+
+    private final NodeId sender;
+    private final Map<K, Timestamp> timestamps;
+    private final Map<K, Timestamp> tombstones;
+
+    /**
+     * Creates a new anti entropy advertisement message.
+     *
+     * @param sender the sender's node ID
+     * @param timestamps map of item key to timestamp for current items
+     * @param tombstones map of item key to timestamp for removed items
+     */
+    public AntiEntropyAdvertisement(NodeId sender,
+                                    Map<K, Timestamp> timestamps,
+                                    Map<K, Timestamp> tombstones) {
+        this.sender = checkNotNull(sender);
+        this.timestamps = checkNotNull(timestamps);
+        this.tombstones = checkNotNull(tombstones);
+    }
+
+    /**
+     * Returns the sender's node ID.
+     *
+     * @return the sender's node ID
+     */
+    public NodeId sender() {
+        return sender;
+    }
+
+    /**
+     * Returns the map of current item timestamps.
+     *
+     * @return current item timestamps
+     */
+    public Map<K, Timestamp> timestamps() {
+        return timestamps;
+    }
+
+    /**
+     * Returns the map of removed item timestamps.
+     *
+     * @return removed item timestamps
+     */
+    public Map<K, Timestamp> tombstones() {
+        return tombstones;
+    }
+
+    // For serializer
+    @SuppressWarnings("unused")
+    private AntiEntropyAdvertisement() {
+        this.sender = null;
+        this.timestamps = null;
+        this.tombstones = null;
+    }
+}