Supporting Atomix classes for DocumentTree distributed primitive

Change-Id: I754222337401f90f976d4152b6abbdf2e1a4df8e

+/*
+ * Copyright 2016-present 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.service;
+
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+
+import javax.annotation.concurrent.NotThreadSafe;
+
+/**
+ * A hierarchical <a href="https://en.wikipedia.org/wiki/Document_Object_Model">document tree</a> data structure.
+ *
+ * @param <V> document tree value type
+ */
+@NotThreadSafe
+public interface AsyncDocumentTree<V> extends DistributedPrimitive {
+
+    /**
+     * Returns the {@link DocumentPath path} to root of the tree.
+     *
+     * @return path to root of the tree
+     */
+    DocumentPath root();
+
+    /**
+     * Returns the child values for this node.
+     *
+     * @param path path to the node
+     * @return future for mapping from a child name to its value
+     * @throws NoSuchDocumentPathException if the path does not point to a valid node
+     */
+    CompletableFuture<Map<String, Versioned<V>>> getChildren(DocumentPath path);
+
+    /**
+     * Returns a value (and version) of the tree node at specified path.
+     *
+     * @param path path to node
+     * @return future for node value or {@code null} if path does not point to a valid node
+     */
+    CompletableFuture<Versioned<V>> get(DocumentPath path);
+
+    /**
+     * Creates or updates a document tree node.
+     *
+     * @param path path for the node to create or update
+     * @param value the non-null value to be associated with the key
+     * @return future for the previous mapping or {@code null} if there was no previous mapping. Future will
+     * be completed with a NoSuchDocumentPathException if the parent node (for the node to create/update) does not exist
+     */
+    CompletableFuture<Versioned<V>> set(DocumentPath path, V value);
+
+    /**
+     * Creates a document tree node if one does not exist already.
+     *
+     * @param path path for the node to create
+     * @param value the non-null value to be associated with the key
+     * @return future that is completed with {@code true} if the mapping could be added
+     * successfully; {@code false} otherwise. Future will be completed with a
+     * IllegalDocumentModificationException if the parent node (for the node to create) does not exist
+     */
+    CompletableFuture<Boolean> create(DocumentPath path, V value);
+
+    /**
+     * Conditionally updates a tree node if the current version matches a specified version.
+     *
+     * @param path path for the node to create
+     * @param newValue the non-null value to be associated with the key
+     * @param version current version of the value for update to occur
+     * @return future that is completed with {@code true} if the update was made and the tree was
+     * modified, {@code false} otherwise.
+     */
+    CompletableFuture<Boolean> replace(DocumentPath path, V newValue, long version);
+
+    /**
+     * Conditionally updates a tree node if the current value matches a specified value.
+     *
+     * @param path path for the node to create
+     * @param newValue the non-null value to be associated with the key
+     * @param currentValue current value for update to occur
+     * @return future that is completed with {@code true} if the update was made and the tree was
+     * modified, {@code false} otherwise.
+     */
+    CompletableFuture<Boolean> replace(DocumentPath path, V newValue, V currentValue);
+
+    /**
+     * Removes the node with the specified path.
+     *
+     * @param path path for the node to remove
+     * @return future for the previous value. Future will be completed with a
+     * IllegalDocumentModificationException if the node to be removed is either the root
+     * node or has one or more children. Future will be completed with a
+     * NoSuchDocumentPathException if the node to be removed does not exist
+     */
+    CompletableFuture<Versioned<V>> removeNode(DocumentPath path);
+
+    /**
+     * Registers a listener to be notified when a subtree rooted at the specified path
+     * is modified.
+     *
+     * @param path path to root of subtree to monitor for updates
+     * @param listener listener to be notified
+     */
+    CompletableFuture<Void> addListener(DocumentPath path, DocumentTreeListener<V> listener);
+
+    /**
+     * Unregisters a previously added listener.
+     *
+     * @param listener listener to unregister
+     */
+    CompletableFuture<Void> removeListener(DocumentTreeListener<V> listener);
+
+    /**
+     * Registers a listener to be notified when the tree is modified.
+     *
+     * @param listener listener to be notified
+     */
+    default CompletableFuture<Void> addListener(DocumentTreeListener<V> listener) {
+        return addListener(root(), listener);
+    }
+}

@@ -72,6 +72,11 @@ public interface DistributedPrimitive {
         WORK_QUEUE,
         WORK_QUEUE,
 
 
         /**
         /**
+         * Document tree.
+         */
+        DOCUMENT_TREE,
+
+        /**
          * Distributed topic.
          * Distributed topic.
          */
          */
         TOPIC,
         TOPIC,

@@ -52,6 +52,14 @@ public class DocumentTreeEvent<V> {
     private final Optional<Versioned<V>> newValue;
     private final Optional<Versioned<V>> newValue;
     private final Optional<Versioned<V>> oldValue;
     private final Optional<Versioned<V>> oldValue;
 
 
+    @SuppressWarnings("unused")
+    private DocumentTreeEvent() {
+        this.path = null;
+        this.type = null;
+        this.newValue = null;
+        this.oldValue = null;
+    }
+
     /**
     /**
      * Constructs a new {@code DocumentTreeEvent}.
      * Constructs a new {@code DocumentTreeEvent}.
      *
      *

@@ -15,12 +15,13 @@
  */
  */
 package org.onosproject.store.primitives.impl;
 package org.onosproject.store.primitives.impl;
 
 
-import com.google.common.collect.ImmutableList;
-import com.google.common.collect.Maps;
 import io.atomix.catalyst.serializer.Serializer;
 import io.atomix.catalyst.serializer.Serializer;
 import io.atomix.catalyst.serializer.TypeSerializerFactory;
 import io.atomix.catalyst.serializer.TypeSerializerFactory;
 import io.atomix.manager.util.ResourceManagerTypeResolver;
 import io.atomix.manager.util.ResourceManagerTypeResolver;
 import io.atomix.variables.internal.LongCommands;
 import io.atomix.variables.internal.LongCommands;
+
+import java.util.Arrays;
+
 import org.onlab.util.Match;
 import org.onlab.util.Match;
 import org.onosproject.cluster.Leader;
 import org.onosproject.cluster.Leader;
 import org.onosproject.cluster.Leadership;
 import org.onosproject.cluster.Leadership;
@@ -34,22 +35,28 @@ import org.onosproject.store.primitives.resources.impl.AtomixConsistentMultimapC
 import org.onosproject.store.primitives.resources.impl.AtomixConsistentSetMultimapFactory;
 import org.onosproject.store.primitives.resources.impl.AtomixConsistentSetMultimapFactory;
 import org.onosproject.store.primitives.resources.impl.AtomixConsistentTreeMapCommands;
 import org.onosproject.store.primitives.resources.impl.AtomixConsistentTreeMapCommands;
 import org.onosproject.store.primitives.resources.impl.AtomixConsistentTreeMapFactory;
 import org.onosproject.store.primitives.resources.impl.AtomixConsistentTreeMapFactory;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeFactory;
 import org.onosproject.store.primitives.resources.impl.AtomixLeaderElectorCommands;
 import org.onosproject.store.primitives.resources.impl.AtomixLeaderElectorCommands;
 import org.onosproject.store.primitives.resources.impl.AtomixLeaderElectorFactory;
 import org.onosproject.store.primitives.resources.impl.AtomixLeaderElectorFactory;
 import org.onosproject.store.primitives.resources.impl.AtomixWorkQueueCommands;
 import org.onosproject.store.primitives.resources.impl.AtomixWorkQueueCommands;
 import org.onosproject.store.primitives.resources.impl.AtomixWorkQueueFactory;
 import org.onosproject.store.primitives.resources.impl.AtomixWorkQueueFactory;
 import org.onosproject.store.primitives.resources.impl.CommitResult;
 import org.onosproject.store.primitives.resources.impl.CommitResult;
+import org.onosproject.store.primitives.resources.impl.DocumentTreeUpdateResult;
 import org.onosproject.store.primitives.resources.impl.MapEntryUpdateResult;
 import org.onosproject.store.primitives.resources.impl.MapEntryUpdateResult;
 import org.onosproject.store.primitives.resources.impl.PrepareResult;
 import org.onosproject.store.primitives.resources.impl.PrepareResult;
 import org.onosproject.store.primitives.resources.impl.RollbackResult;
 import org.onosproject.store.primitives.resources.impl.RollbackResult;
 import org.onosproject.store.serializers.KryoNamespaces;
 import org.onosproject.store.serializers.KryoNamespaces;
+import org.onosproject.store.service.DocumentPath;
+import org.onosproject.store.service.DocumentTreeEvent;
 import org.onosproject.store.service.MapEvent;
 import org.onosproject.store.service.MapEvent;
 import org.onosproject.store.service.MapTransaction;
 import org.onosproject.store.service.MapTransaction;
 import org.onosproject.store.service.Task;
 import org.onosproject.store.service.Task;
 import org.onosproject.store.service.Versioned;
 import org.onosproject.store.service.Versioned;
 import org.onosproject.store.service.WorkQueueStats;
 import org.onosproject.store.service.WorkQueueStats;
 
 
-import java.util.Arrays;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Maps;
 
 
 /**
 /**
  * Serializer utility for Atomix Catalyst.
  * Serializer utility for Atomix Catalyst.
@@ -69,6 +76,11 @@ public final class CatalystSerializers {
                                                                        Transaction.State.class,
                                                                        Transaction.State.class,
                                                                        PrepareResult.class,
                                                                        PrepareResult.class,
                                                                        CommitResult.class,
                                                                        CommitResult.class,
+                                                                       DocumentPath.class,
+                                                                       DocumentTreeUpdateResult.class,
+                                                                       DocumentTreeUpdateResult.Status.class,
+                                                                       DocumentTreeEvent.class,
+                                                                       DocumentTreeEvent.Type.class,
                                                                        RollbackResult.class));
                                                                        RollbackResult.class));
         // ONOS classes
         // ONOS classes
         serializer.register(Change.class, factory);
         serializer.register(Change.class, factory);
@@ -90,6 +102,11 @@ public final class CatalystSerializers {
         serializer.register(MapEvent.class, factory);
         serializer.register(MapEvent.class, factory);
         serializer.register(Task.class, factory);
         serializer.register(Task.class, factory);
         serializer.register(WorkQueueStats.class, factory);
         serializer.register(WorkQueueStats.class, factory);
+        serializer.register(DocumentPath.class, factory);
+        serializer.register(DocumentTreeUpdateResult.class, factory);
+        serializer.register(DocumentTreeUpdateResult.Status.class, factory);
+        serializer.register(DocumentTreeEvent.class, factory);
+        serializer.register(DocumentTreeEvent.Type.class, factory);
         serializer.register(Maps.immutableEntry("a", "b").getClass(), factory);
         serializer.register(Maps.immutableEntry("a", "b").getClass(), factory);
         serializer.register(ImmutableList.of().getClass(), factory);
         serializer.register(ImmutableList.of().getClass(), factory);
 
 
@@ -97,6 +114,7 @@ public final class CatalystSerializers {
         serializer.resolve(new AtomixConsistentMapCommands.TypeResolver());
         serializer.resolve(new AtomixConsistentMapCommands.TypeResolver());
         serializer.resolve(new AtomixLeaderElectorCommands.TypeResolver());
         serializer.resolve(new AtomixLeaderElectorCommands.TypeResolver());
         serializer.resolve(new AtomixWorkQueueCommands.TypeResolver());
         serializer.resolve(new AtomixWorkQueueCommands.TypeResolver());
+        serializer.resolve(new AtomixDocumentTreeCommands.TypeResolver());
         serializer.resolve(new ResourceManagerTypeResolver());
         serializer.resolve(new ResourceManagerTypeResolver());
         serializer.resolve(new AtomixConsistentTreeMapCommands.TypeResolver());
         serializer.resolve(new AtomixConsistentTreeMapCommands.TypeResolver());
         serializer.resolve(new AtomixConsistentMultimapCommands.TypeResolver());
         serializer.resolve(new AtomixConsistentMultimapCommands.TypeResolver());
@@ -104,6 +122,7 @@ public final class CatalystSerializers {
         serializer.registerClassLoader(AtomixConsistentMapFactory.class)
         serializer.registerClassLoader(AtomixConsistentMapFactory.class)
                 .registerClassLoader(AtomixLeaderElectorFactory.class)
                 .registerClassLoader(AtomixLeaderElectorFactory.class)
                 .registerClassLoader(AtomixWorkQueueFactory.class)
                 .registerClassLoader(AtomixWorkQueueFactory.class)
+                .registerClassLoader(AtomixDocumentTreeFactory.class)
                 .registerClassLoader(AtomixConsistentTreeMapFactory.class)
                 .registerClassLoader(AtomixConsistentTreeMapFactory.class)
                 .registerClassLoader(AtomixConsistentSetMultimapFactory.class);
                 .registerClassLoader(AtomixConsistentSetMultimapFactory.class);
 
 

@@ -15,14 +15,15 @@
  */
  */
 package org.onosproject.store.primitives.resources.impl;
 package org.onosproject.store.primitives.resources.impl;
 
 
+import static com.google.common.base.Preconditions.checkState;
 import static org.onosproject.store.service.MapEvent.Type.INSERT;
 import static org.onosproject.store.service.MapEvent.Type.INSERT;
 import static org.onosproject.store.service.MapEvent.Type.REMOVE;
 import static org.onosproject.store.service.MapEvent.Type.REMOVE;
 import static org.onosproject.store.service.MapEvent.Type.UPDATE;
 import static org.onosproject.store.service.MapEvent.Type.UPDATE;
 import static org.slf4j.LoggerFactory.getLogger;
 import static org.slf4j.LoggerFactory.getLogger;
-import io.atomix.copycat.server.session.ServerSession;
 import io.atomix.copycat.server.Commit;
 import io.atomix.copycat.server.Commit;
 import io.atomix.copycat.server.Snapshottable;
 import io.atomix.copycat.server.Snapshottable;
 import io.atomix.copycat.server.StateMachineExecutor;
 import io.atomix.copycat.server.StateMachineExecutor;
+import io.atomix.copycat.server.session.ServerSession;
 import io.atomix.copycat.server.session.SessionListener;
 import io.atomix.copycat.server.session.SessionListener;
 import io.atomix.copycat.server.storage.snapshot.SnapshotReader;
 import io.atomix.copycat.server.storage.snapshot.SnapshotReader;
 import io.atomix.copycat.server.storage.snapshot.SnapshotWriter;
 import io.atomix.copycat.server.storage.snapshot.SnapshotWriter;
@@ -68,15 +69,13 @@ import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
 import com.google.common.collect.Sets;
 
 
-import static com.google.common.base.Preconditions.checkState;
-
 /**
 /**
  * State Machine for {@link AtomixConsistentMap} resource.
  * State Machine for {@link AtomixConsistentMap} resource.
  */
  */
 public class AtomixConsistentMapState extends ResourceStateMachine implements SessionListener, Snapshottable {
 public class AtomixConsistentMapState extends ResourceStateMachine implements SessionListener, Snapshottable {
 
 
     private final Logger log = getLogger(getClass());
     private final Logger log = getLogger(getClass());
-    private final Map<Long, Commit<? extends AtomixConsistentMapCommands.Listen>> listeners = new HashMap<>();
+    private final Map<Long, Commit<? extends Listen>> listeners = new HashMap<>();
     private final Map<String, MapEntryValue> mapEntries = new HashMap<>();
     private final Map<String, MapEntryValue> mapEntries = new HashMap<>();
     private final Set<String> preparedKeys = Sets.newHashSet();
     private final Set<String> preparedKeys = Sets.newHashSet();
     private final Map<TransactionId, Commit<? extends TransactionPrepare>> pendingTransactions = Maps.newHashMap();
     private final Map<TransactionId, Commit<? extends TransactionPrepare>> pendingTransactions = Maps.newHashMap();

+/*
+ * Copyright 2016-present 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.primitives.resources.impl;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import io.atomix.copycat.client.CopycatClient;
+import io.atomix.resource.AbstractResource;
+import io.atomix.resource.ResourceTypeInfo;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Properties;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Executor;
+
+import org.onlab.util.Match;
+import org.onlab.util.Tools;
+import org.onosproject.store.primitives.resources.impl.AtomixConsistentMapCommands.Unlisten;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Clear;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Get;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.GetChildren;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Listen;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Update;
+import org.onosproject.store.service.AsyncDocumentTree;
+import org.onosproject.store.service.DocumentPath;
+import org.onosproject.store.service.DocumentTreeEvent;
+import org.onosproject.store.service.DocumentTreeListener;
+import org.onosproject.store.service.IllegalDocumentModificationException;
+import org.onosproject.store.service.NoSuchDocumentPathException;
+import org.onosproject.store.service.Versioned;
+
+import com.google.common.util.concurrent.MoreExecutors;
+
+/**
+ * Distributed resource providing the {@link AsyncDocumentTree} primitive.
+ */
+@ResourceTypeInfo(id = -156, factory = AtomixDocumentTreeFactory.class)
+public class AtomixDocumentTree extends AbstractResource<AtomixDocumentTree>
+    implements AsyncDocumentTree<byte[]> {
+
+    private final Map<DocumentTreeListener<byte[]>, Executor> eventListeners = new HashMap<>();
+    public static final String CHANGE_SUBJECT = "changeEvents";
+
+    protected AtomixDocumentTree(CopycatClient client, Properties options) {
+        super(client, options);
+    }
+
+    @Override
+    public CompletableFuture<AtomixDocumentTree> open() {
+        return super.open().thenApply(result -> {
+            client.onStateChange(state -> {
+                if (state == CopycatClient.State.CONNECTED && isListening()) {
+                    client.submit(new Listen());
+                }
+            });
+            client.onEvent(CHANGE_SUBJECT, this::processTreeUpdates);
+            return result;
+        });
+    }
+
+    @Override
+    public String name() {
+        return null;
+    }
+
+    @Override
+    public Type primitiveType() {
+        return Type.DOCUMENT_TREE;
+    }
+
+    @Override
+    public CompletableFuture<Void> destroy() {
+        return client.submit(new Clear());
+    }
+
+    @Override
+    public DocumentPath root() {
+        return DocumentPath.from("root");
+    }
+
+    @Override
+    public CompletableFuture<Map<String, Versioned<byte[]>>> getChildren(DocumentPath path) {
+        return client.submit(new GetChildren(checkNotNull(path)));
+    }
+
+    @Override
+    public CompletableFuture<Versioned<byte[]>> get(DocumentPath path) {
+        return client.submit(new Get(checkNotNull(path)));
+    }
+
+    @Override
+    public CompletableFuture<Versioned<byte[]>> set(DocumentPath path, byte[] value) {
+        return client.submit(new Update(checkNotNull(path), checkNotNull(value), Match.any(), Match.any()))
+                .thenCompose(result -> {
+                    if (result.status() == DocumentTreeUpdateResult.Status.INVALID_PATH) {
+                        return Tools.exceptionalFuture(new NoSuchDocumentPathException());
+                    } else if (result.status() == DocumentTreeUpdateResult.Status.ILLEGAL_MODIFICATION) {
+                        return Tools.exceptionalFuture(new IllegalDocumentModificationException());
+                    } else {
+                        return CompletableFuture.completedFuture(result);
+                    }
+                }).thenApply(result -> result.oldValue());
+    }
+
+    @Override
+    public CompletableFuture<Boolean> create(DocumentPath path, byte[] value) {
+        return client.submit(new Update(checkNotNull(path), checkNotNull(value), Match.ifNull(), Match.any()))
+                .thenCompose(result -> {
+                    if (result.status() == DocumentTreeUpdateResult.Status.INVALID_PATH) {
+                        return Tools.exceptionalFuture(new NoSuchDocumentPathException());
+                    } else if (result.status() == DocumentTreeUpdateResult.Status.ILLEGAL_MODIFICATION) {
+                        return Tools.exceptionalFuture(new IllegalDocumentModificationException());
+                    } else {
+                        return CompletableFuture.completedFuture(result);
+                    }
+                }).thenApply(result -> result.created());
+    }
+
+    @Override
+    public CompletableFuture<Boolean> replace(DocumentPath path, byte[] newValue, long version) {
+        return client.submit(new Update(checkNotNull(path), newValue, Match.any(), Match.ifValue(version)))
+                .thenApply(result -> result.updated());
+    }
+
+    @Override
+    public CompletableFuture<Boolean> replace(DocumentPath path, byte[] newValue, byte[] currentValue) {
+        return client.submit(new Update(checkNotNull(path), newValue, Match.ifValue(currentValue), Match.any()))
+                .thenCompose(result -> {
+                    if (result.status() == DocumentTreeUpdateResult.Status.INVALID_PATH) {
+                        return Tools.exceptionalFuture(new NoSuchDocumentPathException());
+                    } else if (result.status() == DocumentTreeUpdateResult.Status.ILLEGAL_MODIFICATION) {
+                        return Tools.exceptionalFuture(new IllegalDocumentModificationException());
+                    } else {
+                        return CompletableFuture.completedFuture(result);
+                    }
+                }).thenApply(result -> result.updated());
+    }
+
+    @Override
+    public CompletableFuture<Versioned<byte[]>> removeNode(DocumentPath path) {
+        if (path.equals(DocumentPath.from("root"))) {
+            return Tools.exceptionalFuture(new IllegalDocumentModificationException());
+        }
+        return client.submit(new Update(checkNotNull(path), null, Match.ifNotNull(), Match.any()))
+                .thenCompose(result -> {
+                    if (result.status() == DocumentTreeUpdateResult.Status.INVALID_PATH) {
+                        return Tools.exceptionalFuture(new NoSuchDocumentPathException());
+                    } else if (result.status() == DocumentTreeUpdateResult.Status.ILLEGAL_MODIFICATION) {
+                        return Tools.exceptionalFuture(new IllegalDocumentModificationException());
+                    } else {
+                        return CompletableFuture.completedFuture(result);
+                    }
+                }).thenApply(result -> result.oldValue());
+    }
+
+    @Override
+    public CompletableFuture<Void> addListener(DocumentPath path, DocumentTreeListener<byte[]> listener) {
+        checkNotNull(path);
+        checkNotNull(listener);
+        // TODO: Support API that takes an executor
+        if (isListening()) {
+            eventListeners.putIfAbsent(listener, MoreExecutors.directExecutor());
+            return CompletableFuture.completedFuture(null);
+        } else {
+            return client.submit(new Listen(path))
+                         .thenRun(() -> eventListeners.put(listener, MoreExecutors.directExecutor()));
+        }
+    }
+
+    @Override
+    public CompletableFuture<Void> removeListener(DocumentTreeListener<byte[]> listener) {
+        checkNotNull(listener);
+        if (eventListeners.remove(listener) != null && eventListeners.isEmpty()) {
+            return client.submit(new Unlisten()).thenApply(v -> null);
+        }
+        return CompletableFuture.completedFuture(null);
+    }
+
+    private boolean isListening() {
+        return !eventListeners.isEmpty();
+    }
+
+    private void processTreeUpdates(List<DocumentTreeEvent<byte[]>> events) {
+        events.forEach(event ->
+            eventListeners.forEach((listener, executor) -> executor.execute(() -> listener.event(event))));
+    }
+}

+/*
+ * Copyright 2016-present 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.primitives.resources.impl;
+
+import io.atomix.catalyst.buffer.BufferInput;
+import io.atomix.catalyst.buffer.BufferOutput;
+import io.atomix.catalyst.serializer.CatalystSerializable;
+import io.atomix.catalyst.serializer.SerializableTypeResolver;
+import io.atomix.catalyst.serializer.Serializer;
+import io.atomix.catalyst.serializer.SerializerRegistry;
+import io.atomix.copycat.Command;
+import io.atomix.copycat.Query;
+
+import java.util.Map;
+
+import org.onlab.util.Match;
+import org.onosproject.store.service.DocumentPath;
+import org.onosproject.store.service.Versioned;
+
+import com.google.common.base.MoreObjects;
+
+/**
+ * {@link AtomixDocumentTree} resource state machine operations.
+ */
+public class AtomixDocumentTreeCommands {
+
+    /**
+     * Abstract DocumentTree operation.
+     */
+    public abstract static class DocumentTreeOperation<V> implements CatalystSerializable {
+
+        private DocumentPath path;
+
+        DocumentTreeOperation(DocumentPath path) {
+            this.path = path;
+        }
+
+        public DocumentPath path() {
+            return path;
+        }
+
+        @Override
+        public void writeObject(BufferOutput<?> buffer, Serializer serializer) {
+            serializer.writeObject(path, buffer);
+        }
+
+        @Override
+        public void readObject(BufferInput<?> buffer, Serializer serializer) {
+            path = serializer.readObject(buffer);
+        }
+    }
+
+    /**
+     * Abstract DocumentTree query.
+     */
+    @SuppressWarnings("serial")
+    public abstract static class DocumentTreeQuery<V> extends DocumentTreeOperation<V> implements Query<V> {
+
+         DocumentTreeQuery(DocumentPath path) {
+             super(path);
+        }
+
+         @Override
+         public ConsistencyLevel consistency() {
+           return ConsistencyLevel.SEQUENTIAL;
+         }
+    }
+
+    /**
+     * Abstract DocumentTree command.
+     */
+    @SuppressWarnings("serial")
+    public abstract static class DocumentTreeCommand<V> extends DocumentTreeOperation<V> implements Command<V> {
+
+        DocumentTreeCommand(DocumentPath path) {
+             super(path);
+        }
+    }
+
+    /**
+     * DocumentTree#get query.
+     */
+    @SuppressWarnings("serial")
+    public static class Get extends DocumentTreeQuery<Versioned<byte[]>> {
+        public Get() {
+            super(null);
+        }
+
+        public Get(DocumentPath path) {
+            super(path);
+        }
+
+        @Override
+        public String toString() {
+            return MoreObjects.toStringHelper(getClass())
+                    .add("path", path())
+                    .toString();
+        }
+    }
+
+    /**
+     * DocumentTree#getChildren query.
+     */
+    @SuppressWarnings("serial")
+    public static class GetChildren extends DocumentTreeQuery<Map<String, Versioned<byte[]>>> {
+        public GetChildren() {
+            super(null);
+        }
+
+        public GetChildren(DocumentPath path) {
+            super(path);
+        }
+
+        @Override
+        public String toString() {
+            return MoreObjects.toStringHelper(getClass())
+                    .add("path", path())
+                    .toString();
+        }
+    }
+
+    /**
+     * DocumentTree update command.
+     */
+    @SuppressWarnings("serial")
+    public static class Update extends DocumentTreeCommand<DocumentTreeUpdateResult<byte[]>> {
+
+        private byte[] value;
+        private Match<byte[]> valueMatch;
+        private Match<Long> versionMatch;
+
+        public Update() {
+            super(null);
+            this.value = null;
+            this.valueMatch = null;
+            this.versionMatch = null;
+        }
+
+        public Update(DocumentPath path, byte[] value, Match<byte[]> valueMatch, Match<Long> versionMatch) {
+            super(path);
+            this.value = value;
+            this.valueMatch = valueMatch;
+            this.versionMatch = versionMatch;
+        }
+
+        public byte[] value() {
+            return value;
+        }
+
+        public Match<byte[]> valueMatch() {
+            return valueMatch;
+        }
+
+        public Match<Long> versionMatch() {
+            return versionMatch;
+        }
+
+        @Override
+        public void writeObject(BufferOutput<?> buffer, Serializer serializer) {
+            super.writeObject(buffer, serializer);
+            serializer.writeObject(value, buffer);
+            serializer.writeObject(valueMatch, buffer);
+            serializer.writeObject(versionMatch, buffer);
+        }
+
+        @Override
+        public void readObject(BufferInput<?> buffer, Serializer serializer) {
+            super.readObject(buffer, serializer);
+            value = serializer.readObject(buffer);
+            valueMatch = serializer.readObject(buffer);
+            versionMatch = serializer.readObject(buffer);
+        }
+
+        @Override
+        public String toString() {
+            return MoreObjects.toStringHelper(getClass())
+                    .add("path", path())
+                    .add("value", value)
+                    .add("valueMatch", valueMatch)
+                    .add("versionMatch", versionMatch)
+                    .toString();
+        }
+    }
+
+    /**
+     * Clear command.
+     */
+    @SuppressWarnings("serial")
+    public static class Clear implements Command<Void>, CatalystSerializable {
+        @Override
+        public void writeObject(BufferOutput<?> buffer, Serializer serializer) {
+        }
+
+        @Override
+        public void readObject(BufferInput<?> buffer, Serializer serializer) {
+        }
+    }
+
+    /**
+     * Change listen.
+     */
+    @SuppressWarnings("serial")
+    public static class Listen extends DocumentTreeCommand<Void> {
+
+        public Listen() {
+            this(DocumentPath.from("root"));
+        }
+
+        public Listen(DocumentPath path) {
+            super(path);
+        }
+
+        @Override
+        public void writeObject(BufferOutput<?> buffer, Serializer serializer) {
+        }
+
+        @Override
+        public void readObject(BufferInput<?> buffer, Serializer serializer) {
+        }
+    }
+
+    /**
+     * Change unlisten.
+     */
+    @SuppressWarnings("serial")
+    public static class Unlisten extends DocumentTreeCommand<Void> {
+
+        public Unlisten() {
+            this(DocumentPath.from("root"));
+        }
+
+        public Unlisten(DocumentPath path) {
+            super(path);
+        }
+
+        @Override
+        public void writeObject(BufferOutput<?> buffer, Serializer serializer) {
+        }
+
+        @Override
+        public void readObject(BufferInput<?> buffer, Serializer serializer) {
+        }
+    }
+
+    /**
+     * DocumentTree command type resolver.
+     */
+    public static class TypeResolver implements SerializableTypeResolver {
+        @Override
+        public void resolve(SerializerRegistry registry) {
+            registry.register(Get.class, -911);
+            registry.register(GetChildren.class, -912);
+            registry.register(Update.class, -913);
+            registry.register(Listen.class, -914);
+            registry.register(Unlisten.class, -915);
+            registry.register(Clear.class, -916);
+        }
+    }
+}

+/*
+ * Copyright 2016-present 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.primitives.resources.impl;
+
+import io.atomix.catalyst.serializer.SerializableTypeResolver;
+import io.atomix.copycat.client.CopycatClient;
+import io.atomix.resource.ResourceFactory;
+import io.atomix.resource.ResourceStateMachine;
+
+import java.util.Properties;
+
+/**
+ * {@link AtomixDocumentTree} resource factory.
+ *
+ */
+public class AtomixDocumentTreeFactory implements ResourceFactory<AtomixDocumentTree> {
+
+    @Override
+    public SerializableTypeResolver createSerializableTypeResolver() {
+      return new AtomixDocumentTreeCommands.TypeResolver();
+    }
+
+    @Override
+    public ResourceStateMachine createStateMachine(Properties config) {
+      return new AtomixDocumentTreeState(config);
+    }
+
+    @Override
+    public AtomixDocumentTree createInstance(CopycatClient client, Properties options) {
+      return new AtomixDocumentTree(client, options);
+    }
+  }
\ No newline at end of file

+/*
+ * Copyright 2016-present 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.primitives.resources.impl;
+
+import static org.slf4j.LoggerFactory.getLogger;
+import io.atomix.copycat.server.Commit;
+import io.atomix.copycat.server.Snapshottable;
+import io.atomix.copycat.server.StateMachineExecutor;
+import io.atomix.copycat.server.session.ServerSession;
+import io.atomix.copycat.server.session.SessionListener;
+import io.atomix.copycat.server.storage.snapshot.SnapshotReader;
+import io.atomix.copycat.server.storage.snapshot.SnapshotWriter;
+import io.atomix.resource.ResourceStateMachine;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Properties;
+import java.util.Queue;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.stream.Collectors;
+
+import org.onlab.util.Match;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Clear;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Get;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.GetChildren;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Listen;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Unlisten;
+import org.onosproject.store.primitives.resources.impl.AtomixDocumentTreeCommands.Update;
+import org.onosproject.store.primitives.resources.impl.DocumentTreeUpdateResult.Status;
+import org.onosproject.store.service.DocumentPath;
+import org.onosproject.store.service.DocumentTree;
+import org.onosproject.store.service.DocumentTreeEvent;
+import org.onosproject.store.service.DocumentTreeEvent.Type;
+import org.onosproject.store.service.IllegalDocumentModificationException;
+import org.onosproject.store.service.NoSuchDocumentPathException;
+import org.onosproject.store.service.Versioned;
+import org.slf4j.Logger;
+
+import com.google.common.base.Throwables;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Queues;
+
+/**
+ * State Machine for {@link AtomixDocumentTree} resource.
+ */
+public class AtomixDocumentTreeState
+    extends ResourceStateMachine
+    implements SessionListener, Snapshottable {
+
+    private final Logger log = getLogger(getClass());
+    private final Map<Long, Commit<? extends Listen>> listeners = new HashMap<>();
+    private final AtomicLong versionCounter = new AtomicLong(0);
+    private final DocumentTree<TreeNodeValue> docTree = new DefaultDocumentTree<>(versionCounter::incrementAndGet);
+
+    public AtomixDocumentTreeState(Properties properties) {
+        super(properties);
+    }
+
+    @Override
+    public void snapshot(SnapshotWriter writer) {
+        writer.writeLong(versionCounter.get());
+    }
+
+    @Override
+    public void install(SnapshotReader reader) {
+        versionCounter.set(reader.readLong());
+    }
+
+    @Override
+    protected void configure(StateMachineExecutor executor) {
+        // Listeners
+        executor.register(Listen.class, this::listen);
+        executor.register(Unlisten.class, this::unlisten);
+        // queries
+        executor.register(Get.class, this::get);
+        executor.register(GetChildren.class, this::getChildren);
+        // commands
+        executor.register(Update.class, this::update);
+        executor.register(Clear.class, this::clear);
+    }
+
+    protected void listen(Commit<? extends Listen> commit) {
+        Long sessionId = commit.session().id();
+        if (listeners.putIfAbsent(sessionId, commit) != null) {
+            commit.close();
+            return;
+        }
+        commit.session()
+                .onStateChange(
+                        state -> {
+                            if (state == ServerSession.State.CLOSED
+                                    || state == ServerSession.State.EXPIRED) {
+                                Commit<? extends Listen> listener = listeners.remove(sessionId);
+                                if (listener != null) {
+                                    listener.close();
+                                }
+                            }
+                        });
+    }
+
+    protected void unlisten(Commit<? extends Unlisten> commit) {
+        try {
+            closeListener(commit.session().id());
+        } finally {
+            commit.close();
+        }
+    }
+
+    protected Versioned<byte[]> get(Commit<? extends Get> commit) {
+        try {
+            Versioned<TreeNodeValue> value = docTree.get(commit.operation().path());
+            return value == null ? null : value.map(node -> node == null ? null : node.value());
+        } finally {
+            commit.close();
+        }
+    }
+
+    protected Map<String, Versioned<byte[]>> getChildren(Commit<? extends GetChildren> commit) {
+        try {
+            Map<String, Versioned<TreeNodeValue>> children = docTree.getChildren(commit.operation().path());
+            return children == null
+                    ? null : Maps.newHashMap(Maps.transformValues(children,
+                                                                  value -> value.map(TreeNodeValue::value)));
+        } finally {
+            commit.close();
+        }
+    }
+
+    protected DocumentTreeUpdateResult<byte[]> update(Commit<? extends Update> commit) {
+        DocumentTreeUpdateResult<byte[]> result = null;
+        DocumentPath path = commit.operation().path();
+        boolean updated = false;
+        Versioned<TreeNodeValue> currentValue = docTree.get(path);
+        try {
+            Match<Long> versionMatch = commit.operation().versionMatch();
+            Match<byte[]> valueMatch = commit.operation().valueMatch();
+
+            if (versionMatch.matches(currentValue == null ? null : currentValue.version())
+                    && valueMatch.matches(currentValue == null ? null : currentValue.value().value())) {
+                if (commit.operation().value() == null) {
+                    docTree.removeNode(path);
+                } else {
+                    docTree.set(path, new NonTransactionalCommit(commit));
+                }
+                updated = true;
+            }
+            Versioned<TreeNodeValue> newValue = updated ? docTree.get(path) : currentValue;
+            Status updateStatus = updated
+                    ? Status.OK : commit.operation().value() == null ? Status.INVALID_PATH : Status.NOOP;
+            result = new DocumentTreeUpdateResult<>(path,
+                    updateStatus,
+                    newValue == null
+                        ? null : newValue.map(TreeNodeValue::value),
+                    currentValue == null
+                        ? null : currentValue.map(TreeNodeValue::value));
+        } catch (IllegalDocumentModificationException e) {
+            result = DocumentTreeUpdateResult.illegalModification(path);
+        } catch (NoSuchDocumentPathException e) {
+            result = DocumentTreeUpdateResult.invalidPath(path);
+        } catch (Exception e) {
+            log.error("Failed to apply {} to state machine", commit.operation(), e);
+            throw Throwables.propagate(e);
+        } finally {
+            if (updated) {
+                if (currentValue != null) {
+                    currentValue.value().discard();
+                }
+            } else {
+                commit.close();
+            }
+        }
+        notifyListeners(path, result);
+        return result;
+    }
+
+    protected void clear(Commit<? extends Clear> commit) {
+        try {
+            Queue<DocumentPath> toClearQueue = Queues.newArrayDeque();
+            Map<String, Versioned<TreeNodeValue>> topLevelChildren = docTree.getChildren(DocumentPath.from("root"));
+            toClearQueue.addAll(topLevelChildren.keySet()
+                                                .stream()
+                                                .map(name -> new DocumentPath(name, DocumentPath.from("root")))
+                                                .collect(Collectors.toList()));
+            while (!toClearQueue.isEmpty()) {
+                DocumentPath path = toClearQueue.remove();
+                Map<String, Versioned<TreeNodeValue>> children = docTree.getChildren(path);
+                if (children.size() == 0) {
+                    docTree.removeNode(path).value().discard();
+                } else {
+                    children.keySet()
+                            .stream()
+                            .forEach(name -> toClearQueue.add(new DocumentPath(name, path)));
+                    toClearQueue.add(path);
+                }
+            }
+        } finally {
+            commit.close();
+        }
+    }
+
+    /**
+     * Interface implemented by tree node values.
+     */
+    private interface TreeNodeValue {
+        /**
+         * Returns the raw {@code byte[]}.
+         *
+         * @return raw value
+         */
+        byte[] value();
+
+        /**
+         * Discards the value by invoke appropriate clean up actions.
+         */
+        void discard();
+    }
+
+    /**
+     * A {@code TreeNodeValue} that is derived from a non-transactional update
+     * i.e. via any standard tree update operation.
+     */
+    private class NonTransactionalCommit implements TreeNodeValue {
+        private final Commit<? extends Update> commit;
+
+        public NonTransactionalCommit(Commit<? extends Update> commit) {
+            this.commit = commit;
+        }
+
+        @Override
+        public byte[] value() {
+            return commit.operation().value();
+        }
+
+        @Override
+        public void discard() {
+            commit.close();
+        }
+    }
+
+    private void notifyListeners(DocumentPath path, DocumentTreeUpdateResult<byte[]> result) {
+        if (result.status() != Status.OK) {
+            return;
+        }
+        DocumentTreeEvent<byte[]> event =
+                new DocumentTreeEvent<>(path,
+                        result.created() ? Type.CREATED : result.newValue() == null ? Type.DELETED : Type.UPDATED,
+                        Optional.ofNullable(result.newValue()),
+                        Optional.ofNullable(result.oldValue()));
+        Object message = ImmutableList.of(event);
+        listeners.values().forEach(commit -> {
+            commit.session().publish(AtomixDocumentTree.CHANGE_SUBJECT, message);
+            System.out.println("Sent " + message + " to " + commit.session().id());
+        });
+    }
+
+    @Override
+    public void register(ServerSession session) {
+    }
+
+    @Override
+    public void unregister(ServerSession session) {
+        closeListener(session.id());
+    }
+
+    @Override
+    public void expire(ServerSession session) {
+        closeListener(session.id());
+    }
+
+    @Override
+    public void close(ServerSession session) {
+        closeListener(session.id());
+    }
+
+    private void closeListener(Long sessionId) {
+        Commit<? extends Listen> commit = listeners.remove(sessionId);
+        if (commit != null) {
+            commit.close();
+        }
+    }
+}

@@ -19,7 +19,7 @@ package org.onosproject.store.primitives.resources.impl;
 import java.util.Iterator;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Objects;
-import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
 
 
 import org.onosproject.store.service.DocumentPath;
 import org.onosproject.store.service.DocumentPath;
 import org.onosproject.store.service.DocumentTree;
 import org.onosproject.store.service.DocumentTree;
@@ -30,6 +30,7 @@ import org.onosproject.store.service.NoSuchDocumentPathException;
 import org.onosproject.store.service.Versioned;
 import org.onosproject.store.service.Versioned;
 
 
 import com.google.common.base.Preconditions;
 import com.google.common.base.Preconditions;
+import com.google.common.base.Supplier;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Maps;
 
 
 /**
 /**
@@ -41,10 +42,17 @@ public class DefaultDocumentTree<V> implements DocumentTree<V> {
 
 
     private static final DocumentPath ROOT_PATH = DocumentPath.from("root");
     private static final DocumentPath ROOT_PATH = DocumentPath.from("root");
     private final DefaultDocumentTreeNode<V> root;
     private final DefaultDocumentTreeNode<V> root;
-    private final AtomicInteger versionCounter = new AtomicInteger(0);
+    private final Supplier<Long> versionSupplier;
 
 
     public DefaultDocumentTree() {
     public DefaultDocumentTree() {
-        root = new DefaultDocumentTreeNode<V>(ROOT_PATH, null, nextVersion(), null);
+        AtomicLong versionCounter = new AtomicLong(0);
+        versionSupplier = versionCounter::incrementAndGet;
+        root = new DefaultDocumentTreeNode<V>(ROOT_PATH, null, versionSupplier.get(), null);
+    }
+
+    public DefaultDocumentTree(Supplier<Long> versionSupplier) {
+        root = new DefaultDocumentTreeNode<V>(ROOT_PATH, null, versionSupplier.get(), null);
+        this.versionSupplier = versionSupplier;
     }
     }
 
 
     @Override
     @Override
@@ -74,7 +82,7 @@ public class DefaultDocumentTree<V> implements DocumentTree<V> {
         checkRootModification(path);
         checkRootModification(path);
         DefaultDocumentTreeNode<V> node = getNode(path);
         DefaultDocumentTreeNode<V> node = getNode(path);
         if (node != null) {
         if (node != null) {
-            return node.update(value, nextVersion());
+            return node.update(value, versionSupplier.get());
         } else {
         } else {
             create(path, value);
             create(path, value);
             return null;
             return null;
@@ -93,7 +101,7 @@ public class DefaultDocumentTree<V> implements DocumentTree<V> {
         if (parentNode == null) {
         if (parentNode == null) {
             throw new IllegalDocumentModificationException();
             throw new IllegalDocumentModificationException();
         }
         }
-        parentNode.addChild(simpleName(path), value, nextVersion());
+        parentNode.addChild(simpleName(path), value, versionSupplier.get());
         return true;
         return true;
     }
     }
 
 
@@ -159,10 +167,6 @@ public class DefaultDocumentTree<V> implements DocumentTree<V> {
         return currentNode;
         return currentNode;
     }
     }
 
 
-    private long nextVersion() {
-        return versionCounter.incrementAndGet();
-    }
-
     private String simpleName(DocumentPath path) {
     private String simpleName(DocumentPath path) {
         return path.pathElements().get(path.pathElements().size() - 1);
         return path.pathElements().get(path.pathElements().size() - 1);
     }
     }

+/*
+ * Copyright 2016-present 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.primitives.resources.impl;
+
+import org.onosproject.store.service.DocumentPath;
+import org.onosproject.store.service.Versioned;
+
+import com.google.common.base.MoreObjects;
+
+/**
+ * Result of a document tree node update operation.
+ * <p>
+ * Both old and new values are accessible along with a status of update.
+ *
+ * @param <V> value type
+ */
+public class DocumentTreeUpdateResult<V> {
+
+    public enum Status {
+        /**
+         * Indicates a successful update.
+         */
+        OK,
+
+        /**
+         * Indicates a noop i.e. existing and new value are both same.
+         */
+        NOOP,
+
+        /**
+         * Indicates a failed update due to a write lock.
+         */
+        WRITE_LOCK,
+
+        /**
+         * Indicates a failed update due to a invalid path.
+         */
+        INVALID_PATH,
+
+        /**
+         * Indicates a failed update due to a illegal modification attempt.
+         */
+        ILLEGAL_MODIFICATION,
+    }
+
+    private final DocumentPath path;
+    private final Status status;
+    private final Versioned<V> oldValue;
+    private final Versioned<V> newValue;
+
+    public DocumentTreeUpdateResult(DocumentPath path,
+            Status status,
+            Versioned<V> newValue,
+            Versioned<V> oldValue) {
+        this.status = status;
+        this.path = path;
+        this.newValue = newValue;
+        this.oldValue = oldValue;
+    }
+
+    public static <V> DocumentTreeUpdateResult<V> invalidPath(DocumentPath path) {
+        return new DocumentTreeUpdateResult<>(path, Status.INVALID_PATH, null, null);
+    }
+
+    public static <V> DocumentTreeUpdateResult<V> illegalModification(DocumentPath path) {
+        return new DocumentTreeUpdateResult<>(path, Status.ILLEGAL_MODIFICATION, null, null);
+    }
+
+    public Status status() {
+        return status;
+    }
+
+    public DocumentPath path() {
+        return path;
+    }
+
+    public Versioned<V> oldValue() {
+        return oldValue;
+    }
+
+    public Versioned<V> newValue() {
+        return this.newValue;
+    }
+
+    public boolean updated() {
+        return status == Status.OK;
+    }
+
+    public boolean created() {
+        return updated() && oldValue == null;
+    }
+
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(getClass())
+                .add("path", path)
+                .add("status", status)
+                .add("newValue", newValue)
+                .add("oldValue", oldValue)
+                .toString();
+    }
+}

+/*
+ * Copyright 2016-present 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.primitives.resources.impl;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import io.atomix.resource.ResourceType;
+
+import java.util.Map;
+import java.util.UUID;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.BlockingQueue;
+
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Ignore;
+import org.junit.Test;
+import org.onosproject.store.service.DocumentPath;
+import org.onosproject.store.service.DocumentTreeEvent;
+import org.onosproject.store.service.DocumentTreeListener;
+import org.onosproject.store.service.IllegalDocumentModificationException;
+import org.onosproject.store.service.NoSuchDocumentPathException;
+import org.onosproject.store.service.Versioned;
+
+import com.google.common.base.Throwables;
+
+/**
+ * Unit tests for {@link AtomixDocumentTree}.
+ */
+public class AtomixDocumentTreeTest extends AtomixTestBase {
+    @BeforeClass
+    public static void preTestSetup() throws Throwable {
+        createCopycatServers(3);
+    }
+
+    @AfterClass
+    public static void postTestCleanup() throws Exception {
+        clearTests();
+    }
+    @Override
+    protected ResourceType resourceType() {
+        return new ResourceType(AtomixDocumentTree.class);
+    }
+    /**
+     * Tests queries (get and getChildren).
+     */
+    @Test
+    public void testQueries() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        Versioned<byte[]> root = tree.get(DocumentPath.from("root")).join();
+        assertEquals(1, root.version());
+        assertNull(root.value());
+    }
+
+    /**
+     * Tests create.
+     */
+    @Test
+    public void testCreate() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        tree.create(DocumentPath.from("root.a"), "a".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.b"), "ab".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+        Versioned<byte[]> a = tree.get(DocumentPath.from("root.a")).join();
+        assertArrayEquals("a".getBytes(), a.value());
+
+        Versioned<byte[]> ab = tree.get(DocumentPath.from("root.a.b")).join();
+        assertArrayEquals("ab".getBytes(), ab.value());
+
+        Versioned<byte[]> ac = tree.get(DocumentPath.from("root.a.c")).join();
+        assertArrayEquals("ac".getBytes(), ac.value());
+    }
+
+    /**
+     * Tests set.
+     */
+    @Test
+    public void testSet() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        tree.create(DocumentPath.from("root.a"), "a".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.b"), "ab".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+
+        tree.set(DocumentPath.from("root.a.d"), "ad".getBytes()).join();
+        Versioned<byte[]> ad = tree.get(DocumentPath.from("root.a.d")).join();
+        assertArrayEquals("ad".getBytes(), ad.value());
+
+        tree.set(DocumentPath.from("root.a"), "newA".getBytes()).join();
+        Versioned<byte[]> newA = tree.get(DocumentPath.from("root.a")).join();
+        assertArrayEquals("newA".getBytes(), newA.value());
+
+        tree.set(DocumentPath.from("root.a.b"), "newAB".getBytes()).join();
+        Versioned<byte[]> newAB = tree.get(DocumentPath.from("root.a.b")).join();
+        assertArrayEquals("newAB".getBytes(), newAB.value());
+    }
+
+    /**
+     * Tests replace if version matches.
+     */
+    @Test
+    public void testReplaceVersion() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        tree.create(DocumentPath.from("root.a"), "a".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.b"), "ab".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+
+        Versioned<byte[]> ab = tree.get(DocumentPath.from("root.a.b")).join();
+        assertTrue(tree.replace(DocumentPath.from("root.a.b"), "newAB".getBytes(), ab.version()).join());
+        Versioned<byte[]> newAB = tree.get(DocumentPath.from("root.a.b")).join();
+        assertArrayEquals("newAB".getBytes(), newAB.value());
+
+        assertFalse(tree.replace(DocumentPath.from("root.a.b"), "newestAB".getBytes(), ab.version()).join());
+        assertArrayEquals("newAB".getBytes(), tree.get(DocumentPath.from("root.a.b")).join().value());
+
+        assertFalse(tree.replace(DocumentPath.from("root.a.d"), "foo".getBytes(), 1).join());
+    }
+
+    /**
+     * Tests replace if value matches.
+     */
+    @Test
+    public void testReplaceValue() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        tree.create(DocumentPath.from("root.a"), "a".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.b"), "ab".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+
+        Versioned<byte[]> ab = tree.get(DocumentPath.from("root.a.b")).join();
+        assertTrue(tree.replace(DocumentPath.from("root.a.b"), "newAB".getBytes(), ab.value()).join());
+        Versioned<byte[]> newAB = tree.get(DocumentPath.from("root.a.b")).join();
+        assertArrayEquals("newAB".getBytes(), newAB.value());
+
+        assertFalse(tree.replace(DocumentPath.from("root.a.b"), "newestAB".getBytes(), ab.value()).join());
+        assertArrayEquals("newAB".getBytes(), tree.get(DocumentPath.from("root.a.b")).join().value());
+
+        assertFalse(tree.replace(DocumentPath.from("root.a.d"), "bar".getBytes(), "foo".getBytes()).join());
+    }
+
+    /**
+     * Tests remove.
+     */
+    @Test
+    public void testRemove() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        tree.create(DocumentPath.from("root.a"), "a".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.b"), "ab".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+
+        Versioned<byte[]> ab = tree.removeNode(DocumentPath.from("root.a.b")).join();
+        assertArrayEquals("ab".getBytes(), ab.value());
+        assertNull(tree.get(DocumentPath.from("root.a.b")).join());
+
+        Versioned<byte[]> ac = tree.removeNode(DocumentPath.from("root.a.c")).join();
+        assertArrayEquals("ac".getBytes(), ac.value());
+        assertNull(tree.get(DocumentPath.from("root.a.c")).join());
+
+        Versioned<byte[]> a = tree.removeNode(DocumentPath.from("root.a")).join();
+        assertArrayEquals("a".getBytes(), a.value());
+        assertNull(tree.get(DocumentPath.from("root.a")).join());
+    }
+
+    /**
+     * Tests invalid removes.
+     */
+    @Test
+    public void testRemoveFailures() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        tree.create(DocumentPath.from("root.a"), "a".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.b"), "ab".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+
+        try {
+            tree.removeNode(DocumentPath.from("root")).join();
+            fail();
+        } catch (Exception e) {
+            assertTrue(Throwables.getRootCause(e) instanceof IllegalDocumentModificationException);
+        }
+
+        try {
+            tree.removeNode(DocumentPath.from("root.a")).join();
+            fail();
+        } catch (Exception e) {
+            assertTrue(Throwables.getRootCause(e) instanceof IllegalDocumentModificationException);
+        }
+
+        try {
+            tree.removeNode(DocumentPath.from("root.d")).join();
+            fail();
+        } catch (Exception e) {
+            assertTrue(Throwables.getRootCause(e) instanceof NoSuchDocumentPathException);
+        }
+    }
+
+    /**
+     * Tests invalid create.
+     */
+    @Test
+    public void testCreateFailures() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        try {
+            tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+            fail();
+        } catch (Exception e) {
+            assertTrue(Throwables.getRootCause(e) instanceof IllegalDocumentModificationException);
+        }
+    }
+
+    /**
+     * Tests invalid set.
+     */
+    @Test
+    public void testSetFailures() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        try {
+            tree.set(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+            fail();
+        } catch (Exception e) {
+            assertTrue(Throwables.getRootCause(e) instanceof IllegalDocumentModificationException);
+        }
+    }
+
+    /**
+     * Tests getChildren.
+     */
+    @Test
+    public void testGetChildren() throws Throwable {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        tree.create(DocumentPath.from("root.a"), "a".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.b"), "ab".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+
+        Map<String, Versioned<byte[]>> rootChildren = tree.getChildren(DocumentPath.from("root")).join();
+        assertEquals(1, rootChildren.size());
+        Versioned<byte[]> a = rootChildren.get("a");
+        assertArrayEquals("a".getBytes(), a.value());
+
+        Map<String, Versioned<byte[]>> children = tree.getChildren(DocumentPath.from("root.a")).join();
+        assertEquals(2, children.size());
+        Versioned<byte[]> ab = children.get("b");
+        assertArrayEquals("ab".getBytes(), ab.value());
+        Versioned<byte[]> ac = children.get("c");
+        assertArrayEquals("ac".getBytes(), ac.value());
+
+        assertEquals(0, tree.getChildren(DocumentPath.from("root.a.b")).join().size());
+        assertEquals(0, tree.getChildren(DocumentPath.from("root.a.c")).join().size());
+    }
+
+    /**
+     * Tests destroy.
+     */
+    @Test
+    public void testClear() {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        tree.create(DocumentPath.from("root.a"), "a".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.b"), "ab".getBytes()).join();
+        tree.create(DocumentPath.from("root.a.c"), "ac".getBytes()).join();
+
+        tree.destroy().join();
+        assertEquals(0, tree.getChildren(DocumentPath.from("root")).join().size());
+    }
+
+    /**
+     * Tests listeners.
+     */
+    @Test
+    @Ignore
+    public void testNotifications() throws Exception {
+        AtomixDocumentTree tree = createAtomixClient().getResource(UUID.randomUUID().toString(),
+                AtomixDocumentTree.class).join();
+        TestEventListener listener = new TestEventListener();
+
+        // add listener; create a node in the tree and verify an CREATED event is received.
+        tree.addListener(listener).thenCompose(v -> tree.set(DocumentPath.from("root.a"), "a".getBytes())).join();
+        DocumentTreeEvent<byte[]> event = listener.event();
+        assertNotNull(event);
+        assertEquals(DocumentTreeEvent.Type.CREATED, event.type());
+        assertArrayEquals("a".getBytes(), event.newValue().get().value());
+    }
+
+    private static class TestEventListener implements DocumentTreeListener<byte[]> {
+
+        private final BlockingQueue<DocumentTreeEvent<byte[]>> queue = new ArrayBlockingQueue<>(1);
+
+        @Override
+        public void event(DocumentTreeEvent<byte[]> event) {
+            try {
+                queue.put(event);
+            } catch (InterruptedException e) {
+                Throwables.propagate(e);
+            }
+        }
+
+        public boolean eventReceived() {
+            return !queue.isEmpty();
+        }
+
+        public DocumentTreeEvent<byte[]> event() throws InterruptedException {
+            return queue.take();
+        }
+    }
+}