Add distributed lock primitive

Change-Id: I60f4581d5acb5fc9b9a21d4191874bb56348af58
diff --git a/core/store/primitives/src/main/java/org/onosproject/store/primitives/resources/impl/LockEvent.java b/core/store/primitives/src/main/java/org/onosproject/store/primitives/resources/impl/LockEvent.java
new file mode 100644
index 0000000..cddb41f
--- /dev/null
+++ b/core/store/primitives/src/main/java/org/onosproject/store/primitives/resources/impl/LockEvent.java
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.MoreObjects.toStringHelper;
+
+/**
+ * Locked event.
+ */
+public class LockEvent {
+  private final int id;
+  private final long version;
+
+  public LockEvent() {
+    this(0, 0);
+  }
+
+  public LockEvent(int id, long version) {
+    this.id = id;
+    this.version = version;
+  }
+
+  /**
+   * Returns the lock ID.
+   *
+   * @return The lock ID.
+   */
+  public int id() {
+    return id;
+  }
+
+  /**
+   * Returns the lock version.
+   *
+   * @return The lock version.
+   */
+  public long version() {
+    return version;
+  }
+
+  @Override
+  public String toString() {
+    return toStringHelper(this)
+        .add("id", id)
+        .add("version", version)
+        .toString();
+  }
+}