[GitHub] [helix] narendly commented on a change in pull request #388: Add ChangeDetector interface and ResourceChangeDetector implementation

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narendly commented on a change in pull request #388: Add ChangeDetector interface and ResourceChangeDetector implementation
URL: https://github.com/apache/helix/pull/388#discussion_r312241912
 
 

 ##########
 File path: helix-core/src/main/java/org/apache/helix/controller/changedetector/ResourceChangeDetector.java
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 @@ -0,0 +1,132 @@
+package org.apache.helix.controller.changedetector;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Map;
+import org.apache.helix.HelixConstants;
+import org.apache.helix.HelixException;
+import org.apache.helix.HelixProperty;
+import org.apache.helix.controller.dataproviders.ResourceControllerDataProvider;
+
+public class ResourceChangeDetector implements ChangeDetector {
+
+  private ResourceChangeCache _oldCache; // cache snapshot for previous pipeline run
+  private ResourceChangeCache _newCache; // cache snapshot for this pipeline run
+  private Map<String, ? extends HelixProperty> _oldPropertyMap;
+  private Map<String, ? extends HelixProperty> _newPropertyMap;
+
+  /**
+   * Compare the underlying HelixProperty objects and produce a collection of names of changed
+   * properties.
+   * @return
+   */
+  private Collection<String> getChangedItems() {
+    Collection<String> changedItems = new HashSet<>();
+    _oldPropertyMap.forEach((name, property) -> {
+      if (_newPropertyMap.containsKey(name) && !property.equals(_newPropertyMap.get(name))) {
 
 Review comment:
   That was an option I considered, but here are the reasons I chose to use HelixProperty:
   
   - It is possible that Stats' version has changed without any modification to the actual content of the ZNode. In this case, it's sort of like a false alarm in that we do not have to react to it. So we need to look at the actual content.
   - HelixProperty.equals() actually is just a wrapper for ZNRecord.equals(). I wanted this component to be agnostic to the actual low-level data format of the metadata store. See:
   `  @Override
     public boolean equals(Object obj) {
       if (obj == null) {
         return false;
       }
       if (obj instanceof HelixProperty) {
         HelixProperty that = (HelixProperty) obj;
         if (that.getRecord() != null) {
           return that.getRecord().equals(this.getRecord());
         }
       }
       return false;
     }`

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