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

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jiajunwang commented on a change in pull request #388: Add ChangeDetector interface and ResourceChangeDetector implementation
URL: https://github.com/apache/helix/pull/388#discussion_r312284218
 
 

 ##########
 File path: helix-core/src/main/java/org/apache/helix/controller/changedetector/ResourceChangeDetector.java
 ##########
 @@ -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))) {
+        changedItems.add(name);
+      }
+    });
+    return changedItems;
+  }
+
+  /**
+   * Return a collection of names that are newly added.
+   * @return
+   */
+  private Collection<String> getAddedItems() {
+    Collection<String> addedItems = new HashSet<>(_newPropertyMap.keySet());
+    addedItems.removeAll(_oldPropertyMap.keySet());
+    return addedItems;
+  }
+
+  /**
+   * Return a collection of names that were removed.
+   * @return
+   */
+  private Collection<String> getRemovedItems() {
+    Collection<String> removedItems = new HashSet<>(_oldPropertyMap.keySet());
+    removedItems.removeAll(_newPropertyMap.keySet());
+    return removedItems;
+  }
+
+  /**
+   * Based on the change type given, call the right getters for two property maps.
+   * @param changeType
+   */
+  private void assignPropertyMapByType(HelixConstants.ChangeType changeType) {
+    switch (changeType) {
+    case INSTANCE_CONFIG:
+      _oldPropertyMap = _oldCache.getInstanceConfigMap();
+      _newPropertyMap = _newCache.getInstanceConfigMap();
+      break;
+    case IDEAL_STATE:
+      _oldPropertyMap = _oldCache.getIdealStateMap();
+      _newPropertyMap = _newCache.getIdealStateMap();
+      break;
+    case RESOURCE_CONFIG:
+      _oldPropertyMap = _oldCache.getResourceConfigMap();
+      _newPropertyMap = _newCache.getResourceConfigMap();
+      break;
+    case LIVE_INSTANCE:
+      _oldPropertyMap = _oldCache.getLiveInstances();
+      _newPropertyMap = _newCache.getLiveInstances();
+      break;
+    default:
+      throw new HelixException(String
+          .format("ResourceChangeDetector does not support the given change type: %s", changeType));
+    }
+  }
+
+  /**
+   * Makes the current newCache the oldCache and reads in the up-to-date cache for change
+   * computation. To be called in the controller pipeline.
+   * @param dataProvider newly refreshed DataProvider (cache)
+   */
+  public void updateCache(ResourceControllerDataProvider dataProvider) {
+    _oldCache = new ResourceChangeCache(_newCache);
+    _newCache = new ResourceChangeCache(dataProvider);
+  }
+
+  @Override
+  public Collection<HelixConstants.ChangeType> getChangeTypes() {
+    return Collections.unmodifiableSet(_newCache.getChangedTypes());
+  }
+
+  @Override
+  public Collection<String> getChangesByType(HelixConstants.ChangeType changeType) {
+    assignPropertyMapByType(changeType);
+    return getChangedItems();
 
 Review comment:
   Is it possible we do the calculation once during the updateCahce()?

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