narendly commented on a change in pull request #388: Add ChangeDetector interface and ResourceChangeDetector implementation URL: https://github.com/apache/helix/pull/388#discussion_r314375719
########## File path: helix-core/src/main/java/org/apache/helix/controller/changedetector/ResourceChangeDetector.java ########## @@ -0,0 +1,167 @@ +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 com.google.common.collect.Sets; +import java.util.Collection; +import java.util.Collections; +import java.util.HashMap; +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; + +/** + * ResourceChangeDetector implements ChangeDetector. It caches resource-related metadata from + * Helix's main resource pipeline cache (DataProvider) and the computation results of change + * detection. + * WARNING: the methods of this class are not thread-safe. + */ +public class ResourceChangeDetector implements ChangeDetector { + + private ResourceChangeSnapshot _oldSnapshot; // snapshot for previous pipeline run + private ResourceChangeSnapshot _newSnapshot; // snapshot for this pipeline run + + // The following caches the computation results + private Map<HelixConstants.ChangeType, Collection<String>> _changedItems = new HashMap<>(); + private Map<HelixConstants.ChangeType, Collection<String>> _addedItems = new HashMap<>(); + private Map<HelixConstants.ChangeType, Collection<String>> _removedItems = new HashMap<>(); + + /** + * Compare the underlying HelixProperty objects and produce a collection of names of changed + * properties. + * @return + */ + private Collection<String> getChangedItems(Map<String, ? extends HelixProperty> oldPropertyMap, + Map<String, ? extends HelixProperty> newPropertyMap) { + Collection<String> changedItems = new HashSet<>(); + oldPropertyMap.forEach((name, property) -> { + if (newPropertyMap.containsKey(name) + && !property.getRecord().equals(newPropertyMap.get(name).getRecord())) { + changedItems.add(name); + } + }); + return changedItems; + } + + /** + * Return a collection of names that are newly added. + * @return + */ + private Collection<String> getAddedItems(Map<String, ? extends HelixProperty> oldPropertyMap, + Map<String, ? extends HelixProperty> newPropertyMap) { + return Sets.difference(newPropertyMap.keySet(), oldPropertyMap.keySet()); + } + + /** + * Return a collection of names that were removed. + * @return + */ + private Collection<String> getRemovedItems(Map<String, ? extends HelixProperty> oldPropertyMap, + Map<String, ? extends HelixProperty> newPropertyMap) { + return Sets.difference(oldPropertyMap.keySet(), newPropertyMap.keySet()); + } + + private void clearCachedComputation() { + _changedItems.clear(); + _addedItems.clear(); + _removedItems.clear(); + } + + /** + * Initializes old and new snapshots when ResourceChangeDetector gets its first update. + */ + private void initializeSnapshots() { + _oldSnapshot = new ResourceChangeSnapshot(); + _newSnapshot = new ResourceChangeSnapshot(); + } + + /** + * Based on the change type given and propertyMap type, call the right getters for propertyMap. + * @param changeType + * @param snapshot + * @return + */ + private Map<String, ? extends HelixProperty> determinePropertyMapByType( + HelixConstants.ChangeType changeType, ResourceChangeSnapshot snapshot) { + switch (changeType) { + case INSTANCE_CONFIG: + return snapshot.getInstanceConfigMap(); + case IDEAL_STATE: + return snapshot.getIdealStateMap(); + case RESOURCE_CONFIG: + return snapshot.getResourceConfigMap(); + case LIVE_INSTANCE: + return snapshot.getLiveInstances(); + default: + throw new HelixException(String.format( + "ResourceChangeDetector cannot compute the names of changes for the given ChangeType: %s", + changeType)); + } + } + + /** + * Makes the current newSnapshot the oldSnapshot and reads in the up-to-date snapshot for change + * computation. To be called in the controller pipeline. + * @param dataProvider newly refreshed DataProvider (cache) + */ + public synchronized void updateSnapshots(ResourceControllerDataProvider dataProvider) { + // If snapshots are null, initialize them + if (_oldSnapshot == null || _newSnapshot == null) { + initializeSnapshots(); + } + + // If there are changes, update internal states + _oldSnapshot = new ResourceChangeSnapshot(_newSnapshot); + _newSnapshot = new ResourceChangeSnapshot(dataProvider); + dataProvider.clearRefreshedChangeTypes(); Review comment: We agreed to cache the results between `updateSnapshots()` calls. If you did `getAndClearRefreshedChangeTypes()`, then getChangeTypes() won't be idempotent between update calls! Do you want to introduce that inconsistency? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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