steveloughran commented on a change in pull request #2069: URL: https://github.com/apache/hadoop/pull/2069#discussion_r474658220
########## File path: hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/statistics/impl/EvaluatingStatisticsMap.java ########## @@ -0,0 +1,191 @@ +/* + * 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. + */ + +package org.apache.hadoop.fs.statistics.impl; + +import java.io.Serializable; +import java.util.Collection; +import java.util.Map; +import java.util.Set; +import java.util.TreeMap; +import java.util.function.Function; +import java.util.stream.Collectors; + +/** + * A map of functions which can be invoked to dynamically + * create the value of an entry. + * @param <E> type of entry value. + */ +final class EvaluatingStatisticsMap<E extends Serializable> implements + Map<String, E> { + + /** + * Functions to invoke when evaluating keys. + */ + private final Map<String, Function<String, E>> evaluators + = new TreeMap<>(); + + /** + * Function to use when copying map values. + */ + private final Function<E, E> copyFn; + + /** + * Name for use in getter/error messages. + */ + private final String name; + + EvaluatingStatisticsMap(final String name) { + this(name, IOStatisticsBinding::passthroughFn); + } + + EvaluatingStatisticsMap(final String name, + final Function<E, E> copyFn) { + this.name = name; + this.copyFn = copyFn; + } + + /** + * add a mapping of a key to a function. + * @param key the key + * @param eval the evaluator + */ + void addFunction(String key, Function<String, E> eval) { + evaluators.put(key, eval); + } Review comment: TreeMap serializes, which is why I'd put it in the snapshot IO statistics (and must stay there). For the others, probably just liked things being in order. All that act of building up the maps of key -> function is done during construction, so we shouldn't have concurrency issues ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
