001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.util;
019
020import java.io.IOException;
021import java.util.concurrent.ConcurrentMap;
022import java.util.function.Supplier;
023import org.apache.yetus.audience.InterfaceAudience;
024
025/**
026 * Utility methods for dealing with Collections, including treating null collections as empty.
027 */
028@InterfaceAudience.Private
029public class ConcurrentMapUtils {
030
031  /**
032   * In HBASE-16648 we found that ConcurrentHashMap.get is much faster than computeIfAbsent if the
033   * value already exists. Notice that the implementation does not guarantee that the supplier will
034   * only be executed once.
035   */
036  public static <K, V> V computeIfAbsent(ConcurrentMap<K, V> map, K key, Supplier<V> supplier) {
037    return computeIfAbsent(map, key, supplier, () -> {
038    });
039  }
040
041  /**
042   * In HBASE-16648 we found that ConcurrentHashMap.get is much faster than computeIfAbsent if the
043   * value already exists. So here we copy the implementation of
044   * {@link ConcurrentMap#computeIfAbsent(Object, java.util.function.Function)}. It uses get and
045   * putIfAbsent to implement computeIfAbsent. And notice that the implementation does not guarantee
046   * that the supplier will only be executed once.
047   */
048  public static <K, V> V computeIfAbsentEx(ConcurrentMap<K, V> map, K key,
049    IOExceptionSupplier<V> supplier) throws IOException {
050    V v, newValue;
051    return ((v = map.get(key)) == null && (newValue = supplier.get()) != null
052      && (v = map.putIfAbsent(key, newValue)) == null) ? newValue : v;
053  }
054
055  public static <K, V> V computeIfAbsent(ConcurrentMap<K, V> map, K key, Supplier<V> supplier,
056    Runnable actionIfAbsent) {
057    V v = map.get(key);
058    if (v != null) {
059      return v;
060    }
061    V newValue = supplier.get();
062    v = map.putIfAbsent(key, newValue);
063    if (v != null) {
064      return v;
065    }
066    actionIfAbsent.run();
067    return newValue;
068  }
069}