hbase-common/src/main/java/org/apache/hadoop/hbase/util/ConcurrentMapUtils.java

   1 /*
   2  * Licensed to the Apache Software Foundation (ASF) under one
   3  * or more contributor license agreements.  See the NOTICE file
   4  * distributed with this work for additional information
   5  * regarding copyright ownership.  The ASF licenses this file
   6  * to you under the Apache License, Version 2.0 (the
   7  * "License"); you may not use this file except in compliance
   8  * with the License.  You may obtain a copy of the License at
   9  *
  10  *     http://www.apache.org/licenses/LICENSE-2.0
  11  *
  12  * Unless required by applicable law or agreed to in writing, software
  13  * distributed under the License is distributed on an "AS IS" BASIS,
  14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15  * See the License for the specific language governing permissions and
  16  * limitations under the License.
  17  */
  18
  19 package org.apache.hadoop.hbase.util;
  20
  21 import java.io.IOException;
  22 import java.util.concurrent.ConcurrentMap;
  23 import java.util.function.Supplier;
  24
  25 import org.apache.yetus.audience.InterfaceAudience;
  26
  27 /**
  28  * Utility methods for dealing with Collections, including treating null collections as empty.
  29  */
  30 @InterfaceAudience.Private
  31 public class ConcurrentMapUtils {
  32
  33   /**
  34    * In HBASE-16648 we found that ConcurrentHashMap.get is much faster than computeIfAbsent if the
  35    * value already exists. Notice that the implementation does not guarantee that the supplier will
  36    * only be executed once.
  37    */
  38   public static <K, V> V computeIfAbsent(ConcurrentMap<K, V> map, K key, Supplier<V> supplier) {
  39     return computeIfAbsent(map, key, supplier, () -> {
  40     });
  41   }
  42
  43   /**
  44    * A supplier that throws IOException when get.
  45    */
  46   @FunctionalInterface
  47   public interface IOExceptionSupplier<V> {
  48     V get() throws IOException;
  49   }
  50
  51   /**
  52    * In HBASE-16648 we found that ConcurrentHashMap.get is much faster than computeIfAbsent if the
  53    * value already exists. So here we copy the implementation of
  54    * {@link ConcurrentMap#computeIfAbsent(Object, java.util.function.Function)}. It uses get and
  55    * putIfAbsent to implement computeIfAbsent. And notice that the implementation does not guarantee
  56    * that the supplier will only be executed once.
  57    */
  58   public static <K, V> V computeIfAbsentEx(ConcurrentMap<K, V> map, K key,
  59       IOExceptionSupplier<V> supplier) throws IOException {
  60     V v, newValue;
  61     return ((v = map.get(key)) == null && (newValue = supplier.get()) != null
  62         && (v = map.putIfAbsent(key, newValue)) == null) ? newValue : v;
  63   }
  64
  65   public static <K, V> V computeIfAbsent(ConcurrentMap<K, V> map, K key, Supplier<V> supplier,
  66       Runnable actionIfAbsent) {
  67     V v = map.get(key);
  68     if (v != null) {
  69       return v;
  70     }
  71     V newValue = supplier.get();
  72     v = map.putIfAbsent(key, newValue);
  73     if (v != null) {
  74       return v;
  75     }
  76     actionIfAbsent.run();
  77     return newValue;
  78   }
  79 }