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1   /**
2    * Copyright The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one or more
5    * contributor license agreements. See the NOTICE file distributed with this
6    * work for additional information regarding copyright ownership. The ASF
7    * licenses this file to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance with the License.
9    * You may obtain a copy of the License at
10   *
11   * http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing, software
14   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
15   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
16   * License for the specific language governing permissions and limitations
17   * under the License.
18   */
19  package org.apache.hadoop.hbase.io.hfile.bucket;
20  
21  import java.io.Serializable;
22  import java.util.concurrent.ConcurrentHashMap;
23  import java.util.concurrent.atomic.AtomicInteger;
24  
25  import org.apache.hadoop.classification.InterfaceAudience;
26  
27  /**
28   * Map from type T to int and vice-versa. Used for reducing bit field item
29   * counts.
30   */
31  @InterfaceAudience.Private
32  public final class UniqueIndexMap<T> implements Serializable {
33    private static final long serialVersionUID = -1145635738654002342L;
34  
35    ConcurrentHashMap<T, Integer> mForwardMap = new ConcurrentHashMap<T, Integer>();
36    ConcurrentHashMap<Integer, T> mReverseMap = new ConcurrentHashMap<Integer, T>();
37    AtomicInteger mIndex = new AtomicInteger(0);
38  
39    // Map a length to an index. If we can't, allocate a new mapping. We might
40    // race here and get two entries with the same deserialiser. This is fine.
41    int map(T parameter) {
42      Integer ret = mForwardMap.get(parameter);
43      if (ret != null) return ret.intValue();
44      int nexti = mIndex.incrementAndGet();
45      assert (nexti < Short.MAX_VALUE);
46      mForwardMap.put(parameter, nexti);
47      mReverseMap.put(nexti, parameter);
48      return nexti;
49    }
50  
51    T unmap(int leni) {
52      Integer len = Integer.valueOf(leni);
53      assert mReverseMap.containsKey(len);
54      return mReverseMap.get(len);
55    }
56  }