content: /*
   * 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.cassandra.utils;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   *
   * A variant of BiMap that permits concurrent access, and expects uniqueness of values in both domain and range.
   * We synchronize on _modifications only_, and use ConcurrentHashMap so that readers can lookup safely. This does mean there
   * could be races to lookup the inverse, but we aren't too worried about that.
   *
   * @param <K>
   * @param <V>
   */
  public class ConcurrentBiMap<K, V> implements Map<K, V>
  {
      protected final Map<K, V> forwardMap;
      protected final Map<V, K> reverseMap;
  
      public ConcurrentBiMap()
      {
          this(new ConcurrentHashMap<K, V>(16, 0.5f, 1), new ConcurrentHashMap<V, K>(16, 0.5f, 1));
      }
  
      protected ConcurrentBiMap(Map<K, V> forwardMap, Map<V, K> reverseMap)
      {
          this.forwardMap = forwardMap;
          this.reverseMap = reverseMap;
      }
  
      public Map<V, K> inverse()
      {
          return Collections.unmodifiableMap(reverseMap);
      }
  
      public void clear()
      {
          forwardMap.clear();
          reverseMap.clear();
      }
  
      public boolean containsKey(Object key)
      {
          return forwardMap.containsKey(key);
      }
  
      public boolean containsValue(Object value)
      {
          return reverseMap.containsKey(value);
      }
  
      public Set<Entry<K, V>> entrySet()
      {
          return forwardMap.entrySet();
      }
  
      public V get(Object key)
      {
          return forwardMap.get(key);
      }
  
      public boolean isEmpty()
      {
          return forwardMap.isEmpty();
      }
  
      public Set<K> keySet()
      {
          return forwardMap.keySet();
      }
  
      public synchronized V put(K key, V value)
      {
          K oldKey = reverseMap.get(value);
          if (oldKey != null && !key.equals(oldKey))
              throw new IllegalArgumentException(value + " is already bound in reverseMap to " + oldKey);
          V oldVal = forwardMap.put(key, value);
          if (oldVal != null && !Objects.equals(reverseMap.remove(oldVal), key))
              throw new IllegalStateException(); // for the prior mapping to be correct, we MUST get back the key from the reverseMap
          reverseMap.put(value, key);
          return oldVal;
      }
  
      public synchronized void putAll(Map<? extends K, ? extends V> m)
      {
          for (Entry<? extends K, ? extends V> entry : m.entrySet())
              put(entry.getKey(), entry.getValue());
      }
  
      public synchronized V remove(Object key)
      {
          V oldVal = forwardMap.remove(key);
          if (oldVal == null)
              return null;
          Object oldKey = reverseMap.remove(oldVal);
          if (oldKey == null || !oldKey.equals(key))
              throw new IllegalStateException(); // for the prior mapping to be correct, we MUST get back the key from the reverseMap
          return oldVal;
      }
  
      public int size()
      {
          return forwardMap.size();
      }
  
      public Collection<V> values()
      {
          return reverseMap.keySet();
      }
  }
  