content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.collections;
  
  import static java.util.stream.Collectors.toSet;
  
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.function.Supplier;
  import javax.annotation.Nullable;
  
  /**
   * A two-level concurrent map implementation. Concurrent usage is managed by the outer map.
   *
   * Users can supply the inner map type of their choice.
   *
   * @param <K1> the first key type
   * @param <K2> the second key type
   * @param <V> the value type
   * @param <M> the type for the inner map
   */
  public class TwoKeyConcurrentMap<K1, K2, V, M extends Map<K2, V>> extends ConcurrentHashMap<K1, M> {
    private static final long serialVersionUID = 1L;
  
    private final Supplier<M> mInnerMapFn;
  
    /**
     * @param innerMapCreator supplier for the inner map type
     */
    public TwoKeyConcurrentMap(Supplier<M> innerMapCreator) {
      mInnerMapFn = innerMapCreator;
    }
  
    /**
     * @param k1 the first key
     * @param k2 the second key
     * @param v the value
     */
    public void addInnerValue(K1 k1, K2 k2, V v) {
      compute(k1, (k, inner) -> {
        if (inner == null) {
          inner = mInnerMapFn.get();
        }
        inner.put(k2, v);
        return inner;
      });
    }
  
    /**
     * @param k1 the first key
     * @param k2 the second key
     */
    @Nullable
    public void removeInnerValue(K1 k1, K2 k2) {
      computeIfPresent(k1, (k, inner) -> {
        inner.remove(k2);
        if (inner.isEmpty()) {
          return null;
        }
        return inner;
      });
    }
  
    /**
     * Flattens the (key1, key2, value) triples according to the given function.
     *
     * @param fn a function to create an entry from the keys and value
     * @param <R> the result type of the function
     * @return the set of entries
     */
    public <R> Set<R> flattenEntries(TriFunction<K1, K2, V, R> fn) {
      return entrySet().stream()
          .flatMap(outer -> outer.getValue().entrySet().stream()
              .map(inner -> fn.apply(outer.getKey(), inner.getKey(), inner.getValue())))
          .collect(toSet());
    }
  
    /**
     * A function with three arguments.
     *
     * @param <A> the first argument
     * @param <B> the second argument
     * @param <C> the third argument
     * @param <R> the return type
     */
    @FunctionalInterface
    public interface TriFunction<A, B, C, R> {
      /**
       * @param a the first argument
       * @param b the second argument
       * @param c the third argument
       * @return the result
       */
      R apply(A a, B b, C c);
    }
  
    /**
     * The equals implementation for this map simply uses the superclass's equals.
     */
    @Override
    public boolean equals(Object o) {
      return super.equals(o);
    }
  
    /**
     * The hashCode implementation for this map simply uses the superclass's.
     */
    @Override
    public int hashCode() {
      return super.hashCode();
    }
  }
  