geode-core/src/main/java/org/apache/geode/internal/concurrent/ConcurrentHashSet.java

/*
 * 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.geode.internal.concurrent;

import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

/**
 * This class is similar to HashSet supporting all the feature of ConcurrentHashMap
 *
 *
 */
public class ConcurrentHashSet<E> extends AbstractSet<E> implements Set<E>, Serializable {

  private static final long serialVersionUID = -3338819662572203596L;

  private ConcurrentHashMap<E, Object> map;

  // Dummy value to associate with an Object in the backing Map
  private static final Object PRESENT = new Object();

  public ConcurrentHashSet() {
    map = new ConcurrentHashMap<E, Object>();
  }

  public ConcurrentHashSet(Collection<? extends E> c) {
    map = new ConcurrentHashMap<E, Object>(Math.max((int) (c.size() / .75f) + 1, 16));
    addAll(c);
  }

  public ConcurrentHashSet(int initialCapacity, float loadFactor, int concurrencyLevel) {
    map = new ConcurrentHashMap<E, Object>(initialCapacity, loadFactor, concurrencyLevel);
  }

  public ConcurrentHashSet(int initialCapacity) {
    map = new ConcurrentHashMap<E, Object>(initialCapacity);
  }


  @Override
  public boolean add(E o) {
    return map.put(o, PRESENT) == null;
  }

  @Override
  public void clear() {
    map.clear();
  }

  @Override
  public boolean contains(Object o) {
    return map.containsKey(o);
  }

  @Override
  public boolean isEmpty() {
    return map.isEmpty();
  }

  @Override
  public Iterator<E> iterator() {
    return map.keySet().iterator();
  }

  @Override
  public boolean remove(Object o) {
    return map.remove(o) == PRESENT;
  }


  @Override
  public int size() {
    return map.size();
  }

}