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.activemq.artemis.utils.collections;
  
  import java.util.AbstractSet;
  import java.util.Iterator;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  /**
   * A ConcurrentHashSet.
   * <p>
   * Offers same concurrency as ConcurrentHashMap but for a Set
   */
  public class ConcurrentHashSet<E> extends AbstractSet<E> implements ConcurrentSet<E> {
  
     private final ConcurrentMap<E, Object> theMap;
  
     private static final Object dummy = new Object();
  
     public ConcurrentHashSet() {
        theMap = new ConcurrentHashMap<>();
     }
  
     @Override
     public int size() {
        return theMap.size();
     }
  
     @Override
     public Iterator<E> iterator() {
        return theMap.keySet().iterator();
     }
  
     @Override
     public boolean isEmpty() {
        return theMap.isEmpty();
     }
  
     @Override
     public boolean add(final E o) {
        return theMap.put(o, ConcurrentHashSet.dummy) == null;
     }
  
     @Override
     public boolean contains(final Object o) {
        return theMap.containsKey(o);
     }
  
     @Override
     public void clear() {
        theMap.clear();
     }
  
     @Override
     public boolean remove(final Object o) {
        return theMap.remove(o) == ConcurrentHashSet.dummy;
     }
  
     @Override
     public boolean addIfAbsent(final E o) {
        Object obj = theMap.putIfAbsent(o, ConcurrentHashSet.dummy);
  
        return obj == null;
     }
  
  }
  