openjpa-lib/src/main/java/org/apache/openjpa/lib/util/concurrent/ConcurrentReferenceHashSet.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.openjpa.lib.util.concurrent;

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

import org.apache.commons.collections4.map.AbstractReferenceMap.ReferenceStrength;
import org.apache.commons.collections4.set.MapBackedSet;

/**
 * A concurrent set whose values may be stored as weak or soft references. If
 * the constructor is invoked with <code>refType</code> set to {@link #HARD},
 * this uses a JDK1.5 {@link ConcurrentHashMap} under the covers. Otherwise,
 * it uses a {@link ConcurrentReferenceHashMap}.
 *
 * @author Abe White
 */
public class ConcurrentReferenceHashSet<E> implements Set<E>, Serializable {
    private static final long serialVersionUID = 1L;

    private static final Object DUMMY_VAL = new Object();

    private final Set<E> _set;

    /**
     * Construct a set with the given reference type.
     */
    public ConcurrentReferenceHashSet(ReferenceStrength refType) {
        if (refType == ReferenceStrength.HARD)
            _set = MapBackedSet.mapBackedSet(new ConcurrentHashMap<>(), DUMMY_VAL);
        else {
            _set = MapBackedSet.mapBackedSet(new ConcurrentReferenceHashMap
                (refType, ReferenceStrength.HARD), DUMMY_VAL);
        }
    }

    @Override
    public boolean add(E obj) {
        return _set.add(obj);
    }

    @Override
    public boolean addAll(Collection<? extends E> coll) {
        return _set.addAll(coll);
    }

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

    @Override
    public boolean contains(Object obj) {
        return _set.contains(obj);
    }

    @Override
    public boolean containsAll(Collection<?> coll) {
        return _set.containsAll(coll);
    }

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

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

    @Override
    public boolean remove(Object obj) {
        return _set.remove(obj);
    }

    @Override
    public boolean removeAll(Collection<?> coll) {
        return _set.removeAll(coll);
    }

    @Override
    public boolean retainAll(Collection<?> coll) {
        return _set.retainAll(coll);
    }

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

    @Override
    public Object[] toArray() {
        return _set.toArray();
    }

    @Override
    public <T> T[] toArray(T[] arr) {
        return _set.toArray(arr);
    }

    @Override
    public int hashCode() {
        return _set.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj instanceof ConcurrentReferenceHashSet)
            obj = ((ConcurrentReferenceHashSet) obj)._set;
        return _set.equals(obj);
    }
}