utils/misc/src/main/java/org/onlab/util/NewConcurrentHashMap.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.onlab.util;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.apache.commons.lang3.concurrent.ConcurrentInitializer;

/**
 * Creates an instance of new ConcurrentHashMap on each {@link #get()} call.
 * <p>
 * To be used with
 * {@link org.apache.commons.lang3.concurrent.ConcurrentUtils#createIfAbsent()
 *  ConcurrentUtils#createIfAbsent}
 *
 * @param <K> ConcurrentHashMap key type
 * @param <V> ConcurrentHashMap value type
 */
public final class NewConcurrentHashMap<K, V>
    implements  ConcurrentInitializer<ConcurrentMap<K, V>> {

    public static final NewConcurrentHashMap<?, ?> INSTANCE = new NewConcurrentHashMap<>();

    @SuppressWarnings("unchecked")
    public static <K, V> NewConcurrentHashMap<K, V> ifNeeded() {
        return (NewConcurrentHashMap<K, V>) INSTANCE;
    }

    @Override
    public ConcurrentMap<K, V> get() {
        return new ConcurrentHashMap<>();
    }
}