| /** |
| * 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.hadoop.hdfs.util; |
| |
| import java.util.HashMap; |
| import java.util.Map; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| import com.google.common.annotations.VisibleForTesting; |
| import com.google.common.collect.ImmutableList; |
| |
| /** |
| * Class for de-duplication of instances. <br> |
| * Hold the references count to a single instance. If there are no references |
| * then the entry will be removed.<br> |
| * Type E should implement {@link ReferenceCounter}<br> |
| * Note: This class is NOT thread-safe. |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Evolving |
| public class ReferenceCountMap<E extends ReferenceCountMap.ReferenceCounter> { |
| |
| private Map<E, E> referenceMap = new HashMap<E, E>(); |
| |
| /** |
| * Add the reference. If the instance already present, just increase the |
| * reference count. |
| * |
| * @param key Key to put in reference map |
| * @return Referenced instance |
| */ |
| public E put(E key) { |
| E value = referenceMap.get(key); |
| if (value == null) { |
| value = key; |
| referenceMap.put(key, value); |
| } |
| value.incrementAndGetRefCount(); |
| return value; |
| } |
| |
| /** |
| * Delete the reference. Decrease the reference count for the instance, if |
| * any. On all references removal delete the instance from the map. |
| * |
| * @param key Key to remove the reference. |
| */ |
| public void remove(E key) { |
| E value = referenceMap.get(key); |
| if (value != null && value.decrementAndGetRefCount() == 0) { |
| referenceMap.remove(key); |
| } |
| } |
| |
| /** |
| * Get entries in the reference Map. |
| * |
| * @return |
| */ |
| @VisibleForTesting |
| public ImmutableList<E> getEntries() { |
| return new ImmutableList.Builder<E>().addAll(referenceMap.keySet()).build(); |
| } |
| |
| /** |
| * Get the reference count for the key |
| */ |
| public long getReferenceCount(E key) { |
| ReferenceCounter counter = referenceMap.get(key); |
| if (counter != null) { |
| return counter.getRefCount(); |
| } |
| return 0; |
| } |
| |
| /** |
| * Get the number of unique elements |
| */ |
| public int getUniqueElementsSize() { |
| return referenceMap.size(); |
| } |
| |
| /** |
| * Clear the contents |
| */ |
| @VisibleForTesting |
| public void clear() { |
| referenceMap.clear(); |
| } |
| |
| /** |
| * Interface for the reference count holder |
| */ |
| public static interface ReferenceCounter { |
| public int getRefCount(); |
| |
| public int incrementAndGetRefCount(); |
| |
| public int decrementAndGetRefCount(); |
| } |
| } |