org.apache.hadoop.hdfs.util.ReferenceCountMap Maven / Gradle / Ivy
/**
* 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.
* Hold the references count to a single instance. If there are no references
* then the entry will be removed.
* Type E should implement {@link ReferenceCounter}
* Note: This class is NOT thread-safe.
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class ReferenceCountMap {
private Map referenceMap = new HashMap();
/**
* 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 getEntries() {
return new ImmutableList.Builder().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();
}
}