/*
* Copyright 2010 Google Inc. All Rights Reserved.
*
* Licensed 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.groovy.util.concurrentlinkedhashmap;
import java.io.Serializable;
import java.util.*;
import static org.apache.groovy.util.concurrentlinkedhashmap.ConcurrentLinkedHashMap.checkNotNull;
/**
* A common set of {@link Weigher} and {@link EntryWeigher} implementations.
*
* @author ben.manes@gmail.com (Ben Manes)
* @see <a href="http://code.google.com/p/concurrentlinkedhashmap/">
* http://code.google.com/p/concurrentlinkedhashmap/</a>
*/
public final class Weighers {
private Weighers() {
throw new AssertionError();
}
/**
* A entry weigher backed by the specified weigher. The weight of the value
* determines the weight of the entry.
*
* @param weigher the weigher to be "wrapped" in a entry weigher.
* @return A entry weigher view of the specified weigher.
*/
public static <K, V> EntryWeigher<K, V> asEntryWeigher(
final Weigher<? super V> weigher) {
return (weigher == singleton())
? Weighers.<K, V>entrySingleton()
: new EntryWeigherView<K, V>(weigher);
}
/**
* A weigher where an entry has a weight of <tt>1</tt>. A map bounded with
* this weigher will evict when the number of key-value pairs exceeds the
* capacity.
*
* @return A weigher where a value takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static <K, V> EntryWeigher<K, V> entrySingleton() {
return (EntryWeigher<K, V>) SingletonEntryWeigher.INSTANCE;
}
/**
* A weigher where a value has a weight of <tt>1</tt>. A map bounded with
* this weigher will evict when the number of key-value pairs exceeds the
* capacity.
*
* @return A weigher where a value takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static <V> Weigher<V> singleton() {
return (Weigher<V>) SingletonWeigher.INSTANCE;
}
/**
* A weigher where the value is a byte array and its weight is the number of
* bytes. A map bounded with this weigher will evict when the number of bytes
* exceeds the capacity rather than the number of key-value pairs in the map.
* This allows for restricting the capacity based on the memory-consumption
* and is primarily for usage by dedicated caching servers that hold the
* serialized data.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each byte takes one unit of capacity.
*/
public static Weigher<byte[]> byteArray() {
return ByteArrayWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Iterable} and its weight is the
* number of elements. This weigher only should be used when the alternative
* {@link #collection()} weigher cannot be, as evaluation takes O(n) time. A
* map bounded with this weigher will evict when the total number of elements
* exceeds the capacity rather than the number of key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static <E> Weigher<? super Iterable<E>> iterable() {
return (Weigher<Iterable<E>>) (Weigher<?>) IterableWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Collection} and its weight is the
* number of elements. A map bounded with this weigher will evict when the
* total number of elements exceeds the capacity rather than the number of
* key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static <E> Weigher<? super Collection<E>> collection() {
return (Weigher<Collection<E>>) (Weigher<?>) CollectionWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link List} and its weight is the number
* of elements. A map bounded with this weigher will evict when the total
* number of elements exceeds the capacity rather than the number of
* key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static <E> Weigher<? super List<E>> list() {
return (Weigher<List<E>>) (Weigher<?>) ListWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Set} and its weight is the number
* of elements. A map bounded with this weigher will evict when the total
* number of elements exceeds the capacity rather than the number of
* key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static <E> Weigher<? super Set<E>> set() {
return (Weigher<Set<E>>) (Weigher<?>) SetWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Map} and its weight is the number of
* entries. A map bounded with this weigher will evict when the total number of
* entries across all values exceeds the capacity rather than the number of
* key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value
* with this weight can occur then the caller should eagerly evaluate the
* value and treat it as a removal operation. Alternatively, a custom weigher
* may be specified on the map to assign an empty value a positive weight.
*
* @return A weigher where each entry takes one unit of capacity.
*/
@SuppressWarnings({"cast", "unchecked"})
public static <A, B> Weigher<? super Map<A, B>> map() {
return (Weigher<Map<A, B>>) (Weigher<?>) MapWeigher.INSTANCE;
}
static final class EntryWeigherView<K, V> implements EntryWeigher<K, V>, Serializable {
static final long serialVersionUID = 1;
final Weigher<? super V> weigher;
EntryWeigherView(Weigher<? super V> weigher) {
checkNotNull(weigher);
this.weigher = weigher;
}
@Override
public int weightOf(K key, V value) {
return weigher.weightOf(value);
}
}
enum SingletonEntryWeigher implements EntryWeigher<Object, Object> {
INSTANCE;
@Override
public int weightOf(Object key, Object value) {
return 1;
}
}
enum SingletonWeigher implements Weigher<Object> {
INSTANCE;
@Override
public int weightOf(Object value) {
return 1;
}
}
enum ByteArrayWeigher implements Weigher<byte[]> {
INSTANCE;
@Override
public int weightOf(byte[] value) {
return value.length;
}
}
enum IterableWeigher implements Weigher<Iterable<?>> {
INSTANCE;
@Override
public int weightOf(Iterable<?> values) {
if (values instanceof Collection<?>) {
return ((Collection<?>) values).size();
}
int size = 0;
for (Iterator<?> i = values.iterator(); i.hasNext();) {
i.next();
size++;
}
return size;
}
}
enum CollectionWeigher implements Weigher<Collection<?>> {
INSTANCE;
@Override
public int weightOf(Collection<?> values) {
return values.size();
}
}
enum ListWeigher implements Weigher<List<?>> {
INSTANCE;
@Override
public int weightOf(List<?> values) {
return values.size();
}
}
enum SetWeigher implements Weigher<Set<?>> {
INSTANCE;
@Override
public int weightOf(Set<?> values) {
return values.size();
}
}
enum MapWeigher implements Weigher<Map<?, ?>> {
INSTANCE;
@Override
public int weightOf(Map<?, ?> values) {
return values.size();
}
}
}