diff options
Diffstat (limited to 'libs/xmpp-addr/src/main/java/rocks/xmpp/util/cache/LruCache.java')
| -rw-r--r-- | libs/xmpp-addr/src/main/java/rocks/xmpp/util/cache/LruCache.java | 228 |
1 files changed, 228 insertions, 0 deletions
diff --git a/libs/xmpp-addr/src/main/java/rocks/xmpp/util/cache/LruCache.java b/libs/xmpp-addr/src/main/java/rocks/xmpp/util/cache/LruCache.java new file mode 100644 index 000000000..c2fbb0c3f --- /dev/null +++ b/libs/xmpp-addr/src/main/java/rocks/xmpp/util/cache/LruCache.java @@ -0,0 +1,228 @@ +/* + * The MIT License (MIT) + * + * Copyright (c) 2014-2016 Christian Schudt + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN + * THE SOFTWARE. + */ + +package rocks.xmpp.util.cache; + +import java.util.Collection; +import java.util.Map; +import java.util.Queue; +import java.util.Set; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.ConcurrentLinkedDeque; +import java.util.function.BiFunction; +import java.util.function.Function; + +/** + * A simple concurrent implementation of a least-recently-used cache. + * <p> + * This cache is keeps a maximal number of items in memory and removes the least-recently-used item, when new items are added. + * + * @param <K> The key. + * @param <V> The value. + * @author Christian Schudt + * @see <a href="http://javadecodedquestions.blogspot.de/2013/02/java-cache-static-data-loading.html">http://javadecodedquestions.blogspot.de/2013/02/java-cache-static-data-loading.html</a> + * @see <a href="http://stackoverflow.com/a/22891780">http://stackoverflow.com/a/22891780</a> + */ +public final class LruCache<K, V> implements Map<K, V> { + private final int maxEntries; + + private final Map<K, V> map; + + final Queue<K> queue; + + public LruCache(final int maxEntries) { + this.maxEntries = maxEntries; + this.map = new ConcurrentHashMap<>(maxEntries); + // Don't use a ConcurrentLinkedQueue here. + // There's a JDK bug, leading to OutOfMemoryError and high CPU usage: + // https://bugs.openjdk.java.net/browse/JDK-8054446 + this.queue = new ConcurrentLinkedDeque<>(); + } + + @Override + public final int size() { + return map.size(); + } + + @Override + public final boolean isEmpty() { + return map.isEmpty(); + } + + @Override + public final boolean containsKey(final Object key) { + return map.containsKey(key); + } + + @Override + public final boolean containsValue(final Object value) { + return map.containsValue(value); + } + + @SuppressWarnings("unchecked") + @Override + public final V get(final Object key) { + final V v = map.get(key); + if (v != null) { + // Remove the key from the queue and re-add it to the tail. It is now the most recently used key. + keyUsed((K) key); + } + return v; + } + + + @Override + public final V put(final K key, final V value) { + V v = map.put(key, value); + keyUsed(key); + limit(); + return v; + } + + @Override + public final V remove(final Object key) { + queue.remove(key); + return map.remove(key); + } + + + @Override + public final void putAll(final Map<? extends K, ? extends V> m) { + for (Map.Entry<? extends K, ? extends V> entry : m.entrySet()) { + put(entry.getKey(), entry.getValue()); + } + } + + @Override + public final void clear() { + queue.clear(); + map.clear(); + } + + @Override + public final Set<K> keySet() { + return map.keySet(); + } + + @Override + public final Collection<V> values() { + return map.values(); + } + + @Override + public final Set<Entry<K, V>> entrySet() { + return map.entrySet(); + } + + + // Default methods + + @Override + public final V putIfAbsent(final K key, final V value) { + final V v = map.putIfAbsent(key, value); + if (v == null) { + keyUsed(key); + } + limit(); + return v; + } + + @Override + public final boolean remove(final Object key, final Object value) { + final boolean removed = map.remove(key, value); + if (removed) { + queue.remove(key); + } + return removed; + } + + @Override + public final boolean replace(final K key, final V oldValue, final V newValue) { + final boolean replaced = map.replace(key, oldValue, newValue); + if (replaced) { + keyUsed(key); + } + return replaced; + } + + @Override + public final V replace(final K key, final V value) { + final V v = map.replace(key, value); + if (v != null) { + keyUsed(key); + } + return v; + } + + @Override + public final V computeIfAbsent(final K key, final Function<? super K, ? extends V> mappingFunction) { + return map.computeIfAbsent(key, mappingFunction.<V>andThen(v -> { + keyUsed(key); + limit(); + return v; + })); + } + + @Override + public final V computeIfPresent(final K key, final BiFunction<? super K, ? super V, ? extends V> remappingFunction) { + return map.computeIfPresent(key, remappingFunction.<V>andThen(v -> { + keyUsed(key); + limit(); + return v; + })); + } + + @Override + public final V compute(final K key, final BiFunction<? super K, ? super V, ? extends V> remappingFunction) { + return map.compute(key, remappingFunction.<V>andThen(v -> { + keyUsed(key); + limit(); + return v; + })); + } + + @Override + public final V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) { + return map.merge(key, value, remappingFunction.<V>andThen(v -> { + keyUsed(key); + limit(); + return v; + })); + } + + private void limit() { + while (queue.size() > maxEntries) { + final K oldestKey = queue.poll(); + if (oldestKey != null) { + map.remove(oldestKey); + } + } + } + + private void keyUsed(final K key) { + // remove it from the queue and re-add it, to make it the most recently used key. + queue.remove(key); + queue.offer(key); + } +}
\ No newline at end of file |