| // Copyright (C) 2008 The Android Open Source Project |
| // |
| // 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 com.google.gerrit.ehcache; |
| |
| import com.google.gerrit.server.cache.Cache; |
| import com.google.gerrit.server.cache.EntryCreator; |
| |
| import net.sf.ehcache.CacheException; |
| import net.sf.ehcache.Ehcache; |
| import net.sf.ehcache.Element; |
| import net.sf.ehcache.constructs.blocking.CacheEntryFactory; |
| |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| /** |
| * A decorator for {@link Cache} which automatically constructs missing entries. |
| * <p> |
| * On a cache miss {@link EntryCreator#createEntry(Object)} is invoked, allowing |
| * the application specific subclass to compute the entry and return it for |
| * caching. During a miss the cache takes a lock related to the missing key, |
| * ensuring that at most one thread performs the creation work, and other |
| * threads wait for the result. Concurrent creations are possible if two |
| * different keys miss and hash to different locks in the internal lock table. |
| * |
| * @param <K> type of key used to name cache entries. |
| * @param <V> type of value stored within a cache entry. |
| */ |
| class PopulatingCache<K, V> implements Cache<K, V> { |
| private static final Logger log = |
| LoggerFactory.getLogger(PopulatingCache.class); |
| |
| private final net.sf.ehcache.constructs.blocking.SelfPopulatingCache self; |
| private final EntryCreator<K, V> creator; |
| |
| PopulatingCache(Ehcache s, EntryCreator<K, V> entryCreator) { |
| creator = entryCreator; |
| final CacheEntryFactory f = new CacheEntryFactory() { |
| @SuppressWarnings("unchecked") |
| @Override |
| public Object createEntry(Object key) throws Exception { |
| return creator.createEntry((K) key); |
| } |
| }; |
| self = new net.sf.ehcache.constructs.blocking.SelfPopulatingCache(s, f); |
| } |
| |
| /** |
| * Get the element from the cache, or {@link EntryCreator#missing(Object)} if not found. |
| * <p> |
| * The {@link EntryCreator#missing(Object)} method is only invoked if: |
| * <ul> |
| * <li>{@code key == null}, in which case the application should return a |
| * suitable return value that callers can accept, or throw a RuntimeException. |
| * <li>{@code createEntry(key)} threw an exception, in which case the entry |
| * was not stored in the cache. An entry was recorded in the application log, |
| * but a return value is still required. |
| * <li>The cache has been shutdown, and access is forbidden. |
| * </ul> |
| * |
| * @param key key to locate. |
| * @return either the cached entry, or {@code missing(key)} if not found. |
| */ |
| @SuppressWarnings("unchecked") |
| public V get(final K key) { |
| if (key == null) { |
| return creator.missing(key); |
| } |
| |
| final Element m; |
| try { |
| m = self.get(key); |
| } catch (IllegalStateException err) { |
| log.error("Cannot lookup " + key + " in \"" + self.getName() + "\"", err); |
| return creator.missing(key); |
| } catch (CacheException err) { |
| log.error("Cannot lookup " + key + " in \"" + self.getName() + "\"", err); |
| return creator.missing(key); |
| } |
| return m != null ? (V) m.getObjectValue() : creator.missing(key); |
| } |
| |
| public void remove(final K key) { |
| if (key != null) { |
| self.remove(key); |
| } |
| } |
| |
| /** Remove all cached items, forcing them to be created again on demand. */ |
| public void removeAll() { |
| self.removeAll(); |
| } |
| |
| public void put(K key, V value) { |
| self.put(new Element(key, value)); |
| } |
| |
| @Override |
| public String toString() { |
| return "Cache[" + self.getName() + "]"; |
| } |
| } |