001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.cache;
018
019import com.google.common.annotations.Beta;
020import com.google.common.annotations.GwtCompatible;
021import com.google.common.collect.ImmutableMap;
022import com.google.common.collect.Maps;
023
024import java.util.Map;
025import java.util.concurrent.Callable;
026import java.util.concurrent.ConcurrentMap;
027import java.util.concurrent.ExecutionException;
028
029/**
030 * This class provides a skeletal implementation of the {@code Cache} interface to minimize the
031 * effort required to implement this interface.
032 *
033 * <p>To implement a cache, the programmer needs only to extend this class and provide an
034 * implementation for the {@link #put} and {@link #getIfPresent} methods. {@link #getAllPresent} is
035 * implemented in terms of {@link #getIfPresent}; {@link #putAll} is implemented in terms of
036 * {@link #put}, {@link #invalidateAll(Iterable)} is implemented in terms of {@link #invalidate}.
037 * The method {@link #cleanUp} is a no-op. All other methods throw an
038 * {@link UnsupportedOperationException}.
039 *
040 * @author Charles Fry
041 * @since 10.0
042 */
043@Beta
044@GwtCompatible
045public abstract class AbstractCache<K, V> implements Cache<K, V> {
046
047  /** Constructor for use by subclasses. */
048  protected AbstractCache() {}
049
050  /**
051   * @since 11.0
052   */
053  @Override
054  public V get(K key, Callable<? extends V> valueLoader) throws ExecutionException {
055    throw new UnsupportedOperationException();
056  }
057
058  /**
059   * This implementation of {@code getAllPresent} lacks any insight into the internal cache data
060   * structure, and is thus forced to return the query keys instead of the cached keys. This is only
061   * possible with an unsafe cast which requires {@code keys} to actually be of type {@code K}.
062   *
063   * {@inheritDoc}
064   *
065   * @since 11.0
066   */
067  @Override
068  public ImmutableMap<K, V> getAllPresent(Iterable<?> keys) {
069    Map<K, V> result = Maps.newLinkedHashMap();
070    for (Object key : keys) {
071      if (!result.containsKey(key)) {
072        @SuppressWarnings("unchecked")
073        K castKey = (K) key;
074        result.put(castKey, getIfPresent(key));
075      }
076    }
077    return ImmutableMap.copyOf(result);
078  }
079
080  /**
081   * @since 11.0
082   */
083  @Override
084  public void put(K key, V value) {
085    throw new UnsupportedOperationException();
086  }
087
088  /**
089   * @since 12.0
090   */
091  @Override
092  public void putAll(Map<? extends K, ? extends V> m) {
093    for (Map.Entry<? extends K, ? extends V> entry : m.entrySet()) {
094      put(entry.getKey(), entry.getValue());
095    }
096  }
097
098  @Override
099  public void cleanUp() {}
100
101  @Override
102  public long size() {
103    throw new UnsupportedOperationException();
104  }
105
106  @Override
107  public void invalidate(Object key) {
108    throw new UnsupportedOperationException();
109  }
110
111  /**
112   * @since 11.0
113   */
114  @Override
115  public void invalidateAll(Iterable<?> keys) {
116    for (Object key : keys) {
117      invalidate(key);
118    }
119  }
120
121  @Override
122  public void invalidateAll() {
123    throw new UnsupportedOperationException();
124  }
125
126  @Override
127  public CacheStats stats() {
128    throw new UnsupportedOperationException();
129  }
130
131  @Override
132  public ConcurrentMap<K, V> asMap() {
133    throw new UnsupportedOperationException();
134  }
135
136  /**
137   * Accumulates statistics during the operation of a {@link Cache} for presentation by {@link
138   * Cache#stats}. This is solely intended for consumption by {@code Cache} implementors.
139   *
140   * @since 10.0
141   */
142  @Beta
143  public interface StatsCounter {
144    /**
145     * Records cache hits. This should be called when a cache request returns a cached value.
146     *
147     * @param count the number of hits to record
148     * @since 11.0
149     */
150    void recordHits(int count);
151
152    /**
153     * Records cache misses. This should be called when a cache request returns a value that was
154     * not found in the cache. This method should be called by the loading thread, as well as by
155     * threads blocking on the load. Multiple concurrent calls to {@link Cache} lookup methods with
156     * the same key on an absent value should result in a single call to either
157     * {@code recordLoadSuccess} or {@code recordLoadException} and multiple calls to this method,
158     * despite all being served by the results of a single load operation.
159     *
160     * @param count the number of misses to record
161     * @since 11.0
162     */
163    void recordMisses(int count);
164
165    /**
166     * Records the successful load of a new entry. This should be called when a cache request
167     * causes an entry to be loaded, and the loading completes successfully. In contrast to
168     * {@link #recordMisses}, this method should only be called by the loading thread.
169     *
170     * @param loadTime the number of nanoseconds the cache spent computing or retrieving the new
171     *     value
172     */
173    void recordLoadSuccess(long loadTime);
174
175    /**
176     * Records the failed load of a new entry. This should be called when a cache request causes
177     * an entry to be loaded, but an exception is thrown while loading the entry. In contrast to
178     * {@link #recordMisses}, this method should only be called by the loading thread.
179     *
180     * @param loadTime the number of nanoseconds the cache spent computing or retrieving the new
181     *     value prior to an exception being thrown
182     */
183    void recordLoadException(long loadTime);
184
185    /**
186     * Records the eviction of an entry from the cache. This should only been called when an entry
187     * is evicted due to the cache's eviction strategy, and not as a result of manual {@linkplain
188     * Cache#invalidate invalidations}.
189     */
190    void recordEviction();
191
192    /**
193     * Returns a snapshot of this counter's values. Note that this may be an inconsistent view, as
194     * it may be interleaved with update operations.
195     */
196    CacheStats snapshot();
197  }
198
199  /**
200   * A thread-safe {@link StatsCounter} implementation for use by {@link Cache} implementors.
201   *
202   * @since 10.0
203   */
204  @Beta
205  public static final class SimpleStatsCounter implements StatsCounter {
206    private final LongAddable hitCount = LongAddables.create();
207    private final LongAddable missCount = LongAddables.create();
208    private final LongAddable loadSuccessCount = LongAddables.create();
209    private final LongAddable loadExceptionCount = LongAddables.create();
210    private final LongAddable totalLoadTime = LongAddables.create();
211    private final LongAddable evictionCount = LongAddables.create();
212
213    /**
214     * Constructs an instance with all counts initialized to zero.
215     */
216    public SimpleStatsCounter() {}
217
218    /**
219     * @since 11.0
220     */
221    @Override
222    public void recordHits(int count) {
223      hitCount.add(count);
224    }
225
226    /**
227     * @since 11.0
228     */
229    @Override
230    public void recordMisses(int count) {
231      missCount.add(count);
232    }
233
234    @Override
235    public void recordLoadSuccess(long loadTime) {
236      loadSuccessCount.increment();
237      totalLoadTime.add(loadTime);
238    }
239
240    @Override
241    public void recordLoadException(long loadTime) {
242      loadExceptionCount.increment();
243      totalLoadTime.add(loadTime);
244    }
245
246    @Override
247    public void recordEviction() {
248      evictionCount.increment();
249    }
250
251    @Override
252    public CacheStats snapshot() {
253      return new CacheStats(
254          hitCount.sum(),
255          missCount.sum(),
256          loadSuccessCount.sum(),
257          loadExceptionCount.sum(),
258          totalLoadTime.sum(),
259          evictionCount.sum());
260    }
261
262    /**
263     * Increments all counters by the values in {@code other}.
264     */
265    public void incrementBy(StatsCounter other) {
266      CacheStats otherStats = other.snapshot();
267      hitCount.add(otherStats.hitCount());
268      missCount.add(otherStats.missCount());
269      loadSuccessCount.add(otherStats.loadSuccessCount());
270      loadExceptionCount.add(otherStats.loadExceptionCount());
271      totalLoadTime.add(otherStats.totalLoadTime());
272      evictionCount.add(otherStats.evictionCount());
273    }
274  }
275}