001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.cache;
016
017import com.google.common.annotations.GwtCompatible;
018import com.google.common.collect.ImmutableMap;
019import com.google.common.collect.Maps;
020import java.util.Map;
021import java.util.Map.Entry;
022import java.util.concurrent.Callable;
023import java.util.concurrent.ConcurrentMap;
024import java.util.concurrent.ExecutionException;
025
026/**
027 * This class provides a skeletal implementation of the {@code Cache} interface to minimize the
028 * effort required to implement this interface.
029 *
030 * <p>To implement a cache, the programmer needs only to extend this class and provide an
031 * implementation for the {@link #put} and {@link #getIfPresent} methods. {@link #getAllPresent} is
032 * implemented in terms of {@link #getIfPresent}; {@link #putAll} is implemented in terms of {@link
033 * #put}, {@link #invalidateAll(Iterable)} is implemented in terms of {@link #invalidate}. The
034 * method {@link #cleanUp} is a no-op. All other methods throw an {@link
035 * UnsupportedOperationException}.
036 *
037 * @author Charles Fry
038 * @since 10.0
039 */
040@GwtCompatible
041public abstract class AbstractCache<K, V> implements Cache<K, V> {
042
043  /** Constructor for use by subclasses. */
044  protected AbstractCache() {}
045
046  /** @since 11.0 */
047  @Override
048  public V get(K key, Callable<? extends V> valueLoader) throws ExecutionException {
049    throw new UnsupportedOperationException();
050  }
051
052  /**
053   * {@inheritDoc}
054   *
055   * <p>This implementation of {@code getAllPresent} lacks any insight into the internal cache data
056   * structure, and is thus forced to return the query keys instead of the cached keys. This is only
057   * possible with an unsafe cast which requires {@code keys} to actually be of type {@code K}.
058   *
059   * @since 11.0
060   */
061  /*
062   * <? extends Object> is mostly the same as <?> to plain Java. But to nullness checkers, they
063   * differ: <? extends Object> means "non-null types," while <?> means "all types."
064   */
065  @Override
066  public ImmutableMap<K, V> getAllPresent(Iterable<? extends Object> keys) {
067    Map<K, V> result = Maps.newLinkedHashMap();
068    for (Object key : keys) {
069      if (!result.containsKey(key)) {
070        @SuppressWarnings("unchecked")
071        K castKey = (K) key;
072        V value = getIfPresent(key);
073        if (value != null) {
074          result.put(castKey, value);
075        }
076      }
077    }
078    return ImmutableMap.copyOf(result);
079  }
080
081  /** @since 11.0 */
082  @Override
083  public void put(K key, V value) {
084    throw new UnsupportedOperationException();
085  }
086
087  /** @since 12.0 */
088  @Override
089  public void putAll(Map<? extends K, ? extends V> m) {
090    for (Entry<? extends K, ? extends V> entry : m.entrySet()) {
091      put(entry.getKey(), entry.getValue());
092    }
093  }
094
095  @Override
096  public void cleanUp() {}
097
098  @Override
099  public long size() {
100    throw new UnsupportedOperationException();
101  }
102
103  @Override
104  public void invalidate(Object key) {
105    throw new UnsupportedOperationException();
106  }
107
108  /** @since 11.0 */
109  @Override
110  // For discussion of <? extends Object>, see getAllPresent.
111  public void invalidateAll(Iterable<? extends Object> keys) {
112    for (Object key : keys) {
113      invalidate(key);
114    }
115  }
116
117  @Override
118  public void invalidateAll() {
119    throw new UnsupportedOperationException();
120  }
121
122  @Override
123  public CacheStats stats() {
124    throw new UnsupportedOperationException();
125  }
126
127  @Override
128  public ConcurrentMap<K, V> asMap() {
129    throw new UnsupportedOperationException();
130  }
131
132  /**
133   * Accumulates statistics during the operation of a {@link Cache} for presentation by {@link
134   * Cache#stats}. This is solely intended for consumption by {@code Cache} implementors.
135   *
136   * @since 10.0
137   */
138  public interface StatsCounter {
139    /**
140     * Records cache hits. This should be called when a cache request returns a cached value.
141     *
142     * @param count the number of hits to record
143     * @since 11.0
144     */
145    void recordHits(int count);
146
147    /**
148     * Records cache misses. This should be called when a cache request returns a value that was not
149     * found in the cache. This method should be called by the loading thread, as well as by threads
150     * blocking on the load. Multiple concurrent calls to {@link Cache} lookup methods with the same
151     * key on an absent value should result in a single call to either {@code recordLoadSuccess} or
152     * {@code recordLoadException} and multiple calls to this method, despite all being served by
153     * the results of a single load operation.
154     *
155     * @param count the number of misses to record
156     * @since 11.0
157     */
158    void recordMisses(int count);
159
160    /**
161     * Records the successful load of a new entry. This should be called when a cache request causes
162     * an entry to be loaded, and the loading completes successfully. In contrast to {@link
163     * #recordMisses}, this method should only be called by the loading thread.
164     *
165     * @param loadTime the number of nanoseconds the cache spent computing or retrieving the new
166     *     value
167     */
168    @SuppressWarnings("GoodTime") // should accept a java.time.Duration
169    void recordLoadSuccess(long loadTime);
170
171    /**
172     * Records the failed load of a new entry. This should be called when a cache request causes an
173     * entry to be loaded, but an exception is thrown while loading the entry. In contrast to {@link
174     * #recordMisses}, this method should only be called by the loading thread.
175     *
176     * @param loadTime the number of nanoseconds the cache spent computing or retrieving the new
177     *     value prior to an exception being thrown
178     */
179    @SuppressWarnings("GoodTime") // should accept a java.time.Duration
180    void recordLoadException(long loadTime);
181
182    /**
183     * Records the eviction of an entry from the cache. This should only been called when an entry
184     * is evicted due to the cache's eviction strategy, and not as a result of manual {@linkplain
185     * Cache#invalidate invalidations}.
186     */
187    void recordEviction();
188
189    /**
190     * Returns a snapshot of this counter's values. Note that this may be an inconsistent view, as
191     * it may be interleaved with update operations.
192     */
193    CacheStats snapshot();
194  }
195
196  /**
197   * A thread-safe {@link StatsCounter} implementation for use by {@link Cache} implementors.
198   *
199   * @since 10.0
200   */
201  public static final class SimpleStatsCounter implements StatsCounter {
202    private final LongAddable hitCount = LongAddables.create();
203    private final LongAddable missCount = LongAddables.create();
204    private final LongAddable loadSuccessCount = LongAddables.create();
205    private final LongAddable loadExceptionCount = LongAddables.create();
206    private final LongAddable totalLoadTime = LongAddables.create();
207    private final LongAddable evictionCount = LongAddables.create();
208
209    /** Constructs an instance with all counts initialized to zero. */
210    public SimpleStatsCounter() {}
211
212    /** @since 11.0 */
213    @Override
214    public void recordHits(int count) {
215      hitCount.add(count);
216    }
217
218    /** @since 11.0 */
219    @Override
220    public void recordMisses(int count) {
221      missCount.add(count);
222    }
223
224    @SuppressWarnings("GoodTime") // b/122668874
225    @Override
226    public void recordLoadSuccess(long loadTime) {
227      loadSuccessCount.increment();
228      totalLoadTime.add(loadTime);
229    }
230
231    @SuppressWarnings("GoodTime") // b/122668874
232    @Override
233    public void recordLoadException(long loadTime) {
234      loadExceptionCount.increment();
235      totalLoadTime.add(loadTime);
236    }
237
238    @Override
239    public void recordEviction() {
240      evictionCount.increment();
241    }
242
243    @Override
244    public CacheStats snapshot() {
245      return new CacheStats(
246          negativeToMaxValue(hitCount.sum()),
247          negativeToMaxValue(missCount.sum()),
248          negativeToMaxValue(loadSuccessCount.sum()),
249          negativeToMaxValue(loadExceptionCount.sum()),
250          negativeToMaxValue(totalLoadTime.sum()),
251          negativeToMaxValue(evictionCount.sum()));
252    }
253
254    /** Returns {@code value}, if non-negative. Otherwise, returns {@link Long#MAX_VALUE}. */
255    private static long negativeToMaxValue(long value) {
256      return (value >= 0) ? value : Long.MAX_VALUE;
257    }
258
259    /** Increments all counters by the values in {@code other}. */
260    public void incrementBy(StatsCounter other) {
261      CacheStats otherStats = other.snapshot();
262      hitCount.add(otherStats.hitCount());
263      missCount.add(otherStats.missCount());
264      loadSuccessCount.add(otherStats.loadSuccessCount());
265      loadExceptionCount.add(otherStats.loadExceptionCount());
266      totalLoadTime.add(otherStats.totalLoadTime());
267      evictionCount.add(otherStats.evictionCount());
268    }
269  }
270}