001/*
002 * Copyright (C) 2009 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 static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkNotNull;
019import static com.google.common.base.Preconditions.checkState;
020
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.base.Ascii;
024import com.google.common.base.Equivalence;
025import com.google.common.base.MoreObjects;
026import com.google.common.base.Supplier;
027import com.google.common.base.Suppliers;
028import com.google.common.base.Ticker;
029import com.google.common.cache.AbstractCache.SimpleStatsCounter;
030import com.google.common.cache.AbstractCache.StatsCounter;
031import com.google.common.cache.LocalCache.Strength;
032import com.google.errorprone.annotations.CanIgnoreReturnValue;
033import java.lang.ref.SoftReference;
034import java.lang.ref.WeakReference;
035import java.util.ConcurrentModificationException;
036import java.util.IdentityHashMap;
037import java.util.Map;
038import java.util.concurrent.TimeUnit;
039import java.util.logging.Level;
040import java.util.logging.Logger;
041import javax.annotation.CheckForNull;
042
043/**
044 * A builder of {@link LoadingCache} and {@link Cache} instances.
045 *
046 * <h2>Prefer <a href="https://github.com/ben-manes/caffeine/wiki">Caffeine</a> over Guava's caching
047 * API</h2>
048 *
049 * <p>The successor to Guava's caching API is <a
050 * href="https://github.com/ben-manes/caffeine/wiki">Caffeine</a>. Its API is designed to make it a
051 * nearly drop-in replacement. It requires Java 8+, and is not available for Android or GWT/J2CL,
052 * and may have <a href="https://github.com/ben-manes/caffeine/wiki/Guava">different (usually
053 * better) behavior</a> when multiple threads attempt concurrent mutations. Its equivalent to {@code
054 * CacheBuilder} is its <a
055 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/caffeine/latest/com.github.benmanes.caffeine/com/github/benmanes/caffeine/cache/Caffeine.html">{@code
056 * Caffeine}</a> class. Caffeine offers better performance, more features (including asynchronous
057 * loading), and fewer <a
058 * href="https://github.com/google/guava/issues?q=is%3Aopen+is%3Aissue+label%3Apackage%3Dcache+label%3Atype%3Ddefect">bugs</a>.
059 *
060 * <p>Caffeine defines its own interfaces (<a
061 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/caffeine/latest/com.github.benmanes.caffeine/com/github/benmanes/caffeine/cache/Cache.html">{@code
062 * Cache}</a>, <a
063 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/caffeine/latest/com.github.benmanes.caffeine/com/github/benmanes/caffeine/cache/LoadingCache.html">{@code
064 * LoadingCache}</a>, <a
065 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/caffeine/latest/com.github.benmanes.caffeine/com/github/benmanes/caffeine/cache/CacheLoader.html">{@code
066 * CacheLoader}</a>, etc.), so you can use Caffeine without needing to use any Guava types.
067 * Caffeine's types are better than Guava's, especially for <a
068 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/caffeine/latest/com.github.benmanes.caffeine/com/github/benmanes/caffeine/cache/AsyncLoadingCache.html">their
069 * deep support for asynchronous operations</a>. But if you want to migrate to Caffeine with minimal
070 * code changes, you can use <a
071 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/guava/latest/com.github.benmanes.caffeine.guava/com/github/benmanes/caffeine/guava/CaffeinatedGuava.html">its
072 * {@code CaffeinatedGuava} adapter class</a>, which lets you build a Guava {@code Cache} or a Guava
073 * {@code LoadingCache} backed by a Guava {@code CacheLoader}.
074 *
075 * <p>Caffeine's API for asynchronous operations uses {@code CompletableFuture}: <a
076 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/caffeine/latest/com.github.benmanes.caffeine/com/github/benmanes/caffeine/cache/AsyncLoadingCache.html#get(K)">{@code
077 * AsyncLoadingCache.get}</a> returns a {@code CompletableFuture}, and implementations of <a
078 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/caffeine/latest/com.github.benmanes.caffeine/com/github/benmanes/caffeine/cache/AsyncCacheLoader.html#asyncLoad(K,java.util.concurrent.Executor)">{@code
079 * AsyncCacheLoader.asyncLoad}</a> must return a {@code CompletableFuture}. Users of Guava's {@link
080 * com.google.common.util.concurrent.ListenableFuture} can adapt between the two {@code Future}
081 * types by using <a href="https://github.com/lukas-krecan/future-converter#java8-guava">{@code
082 * net.javacrumbs.futureconverter.java8guava.FutureConverter}</a>.
083 *
084 * <h2>More on {@code CacheBuilder}</h2>
085 *
086 * {@code CacheBuilder} builds caches with any combination of the following features:
087 *
088 * <ul>
089 *   <li>automatic loading of entries into the cache
090 *   <li>least-recently-used eviction when a maximum size is exceeded (note that the cache is
091 *       divided into segments, each of which does LRU internally)
092 *   <li>time-based expiration of entries, measured since last access or last write
093 *   <li>keys automatically wrapped in {@code WeakReference}
094 *   <li>values automatically wrapped in {@code WeakReference} or {@code SoftReference}
095 *   <li>notification of evicted (or otherwise removed) entries
096 *   <li>accumulation of cache access statistics
097 * </ul>
098 *
099 * <p>These features are all optional; caches can be created using all or none of them. By default,
100 * cache instances created by {@code CacheBuilder} will not perform any type of eviction.
101 *
102 * <p>Usage example:
103 *
104 * <pre>{@code
105 * LoadingCache<Key, Graph> graphs = CacheBuilder.newBuilder()
106 *     .maximumSize(10000)
107 *     .expireAfterWrite(10, TimeUnit.MINUTES)
108 *     .removalListener(MY_LISTENER)
109 *     .build(
110 *         new CacheLoader<Key, Graph>() {
111 *           public Graph load(Key key) throws AnyException {
112 *             return createExpensiveGraph(key);
113 *           }
114 *         });
115 * }</pre>
116 *
117 * <p>Or equivalently,
118 *
119 * <pre>{@code
120 * // In real life this would come from a command-line flag or config file
121 * String spec = "maximumSize=10000,expireAfterWrite=10m";
122 *
123 * LoadingCache<Key, Graph> graphs = CacheBuilder.from(spec)
124 *     .removalListener(MY_LISTENER)
125 *     .build(
126 *         new CacheLoader<Key, Graph>() {
127 *           public Graph load(Key key) throws AnyException {
128 *             return createExpensiveGraph(key);
129 *           }
130 *         });
131 * }</pre>
132 *
133 * <p>The returned cache implements all optional operations of the {@link LoadingCache} and {@link
134 * Cache} interfaces. The {@code asMap} view (and its collection views) have <i>weakly consistent
135 * iterators</i>. This means that they are safe for concurrent use, but if other threads modify the
136 * cache after the iterator is created, it is undefined which of these changes, if any, are
137 * reflected in that iterator. These iterators never throw {@link ConcurrentModificationException}.
138 *
139 * <p><b>Note:</b> by default, the returned cache uses equality comparisons (the {@link
140 * Object#equals equals} method) to determine equality for keys or values. However, if {@link
141 * #weakKeys} was specified, the cache uses identity ({@code ==}) comparisons instead for keys.
142 * Likewise, if {@link #weakValues} or {@link #softValues} was specified, the cache uses identity
143 * comparisons for values.
144 *
145 * <p>Entries are automatically evicted from the cache when any of {@link #maximumSize(long)
146 * maximumSize}, {@link #maximumWeight(long) maximumWeight}, {@link #expireAfterWrite
147 * expireAfterWrite}, {@link #expireAfterAccess expireAfterAccess}, {@link #weakKeys weakKeys},
148 * {@link #weakValues weakValues}, or {@link #softValues softValues} are requested.
149 *
150 * <p>If {@link #maximumSize(long) maximumSize} or {@link #maximumWeight(long) maximumWeight} is
151 * requested entries may be evicted on each cache modification.
152 *
153 * <p>If {@link #expireAfterWrite expireAfterWrite} or {@link #expireAfterAccess expireAfterAccess}
154 * is requested entries may be evicted on each cache modification, on occasional cache accesses, or
155 * on calls to {@link Cache#cleanUp}. Expired entries may be counted by {@link Cache#size}, but will
156 * never be visible to read or write operations.
157 *
158 * <p>If {@link #weakKeys weakKeys}, {@link #weakValues weakValues}, or {@link #softValues
159 * softValues} are requested, it is possible for a key or value present in the cache to be reclaimed
160 * by the garbage collector. Entries with reclaimed keys or values may be removed from the cache on
161 * each cache modification, on occasional cache accesses, or on calls to {@link Cache#cleanUp}; such
162 * entries may be counted in {@link Cache#size}, but will never be visible to read or write
163 * operations.
164 *
165 * <p>Certain cache configurations will result in the accrual of periodic maintenance tasks which
166 * will be performed during write operations, or during occasional read operations in the absence of
167 * writes. The {@link Cache#cleanUp} method of the returned cache will also perform maintenance, but
168 * calling it should not be necessary with a high throughput cache. Only caches built with {@link
169 * #removalListener removalListener}, {@link #expireAfterWrite expireAfterWrite}, {@link
170 * #expireAfterAccess expireAfterAccess}, {@link #weakKeys weakKeys}, {@link #weakValues
171 * weakValues}, or {@link #softValues softValues} perform periodic maintenance.
172 *
173 * <p>The caches produced by {@code CacheBuilder} are serializable, and the deserialized caches
174 * retain all the configuration properties of the original cache. Note that the serialized form does
175 * <i>not</i> include cache contents, but only configuration.
176 *
177 * <p>See the Guava User Guide article on <a
178 * href="https://github.com/google/guava/wiki/CachesExplained">caching</a> for a higher-level
179 * explanation.
180 *
181 * @param <K> the most general key type this builder will be able to create caches for. This is
182 *     normally {@code Object} unless it is constrained by using a method like {@code
183 *     #removalListener}. Cache keys may not be null.
184 * @param <V> the most general value type this builder will be able to create caches for. This is
185 *     normally {@code Object} unless it is constrained by using a method like {@code
186 *     #removalListener}. Cache values may not be null.
187 * @author Charles Fry
188 * @author Kevin Bourrillion
189 * @since 10.0
190 */
191@GwtCompatible(emulated = true)
192@ElementTypesAreNonnullByDefault
193public final class CacheBuilder<K, V> {
194  private static final int DEFAULT_INITIAL_CAPACITY = 16;
195  private static final int DEFAULT_CONCURRENCY_LEVEL = 4;
196
197  @SuppressWarnings("GoodTime") // should be a java.time.Duration
198  private static final int DEFAULT_EXPIRATION_NANOS = 0;
199
200  @SuppressWarnings("GoodTime") // should be a java.time.Duration
201  private static final int DEFAULT_REFRESH_NANOS = 0;
202
203  static final Supplier<? extends StatsCounter> NULL_STATS_COUNTER =
204      Suppliers.ofInstance(
205          new StatsCounter() {
206            @Override
207            public void recordHits(int count) {}
208
209            @Override
210            public void recordMisses(int count) {}
211
212            @SuppressWarnings("GoodTime") // b/122668874
213            @Override
214            public void recordLoadSuccess(long loadTime) {}
215
216            @SuppressWarnings("GoodTime") // b/122668874
217            @Override
218            public void recordLoadException(long loadTime) {}
219
220            @Override
221            public void recordEviction() {}
222
223            @Override
224            public CacheStats snapshot() {
225              return EMPTY_STATS;
226            }
227          });
228  static final CacheStats EMPTY_STATS = new CacheStats(0, 0, 0, 0, 0, 0);
229
230  /*
231   * We avoid using a method reference or lambda here for now:
232   *
233   * - method reference: Inside Google, CacheBuilder is used from the implementation of a custom
234   *   ClassLoader that is sometimes used as a system classloader. That's a problem because
235   *   method-reference linking tries to look up the system classloader, and it fails because there
236   *   isn't one yet.
237   *
238   * - lambda: Outside Google, we got a report of a similar problem in
239   *   https://github.com/google/guava/issues/6565
240   */
241  @SuppressWarnings("AnonymousToLambda")
242  static final Supplier<StatsCounter> CACHE_STATS_COUNTER =
243      new Supplier<StatsCounter>() {
244        @Override
245        public StatsCounter get() {
246          return new SimpleStatsCounter();
247        }
248      };
249
250  enum NullListener implements RemovalListener<Object, Object> {
251    INSTANCE;
252
253    @Override
254    public void onRemoval(RemovalNotification<Object, Object> notification) {}
255  }
256
257  enum OneWeigher implements Weigher<Object, Object> {
258    INSTANCE;
259
260    @Override
261    public int weigh(Object key, Object value) {
262      return 1;
263    }
264  }
265
266  static final Ticker NULL_TICKER =
267      new Ticker() {
268        @Override
269        public long read() {
270          return 0;
271        }
272      };
273
274  // We use a holder class to delay initialization: https://github.com/google/guava/issues/6566
275  private static final class LoggerHolder {
276    static final Logger logger = Logger.getLogger(CacheBuilder.class.getName());
277  }
278
279  static final int UNSET_INT = -1;
280
281  boolean strictParsing = true;
282
283  int initialCapacity = UNSET_INT;
284  int concurrencyLevel = UNSET_INT;
285  long maximumSize = UNSET_INT;
286  long maximumWeight = UNSET_INT;
287  @CheckForNull Weigher<? super K, ? super V> weigher;
288
289  @CheckForNull Strength keyStrength;
290  @CheckForNull Strength valueStrength;
291
292  @SuppressWarnings("GoodTime") // should be a java.time.Duration
293  long expireAfterWriteNanos = UNSET_INT;
294
295  @SuppressWarnings("GoodTime") // should be a java.time.Duration
296  long expireAfterAccessNanos = UNSET_INT;
297
298  @SuppressWarnings("GoodTime") // should be a java.time.Duration
299  long refreshNanos = UNSET_INT;
300
301  @CheckForNull Equivalence<Object> keyEquivalence;
302  @CheckForNull Equivalence<Object> valueEquivalence;
303
304  @CheckForNull RemovalListener<? super K, ? super V> removalListener;
305  @CheckForNull Ticker ticker;
306
307  Supplier<? extends StatsCounter> statsCounterSupplier = NULL_STATS_COUNTER;
308
309  private CacheBuilder() {}
310
311  /**
312   * Constructs a new {@code CacheBuilder} instance with default settings, including strong keys,
313   * strong values, and no automatic eviction of any kind.
314   *
315   * <p>Note that while this return type is {@code CacheBuilder<Object, Object>}, type parameters on
316   * the {@link #build} methods allow you to create a cache of any key and value type desired.
317   */
318  public static CacheBuilder<Object, Object> newBuilder() {
319    return new CacheBuilder<>();
320  }
321
322  /**
323   * Constructs a new {@code CacheBuilder} instance with the settings specified in {@code spec}.
324   *
325   * @since 12.0
326   */
327  @GwtIncompatible // To be supported
328  public static CacheBuilder<Object, Object> from(CacheBuilderSpec spec) {
329    return spec.toCacheBuilder().lenientParsing();
330  }
331
332  /**
333   * Constructs a new {@code CacheBuilder} instance with the settings specified in {@code spec}.
334   * This is especially useful for command-line configuration of a {@code CacheBuilder}.
335   *
336   * @param spec a String in the format specified by {@link CacheBuilderSpec}
337   * @since 12.0
338   */
339  @GwtIncompatible // To be supported
340  public static CacheBuilder<Object, Object> from(String spec) {
341    return from(CacheBuilderSpec.parse(spec));
342  }
343
344  /**
345   * Enables lenient parsing. Useful for tests and spec parsing.
346   *
347   * @return this {@code CacheBuilder} instance (for chaining)
348   */
349  @GwtIncompatible // To be supported
350  @CanIgnoreReturnValue
351  CacheBuilder<K, V> lenientParsing() {
352    strictParsing = false;
353    return this;
354  }
355
356  /**
357   * Sets a custom {@code Equivalence} strategy for comparing keys.
358   *
359   * <p>By default, the cache uses {@link Equivalence#identity} to determine key equality when
360   * {@link #weakKeys} is specified, and {@link Equivalence#equals()} otherwise.
361   *
362   * @return this {@code CacheBuilder} instance (for chaining)
363   */
364  @GwtIncompatible // To be supported
365  @CanIgnoreReturnValue
366  CacheBuilder<K, V> keyEquivalence(Equivalence<Object> equivalence) {
367    checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);
368    keyEquivalence = checkNotNull(equivalence);
369    return this;
370  }
371
372  Equivalence<Object> getKeyEquivalence() {
373    return MoreObjects.firstNonNull(keyEquivalence, getKeyStrength().defaultEquivalence());
374  }
375
376  /**
377   * Sets a custom {@code Equivalence} strategy for comparing values.
378   *
379   * <p>By default, the cache uses {@link Equivalence#identity} to determine value equality when
380   * {@link #weakValues} or {@link #softValues} is specified, and {@link Equivalence#equals()}
381   * otherwise.
382   *
383   * @return this {@code CacheBuilder} instance (for chaining)
384   */
385  @GwtIncompatible // To be supported
386  @CanIgnoreReturnValue
387  CacheBuilder<K, V> valueEquivalence(Equivalence<Object> equivalence) {
388    checkState(
389        valueEquivalence == null, "value equivalence was already set to %s", valueEquivalence);
390    this.valueEquivalence = checkNotNull(equivalence);
391    return this;
392  }
393
394  Equivalence<Object> getValueEquivalence() {
395    return MoreObjects.firstNonNull(valueEquivalence, getValueStrength().defaultEquivalence());
396  }
397
398  /**
399   * Sets the minimum total size for the internal hash tables. For example, if the initial capacity
400   * is {@code 60}, and the concurrency level is {@code 8}, then eight segments are created, each
401   * having a hash table of size eight. Providing a large enough estimate at construction time
402   * avoids the need for expensive resizing operations later, but setting this value unnecessarily
403   * high wastes memory.
404   *
405   * @return this {@code CacheBuilder} instance (for chaining)
406   * @throws IllegalArgumentException if {@code initialCapacity} is negative
407   * @throws IllegalStateException if an initial capacity was already set
408   */
409  @CanIgnoreReturnValue
410  public CacheBuilder<K, V> initialCapacity(int initialCapacity) {
411    checkState(
412        this.initialCapacity == UNSET_INT,
413        "initial capacity was already set to %s",
414        this.initialCapacity);
415    checkArgument(initialCapacity >= 0);
416    this.initialCapacity = initialCapacity;
417    return this;
418  }
419
420  int getInitialCapacity() {
421    return (initialCapacity == UNSET_INT) ? DEFAULT_INITIAL_CAPACITY : initialCapacity;
422  }
423
424  /**
425   * Guides the allowed concurrency among update operations. Used as a hint for internal sizing. The
426   * table is internally partitioned to try to permit the indicated number of concurrent updates
427   * without contention. Because assignment of entries to these partitions is not necessarily
428   * uniform, the actual concurrency observed may vary. Ideally, you should choose a value to
429   * accommodate as many threads as will ever concurrently modify the table. Using a significantly
430   * higher value than you need can waste space and time, and a significantly lower value can lead
431   * to thread contention. But overestimates and underestimates within an order of magnitude do not
432   * usually have much noticeable impact. A value of one permits only one thread to modify the cache
433   * at a time, but since read operations and cache loading computations can proceed concurrently,
434   * this still yields higher concurrency than full synchronization.
435   *
436   * <p>Defaults to 4. <b>Note:</b>The default may change in the future. If you care about this
437   * value, you should always choose it explicitly.
438   *
439   * <p>The current implementation uses the concurrency level to create a fixed number of hashtable
440   * segments, each governed by its own write lock. The segment lock is taken once for each explicit
441   * write, and twice for each cache loading computation (once prior to loading the new value, and
442   * once after loading completes). Much internal cache management is performed at the segment
443   * granularity. For example, access queues and write queues are kept per segment when they are
444   * required by the selected eviction algorithm. As such, when writing unit tests it is not
445   * uncommon to specify {@code concurrencyLevel(1)} in order to achieve more deterministic eviction
446   * behavior.
447   *
448   * <p>Note that future implementations may abandon segment locking in favor of more advanced
449   * concurrency controls.
450   *
451   * @return this {@code CacheBuilder} instance (for chaining)
452   * @throws IllegalArgumentException if {@code concurrencyLevel} is nonpositive
453   * @throws IllegalStateException if a concurrency level was already set
454   */
455  @CanIgnoreReturnValue
456  public CacheBuilder<K, V> concurrencyLevel(int concurrencyLevel) {
457    checkState(
458        this.concurrencyLevel == UNSET_INT,
459        "concurrency level was already set to %s",
460        this.concurrencyLevel);
461    checkArgument(concurrencyLevel > 0);
462    this.concurrencyLevel = concurrencyLevel;
463    return this;
464  }
465
466  int getConcurrencyLevel() {
467    return (concurrencyLevel == UNSET_INT) ? DEFAULT_CONCURRENCY_LEVEL : concurrencyLevel;
468  }
469
470  /**
471   * Specifies the maximum number of entries the cache may contain.
472   *
473   * <p>Note that the cache <b>may evict an entry before this limit is exceeded</b>. For example, in
474   * the current implementation, when {@code concurrencyLevel} is greater than {@code 1}, each
475   * resulting segment inside the cache <i>independently</i> limits its own size to approximately
476   * {@code maximumSize / concurrencyLevel}.
477   *
478   * <p>When eviction is necessary, the cache evicts entries that are less likely to be used again.
479   * For example, the cache may evict an entry because it hasn't been used recently or very often.
480   *
481   * <p>If {@code maximumSize} is zero, elements will be evicted immediately after being loaded into
482   * cache. This can be useful in testing, or to disable caching temporarily.
483   *
484   * <p>This feature cannot be used in conjunction with {@link #maximumWeight}.
485   *
486   * @param maximumSize the maximum size of the cache
487   * @return this {@code CacheBuilder} instance (for chaining)
488   * @throws IllegalArgumentException if {@code maximumSize} is negative
489   * @throws IllegalStateException if a maximum size or weight was already set
490   */
491  @CanIgnoreReturnValue
492  public CacheBuilder<K, V> maximumSize(long maximumSize) {
493    checkState(
494        this.maximumSize == UNSET_INT, "maximum size was already set to %s", this.maximumSize);
495    checkState(
496        this.maximumWeight == UNSET_INT,
497        "maximum weight was already set to %s",
498        this.maximumWeight);
499    checkState(this.weigher == null, "maximum size can not be combined with weigher");
500    checkArgument(maximumSize >= 0, "maximum size must not be negative");
501    this.maximumSize = maximumSize;
502    return this;
503  }
504
505  /**
506   * Specifies the maximum weight of entries the cache may contain. Weight is determined using the
507   * {@link Weigher} specified with {@link #weigher}, and use of this method requires a
508   * corresponding call to {@link #weigher} prior to calling {@link #build}.
509   *
510   * <p>Note that the cache <b>may evict an entry before this limit is exceeded</b>. For example, in
511   * the current implementation, when {@code concurrencyLevel} is greater than {@code 1}, each
512   * resulting segment inside the cache <i>independently</i> limits its own weight to approximately
513   * {@code maximumWeight / concurrencyLevel}.
514   *
515   * <p>When eviction is necessary, the cache evicts entries that are less likely to be used again.
516   * For example, the cache may evict an entry because it hasn't been used recently or very often.
517   *
518   * <p>If {@code maximumWeight} is zero, elements will be evicted immediately after being loaded
519   * into cache. This can be useful in testing, or to disable caching temporarily.
520   *
521   * <p>Note that weight is only used to determine whether the cache is over capacity; it has no
522   * effect on selecting which entry should be evicted next.
523   *
524   * <p>This feature cannot be used in conjunction with {@link #maximumSize}.
525   *
526   * @param maximumWeight the maximum total weight of entries the cache may contain
527   * @return this {@code CacheBuilder} instance (for chaining)
528   * @throws IllegalArgumentException if {@code maximumWeight} is negative
529   * @throws IllegalStateException if a maximum weight or size was already set
530   * @since 11.0
531   */
532  @GwtIncompatible // To be supported
533  @CanIgnoreReturnValue
534  public CacheBuilder<K, V> maximumWeight(long maximumWeight) {
535    checkState(
536        this.maximumWeight == UNSET_INT,
537        "maximum weight was already set to %s",
538        this.maximumWeight);
539    checkState(
540        this.maximumSize == UNSET_INT, "maximum size was already set to %s", this.maximumSize);
541    checkArgument(maximumWeight >= 0, "maximum weight must not be negative");
542    this.maximumWeight = maximumWeight;
543    return this;
544  }
545
546  /**
547   * Specifies the weigher to use in determining the weight of entries. Entry weight is taken into
548   * consideration by {@link #maximumWeight(long)} when determining which entries to evict, and use
549   * of this method requires a corresponding call to {@link #maximumWeight(long)} prior to calling
550   * {@link #build}. Weights are measured and recorded when entries are inserted into the cache, and
551   * are thus effectively static during the lifetime of a cache entry.
552   *
553   * <p>When the weight of an entry is zero it will not be considered for size-based eviction
554   * (though it still may be evicted by other means).
555   *
556   * <p><b>Important note:</b> Instead of returning <em>this</em> as a {@code CacheBuilder}
557   * instance, this method returns {@code CacheBuilder<K1, V1>}. From this point on, either the
558   * original reference or the returned reference may be used to complete configuration and build
559   * the cache, but only the "generic" one is type-safe. That is, it will properly prevent you from
560   * building caches whose key or value types are incompatible with the types accepted by the
561   * weigher already provided; the {@code CacheBuilder} type cannot do this. For best results,
562   * simply use the standard method-chaining idiom, as illustrated in the documentation at top,
563   * configuring a {@code CacheBuilder} and building your {@link Cache} all in a single statement.
564   *
565   * <p><b>Warning:</b> if you ignore the above advice, and use this {@code CacheBuilder} to build a
566   * cache whose key or value type is incompatible with the weigher, you will likely experience a
567   * {@link ClassCastException} at some <i>undefined</i> point in the future.
568   *
569   * @param weigher the weigher to use in calculating the weight of cache entries
570   * @return this {@code CacheBuilder} instance (for chaining)
571   * @throws IllegalStateException if a weigher was already set or {@link #maximumSize(long)} was
572   *     previously called
573   * @since 11.0
574   */
575  @GwtIncompatible // To be supported
576  @CanIgnoreReturnValue // TODO(b/27479612): consider removing this
577  public <K1 extends K, V1 extends V> CacheBuilder<K1, V1> weigher(
578      Weigher<? super K1, ? super V1> weigher) {
579    checkState(this.weigher == null);
580    if (strictParsing) {
581      checkState(
582          this.maximumSize == UNSET_INT,
583          "weigher can not be combined with maximum size (%s provided)",
584          this.maximumSize);
585    }
586
587    // safely limiting the kinds of caches this can produce
588    @SuppressWarnings("unchecked")
589    CacheBuilder<K1, V1> me = (CacheBuilder<K1, V1>) this;
590    me.weigher = checkNotNull(weigher);
591    return me;
592  }
593
594  long getMaximumWeight() {
595    if (expireAfterWriteNanos == 0 || expireAfterAccessNanos == 0) {
596      return 0;
597    }
598    return (weigher == null) ? maximumSize : maximumWeight;
599  }
600
601  // Make a safe contravariant cast now so we don't have to do it over and over.
602  @SuppressWarnings("unchecked")
603  <K1 extends K, V1 extends V> Weigher<K1, V1> getWeigher() {
604    return (Weigher<K1, V1>) MoreObjects.firstNonNull(weigher, OneWeigher.INSTANCE);
605  }
606
607  /**
608   * Specifies that each key (not value) stored in the cache should be wrapped in a {@link
609   * WeakReference} (by default, strong references are used).
610   *
611   * <p><b>Warning:</b> when this method is used, the resulting cache will use identity ({@code ==})
612   * comparison to determine equality of keys. Its {@link Cache#asMap} view will therefore
613   * technically violate the {@link Map} specification (in the same way that {@link IdentityHashMap}
614   * does).
615   *
616   * <p>Entries with keys that have been garbage collected may be counted in {@link Cache#size}, but
617   * will never be visible to read or write operations; such entries are cleaned up as part of the
618   * routine maintenance described in the class javadoc.
619   *
620   * @return this {@code CacheBuilder} instance (for chaining)
621   * @throws IllegalStateException if the key strength was already set
622   */
623  @GwtIncompatible // java.lang.ref.WeakReference
624  @CanIgnoreReturnValue
625  public CacheBuilder<K, V> weakKeys() {
626    return setKeyStrength(Strength.WEAK);
627  }
628
629  @CanIgnoreReturnValue
630  CacheBuilder<K, V> setKeyStrength(Strength strength) {
631    checkState(keyStrength == null, "Key strength was already set to %s", keyStrength);
632    keyStrength = checkNotNull(strength);
633    return this;
634  }
635
636  Strength getKeyStrength() {
637    return MoreObjects.firstNonNull(keyStrength, Strength.STRONG);
638  }
639
640  /**
641   * Specifies that each value (not key) stored in the cache should be wrapped in a {@link
642   * WeakReference} (by default, strong references are used).
643   *
644   * <p>Weak values will be garbage collected once they are weakly reachable. This makes them a poor
645   * candidate for caching; consider {@link #softValues} instead.
646   *
647   * <p><b>Note:</b> when this method is used, the resulting cache will use identity ({@code ==})
648   * comparison to determine equality of values.
649   *
650   * <p>Entries with values that have been garbage collected may be counted in {@link Cache#size},
651   * but will never be visible to read or write operations; such entries are cleaned up as part of
652   * the routine maintenance described in the class javadoc.
653   *
654   * @return this {@code CacheBuilder} instance (for chaining)
655   * @throws IllegalStateException if the value strength was already set
656   */
657  @GwtIncompatible // java.lang.ref.WeakReference
658  @CanIgnoreReturnValue
659  public CacheBuilder<K, V> weakValues() {
660    return setValueStrength(Strength.WEAK);
661  }
662
663  /**
664   * Specifies that each value (not key) stored in the cache should be wrapped in a {@link
665   * SoftReference} (by default, strong references are used). Softly-referenced objects will be
666   * garbage-collected in a <i>globally</i> least-recently-used manner, in response to memory
667   * demand.
668   *
669   * <p><b>Warning:</b> in most circumstances it is better to set a per-cache {@linkplain
670   * #maximumSize(long) maximum size} instead of using soft references. You should only use this
671   * method if you are well familiar with the practical consequences of soft references.
672   *
673   * <p><b>Note:</b> when this method is used, the resulting cache will use identity ({@code ==})
674   * comparison to determine equality of values.
675   *
676   * <p>Entries with values that have been garbage collected may be counted in {@link Cache#size},
677   * but will never be visible to read or write operations; such entries are cleaned up as part of
678   * the routine maintenance described in the class javadoc.
679   *
680   * @return this {@code CacheBuilder} instance (for chaining)
681   * @throws IllegalStateException if the value strength was already set
682   */
683  @GwtIncompatible // java.lang.ref.SoftReference
684  @CanIgnoreReturnValue
685  public CacheBuilder<K, V> softValues() {
686    return setValueStrength(Strength.SOFT);
687  }
688
689  @CanIgnoreReturnValue
690  CacheBuilder<K, V> setValueStrength(Strength strength) {
691    checkState(valueStrength == null, "Value strength was already set to %s", valueStrength);
692    valueStrength = checkNotNull(strength);
693    return this;
694  }
695
696  Strength getValueStrength() {
697    return MoreObjects.firstNonNull(valueStrength, Strength.STRONG);
698  }
699
700  /**
701   * Specifies that each entry should be automatically removed from the cache once a fixed duration
702   * has elapsed after the entry's creation, or the most recent replacement of its value.
703   *
704   * <p>When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
705   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
706   * useful in testing, or to disable caching temporarily without a code change.
707   *
708   * <p>Expired entries may be counted in {@link Cache#size}, but will never be visible to read or
709   * write operations. Expired entries are cleaned up as part of the routine maintenance described
710   * in the class javadoc.
711   *
712   * @param duration the length of time after an entry is created that it should be automatically
713   *     removed
714   * @param unit the unit that {@code duration} is expressed in
715   * @return this {@code CacheBuilder} instance (for chaining)
716   * @throws IllegalArgumentException if {@code duration} is negative
717   * @throws IllegalStateException if {@link #expireAfterWrite} was already set
718   */
719  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
720  @CanIgnoreReturnValue
721  public CacheBuilder<K, V> expireAfterWrite(long duration, TimeUnit unit) {
722    checkState(
723        expireAfterWriteNanos == UNSET_INT,
724        "expireAfterWrite was already set to %s ns",
725        expireAfterWriteNanos);
726    checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
727    this.expireAfterWriteNanos = unit.toNanos(duration);
728    return this;
729  }
730
731  @SuppressWarnings("GoodTime") // nanos internally, should be Duration
732  long getExpireAfterWriteNanos() {
733    return (expireAfterWriteNanos == UNSET_INT) ? DEFAULT_EXPIRATION_NANOS : expireAfterWriteNanos;
734  }
735
736  /**
737   * Specifies that each entry should be automatically removed from the cache once a fixed duration
738   * has elapsed after the entry's creation, the most recent replacement of its value, or its last
739   * access. Access time is reset by all cache read and write operations (including {@code
740   * Cache.asMap().get(Object)} and {@code Cache.asMap().put(K, V)}), but not by {@code
741   * containsKey(Object)}, nor by operations on the collection-views of {@link Cache#asMap}. So, for
742   * example, iterating through {@code Cache.asMap().entrySet()} does not reset access time for the
743   * entries you retrieve.
744   *
745   * <p>When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
746   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
747   * useful in testing, or to disable caching temporarily without a code change.
748   *
749   * <p>Expired entries may be counted in {@link Cache#size}, but will never be visible to read or
750   * write operations. Expired entries are cleaned up as part of the routine maintenance described
751   * in the class javadoc.
752   *
753   * @param duration the length of time after an entry is last accessed that it should be
754   *     automatically removed
755   * @param unit the unit that {@code duration} is expressed in
756   * @return this {@code CacheBuilder} instance (for chaining)
757   * @throws IllegalArgumentException if {@code duration} is negative
758   * @throws IllegalStateException if {@link #expireAfterAccess} was already set
759   */
760  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
761  @CanIgnoreReturnValue
762  public CacheBuilder<K, V> expireAfterAccess(long duration, TimeUnit unit) {
763    checkState(
764        expireAfterAccessNanos == UNSET_INT,
765        "expireAfterAccess was already set to %s ns",
766        expireAfterAccessNanos);
767    checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
768    this.expireAfterAccessNanos = unit.toNanos(duration);
769    return this;
770  }
771
772  @SuppressWarnings("GoodTime") // nanos internally, should be Duration
773  long getExpireAfterAccessNanos() {
774    return (expireAfterAccessNanos == UNSET_INT)
775        ? DEFAULT_EXPIRATION_NANOS
776        : expireAfterAccessNanos;
777  }
778
779  /**
780   * Specifies that active entries are eligible for automatic refresh once a fixed duration has
781   * elapsed after the entry's creation, or the most recent replacement of its value. The semantics
782   * of refreshes are specified in {@link LoadingCache#refresh}, and are performed by calling {@link
783   * CacheLoader#reload}.
784   *
785   * <p>As the default implementation of {@link CacheLoader#reload} is synchronous, it is
786   * recommended that users of this method override {@link CacheLoader#reload} with an asynchronous
787   * implementation; otherwise refreshes will be performed during unrelated cache read and write
788   * operations.
789   *
790   * <p>Currently automatic refreshes are performed when the first stale request for an entry
791   * occurs. The request triggering refresh will make a synchronous call to {@link
792   * CacheLoader#reload}
793   * and immediately return the new value if the returned future is complete, and the old value
794   * otherwise.
795   *
796   * <p><b>Note:</b> <i>all exceptions thrown during refresh will be logged and then swallowed</i>.
797   *
798   * @param duration the length of time after an entry is created that it should be considered
799   *     stale, and thus eligible for refresh
800   * @param unit the unit that {@code duration} is expressed in
801   * @return this {@code CacheBuilder} instance (for chaining)
802   * @throws IllegalArgumentException if {@code duration} is negative
803   * @throws IllegalStateException if {@link #refreshAfterWrite} was already set
804   * @since 11.0
805   */
806  @GwtIncompatible // To be supported (synchronously).
807  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
808  @CanIgnoreReturnValue
809  public CacheBuilder<K, V> refreshAfterWrite(long duration, TimeUnit unit) {
810    checkNotNull(unit);
811    checkState(refreshNanos == UNSET_INT, "refresh was already set to %s ns", refreshNanos);
812    checkArgument(duration > 0, "duration must be positive: %s %s", duration, unit);
813    this.refreshNanos = unit.toNanos(duration);
814    return this;
815  }
816
817  @SuppressWarnings("GoodTime") // nanos internally, should be Duration
818  long getRefreshNanos() {
819    return (refreshNanos == UNSET_INT) ? DEFAULT_REFRESH_NANOS : refreshNanos;
820  }
821
822  /**
823   * Specifies a nanosecond-precision time source for this cache. By default, {@link
824   * System#nanoTime} is used.
825   *
826   * <p>The primary intent of this method is to facilitate testing of caches with a fake or mock
827   * time source.
828   *
829   * @return this {@code CacheBuilder} instance (for chaining)
830   * @throws IllegalStateException if a ticker was already set
831   */
832  @CanIgnoreReturnValue
833  public CacheBuilder<K, V> ticker(Ticker ticker) {
834    checkState(this.ticker == null);
835    this.ticker = checkNotNull(ticker);
836    return this;
837  }
838
839  Ticker getTicker(boolean recordsTime) {
840    if (ticker != null) {
841      return ticker;
842    }
843    return recordsTime ? Ticker.systemTicker() : NULL_TICKER;
844  }
845
846  /**
847   * Specifies a listener instance that caches should notify each time an entry is removed for any
848   * {@linkplain RemovalCause reason}. Each cache created by this builder will invoke this listener
849   * as part of the routine maintenance described in the class documentation above.
850   *
851   * <p><b>Warning:</b> after invoking this method, do not continue to use <i>this</i> cache builder
852   * reference; instead use the reference this method <i>returns</i>. At runtime, these point to the
853   * same instance, but only the returned reference has the correct generic type information to
854   * ensure type safety. For best results, use the standard method-chaining idiom illustrated in the
855   * class documentation above, configuring a builder and building your cache in a single statement.
856   * Failure to heed this advice can result in a {@link ClassCastException} being thrown by a cache
857   * operation at some <i>undefined</i> point in the future.
858   *
859   * <p><b>Warning:</b> any exception thrown by {@code listener} will <i>not</i> be propagated to
860   * the {@code Cache} user, only logged via a {@link Logger}.
861   *
862   * @return the cache builder reference that should be used instead of {@code this} for any
863   *     remaining configuration and cache building
864   * @return this {@code CacheBuilder} instance (for chaining)
865   * @throws IllegalStateException if a removal listener was already set
866   */
867  public <K1 extends K, V1 extends V> CacheBuilder<K1, V1> removalListener(
868      RemovalListener<? super K1, ? super V1> listener) {
869    checkState(this.removalListener == null);
870
871    // safely limiting the kinds of caches this can produce
872    @SuppressWarnings("unchecked")
873    CacheBuilder<K1, V1> me = (CacheBuilder<K1, V1>) this;
874    me.removalListener = checkNotNull(listener);
875    return me;
876  }
877
878  // Make a safe contravariant cast now so we don't have to do it over and over.
879  @SuppressWarnings("unchecked")
880  <K1 extends K, V1 extends V> RemovalListener<K1, V1> getRemovalListener() {
881    return (RemovalListener<K1, V1>)
882        MoreObjects.firstNonNull(removalListener, NullListener.INSTANCE);
883  }
884
885  /**
886   * Enable the accumulation of {@link CacheStats} during the operation of the cache. Without this
887   * {@link Cache#stats} will return zero for all statistics. Note that recording stats requires
888   * bookkeeping to be performed with each operation, and thus imposes a performance penalty on
889   * cache operation.
890   *
891   * @return this {@code CacheBuilder} instance (for chaining)
892   * @since 12.0 (previously, stats collection was automatic)
893   */
894  @CanIgnoreReturnValue
895  public CacheBuilder<K, V> recordStats() {
896    statsCounterSupplier = CACHE_STATS_COUNTER;
897    return this;
898  }
899
900  boolean isRecordingStats() {
901    return statsCounterSupplier == CACHE_STATS_COUNTER;
902  }
903
904  Supplier<? extends StatsCounter> getStatsCounterSupplier() {
905    return statsCounterSupplier;
906  }
907
908  /**
909   * Builds a cache, which either returns an already-loaded value for a given key or atomically
910   * computes or retrieves it using the supplied {@code CacheLoader}. If another thread is currently
911   * loading the value for this key, simply waits for that thread to finish and returns its loaded
912   * value. Note that multiple threads can concurrently load values for distinct keys.
913   *
914   * <p>This method does not alter the state of this {@code CacheBuilder} instance, so it can be
915   * invoked again to create multiple independent caches.
916   *
917   * @param loader the cache loader used to obtain new values
918   * @return a cache having the requested features
919   */
920  public <K1 extends K, V1 extends V> LoadingCache<K1, V1> build(
921      CacheLoader<? super K1, V1> loader) {
922    checkWeightWithWeigher();
923    return new LocalCache.LocalLoadingCache<>(this, loader);
924  }
925
926  /**
927   * Builds a cache which does not automatically load values when keys are requested.
928   *
929   * <p>Consider {@link #build(CacheLoader)} instead, if it is feasible to implement a {@code
930   * CacheLoader}.
931   *
932   * <p>This method does not alter the state of this {@code CacheBuilder} instance, so it can be
933   * invoked again to create multiple independent caches.
934   *
935   * @return a cache having the requested features
936   * @since 11.0
937   */
938  public <K1 extends K, V1 extends V> Cache<K1, V1> build() {
939    checkWeightWithWeigher();
940    checkNonLoadingCache();
941    return new LocalCache.LocalManualCache<>(this);
942  }
943
944  private void checkNonLoadingCache() {
945    checkState(refreshNanos == UNSET_INT, "refreshAfterWrite requires a LoadingCache");
946  }
947
948  private void checkWeightWithWeigher() {
949    if (weigher == null) {
950      checkState(maximumWeight == UNSET_INT, "maximumWeight requires weigher");
951    } else {
952      if (strictParsing) {
953        checkState(maximumWeight != UNSET_INT, "weigher requires maximumWeight");
954      } else {
955        if (maximumWeight == UNSET_INT) {
956          LoggerHolder.logger.log(
957              Level.WARNING, "ignoring weigher specified without maximumWeight");
958        }
959      }
960    }
961  }
962
963  /**
964   * Returns a string representation for this CacheBuilder instance. The exact form of the returned
965   * string is not specified.
966   */
967  @Override
968  public String toString() {
969    MoreObjects.ToStringHelper s = MoreObjects.toStringHelper(this);
970    if (initialCapacity != UNSET_INT) {
971      s.add("initialCapacity", initialCapacity);
972    }
973    if (concurrencyLevel != UNSET_INT) {
974      s.add("concurrencyLevel", concurrencyLevel);
975    }
976    if (maximumSize != UNSET_INT) {
977      s.add("maximumSize", maximumSize);
978    }
979    if (maximumWeight != UNSET_INT) {
980      s.add("maximumWeight", maximumWeight);
981    }
982    if (expireAfterWriteNanos != UNSET_INT) {
983      s.add("expireAfterWrite", expireAfterWriteNanos + "ns");
984    }
985    if (expireAfterAccessNanos != UNSET_INT) {
986      s.add("expireAfterAccess", expireAfterAccessNanos + "ns");
987    }
988    if (keyStrength != null) {
989      s.add("keyStrength", Ascii.toLowerCase(keyStrength.toString()));
990    }
991    if (valueStrength != null) {
992      s.add("valueStrength", Ascii.toLowerCase(valueStrength.toString()));
993    }
994    if (keyEquivalence != null) {
995      s.addValue("keyEquivalence");
996    }
997    if (valueEquivalence != null) {
998      s.addValue("valueEquivalence");
999    }
1000    if (removalListener != null) {
1001      s.addValue("removalListener");
1002    }
1003    return s.toString();
1004  }
1005}