001 /*
002 * Copyright (C) 2009 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
017 package com.google.common.cache;
018
019 import static com.google.common.base.Objects.firstNonNull;
020 import static com.google.common.base.Preconditions.checkArgument;
021 import static com.google.common.base.Preconditions.checkNotNull;
022 import static com.google.common.base.Preconditions.checkState;
023
024 import com.google.common.annotations.Beta;
025 import com.google.common.annotations.GwtCompatible;
026 import com.google.common.annotations.GwtIncompatible;
027 import com.google.common.base.Ascii;
028 import com.google.common.base.Equivalence;
029 import com.google.common.base.Equivalences;
030 import com.google.common.base.Objects;
031 import com.google.common.base.Supplier;
032 import com.google.common.base.Suppliers;
033 import com.google.common.base.Ticker;
034 import com.google.common.cache.AbstractCache.SimpleStatsCounter;
035 import com.google.common.cache.AbstractCache.StatsCounter;
036 import com.google.common.cache.LocalCache.Strength;
037
038 import java.lang.ref.SoftReference;
039 import java.lang.ref.WeakReference;
040 import java.util.ConcurrentModificationException;
041 import java.util.concurrent.ConcurrentHashMap;
042 import java.util.concurrent.TimeUnit;
043 import java.util.logging.Level;
044 import java.util.logging.Logger;
045
046 import javax.annotation.CheckReturnValue;
047
048 /**
049 * <p>A builder of {@link LoadingCache} and {@link Cache} instances having any combination of the
050 * following features:
051 *
052 * <ul>
053 * <li>automatic loading of entries into the cache
054 * <li>least-recently-used eviction when a maximum size is exceeded
055 * <li>time-based expiration of entries, measured since last access or last write
056 * <li>keys automatically wrapped in {@linkplain WeakReference weak} references
057 * <li>values automatically wrapped in {@linkplain WeakReference weak} or
058 * {@linkplain SoftReference soft} references
059 * <li>notification of evicted (or otherwise removed) entries
060 * </ul>
061 *
062 * <p>Usage example: <pre> {@code
063 *
064 * LoadingCache<Key, Graph> graphs = CacheBuilder.newBuilder()
065 * .maximumSize(10000)
066 * .expireAfterWrite(10, TimeUnit.MINUTES)
067 * .removalListener(MY_LISTENER)
068 * .build(
069 * new CacheLoader<Key, Graph>() {
070 * public Graph load(Key key) throws AnyException {
071 * return createExpensiveGraph(key);
072 * }
073 * });}</pre>
074 *
075 *
076 * These features are all optional.
077 *
078 * <p>The returned cache is implemented as a hash table with similar performance characteristics to
079 * {@link ConcurrentHashMap}. It implements all optional operations of the {@link LoadingCache} and
080 * {@link Cache} interfaces. The {@code asMap} view (and its collection views) have <i>weakly
081 * consistent iterators</i>. This means that they are safe for concurrent use, but if other threads
082 * modify the cache after the iterator is created, it is undefined which of these changes, if any,
083 * are reflected in that iterator. These iterators never throw {@link
084 * ConcurrentModificationException}.
085 *
086 * <p><b>Note:</b> by default, the returned cache uses equality comparisons (the
087 * {@link Object#equals equals} method) to determine equality for keys or values. However, if
088 * {@link #weakKeys} was specified, the cache uses identity ({@code ==})
089 * comparisons instead for keys. Likewise, if {@link #weakValues} or {@link #softValues} was
090 * specified, the cache uses identity comparisons for values.
091 *
092 * <p>Entries are automatically evicted from the cache when any of
093 * {@linkplain #maximumSize(long) maximumSize}, {@linkplain #maximumWeight(long) maximumWeight},
094 * {@linkplain #expireAfterWrite expireAfterWrite},
095 * {@linkplain #expireAfterAccess expireAfterAccess}, {@linkplain #weakKeys weakKeys},
096 * {@linkplain #weakValues weakValues}, or {@linkplain #softValues softValues} are requested.
097 *
098 * <p>If {@linkplain #maximumSize(long) maximumSize} or
099 * {@linkplain #maximumWeight(long) maximumWeight} is requested entries may be evicted on each cache
100 * modification.
101 *
102 * <p>If {@linkplain #expireAfterWrite expireAfterWrite} or
103 * {@linkplain #expireAfterAccess expireAfterAccess} is requested entries may be evicted on each
104 * cache modification, on occasional cache accesses, or on calls to {@link Cache#cleanUp}. Expired
105 * entries may be counted in {@link Cache#size}, but will never be visible to read or write
106 * operations.
107 *
108 * <p>If {@linkplain #weakKeys weakKeys}, {@linkplain #weakValues weakValues}, or
109 * {@linkplain #softValues softValues} are requested, it is possible for a key or value present in
110 * the cache to be reclaimed by the garbage collector. Entries with reclaimed keys or values may be
111 * removed from the cache on each cache modification, on occasional cache accesses, or on calls to
112 * {@link Cache#cleanUp}; such entries may be counted in {@link Cache#size}, but will never be
113 * visible to read or write operations.
114 *
115 * <p>Certain cache configurations will result in the accrual of periodic maintenance tasks which
116 * will be performed during write operations, or during occasional read operations in the absense of
117 * writes. The {@link Cache#cleanUp} method of the returned cache will also perform maintenance, but
118 * calling it should not be necessary with a high throughput cache. Only caches built with
119 * {@linkplain #removalListener removalListener}, {@linkplain #expireAfterWrite expireAfterWrite},
120 * {@linkplain #expireAfterAccess expireAfterAccess}, {@linkplain #weakKeys weakKeys},
121 * {@linkplain #weakValues weakValues}, or {@linkplain #softValues softValues} perform periodic
122 * maintenance.
123 *
124 * <p>The caches produced by {@code CacheBuilder} are serializable, and the deserialized caches
125 * retain all the configuration properties of the original cache. Note that the serialized form does
126 * <i>not</i> include cache contents, but only configuration.
127 *
128 * @param <K> the base key type for all caches created by this builder
129 * @param <V> the base value type for all caches created by this builder
130 * @author Charles Fry
131 * @author Kevin Bourrillion
132 * @since 10.0
133 */
134 @Beta
135 @GwtCompatible(emulated = true)
136 public final class CacheBuilder<K, V> {
137 private static final int DEFAULT_INITIAL_CAPACITY = 16;
138 private static final int DEFAULT_CONCURRENCY_LEVEL = 4;
139 private static final int DEFAULT_EXPIRATION_NANOS = 0;
140 private static final int DEFAULT_REFRESH_NANOS = 0;
141
142 static final Supplier<? extends StatsCounter> NULL_STATS_COUNTER = Suppliers.ofInstance(
143 new StatsCounter() {
144 @Override
145 public void recordHits(int count) {}
146
147 @Override
148 public void recordMisses(int count) {}
149
150 @Override
151 public void recordLoadSuccess(long loadTime) {}
152
153 @Override
154 public void recordLoadException(long loadTime) {}
155
156 @Override
157 public void recordEviction() {}
158
159 @Override
160 public CacheStats snapshot() {
161 return EMPTY_STATS;
162 }
163 });
164 static final CacheStats EMPTY_STATS = new CacheStats(0, 0, 0, 0, 0, 0);
165
166 static final Supplier<SimpleStatsCounter> CACHE_STATS_COUNTER =
167 new Supplier<SimpleStatsCounter>() {
168 @Override
169 public SimpleStatsCounter get() {
170 return new SimpleStatsCounter();
171 }
172 };
173
174 enum NullListener implements RemovalListener<Object, Object> {
175 INSTANCE;
176
177 @Override
178 public void onRemoval(RemovalNotification<Object, Object> notification) {}
179 }
180
181 enum OneWeigher implements Weigher<Object, Object> {
182 INSTANCE;
183
184 @Override
185 public int weigh(Object key, Object value) {
186 return 1;
187 }
188 }
189
190 static final Ticker NULL_TICKER = new Ticker() {
191 @Override
192 public long read() {
193 return 0;
194 }
195 };
196
197 private static final Logger logger = Logger.getLogger(CacheBuilder.class.getName());
198
199 static final int UNSET_INT = -1;
200
201 boolean strictParsing = true;
202
203 int initialCapacity = UNSET_INT;
204 int concurrencyLevel = UNSET_INT;
205 long maximumSize = UNSET_INT;
206 long maximumWeight = UNSET_INT;
207 Weigher<? super K, ? super V> weigher;
208
209 Strength keyStrength;
210 Strength valueStrength;
211
212 long expireAfterWriteNanos = UNSET_INT;
213 long expireAfterAccessNanos = UNSET_INT;
214 long refreshNanos = UNSET_INT;
215
216 Equivalence<Object> keyEquivalence;
217 Equivalence<Object> valueEquivalence;
218
219 RemovalListener<? super K, ? super V> removalListener;
220 Ticker ticker;
221
222 Supplier<? extends StatsCounter> statsCounterSupplier = CACHE_STATS_COUNTER;
223
224 // TODO(fry): make constructor private and update tests to use newBuilder
225 CacheBuilder() {}
226
227 /**
228 * Constructs a new {@code CacheBuilder} instance with default settings, including strong keys,
229 * strong values, and no automatic eviction of any kind.
230 */
231 public static CacheBuilder<Object, Object> newBuilder() {
232 return new CacheBuilder<Object, Object>();
233 }
234
235 /**
236 * Enables lenient parsing. Useful for tests and spec parsing.
237 */
238 CacheBuilder<K, V> lenientParsing() {
239 strictParsing = false;
240 return this;
241 }
242
243 /**
244 * Sets a custom {@code Equivalence} strategy for comparing keys.
245 *
246 * <p>By default, the cache uses {@link Equivalences#identity} to determine key equality when
247 * {@link #weakKeys} is specified, and {@link Equivalences#equals()} otherwise.
248 */
249 CacheBuilder<K, V> keyEquivalence(Equivalence<Object> equivalence) {
250 checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);
251 keyEquivalence = checkNotNull(equivalence);
252 return this;
253 }
254
255 Equivalence<Object> getKeyEquivalence() {
256 return firstNonNull(keyEquivalence, getKeyStrength().defaultEquivalence());
257 }
258
259 /**
260 * Sets a custom {@code Equivalence} strategy for comparing values.
261 *
262 * <p>By default, the cache uses {@link Equivalences#identity} to determine value equality when
263 * {@link #weakValues} or {@link #softValues} is specified, and {@link Equivalences#equals()}
264 * otherwise.
265 */
266 CacheBuilder<K, V> valueEquivalence(Equivalence<Object> equivalence) {
267 checkState(valueEquivalence == null,
268 "value equivalence was already set to %s", valueEquivalence);
269 this.valueEquivalence = checkNotNull(equivalence);
270 return this;
271 }
272
273 Equivalence<Object> getValueEquivalence() {
274 return firstNonNull(valueEquivalence, getValueStrength().defaultEquivalence());
275 }
276
277 /**
278 * Sets the minimum total size for the internal hash tables. For example, if the initial capacity
279 * is {@code 60}, and the concurrency level is {@code 8}, then eight segments are created, each
280 * having a hash table of size eight. Providing a large enough estimate at construction time
281 * avoids the need for expensive resizing operations later, but setting this value unnecessarily
282 * high wastes memory.
283 *
284 * @throws IllegalArgumentException if {@code initialCapacity} is negative
285 * @throws IllegalStateException if an initial capacity was already set
286 */
287 public CacheBuilder<K, V> initialCapacity(int initialCapacity) {
288 checkState(this.initialCapacity == UNSET_INT, "initial capacity was already set to %s",
289 this.initialCapacity);
290 checkArgument(initialCapacity >= 0);
291 this.initialCapacity = initialCapacity;
292 return this;
293 }
294
295 int getInitialCapacity() {
296 return (initialCapacity == UNSET_INT) ? DEFAULT_INITIAL_CAPACITY : initialCapacity;
297 }
298
299 /**
300 * Guides the allowed concurrency among update operations. Used as a hint for internal sizing. The
301 * table is internally partitioned to try to permit the indicated number of concurrent updates
302 * without contention. Because assignment of entries to these partitions is not necessarily
303 * uniform, the actual concurrency observed may vary. Ideally, you should choose a value to
304 * accommodate as many threads as will ever concurrently modify the table. Using a significantly
305 * higher value than you need can waste space and time, and a significantly lower value can lead
306 * to thread contention. But overestimates and underestimates within an order of magnitude do not
307 * usually have much noticeable impact. A value of one permits only one thread to modify the cache
308 * at a time, but since read operations can proceed concurrently, this still yields higher
309 * concurrency than full synchronization. Defaults to 4.
310 *
311 * <p><b>Note:</b>The default may change in the future. If you care about this value, you should
312 * always choose it explicitly.
313 *
314 * @throws IllegalArgumentException if {@code concurrencyLevel} is nonpositive
315 * @throws IllegalStateException if a concurrency level was already set
316 */
317 public CacheBuilder<K, V> concurrencyLevel(int concurrencyLevel) {
318 checkState(this.concurrencyLevel == UNSET_INT, "concurrency level was already set to %s",
319 this.concurrencyLevel);
320 checkArgument(concurrencyLevel > 0);
321 this.concurrencyLevel = concurrencyLevel;
322 return this;
323 }
324
325 int getConcurrencyLevel() {
326 return (concurrencyLevel == UNSET_INT) ? DEFAULT_CONCURRENCY_LEVEL : concurrencyLevel;
327 }
328
329 /**
330 * Specifies the maximum number of entries the cache may contain. Note that the cache <b>may evict
331 * an entry before this limit is exceeded</b>. As the cache size grows close to the maximum, the
332 * cache evicts entries that are less likely to be used again. For example, the cache may evict an
333 * entry because it hasn't been used recently or very often.
334 *
335 * <p>When {@code size} is zero, elements will be evicted immediately after being loaded into the
336 * cache. This can be useful in testing, or to disable caching temporarily without a code change.
337 *
338 * @param size the maximum size of the cache
339 * @throws IllegalArgumentException if {@code size} is negative
340 * @throws IllegalStateException if a maximum size was already set
341 */
342 public CacheBuilder<K, V> maximumSize(long size) {
343 checkState(this.maximumSize == UNSET_INT, "maximum size was already set to %s",
344 this.maximumSize);
345 checkState(this.maximumWeight == UNSET_INT, "maximum weight was already set to %s",
346 this.maximumWeight);
347 checkState(this.weigher == null, "maximum size can not be combined with weigher");
348 checkArgument(size >= 0, "maximum size must not be negative");
349 this.maximumSize = size;
350 return this;
351 }
352
353 /**
354 * Specifies the maximum weight of entries the cache may contain. Weight is determined using the
355 * {@link Weigher} specified with {@link #weigher}, and use of this method requires a
356 * corresponding call to {@link #weigher} prior to calling {@link #build}.
357 *
358 * <p>Note that the cache <b>may evict an entry before this limit is exceeded</b>. As the cache
359 * size grows close to the maximum, the cache evicts entries that are less likely to be used
360 * again. For example, the cache may evict an entry because it hasn't been used recently or very
361 * often.
362 *
363 * <p>When {@code weight} is zero, elements will be evicted immediately after being loaded into
364 * cache. This can be useful in testing, or to disable caching temporarily without a code
365 * change.
366 *
367 * @param weight the maximum weight the cache may contain
368 * @throws IllegalArgumentException if {@code size} is negative
369 * @throws IllegalStateException if a maximum size was already set
370 * @since 11.0
371 */
372 public CacheBuilder<K, V> maximumWeight(long weight) {
373 checkState(this.maximumWeight == UNSET_INT, "maximum weight was already set to %s",
374 this.maximumWeight);
375 checkState(this.maximumSize == UNSET_INT, "maximum size was already set to %s",
376 this.maximumSize);
377 this.maximumWeight = weight;
378 checkArgument(weight >= 0, "maximum weight must not be negative");
379 return this;
380 }
381
382 /**
383 * Specifies the weigher to use in determining the weight of entries. Entry weight is taken
384 * into consideration by {@link #maximumWeight(long)} when determining which entries to evict, and
385 * use of this method requires a corresponding call to {@link #maximumWeight(long)} prior to
386 * calling {@link #build}. Weights are measured and recorded when entries are inserted into the
387 * cache, and are thus effectively static during the lifetime of a cache entry.
388 *
389 * <p>When the weight of an entry is zero it will not be considered for size-based eviction
390 * (though it still may be evicted by other means).
391 *
392 * <p><b>Important note:</b> Instead of returning <em>this</em> as a {@code CacheBuilder}
393 * instance, this method returns {@code CacheBuilder<K1, V1>}. From this point on, either the
394 * original reference or the returned reference may be used to complete configuration and build
395 * the cache, but only the "generic" one is type-safe. That is, it will properly prevent you from
396 * building caches whose key or value types are incompatible with the types accepted by the
397 * weigher already provided; the {@code CacheBuilder} type cannot do this. For best results,
398 * simply use the standard method-chaining idiom, as illustrated in the documentation at top,
399 * configuring a {@code CacheBuilder} and building your {@link Cache} all in a single statement.
400 *
401 * <p><b>Warning:</b> if you ignore the above advice, and use this {@code CacheBuilder} to build
402 * a cache whose key or value type is incompatible with the weigher, you will likely experience
403 * a {@link ClassCastException} at some <i>undefined</i> point in the future.
404 *
405 * @param weigher the weigher to use in calculating the weight of cache entries
406 * @throws IllegalArgumentException if {@code size} is negative
407 * @throws IllegalStateException if a maximum size was already set
408 * @since 11.0
409 */
410 public <K1 extends K, V1 extends V> CacheBuilder<K1, V1> weigher(
411 Weigher<? super K1, ? super V1> weigher) {
412 checkState(this.weigher == null);
413 if (strictParsing) {
414 checkState(this.maximumSize == UNSET_INT, "weigher can not be combined with maximum size",
415 this.maximumSize);
416 }
417
418 // safely limiting the kinds of caches this can produce
419 @SuppressWarnings("unchecked")
420 CacheBuilder<K1, V1> me = (CacheBuilder<K1, V1>) this;
421 me.weigher = checkNotNull(weigher);
422 return me;
423 }
424
425 long getMaximumWeight() {
426 if (expireAfterWriteNanos == 0 || expireAfterAccessNanos == 0) {
427 return 0;
428 }
429 return (weigher == null) ? maximumSize : maximumWeight;
430 }
431
432 // Make a safe contravariant cast now so we don't have to do it over and over.
433 @SuppressWarnings("unchecked")
434 <K1 extends K, V1 extends V> Weigher<K1, V1> getWeigher() {
435 return (Weigher<K1, V1>) Objects.firstNonNull(weigher, OneWeigher.INSTANCE);
436 }
437
438 /**
439 * Specifies that each key (not value) stored in the cache should be strongly referenced.
440 *
441 * @throws IllegalStateException if the key strength was already set
442 */
443 CacheBuilder<K, V> strongKeys() {
444 return setKeyStrength(Strength.STRONG);
445 }
446
447 /**
448 * Specifies that each key (not value) stored in the cache should be wrapped in a {@link
449 * WeakReference} (by default, strong references are used).
450 *
451 * <p><b>Warning:</b> when this method is used, the resulting cache will use identity ({@code ==})
452 * comparison to determine equality of keys.
453 *
454 * <p>Entries with keys that have been garbage collected may be counted in {@link Cache#size},
455 * but will never be visible to read or write operations; such entries are cleaned up as part of
456 * the routine maintenance described in the class javadoc.
457 *
458 * @throws IllegalStateException if the key strength was already set
459 */
460 @GwtIncompatible("java.lang.ref.WeakReference")
461 public CacheBuilder<K, V> weakKeys() {
462 return setKeyStrength(Strength.WEAK);
463 }
464
465 CacheBuilder<K, V> setKeyStrength(Strength strength) {
466 checkState(keyStrength == null, "Key strength was already set to %s", keyStrength);
467 keyStrength = checkNotNull(strength);
468 return this;
469 }
470
471 Strength getKeyStrength() {
472 return firstNonNull(keyStrength, Strength.STRONG);
473 }
474
475 /**
476 * Specifies that each value (not key) stored in the cache should be strongly referenced.
477 *
478 * @throws IllegalStateException if the value strength was already set
479 */
480 CacheBuilder<K, V> strongValues() {
481 return setValueStrength(Strength.STRONG);
482 }
483
484 /**
485 * Specifies that each value (not key) stored in the cache should be wrapped in a
486 * {@link WeakReference} (by default, strong references are used).
487 *
488 * <p>Weak values will be garbage collected once they are weakly reachable. This makes them a poor
489 * candidate for caching; consider {@link #softValues} instead.
490 *
491 * <p><b>Note:</b> when this method is used, the resulting cache will use identity ({@code ==})
492 * comparison to determine equality of values.
493 *
494 * <p>Entries with values that have been garbage collected may be counted in {@link Cache#size},
495 * but will never be visible to read or write operations; such entries are cleaned up as part of
496 * the routine maintenance described in the class javadoc.
497 *
498 * @throws IllegalStateException if the value strength was already set
499 */
500 @GwtIncompatible("java.lang.ref.WeakReference")
501 public CacheBuilder<K, V> weakValues() {
502 return setValueStrength(Strength.WEAK);
503 }
504
505 /**
506 * Specifies that each value (not key) stored in the cache should be wrapped in a
507 * {@link SoftReference} (by default, strong references are used). Softly-referenced objects will
508 * be garbage-collected in a <i>globally</i> least-recently-used manner, in response to memory
509 * demand.
510 *
511 * <p><b>Warning:</b> in most circumstances it is better to set a per-cache {@linkplain
512 * #maximumSize(long) maximum size} instead of using soft references. You should only use this
513 * method if you are well familiar with the practical consequences of soft references.
514 *
515 * <p><b>Note:</b> when this method is used, the resulting cache will use identity ({@code ==})
516 * comparison to determine equality of values.
517 *
518 * <p>Entries with values that have been garbage collected may be counted in {@link Cache#size},
519 * but will never be visible to read or write operations; such entries are cleaned up as part of
520 * the routine maintenance described in the class javadoc.
521 *
522 * @throws IllegalStateException if the value strength was already set
523 */
524 @GwtIncompatible("java.lang.ref.SoftReference")
525 public CacheBuilder<K, V> softValues() {
526 return setValueStrength(Strength.SOFT);
527 }
528
529 CacheBuilder<K, V> setValueStrength(Strength strength) {
530 checkState(valueStrength == null, "Value strength was already set to %s", valueStrength);
531 valueStrength = checkNotNull(strength);
532 return this;
533 }
534
535 Strength getValueStrength() {
536 return firstNonNull(valueStrength, Strength.STRONG);
537 }
538
539 /**
540 * Specifies that each entry should be automatically removed from the cache once a fixed duration
541 * has elapsed after the entry's creation, or the most recent replacement of its value.
542 *
543 * <p>When {@code duration} is zero, this method hands off to
544 * {@link #maximumSize(long) maximumSize}{@code (0)}, ignoring any otherwise-specificed maximum
545 * size or weight. This can be useful in testing, or to disable caching temporarily without a code
546 * change.
547 *
548 * <p>Expired entries may be counted in {@link Cache#size}, but will never be visible to read or
549 * write operations. Expired entries are cleaned up as part of the routine maintenance described
550 * in the class javadoc.
551 *
552 * @param duration the length of time after an entry is created that it should be automatically
553 * removed
554 * @param unit the unit that {@code duration} is expressed in
555 * @throws IllegalArgumentException if {@code duration} is negative
556 * @throws IllegalStateException if the time to live or time to idle was already set
557 */
558 public CacheBuilder<K, V> expireAfterWrite(long duration, TimeUnit unit) {
559 checkState(expireAfterWriteNanos == UNSET_INT, "expireAfterWrite was already set to %s ns",
560 expireAfterWriteNanos);
561 checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
562 this.expireAfterWriteNanos = unit.toNanos(duration);
563 return this;
564 }
565
566 long getExpireAfterWriteNanos() {
567 return (expireAfterWriteNanos == UNSET_INT) ? DEFAULT_EXPIRATION_NANOS : expireAfterWriteNanos;
568 }
569
570 /**
571 * Specifies that each entry should be automatically removed from the cache once a fixed duration
572 * has elapsed after the entry's creation, the most recent replacement of its value, or its last
573 * access. Access time is reset by all cache read and write operations (including
574 * {@code Cache.asMap().get(Object)} and {@code Cache.asMap().put(K, V)}), but not by operations
575 * on the collection-views of {@link Cache#asMap}.
576 *
577 * <p>When {@code duration} is zero, this method hands off to
578 * {@link #maximumSize(long) maximumSize}{@code (0)}, ignoring any otherwise-specificed maximum
579 * size or weight. This can be useful in testing, or to disable caching temporarily without a code
580 * change.
581 *
582 * <p>Expired entries may be counted in {@link Cache#size}, but will never be visible to read or
583 * write operations. Expired entries are cleaned up as part of the routine maintenance described
584 * in the class javadoc.
585 *
586 * @param duration the length of time after an entry is last accessed that it should be
587 * automatically removed
588 * @param unit the unit that {@code duration} is expressed in
589 * @throws IllegalArgumentException if {@code duration} is negative
590 * @throws IllegalStateException if the time to idle or time to live was already set
591 */
592 public CacheBuilder<K, V> expireAfterAccess(long duration, TimeUnit unit) {
593 checkState(expireAfterAccessNanos == UNSET_INT, "expireAfterAccess was already set to %s ns",
594 expireAfterAccessNanos);
595 checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
596 this.expireAfterAccessNanos = unit.toNanos(duration);
597 return this;
598 }
599
600 long getExpireAfterAccessNanos() {
601 return (expireAfterAccessNanos == UNSET_INT)
602 ? DEFAULT_EXPIRATION_NANOS : expireAfterAccessNanos;
603 }
604
605 /**
606 * Specifies that active entries are eligible for automatic refresh once a fixed duration has
607 * elapsed after the entry's creation, or the most recent replacement of its value. The semantics
608 * of refreshes are specified in {@link LoadingCache#refresh}, and are performed by calling
609 * {@link CacheLoader#reload}.
610 *
611 * <p>As the default implementation of {@link CacheLoader#reload} is synchronous, it is
612 * recommended that users of this method override {@link CacheLoader#reload} with an asynchrnous
613 * implementation; otherwise refreshes will block other cache operations.
614 *
615 * <p>Currently automatic refreshes are performed when the first stale request for an entry
616 * occurs. The request triggering refresh will make a blocking call to {@link CacheLoader#reload}
617 * and immediately return the new value if the returned future is complete, and the old value
618 * otherwise.
619 *
620 * <p><b>Note:</b> <i>all exceptions thrown during refresh will be logged and then swallowed</i>.
621 *
622 * @param duration the length of time after an entry is created that it should be considered
623 * stale, and thus eligible for refresh
624 * @param unit the unit that {@code duration} is expressed in
625 * @throws IllegalArgumentException if {@code duration} is negative
626 * @throws IllegalStateException if the refresh interval was already set
627 * @since 11.0
628 */
629 @GwtIncompatible("To be supported")
630 public CacheBuilder<K, V> refreshAfterWrite(long duration, TimeUnit unit) {
631 checkNotNull(unit);
632 checkState(refreshNanos == UNSET_INT, "refresh was already set to %s ns", refreshNanos);
633 checkArgument(duration > 0, "duration must be positive: %s %s", duration, unit);
634 this.refreshNanos = unit.toNanos(duration);
635 return this;
636 }
637
638 long getRefreshNanos() {
639 return (refreshNanos == UNSET_INT) ? DEFAULT_REFRESH_NANOS : refreshNanos;
640 }
641
642 /**
643 * Specifies a nanosecond-precision time source for use in determining when entries should be
644 * expired. By default, {@link System#nanoTime} is used.
645 *
646 * <p>The primary intent of this method is to facilitate testing of caches which have been
647 * configured with {@link #expireAfterWrite} or {@link #expireAfterAccess}.
648 *
649 * @throws IllegalStateException if a ticker was already set
650 */
651 @GwtIncompatible("To be supported")
652 public CacheBuilder<K, V> ticker(Ticker ticker) {
653 checkState(this.ticker == null);
654 this.ticker = checkNotNull(ticker);
655 return this;
656 }
657
658 Ticker getTicker(boolean recordsTime) {
659 if (ticker != null) {
660 return ticker;
661 }
662 return recordsTime ? Ticker.systemTicker() : NULL_TICKER;
663 }
664
665 /**
666 * Specifies a listener instance, which all caches built using this {@code CacheBuilder} will
667 * notify each time an entry is removed from the cache by any means.
668 *
669 * <p>Each cache built by this {@code CacheBuilder} after this method is called invokes the
670 * supplied listener after removing an element for any reason (see removal causes in {@link
671 * RemovalCause}). It will invoke the listener as part of the routine maintenance described
672 * in the class javadoc.
673 *
674 * <p><b>Note:</b> <i>all exceptions thrown by {@code listener} will be logged (using
675 * {@link java.util.logging.Logger})and then swallowed</i>.
676 *
677 * <p><b>Important note:</b> Instead of returning <em>this</em> as a {@code CacheBuilder}
678 * instance, this method returns {@code CacheBuilder<K1, V1>}. From this point on, either the
679 * original reference or the returned reference may be used to complete configuration and build
680 * the cache, but only the "generic" one is type-safe. That is, it will properly prevent you from
681 * building caches whose key or value types are incompatible with the types accepted by the
682 * listener already provided; the {@code CacheBuilder} type cannot do this. For best results,
683 * simply use the standard method-chaining idiom, as illustrated in the documentation at top,
684 * configuring a {@code CacheBuilder} and building your {@link Cache} all in a single statement.
685 *
686 * <p><b>Warning:</b> if you ignore the above advice, and use this {@code CacheBuilder} to build
687 * a cache whose key or value type is incompatible with the listener, you will likely experience
688 * a {@link ClassCastException} at some <i>undefined</i> point in the future.
689 *
690 * @throws IllegalStateException if a removal listener was already set
691 */
692 @CheckReturnValue
693 @GwtIncompatible("To be supported")
694 public <K1 extends K, V1 extends V> CacheBuilder<K1, V1> removalListener(
695 RemovalListener<? super K1, ? super V1> listener) {
696 checkState(this.removalListener == null);
697
698 // safely limiting the kinds of caches this can produce
699 @SuppressWarnings("unchecked")
700 CacheBuilder<K1, V1> me = (CacheBuilder<K1, V1>) this;
701 me.removalListener = checkNotNull(listener);
702 return me;
703 }
704
705 // Make a safe contravariant cast now so we don't have to do it over and over.
706 @SuppressWarnings("unchecked")
707 <K1 extends K, V1 extends V> RemovalListener<K1, V1> getRemovalListener() {
708 return (RemovalListener<K1, V1>) Objects.firstNonNull(removalListener, NullListener.INSTANCE);
709 }
710
711 /**
712 * Disable the accumulation of {@link CacheStats} during the operation of the cache.
713 */
714 CacheBuilder<K, V> disableStats() {
715 checkState(statsCounterSupplier == CACHE_STATS_COUNTER);
716 statsCounterSupplier = NULL_STATS_COUNTER;
717 return this;
718 }
719
720 Supplier<? extends StatsCounter> getStatsCounterSupplier() {
721 return statsCounterSupplier;
722 }
723
724 /**
725 * Builds a cache, which either returns an already-loaded value for a given key or atomically
726 * computes or retrieves it using the supplied {@code CacheLoader}. If another thread is currently
727 * loading the value for this key, simply waits for that thread to finish and returns its
728 * loaded value. Note that multiple threads can concurrently load values for distinct keys.
729 *
730 * <p>This method does not alter the state of this {@code CacheBuilder} instance, so it can be
731 * invoked again to create multiple independent caches.
732 *
733 * @param loader the cache loader used to obtain new values
734 * @return a cache having the requested features
735 */
736 public <K1 extends K, V1 extends V> LoadingCache<K1, V1> build(
737 CacheLoader<? super K1, V1> loader) {
738 checkWeightWithWeigher();
739 return new LocalCache.LocalLoadingCache<K1, V1>(this, loader);
740 }
741
742 /**
743 * Builds a cache which does not automatically load values when keys are requested.
744 *
745 * <p>Consider {@link #build(CacheLoader)} instead, if it is feasible to implement a
746 * {@code CacheLoader}.
747 *
748 * <p>This method does not alter the state of this {@code CacheBuilder} instance, so it can be
749 * invoked again to create multiple independent caches.
750 *
751 * @return a cache having the requested features
752 * @since 11.0
753 */
754 public <K1 extends K, V1 extends V> Cache<K1, V1> build() {
755 checkWeightWithWeigher();
756 checkNonLoadingCache();
757 return new LocalCache.LocalManualCache<K1, V1>(this);
758 }
759
760 private void checkNonLoadingCache() {
761 checkState(refreshNanos == UNSET_INT, "refreshAfterWrite requires a LoadingCache");
762 }
763
764 private void checkWeightWithWeigher() {
765 if (weigher == null) {
766 checkState(maximumWeight == UNSET_INT, "maximumWeight requires weigher");
767 } else {
768 if (strictParsing) {
769 checkState(maximumWeight != UNSET_INT, "weigher requires maximumWeight");
770 } else {
771 if (maximumWeight == UNSET_INT) {
772 logger.log(Level.WARNING, "ignoring weigher specified without maximumWeight");
773 }
774 }
775 }
776 }
777
778 /**
779 * Returns a string representation for this CacheBuilder instance. The exact form of the returned
780 * string is not specified.
781 */
782 @Override
783 public String toString() {
784 Objects.ToStringHelper s = Objects.toStringHelper(this);
785 if (initialCapacity != UNSET_INT) {
786 s.add("initialCapacity", initialCapacity);
787 }
788 if (concurrencyLevel != UNSET_INT) {
789 s.add("concurrencyLevel", concurrencyLevel);
790 }
791 if (maximumWeight != UNSET_INT) {
792 if (weigher == null) {
793 s.add("maximumSize", maximumWeight);
794 } else {
795 s.add("maximumWeight", maximumWeight);
796 }
797 }
798 if (expireAfterWriteNanos != UNSET_INT) {
799 s.add("expireAfterWrite", expireAfterWriteNanos + "ns");
800 }
801 if (expireAfterAccessNanos != UNSET_INT) {
802 s.add("expireAfterAccess", expireAfterAccessNanos + "ns");
803 }
804 if (keyStrength != null) {
805 s.add("keyStrength", Ascii.toLowerCase(keyStrength.toString()));
806 }
807 if (valueStrength != null) {
808 s.add("valueStrength", Ascii.toLowerCase(valueStrength.toString()));
809 }
810 if (keyEquivalence != null) {
811 s.addValue("keyEquivalence");
812 }
813 if (valueEquivalence != null) {
814 s.addValue("valueEquivalence");
815 }
816 if (removalListener != null) {
817 s.addValue("removalListener");
818 }
819 return s.toString();
820 }
821 }