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
015 package com.google.common.collect;
016
017 import static com.google.common.base.Objects.firstNonNull;
018 import static com.google.common.base.Preconditions.checkArgument;
019 import static com.google.common.base.Preconditions.checkNotNull;
020 import static com.google.common.base.Preconditions.checkState;
021
022 import com.google.common.annotations.GwtCompatible;
023 import com.google.common.annotations.GwtIncompatible;
024 import com.google.common.base.Ascii;
025 import com.google.common.base.Equivalence;
026 import com.google.common.base.Equivalences;
027 import com.google.common.base.Function;
028 import com.google.common.base.Objects;
029 import com.google.common.base.Ticker;
030 import com.google.common.collect.ComputingConcurrentHashMap.ComputingMapAdapter;
031 import com.google.common.collect.MapMakerInternalMap.Strength;
032
033 import java.io.Serializable;
034 import java.lang.ref.SoftReference;
035 import java.lang.ref.WeakReference;
036 import java.util.AbstractMap;
037 import java.util.Collections;
038 import java.util.ConcurrentModificationException;
039 import java.util.Map;
040 import java.util.Set;
041 import java.util.concurrent.ConcurrentHashMap;
042 import java.util.concurrent.ConcurrentMap;
043 import java.util.concurrent.TimeUnit;
044
045 import javax.annotation.Nullable;
046
047 /**
048 * <p>A builder of {@link ConcurrentMap} instances having any combination of the following features:
049 *
050 * <ul>
051 * <li>keys or values automatically wrapped in {@linkplain WeakReference weak} or {@linkplain
052 * SoftReference soft} references
053 * <li>least-recently-used eviction when a maximum size is exceeded
054 * <li>time-based expiration of entries, measured since last access or last write
055 * <li>notification of evicted (or otherwise removed) entries
056 * <li>on-demand computation of values for keys not already present
057 * </ul>
058 *
059 * <p>Usage example: <pre> {@code
060 *
061 * ConcurrentMap<Key, Graph> graphs = new MapMaker()
062 * .concurrencyLevel(4)
063 * .weakKeys()
064 * .maximumSize(10000)
065 * .expireAfterWrite(10, TimeUnit.MINUTES)
066 * .makeComputingMap(
067 * new Function<Key, Graph>() {
068 * public Graph apply(Key key) {
069 * return createExpensiveGraph(key);
070 * }
071 * });}</pre>
072 *
073 * These features are all optional; {@code new MapMaker().makeMap()} returns a valid concurrent map
074 * that behaves similarly to a {@link ConcurrentHashMap}.
075 *
076 * <p>The returned map is implemented as a hash table with similar performance characteristics to
077 * {@link ConcurrentHashMap}. It supports all optional operations of the {@code ConcurrentMap}
078 * interface. It does not permit null keys or values.
079 *
080 * <p><b>Note:</b> by default, the returned map uses equality comparisons (the {@link Object#equals
081 * equals} method) to determine equality for keys or values. However, if {@link #weakKeys} or {@link
082 * #softKeys} was specified, the map uses identity ({@code ==}) comparisons instead for keys.
083 * Likewise, if {@link #weakValues} or {@link #softValues} was specified, the map uses identity
084 * comparisons for values.
085 *
086 * <p>The view collections of the returned map have <i>weakly consistent iterators</i>. This means
087 * that they are safe for concurrent use, but if other threads modify the map after the iterator is
088 * created, it is undefined which of these changes, if any, are reflected in that iterator. These
089 * iterators never throw {@link ConcurrentModificationException}.
090 *
091 * <p>If soft or weak references were requested, it is possible for a key or value present in the
092 * the map to be reclaimed by the garbage collector. If this happens, the entry automatically
093 * disappears from the map. A partially-reclaimed entry is never exposed to the user. Any {@link
094 * java.util.Map.Entry} instance retrieved from the map's {@linkplain Map#entrySet entry set} is a
095 * snapshot of that entry's state at the time of retrieval; such entries do, however, support {@link
096 * java.util.Map.Entry#setValue}, which simply calls {@link Map#put} on the entry's key.
097 *
098 * <p>The maps produced by {@code MapMaker} are serializable, and the deserialized maps retain all
099 * the configuration properties of the original map. During deserialization, if the original map had
100 * used soft or weak references, the entries are reconstructed as they were, but it's not unlikely
101 * they'll be quickly garbage-collected before they are ever accessed.
102 *
103 * <p>{@code new MapMaker().weakKeys().makeMap()} is a recommended replacement for {@link
104 * java.util.WeakHashMap}, but note that it compares keys using object identity whereas {@code
105 * WeakHashMap} uses {@link Object#equals}.
106 *
107 * @author Bob Lee
108 * @author Charles Fry
109 * @author Kevin Bourrillion
110 * @since 2.0 (imported from Google Collections Library)
111 */
112 @GwtCompatible(emulated = true)
113 public final class MapMaker extends GenericMapMaker<Object, Object> {
114 private static final int DEFAULT_INITIAL_CAPACITY = 16;
115 private static final int DEFAULT_CONCURRENCY_LEVEL = 4;
116 private static final int DEFAULT_EXPIRATION_NANOS = 0;
117
118 static final int UNSET_INT = -1;
119
120 // TODO(kevinb): dispense with this after benchmarking
121 boolean useCustomMap;
122
123 int initialCapacity = UNSET_INT;
124 int concurrencyLevel = UNSET_INT;
125 int maximumSize = UNSET_INT;
126
127 Strength keyStrength;
128 Strength valueStrength;
129
130 long expireAfterWriteNanos = UNSET_INT;
131 long expireAfterAccessNanos = UNSET_INT;
132
133 RemovalCause nullRemovalCause;
134
135 Equivalence<Object> keyEquivalence;
136 Equivalence<Object> valueEquivalence;
137
138 Ticker ticker;
139
140 /**
141 * Constructs a new {@code MapMaker} instance with default settings, including strong keys, strong
142 * values, and no automatic eviction of any kind.
143 */
144 public MapMaker() {}
145
146 private boolean useNullMap() {
147 return (nullRemovalCause == null);
148 }
149
150 /**
151 * Sets a custom {@code Equivalence} strategy for comparing keys.
152 *
153 * <p>By default, the map uses {@link Equivalences#identity} to determine key equality when
154 * {@link #weakKeys} or {@link #softKeys} is specified, and {@link Equivalences#equals()}
155 * otherwise.
156 */
157 @GwtIncompatible("To be supported")
158 @Override
159 MapMaker keyEquivalence(Equivalence<Object> equivalence) {
160 checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);
161 keyEquivalence = checkNotNull(equivalence);
162 this.useCustomMap = true;
163 return this;
164 }
165
166 Equivalence<Object> getKeyEquivalence() {
167 return firstNonNull(keyEquivalence, getKeyStrength().defaultEquivalence());
168 }
169
170 /**
171 * Sets a custom {@code Equivalence} strategy for comparing values.
172 *
173 * <p>By default, the map uses {@link Equivalences#identity} to determine value equality when
174 * {@link #weakValues} or {@link #softValues} is specified, and {@link Equivalences#equals()}
175 * otherwise.
176 */
177 @GwtIncompatible("To be supported")
178 @Override
179 MapMaker valueEquivalence(Equivalence<Object> equivalence) {
180 checkState(valueEquivalence == null,
181 "value equivalence was already set to %s", valueEquivalence);
182 this.valueEquivalence = checkNotNull(equivalence);
183 this.useCustomMap = true;
184 return this;
185 }
186
187 Equivalence<Object> getValueEquivalence() {
188 return firstNonNull(valueEquivalence, getValueStrength().defaultEquivalence());
189 }
190
191 /**
192 * Sets the minimum total size for the internal hash tables. For example, if the initial capacity
193 * is {@code 60}, and the concurrency level is {@code 8}, then eight segments are created, each
194 * having a hash table of size eight. Providing a large enough estimate at construction time
195 * avoids the need for expensive resizing operations later, but setting this value unnecessarily
196 * high wastes memory.
197 *
198 * @throws IllegalArgumentException if {@code initialCapacity} is negative
199 * @throws IllegalStateException if an initial capacity was already set
200 */
201 @Override
202 public MapMaker initialCapacity(int initialCapacity) {
203 checkState(this.initialCapacity == UNSET_INT, "initial capacity was already set to %s",
204 this.initialCapacity);
205 checkArgument(initialCapacity >= 0);
206 this.initialCapacity = initialCapacity;
207 return this;
208 }
209
210 int getInitialCapacity() {
211 return (initialCapacity == UNSET_INT) ? DEFAULT_INITIAL_CAPACITY : initialCapacity;
212 }
213
214 /**
215 * Specifies the maximum number of entries the map may contain. Note that the map <b>may evict an
216 * entry before this limit is exceeded</b>. As the map size grows close to the maximum, the map
217 * evicts entries that are less likely to be used again. For example, the map may evict an entry
218 * because it hasn't been used recently or very often.
219 *
220 * <p>When {@code size} is zero, elements can be successfully added to the map, but are evicted
221 * immediately. This has the same effect as invoking {@link #expireAfterWrite
222 * expireAfterWrite}{@code (0, unit)} or {@link #expireAfterAccess expireAfterAccess}{@code (0,
223 * unit)}. It can be useful in testing, or to disable caching temporarily without a code change.
224 *
225 * <p>Caching functionality in {@code MapMaker} is being moved to
226 * {@link com.google.common.cache.CacheBuilder}.
227 *
228 * @param size the maximum size of the map
229 * @throws IllegalArgumentException if {@code size} is negative
230 * @throws IllegalStateException if a maximum size was already set
231 * @deprecated Caching functionality in {@code MapMaker} is being moved to
232 * {@link com.google.common.cache.CacheBuilder}, with {@link #maximumSize} being
233 * replaced by {@link com.google.common.cache.CacheBuilder#maximumSize}.
234 */
235 @Deprecated
236 @Override
237 MapMaker maximumSize(int size) {
238 checkState(this.maximumSize == UNSET_INT, "maximum size was already set to %s",
239 this.maximumSize);
240 checkArgument(size >= 0, "maximum size must not be negative");
241 this.maximumSize = size;
242 this.useCustomMap = true;
243 if (maximumSize == 0) {
244 // SIZE trumps EXPIRED
245 this.nullRemovalCause = RemovalCause.SIZE;
246 }
247 return this;
248 }
249
250 /**
251 * Guides the allowed concurrency among update operations. Used as a hint for internal sizing. The
252 * table is internally partitioned to try to permit the indicated number of concurrent updates
253 * without contention. Because assignment of entries to these partitions is not necessarily
254 * uniform, the actual concurrency observed may vary. Ideally, you should choose a value to
255 * accommodate as many threads as will ever concurrently modify the table. Using a significantly
256 * higher value than you need can waste space and time, and a significantly lower value can lead
257 * to thread contention. But overestimates and underestimates within an order of magnitude do not
258 * usually have much noticeable impact. A value of one permits only one thread to modify the map
259 * at a time, but since read operations can proceed concurrently, this still yields higher
260 * concurrency than full synchronization. Defaults to 4.
261 *
262 * <p><b>Note:</b> Prior to Guava release 9.0, the default was 16. It is possible the default will
263 * change again in the future. If you care about this value, you should always choose it
264 * explicitly.
265 *
266 * @throws IllegalArgumentException if {@code concurrencyLevel} is nonpositive
267 * @throws IllegalStateException if a concurrency level was already set
268 */
269 @Override
270 public MapMaker concurrencyLevel(int concurrencyLevel) {
271 checkState(this.concurrencyLevel == UNSET_INT, "concurrency level was already set to %s",
272 this.concurrencyLevel);
273 checkArgument(concurrencyLevel > 0);
274 this.concurrencyLevel = concurrencyLevel;
275 return this;
276 }
277
278 int getConcurrencyLevel() {
279 return (concurrencyLevel == UNSET_INT) ? DEFAULT_CONCURRENCY_LEVEL : concurrencyLevel;
280 }
281
282 /**
283 * Specifies that each key (not value) stored in the map should be strongly referenced.
284 *
285 * @throws IllegalStateException if the key strength was already set
286 */
287 @Override
288 MapMaker strongKeys() {
289 return setKeyStrength(Strength.STRONG);
290 }
291
292 /**
293 * Specifies that each key (not value) stored in the map should be wrapped in a {@link
294 * WeakReference} (by default, strong references are used).
295 *
296 * <p><b>Warning:</b> when this method is used, the resulting map will use identity ({@code ==})
297 * comparison to determine equality of keys, which is a technical violation of the {@link Map}
298 * specification, and may not be what you expect.
299 *
300 * @throws IllegalStateException if the key strength was already set
301 * @see WeakReference
302 */
303 @GwtIncompatible("java.lang.ref.WeakReference")
304 @Override
305 public MapMaker weakKeys() {
306 return setKeyStrength(Strength.WEAK);
307 }
308
309 /**
310 * Specifies that each key (not value) stored in the map should be wrapped in a
311 * {@link SoftReference} (by default, strong references are used). Softly-referenced objects will
312 * be garbage-collected in a <i>globally</i> least-recently-used manner, in response to memory
313 * demand.
314 *
315 * <p><b>Warning:</b> when this method is used, the resulting map will use identity ({@code ==})
316 * comparison to determine equality of keys, which is a technical violation of the {@link Map}
317 * specification, and may not be what you expect.
318 *
319 * @throws IllegalStateException if the key strength was already set
320 * @see SoftReference
321 * @deprecated use {@link #softValues} to create a memory-sensitive map, or {@link #weakKeys} to
322 * create a map that doesn't hold strong references to the keys.
323 * <b>This method is scheduled for deletion in January 2013.</b>
324 */
325 @Deprecated
326 @GwtIncompatible("java.lang.ref.SoftReference")
327 @Override
328 public MapMaker softKeys() {
329 return setKeyStrength(Strength.SOFT);
330 }
331
332 MapMaker setKeyStrength(Strength strength) {
333 checkState(keyStrength == null, "Key strength was already set to %s", keyStrength);
334 keyStrength = checkNotNull(strength);
335 if (strength != Strength.STRONG) {
336 // STRONG could be used during deserialization.
337 useCustomMap = true;
338 }
339 return this;
340 }
341
342 Strength getKeyStrength() {
343 return firstNonNull(keyStrength, Strength.STRONG);
344 }
345
346 /**
347 * Specifies that each value (not key) stored in the map should be strongly referenced.
348 *
349 * @throws IllegalStateException if the value strength was already set
350 */
351 @Override
352 MapMaker strongValues() {
353 return setValueStrength(Strength.STRONG);
354 }
355
356 /**
357 * Specifies that each value (not key) stored in the map should be wrapped in a
358 * {@link WeakReference} (by default, strong references are used).
359 *
360 * <p>Weak values will be garbage collected once they are weakly reachable. This makes them a poor
361 * candidate for caching; consider {@link #softValues} instead.
362 *
363 * <p><b>Warning:</b> when this method is used, the resulting map will use identity ({@code ==})
364 * comparison to determine equality of values. This technically violates the specifications of
365 * the methods {@link Map#containsValue containsValue},
366 * {@link ConcurrentMap#remove(Object, Object) remove(Object, Object)} and
367 * {@link ConcurrentMap#replace(Object, Object, Object) replace(K, V, V)}, and may not be what you
368 * expect.
369 *
370 * @throws IllegalStateException if the value strength was already set
371 * @see WeakReference
372 */
373 @GwtIncompatible("java.lang.ref.WeakReference")
374 @Override
375 public MapMaker weakValues() {
376 return setValueStrength(Strength.WEAK);
377 }
378
379 /**
380 * Specifies that each value (not key) stored in the map should be wrapped in a
381 * {@link SoftReference} (by default, strong references are used). Softly-referenced objects will
382 * be garbage-collected in a <i>globally</i> least-recently-used manner, in response to memory
383 * demand.
384 *
385 * <p><b>Warning:</b> in most circumstances it is better to set a per-cache {@linkplain
386 * #maximumSize maximum size} instead of using soft references. You should only use this method if
387 * you are well familiar with the practical consequences of soft references.
388 *
389 * <p><b>Warning:</b> when this method is used, the resulting map will use identity ({@code ==})
390 * comparison to determine equality of values. This technically violates the specifications of
391 * the methods {@link Map#containsValue containsValue},
392 * {@link ConcurrentMap#remove(Object, Object) remove(Object, Object)} and
393 * {@link ConcurrentMap#replace(Object, Object, Object) replace(K, V, V)}, and may not be what you
394 * expect.
395 *
396 * @throws IllegalStateException if the value strength was already set
397 * @see SoftReference
398 */
399 @GwtIncompatible("java.lang.ref.SoftReference")
400 @Override
401 public MapMaker softValues() {
402 return setValueStrength(Strength.SOFT);
403 }
404
405 MapMaker setValueStrength(Strength strength) {
406 checkState(valueStrength == null, "Value strength was already set to %s", valueStrength);
407 valueStrength = checkNotNull(strength);
408 if (strength != Strength.STRONG) {
409 // STRONG could be used during deserialization.
410 useCustomMap = true;
411 }
412 return this;
413 }
414
415 Strength getValueStrength() {
416 return firstNonNull(valueStrength, Strength.STRONG);
417 }
418
419 /**
420 * Old name of {@link #expireAfterWrite}.
421 *
422 * @deprecated Caching functionality in {@code MapMaker} is being moved to
423 * {@link com.google.common.cache.CacheBuilder}. Functionality equivalent to
424 * {@link MapMaker#expiration} is provided by
425 * {@link com.google.common.cache.CacheBuilder#expireAfterWrite}.
426 * <b>This method is scheduled for deletion in July 2012.</b>
427 */
428 @Deprecated
429 @Override
430 public
431 MapMaker expiration(long duration, TimeUnit unit) {
432 return expireAfterWrite(duration, unit);
433 }
434
435 /**
436 * Specifies that each entry should be automatically removed from the map once a fixed duration
437 * has elapsed after the entry's creation, or the most recent replacement of its value.
438 *
439 * <p>When {@code duration} is zero, elements can be successfully added to the map, but are
440 * evicted immediately. This has a very similar effect to invoking {@link #maximumSize
441 * maximumSize}{@code (0)}. It can be useful in testing, or to disable caching temporarily without
442 * a code change.
443 *
444 * <p>Expired entries may be counted by {@link Map#size}, but will never be visible to read or
445 * write operations. Expired entries are currently cleaned up during write operations, or during
446 * occasional read operations in the absense of writes; though this behavior may change in the
447 * future.
448 *
449 * @param duration the length of time after an entry is created that it should be automatically
450 * removed
451 * @param unit the unit that {@code duration} is expressed in
452 * @throws IllegalArgumentException if {@code duration} is negative
453 * @throws IllegalStateException if the time to live or time to idle was already set
454 * @deprecated Caching functionality in {@code MapMaker} is being moved to
455 * {@link com.google.common.cache.CacheBuilder}, with {@link #expireAfterWrite} being
456 * replaced by {@link com.google.common.cache.CacheBuilder#expireAfterWrite}.
457 */
458 @Deprecated
459 @Override
460 MapMaker expireAfterWrite(long duration, TimeUnit unit) {
461 checkExpiration(duration, unit);
462 this.expireAfterWriteNanos = unit.toNanos(duration);
463 if (duration == 0 && this.nullRemovalCause == null) {
464 // SIZE trumps EXPIRED
465 this.nullRemovalCause = RemovalCause.EXPIRED;
466 }
467 useCustomMap = true;
468 return this;
469 }
470
471 private void checkExpiration(long duration, TimeUnit unit) {
472 checkState(expireAfterWriteNanos == UNSET_INT, "expireAfterWrite was already set to %s ns",
473 expireAfterWriteNanos);
474 checkState(expireAfterAccessNanos == UNSET_INT, "expireAfterAccess was already set to %s ns",
475 expireAfterAccessNanos);
476 checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
477 }
478
479 long getExpireAfterWriteNanos() {
480 return (expireAfterWriteNanos == UNSET_INT) ? DEFAULT_EXPIRATION_NANOS : expireAfterWriteNanos;
481 }
482
483 /**
484 * Specifies that each entry should be automatically removed from the map once a fixed duration
485 * has elapsed after the entry's last read or write access.
486 *
487 * <p>When {@code duration} is zero, elements can be successfully added to the map, but are
488 * evicted immediately. This has a very similar effect to invoking {@link #maximumSize
489 * maximumSize}{@code (0)}. It can be useful in testing, or to disable caching temporarily without
490 * a code change.
491 *
492 * <p>Expired entries may be counted by {@link Map#size}, but will never be visible to read or
493 * write operations. Expired entries are currently cleaned up during write operations, or during
494 * occasional read operations in the absense of writes; though this behavior may change in the
495 * future.
496 *
497 * @param duration the length of time after an entry is last accessed that it should be
498 * automatically removed
499 * @param unit the unit that {@code duration} is expressed in
500 * @throws IllegalArgumentException if {@code duration} is negative
501 * @throws IllegalStateException if the time to idle or time to live was already set
502 * @deprecated Caching functionality in {@code MapMaker} is being moved to
503 * {@link com.google.common.cache.CacheBuilder}, with {@link #expireAfterAccess} being
504 * replaced by {@link com.google.common.cache.CacheBuilder#expireAfterAccess}.
505 */
506 @Deprecated
507 @GwtIncompatible("To be supported")
508 @Override
509 MapMaker expireAfterAccess(long duration, TimeUnit unit) {
510 checkExpiration(duration, unit);
511 this.expireAfterAccessNanos = unit.toNanos(duration);
512 if (duration == 0 && this.nullRemovalCause == null) {
513 // SIZE trumps EXPIRED
514 this.nullRemovalCause = RemovalCause.EXPIRED;
515 }
516 useCustomMap = true;
517 return this;
518 }
519
520 long getExpireAfterAccessNanos() {
521 return (expireAfterAccessNanos == UNSET_INT)
522 ? DEFAULT_EXPIRATION_NANOS : expireAfterAccessNanos;
523 }
524
525 Ticker getTicker() {
526 return firstNonNull(ticker, Ticker.systemTicker());
527 }
528
529 /**
530 * Specifies a listener instance, which all maps built using this {@code MapMaker} will notify
531 * each time an entry is removed from the map by any means.
532 *
533 * <p>Each map built by this map maker after this method is called invokes the supplied listener
534 * after removing an element for any reason (see removal causes in {@link RemovalCause}). It will
535 * invoke the listener during invocations of any of that map's public methods (even read-only
536 * methods).
537 *
538 * <p><b>Important note:</b> Instead of returning <i>this</i> as a {@code MapMaker} instance,
539 * this method returns {@code GenericMapMaker<K, V>}. From this point on, either the original
540 * reference or the returned reference may be used to complete configuration and build the map,
541 * but only the "generic" one is type-safe. That is, it will properly prevent you from building
542 * maps whose key or value types are incompatible with the types accepted by the listener already
543 * provided; the {@code MapMaker} type cannot do this. For best results, simply use the standard
544 * method-chaining idiom, as illustrated in the documentation at top, configuring a {@code
545 * MapMaker} and building your {@link Map} all in a single statement.
546 *
547 * <p><b>Warning:</b> if you ignore the above advice, and use this {@code MapMaker} to build a map
548 * or cache whose key or value type is incompatible with the listener, you will likely experience
549 * a {@link ClassCastException} at some <i>undefined</i> point in the future.
550 *
551 * @throws IllegalStateException if a removal listener was already set
552 * @deprecated Caching functionality in {@code MapMaker} is being moved to
553 * {@link com.google.common.cache.CacheBuilder}, with {@link #removalListener} being
554 * replaced by {@link com.google.common.cache.CacheBuilder#removalListener}.
555 */
556 @Deprecated
557 @GwtIncompatible("To be supported")
558 <K, V> GenericMapMaker<K, V> removalListener(RemovalListener<K, V> listener) {
559 checkState(this.removalListener == null);
560
561 // safely limiting the kinds of maps this can produce
562 @SuppressWarnings("unchecked")
563 GenericMapMaker<K, V> me = (GenericMapMaker<K, V>) this;
564 me.removalListener = checkNotNull(listener);
565 useCustomMap = true;
566 return me;
567 }
568
569 /**
570 * Builds a thread-safe map, without on-demand computation of values. This method does not alter
571 * the state of this {@code MapMaker} instance, so it can be invoked again to create multiple
572 * independent maps.
573 *
574 * <p>The bulk operations {@code putAll}, {@code equals}, and {@code clear} are not guaranteed to
575 * be performed atomically on the returned map. Additionally, {@code size} and {@code
576 * containsValue} are implemented as bulk read operations, and thus may fail to observe concurrent
577 * writes.
578 *
579 * @return a serializable concurrent map having the requested features
580 */
581 @Override
582 public <K, V> ConcurrentMap<K, V> makeMap() {
583 if (!useCustomMap) {
584 return new ConcurrentHashMap<K, V>(getInitialCapacity(), 0.75f, getConcurrencyLevel());
585 }
586 return (nullRemovalCause == null)
587 ? new MapMakerInternalMap<K, V>(this)
588 : new NullConcurrentMap<K, V>(this);
589 }
590
591 /**
592 * Returns a MapMakerInternalMap for the benefit of internal callers that use features of
593 * that class not exposed through ConcurrentMap.
594 */
595 @Override
596 @GwtIncompatible("MapMakerInternalMap")
597 <K, V> MapMakerInternalMap<K, V> makeCustomMap() {
598 return new MapMakerInternalMap<K, V>(this);
599 }
600
601 /**
602 * Builds a map that supports atomic, on-demand computation of values. {@link Map#get} either
603 * returns an already-computed value for the given key, atomically computes it using the supplied
604 * function, or, if another thread is currently computing the value for this key, simply waits for
605 * that thread to finish and returns its computed value. Note that the function may be executed
606 * concurrently by multiple threads, but only for distinct keys.
607 *
608 * <p>New code should use {@link com.google.common.cache.CacheBuilder}, which supports
609 * {@linkplain com.google.common.cache.CacheStats statistics} collection, introduces the
610 * {@link com.google.common.cache.CacheLoader} interface for loading entries into the cache
611 * (allowing checked exceptions to be thrown in the process), and more cleanly separates
612 * computation from the cache's {@code Map} view.
613 *
614 * <p>If an entry's value has not finished computing yet, query methods besides {@code get} return
615 * immediately as if an entry doesn't exist. In other words, an entry isn't externally visible
616 * until the value's computation completes.
617 *
618 * <p>{@link Map#get} on the returned map will never return {@code null}. It may throw:
619 *
620 * <ul>
621 * <li>{@link NullPointerException} if the key is null or the computing function returns a null
622 * result
623 * <li>{@link ComputationException} if an exception was thrown by the computing function. If that
624 * exception is already of type {@link ComputationException} it is propagated directly; otherwise
625 * it is wrapped.
626 * </ul>
627 *
628 * <p><b>Note:</b> Callers of {@code get} <i>must</i> ensure that the key argument is of type
629 * {@code K}. The {@code get} method accepts {@code Object}, so the key type is not checked at
630 * compile time. Passing an object of a type other than {@code K} can result in that object being
631 * unsafely passed to the computing function as type {@code K}, and unsafely stored in the map.
632 *
633 * <p>If {@link Map#put} is called before a computation completes, other threads waiting on the
634 * computation will wake up and return the stored value.
635 *
636 * <p>This method does not alter the state of this {@code MapMaker} instance, so it can be invoked
637 * again to create multiple independent maps.
638 *
639 * <p>Insertion, removal, update, and access operations on the returned map safely execute
640 * concurrently by multiple threads. Iterators on the returned map are weakly consistent,
641 * returning elements reflecting the state of the map at some point at or since the creation of
642 * the iterator. They do not throw {@link ConcurrentModificationException}, and may proceed
643 * concurrently with other operations.
644 *
645 * <p>The bulk operations {@code putAll}, {@code equals}, and {@code clear} are not guaranteed to
646 * be performed atomically on the returned map. Additionally, {@code size} and {@code
647 * containsValue} are implemented as bulk read operations, and thus may fail to observe concurrent
648 * writes.
649 *
650 * @param computingFunction the function used to compute new values
651 * @return a serializable concurrent map having the requested features
652 * @deprecated Caching functionality in {@code MapMaker} is being moved to
653 * {@link com.google.common.cache.CacheBuilder}, with {@link #makeComputingMap} being replaced
654 * by {@link com.google.common.cache.CacheBuilder#build}. Note that uses of
655 * {@link #makeComputingMap} with {@code AtomicLong} values can often be migrated to
656 * {@link AtomicLongMap}.
657 * <b>This method is scheduled for deletion in February 2013.</b>
658 *
659 */
660 @Deprecated
661 @Override
662 public <K, V> ConcurrentMap<K, V> makeComputingMap(
663 Function<? super K, ? extends V> computingFunction) {
664 return useNullMap()
665 ? new ComputingMapAdapter<K, V>(this, computingFunction)
666 : new NullComputingConcurrentMap<K, V>(this, computingFunction);
667 }
668
669 /**
670 * Returns a string representation for this MapMaker instance. The exact form of the returned
671 * string is not specificed.
672 */
673 @Override
674 public String toString() {
675 Objects.ToStringHelper s = Objects.toStringHelper(this);
676 if (initialCapacity != UNSET_INT) {
677 s.add("initialCapacity", initialCapacity);
678 }
679 if (concurrencyLevel != UNSET_INT) {
680 s.add("concurrencyLevel", concurrencyLevel);
681 }
682 if (maximumSize != UNSET_INT) {
683 s.add("maximumSize", maximumSize);
684 }
685 if (expireAfterWriteNanos != UNSET_INT) {
686 s.add("expireAfterWrite", expireAfterWriteNanos + "ns");
687 }
688 if (expireAfterAccessNanos != UNSET_INT) {
689 s.add("expireAfterAccess", expireAfterAccessNanos + "ns");
690 }
691 if (keyStrength != null) {
692 s.add("keyStrength", Ascii.toLowerCase(keyStrength.toString()));
693 }
694 if (valueStrength != null) {
695 s.add("valueStrength", Ascii.toLowerCase(valueStrength.toString()));
696 }
697 if (keyEquivalence != null) {
698 s.addValue("keyEquivalence");
699 }
700 if (valueEquivalence != null) {
701 s.addValue("valueEquivalence");
702 }
703 if (removalListener != null) {
704 s.addValue("removalListener");
705 }
706 return s.toString();
707 }
708
709 /**
710 * An object that can receive a notification when an entry is removed from a map. The removal
711 * resulting in notification could have occured to an entry being manually removed or replaced, or
712 * due to eviction resulting from timed expiration, exceeding a maximum size, or garbage
713 * collection.
714 *
715 * <p>An instance may be called concurrently by multiple threads to process different entries.
716 * Implementations of this interface should avoid performing blocking calls or synchronizing on
717 * shared resources.
718 *
719 * @param <K> the most general type of keys this listener can listen for; for
720 * example {@code Object} if any key is acceptable
721 * @param <V> the most general type of values this listener can listen for; for
722 * example {@code Object} if any key is acceptable
723 */
724 interface RemovalListener<K, V> {
725 /**
726 * Notifies the listener that a removal occurred at some point in the past.
727 */
728 void onRemoval(RemovalNotification<K, V> notification);
729 }
730
731 /**
732 * A notification of the removal of a single entry. The key or value may be null if it was already
733 * garbage collected.
734 *
735 * <p>Like other {@code Map.Entry} instances associated with MapMaker, this class holds strong
736 * references to the key and value, regardless of the type of references the map may be using.
737 */
738 static final class RemovalNotification<K, V> extends ImmutableEntry<K, V> {
739 private static final long serialVersionUID = 0;
740
741 private final RemovalCause cause;
742
743 RemovalNotification(@Nullable K key, @Nullable V value, RemovalCause cause) {
744 super(key, value);
745 this.cause = cause;
746 }
747
748 /**
749 * Returns the cause for which the entry was removed.
750 */
751 public RemovalCause getCause() {
752 return cause;
753 }
754
755 /**
756 * Returns {@code true} if there was an automatic removal due to eviction (the cause is neither
757 * {@link RemovalCause#EXPLICIT} nor {@link RemovalCause#REPLACED}).
758 */
759 public boolean wasEvicted() {
760 return cause.wasEvicted();
761 }
762 }
763
764 /**
765 * The reason why an entry was removed.
766 */
767 enum RemovalCause {
768 /**
769 * The entry was manually removed by the user. This can result from the user invoking
770 * {@link Map#remove}, {@link ConcurrentMap#remove}, or {@link java.util.Iterator#remove}.
771 */
772 EXPLICIT {
773 @Override
774 boolean wasEvicted() {
775 return false;
776 }
777 },
778
779 /**
780 * The entry itself was not actually removed, but its value was replaced by the user. This can
781 * result from the user invoking {@link Map#put}, {@link Map#putAll},
782 * {@link ConcurrentMap#replace(Object, Object)}, or
783 * {@link ConcurrentMap#replace(Object, Object, Object)}.
784 */
785 REPLACED {
786 @Override
787 boolean wasEvicted() {
788 return false;
789 }
790 },
791
792 /**
793 * The entry was removed automatically because its key or value was garbage-collected. This
794 * can occur when using {@link #softKeys}, {@link #softValues}, {@link #weakKeys}, or {@link
795 * #weakValues}.
796 */
797 COLLECTED {
798 @Override
799 boolean wasEvicted() {
800 return true;
801 }
802 },
803
804 /**
805 * The entry's expiration timestamp has passed. This can occur when using {@link
806 * #expireAfterWrite} or {@link #expireAfterAccess}.
807 */
808 EXPIRED {
809 @Override
810 boolean wasEvicted() {
811 return true;
812 }
813 },
814
815 /**
816 * The entry was evicted due to size constraints. This can occur when using {@link
817 * #maximumSize}.
818 */
819 SIZE {
820 @Override
821 boolean wasEvicted() {
822 return true;
823 }
824 };
825
826 /**
827 * Returns {@code true} if there was an automatic removal due to eviction (the cause is neither
828 * {@link #EXPLICIT} nor {@link #REPLACED}).
829 */
830 abstract boolean wasEvicted();
831 }
832
833 /** A map that is always empty and evicts on insertion. */
834 static class NullConcurrentMap<K, V> extends AbstractMap<K, V>
835 implements ConcurrentMap<K, V>, Serializable {
836 private static final long serialVersionUID = 0;
837
838 private final RemovalListener<K, V> removalListener;
839 private final RemovalCause removalCause;
840
841 NullConcurrentMap(MapMaker mapMaker) {
842 removalListener = mapMaker.getRemovalListener();
843 removalCause = mapMaker.nullRemovalCause;
844 }
845
846 // implements ConcurrentMap
847
848 @Override
849 public boolean containsKey(@Nullable Object key) {
850 return false;
851 }
852
853 @Override
854 public boolean containsValue(@Nullable Object value) {
855 return false;
856 }
857
858 @Override
859 public V get(@Nullable Object key) {
860 return null;
861 }
862
863 void notifyRemoval(K key, V value) {
864 RemovalNotification<K, V> notification =
865 new RemovalNotification<K, V>(key, value, removalCause);
866 removalListener.onRemoval(notification);
867 }
868
869 @Override
870 public V put(K key, V value) {
871 checkNotNull(key);
872 checkNotNull(value);
873 notifyRemoval(key, value);
874 return null;
875 }
876
877 @Override
878 public V putIfAbsent(K key, V value) {
879 return put(key, value);
880 }
881
882 @Override
883 public V remove(@Nullable Object key) {
884 return null;
885 }
886
887 @Override
888 public boolean remove(@Nullable Object key, @Nullable Object value) {
889 return false;
890 }
891
892 @Override
893 public V replace(K key, V value) {
894 checkNotNull(key);
895 checkNotNull(value);
896 return null;
897 }
898
899 @Override
900 public boolean replace(K key, @Nullable V oldValue, V newValue) {
901 checkNotNull(key);
902 checkNotNull(newValue);
903 return false;
904 }
905
906 @Override
907 public Set<Entry<K, V>> entrySet() {
908 return Collections.emptySet();
909 }
910 }
911
912 /** Computes on retrieval and evicts the result. */
913 static final class NullComputingConcurrentMap<K, V> extends NullConcurrentMap<K, V> {
914 private static final long serialVersionUID = 0;
915
916 final Function<? super K, ? extends V> computingFunction;
917
918 NullComputingConcurrentMap(
919 MapMaker mapMaker, Function<? super K, ? extends V> computingFunction) {
920 super(mapMaker);
921 this.computingFunction = checkNotNull(computingFunction);
922 }
923
924 @SuppressWarnings("unchecked") // unsafe, which is why Cache is preferred
925 @Override
926 public V get(Object k) {
927 K key = (K) k;
928 V value = compute(key);
929 checkNotNull(value, computingFunction + " returned null for key " + key + ".");
930 notifyRemoval(key, value);
931 return value;
932 }
933
934 private V compute(K key) {
935 checkNotNull(key);
936 try {
937 return computingFunction.apply(key);
938 } catch (ComputationException e) {
939 throw e;
940 } catch (Throwable t) {
941 throw new ComputationException(t);
942 }
943 }
944 }
945
946 }