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 * <b>This method is broken.</b> Maps with soft keys offer no functional advantage over maps with
311 * weak keys, and they waste memory by keeping unreachable elements in the map. If your goal is to
312 * create a memory-sensitive map, then consider using soft values instead.
313 *
314 * <p>Specifies that each key (not value) stored in the map should be wrapped in a
315 * {@link SoftReference} (by default, strong references are used). Softly-referenced objects will
316 * be garbage-collected in a <i>globally</i> least-recently-used manner, in response to memory
317 * demand.
318 *
319 * <p><b>Warning:</b> when this method is used, the resulting map will use identity ({@code ==})
320 * comparison to determine equality of keys, which is a technical violation of the {@link Map}
321 * specification, and may not be what you expect.
322 *
323 * @throws IllegalStateException if the key strength was already set
324 * @see SoftReference
325 * @deprecated use {@link #softValues} to create a memory-sensitive map, or {@link #weakKeys} to
326 * create a map that doesn't hold strong references to the keys.
327 * <b>This method is scheduled for deletion in January 2013.</b>
328 */
329 @Deprecated
330 @GwtIncompatible("java.lang.ref.SoftReference")
331 @Override
332 public MapMaker softKeys() {
333 return setKeyStrength(Strength.SOFT);
334 }
335
336 MapMaker setKeyStrength(Strength strength) {
337 checkState(keyStrength == null, "Key strength was already set to %s", keyStrength);
338 keyStrength = checkNotNull(strength);
339 if (strength != Strength.STRONG) {
340 // STRONG could be used during deserialization.
341 useCustomMap = true;
342 }
343 return this;
344 }
345
346 Strength getKeyStrength() {
347 return firstNonNull(keyStrength, Strength.STRONG);
348 }
349
350 /**
351 * Specifies that each value (not key) stored in the map should be strongly referenced.
352 *
353 * @throws IllegalStateException if the value strength was already set
354 */
355 @Override
356 MapMaker strongValues() {
357 return setValueStrength(Strength.STRONG);
358 }
359
360 /**
361 * Specifies that each value (not key) stored in the map should be wrapped in a
362 * {@link WeakReference} (by default, strong references are used).
363 *
364 * <p>Weak values will be garbage collected once they are weakly reachable. This makes them a poor
365 * candidate for caching; consider {@link #softValues} instead.
366 *
367 * <p><b>Warning:</b> when this method is used, the resulting map will use identity ({@code ==})
368 * comparison to determine equality of values. This technically violates the specifications of
369 * the methods {@link Map#containsValue containsValue},
370 * {@link ConcurrentMap#remove(Object, Object) remove(Object, Object)} and
371 * {@link ConcurrentMap#replace(Object, Object, Object) replace(K, V, V)}, and may not be what you
372 * expect.
373 *
374 * @throws IllegalStateException if the value strength was already set
375 * @see WeakReference
376 */
377 @GwtIncompatible("java.lang.ref.WeakReference")
378 @Override
379 public MapMaker weakValues() {
380 return setValueStrength(Strength.WEAK);
381 }
382
383 /**
384 * Specifies that each value (not key) stored in the map should be wrapped in a
385 * {@link SoftReference} (by default, strong references are used). Softly-referenced objects will
386 * be garbage-collected in a <i>globally</i> least-recently-used manner, in response to memory
387 * demand.
388 *
389 * <p><b>Warning:</b> in most circumstances it is better to set a per-cache {@linkplain
390 * #maximumSize maximum size} instead of using soft references. You should only use this method if
391 * you are well familiar with the practical consequences of soft references.
392 *
393 * <p><b>Warning:</b> when this method is used, the resulting map will use identity ({@code ==})
394 * comparison to determine equality of values. This technically violates the specifications of
395 * the methods {@link Map#containsValue containsValue},
396 * {@link ConcurrentMap#remove(Object, Object) remove(Object, Object)} and
397 * {@link ConcurrentMap#replace(Object, Object, Object) replace(K, V, V)}, and may not be what you
398 * expect.
399 *
400 * @throws IllegalStateException if the value strength was already set
401 * @see SoftReference
402 */
403 @GwtIncompatible("java.lang.ref.SoftReference")
404 @Override
405 public MapMaker softValues() {
406 return setValueStrength(Strength.SOFT);
407 }
408
409 MapMaker setValueStrength(Strength strength) {
410 checkState(valueStrength == null, "Value strength was already set to %s", valueStrength);
411 valueStrength = checkNotNull(strength);
412 if (strength != Strength.STRONG) {
413 // STRONG could be used during deserialization.
414 useCustomMap = true;
415 }
416 return this;
417 }
418
419 Strength getValueStrength() {
420 return firstNonNull(valueStrength, Strength.STRONG);
421 }
422
423 /**
424 * Old name of {@link #expireAfterWrite}.
425 *
426 * @deprecated Caching functionality in {@code MapMaker} is being moved to
427 * {@link com.google.common.cache.CacheBuilder}. Functionality equivalent to
428 * {@link MapMaker#expiration} is provided by
429 * {@link com.google.common.cache.CacheBuilder#expireAfterWrite}.
430 * <b>This method is scheduled for deletion in July 2012.</b>
431 */
432 @Deprecated
433 @Override
434 public
435 MapMaker expiration(long duration, TimeUnit unit) {
436 return expireAfterWrite(duration, unit);
437 }
438
439 /**
440 * Specifies that each entry should be automatically removed from the map once a fixed duration
441 * has elapsed after the entry's creation, or the most recent replacement of its value.
442 *
443 * <p>When {@code duration} is zero, elements can be successfully added to the map, but are
444 * evicted immediately. This has a very similar effect to invoking {@link #maximumSize
445 * maximumSize}{@code (0)}. It can be useful in testing, or to disable caching temporarily without
446 * a code change.
447 *
448 * <p>Expired entries may be counted by {@link Map#size}, but will never be visible to read or
449 * write operations. Expired entries are currently cleaned up during write operations, or during
450 * occasional read operations in the absense of writes; though this behavior may change in the
451 * future.
452 *
453 * @param duration the length of time after an entry is created that it should be automatically
454 * removed
455 * @param unit the unit that {@code duration} is expressed in
456 * @throws IllegalArgumentException if {@code duration} is negative
457 * @throws IllegalStateException if the time to live or time to idle was already set
458 * @deprecated Caching functionality in {@code MapMaker} is being moved to
459 * {@link com.google.common.cache.CacheBuilder}, with {@link #expireAfterWrite} being
460 * replaced by {@link com.google.common.cache.CacheBuilder#expireAfterWrite}.
461 */
462 @Deprecated
463 @Override
464 MapMaker expireAfterWrite(long duration, TimeUnit unit) {
465 checkExpiration(duration, unit);
466 this.expireAfterWriteNanos = unit.toNanos(duration);
467 if (duration == 0 && this.nullRemovalCause == null) {
468 // SIZE trumps EXPIRED
469 this.nullRemovalCause = RemovalCause.EXPIRED;
470 }
471 useCustomMap = true;
472 return this;
473 }
474
475 private void checkExpiration(long duration, TimeUnit unit) {
476 checkState(expireAfterWriteNanos == UNSET_INT, "expireAfterWrite was already set to %s ns",
477 expireAfterWriteNanos);
478 checkState(expireAfterAccessNanos == UNSET_INT, "expireAfterAccess was already set to %s ns",
479 expireAfterAccessNanos);
480 checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
481 }
482
483 long getExpireAfterWriteNanos() {
484 return (expireAfterWriteNanos == UNSET_INT) ? DEFAULT_EXPIRATION_NANOS : expireAfterWriteNanos;
485 }
486
487 /**
488 * Specifies that each entry should be automatically removed from the map once a fixed duration
489 * has elapsed after the entry's last read or write access.
490 *
491 * <p>When {@code duration} is zero, elements can be successfully added to the map, but are
492 * evicted immediately. This has a very similar effect to invoking {@link #maximumSize
493 * maximumSize}{@code (0)}. It can be useful in testing, or to disable caching temporarily without
494 * a code change.
495 *
496 * <p>Expired entries may be counted by {@link Map#size}, but will never be visible to read or
497 * write operations. Expired entries are currently cleaned up during write operations, or during
498 * occasional read operations in the absense of writes; though this behavior may change in the
499 * future.
500 *
501 * @param duration the length of time after an entry is last accessed that it should be
502 * automatically removed
503 * @param unit the unit that {@code duration} is expressed in
504 * @throws IllegalArgumentException if {@code duration} is negative
505 * @throws IllegalStateException if the time to idle or time to live was already set
506 * @deprecated Caching functionality in {@code MapMaker} is being moved to
507 * {@link com.google.common.cache.CacheBuilder}, with {@link #expireAfterAccess} being
508 * replaced by {@link com.google.common.cache.CacheBuilder#expireAfterAccess}.
509 */
510 @Deprecated
511 @GwtIncompatible("To be supported")
512 @Override
513 MapMaker expireAfterAccess(long duration, TimeUnit unit) {
514 checkExpiration(duration, unit);
515 this.expireAfterAccessNanos = unit.toNanos(duration);
516 if (duration == 0 && this.nullRemovalCause == null) {
517 // SIZE trumps EXPIRED
518 this.nullRemovalCause = RemovalCause.EXPIRED;
519 }
520 useCustomMap = true;
521 return this;
522 }
523
524 long getExpireAfterAccessNanos() {
525 return (expireAfterAccessNanos == UNSET_INT)
526 ? DEFAULT_EXPIRATION_NANOS : expireAfterAccessNanos;
527 }
528
529 Ticker getTicker() {
530 return firstNonNull(ticker, Ticker.systemTicker());
531 }
532
533 /**
534 * Specifies a listener instance, which all maps built using this {@code MapMaker} will notify
535 * each time an entry is removed from the map by any means.
536 *
537 * <p>Each map built by this map maker after this method is called invokes the supplied listener
538 * after removing an element for any reason (see removal causes in {@link RemovalCause}). It will
539 * invoke the listener during invocations of any of that map's public methods (even read-only
540 * methods).
541 *
542 * <p><b>Important note:</b> Instead of returning <i>this</i> as a {@code MapMaker} instance,
543 * this method returns {@code GenericMapMaker<K, V>}. From this point on, either the original
544 * reference or the returned reference may be used to complete configuration and build the map,
545 * but only the "generic" one is type-safe. That is, it will properly prevent you from building
546 * maps whose key or value types are incompatible with the types accepted by the listener already
547 * provided; the {@code MapMaker} type cannot do this. For best results, simply use the standard
548 * method-chaining idiom, as illustrated in the documentation at top, configuring a {@code
549 * MapMaker} and building your {@link Map} all in a single statement.
550 *
551 * <p><b>Warning:</b> if you ignore the above advice, and use this {@code MapMaker} to build a map
552 * or cache whose key or value type is incompatible with the listener, you will likely experience
553 * a {@link ClassCastException} at some <i>undefined</i> point in the future.
554 *
555 * @throws IllegalStateException if a removal listener was already set
556 * @deprecated Caching functionality in {@code MapMaker} is being moved to
557 * {@link com.google.common.cache.CacheBuilder}, with {@link #removalListener} being
558 * replaced by {@link com.google.common.cache.CacheBuilder#removalListener}.
559 */
560 @Deprecated
561 @GwtIncompatible("To be supported")
562 <K, V> GenericMapMaker<K, V> removalListener(RemovalListener<K, V> listener) {
563 checkState(this.removalListener == null);
564
565 // safely limiting the kinds of maps this can produce
566 @SuppressWarnings("unchecked")
567 GenericMapMaker<K, V> me = (GenericMapMaker<K, V>) this;
568 me.removalListener = checkNotNull(listener);
569 useCustomMap = true;
570 return me;
571 }
572
573 /**
574 * Builds a thread-safe map, without on-demand computation of values. This method does not alter
575 * the state of this {@code MapMaker} instance, so it can be invoked again to create multiple
576 * independent maps.
577 *
578 * <p>The bulk operations {@code putAll}, {@code equals}, and {@code clear} are not guaranteed to
579 * be performed atomically on the returned map. Additionally, {@code size} and {@code
580 * containsValue} are implemented as bulk read operations, and thus may fail to observe concurrent
581 * writes.
582 *
583 * @return a serializable concurrent map having the requested features
584 */
585 @Override
586 public <K, V> ConcurrentMap<K, V> makeMap() {
587 if (!useCustomMap) {
588 return new ConcurrentHashMap<K, V>(getInitialCapacity(), 0.75f, getConcurrencyLevel());
589 }
590 return (nullRemovalCause == null)
591 ? new MapMakerInternalMap<K, V>(this)
592 : new NullConcurrentMap<K, V>(this);
593 }
594
595 /**
596 * Returns a MapMakerInternalMap for the benefit of internal callers that use features of
597 * that class not exposed through ConcurrentMap.
598 */
599 @Override
600 @GwtIncompatible("MapMakerInternalMap")
601 <K, V> MapMakerInternalMap<K, V> makeCustomMap() {
602 return new MapMakerInternalMap<K, V>(this);
603 }
604
605 /**
606 * Builds a map that supports atomic, on-demand computation of values. {@link Map#get} either
607 * returns an already-computed value for the given key, atomically computes it using the supplied
608 * function, or, if another thread is currently computing the value for this key, simply waits for
609 * that thread to finish and returns its computed value. Note that the function may be executed
610 * concurrently by multiple threads, but only for distinct keys.
611 *
612 * <p>New code should use {@link com.google.common.cache.CacheBuilder}, which supports
613 * {@linkplain com.google.common.cache.CacheStats statistics} collection, introduces the
614 * {@link com.google.common.cache.CacheLoader} interface for loading entries into the cache
615 * (allowing checked exceptions to be thrown in the process), and more cleanly separates
616 * computation from the cache's {@code Map} view.
617 *
618 * <p>If an entry's value has not finished computing yet, query methods besides {@code get} return
619 * immediately as if an entry doesn't exist. In other words, an entry isn't externally visible
620 * until the value's computation completes.
621 *
622 * <p>{@link Map#get} on the returned map will never return {@code null}. It may throw:
623 *
624 * <ul>
625 * <li>{@link NullPointerException} if the key is null or the computing function returns a null
626 * result
627 * <li>{@link ComputationException} if an exception was thrown by the computing function. If that
628 * exception is already of type {@link ComputationException} it is propagated directly; otherwise
629 * it is wrapped.
630 * </ul>
631 *
632 * <p><b>Note:</b> Callers of {@code get} <i>must</i> ensure that the key argument is of type
633 * {@code K}. The {@code get} method accepts {@code Object}, so the key type is not checked at
634 * compile time. Passing an object of a type other than {@code K} can result in that object being
635 * unsafely passed to the computing function as type {@code K}, and unsafely stored in the map.
636 *
637 * <p>If {@link Map#put} is called before a computation completes, other threads waiting on the
638 * computation will wake up and return the stored value.
639 *
640 * <p>This method does not alter the state of this {@code MapMaker} instance, so it can be invoked
641 * again to create multiple independent maps.
642 *
643 * <p>Insertion, removal, update, and access operations on the returned map safely execute
644 * concurrently by multiple threads. Iterators on the returned map are weakly consistent,
645 * returning elements reflecting the state of the map at some point at or since the creation of
646 * the iterator. They do not throw {@link ConcurrentModificationException}, and may proceed
647 * concurrently with other operations.
648 *
649 * <p>The bulk operations {@code putAll}, {@code equals}, and {@code clear} are not guaranteed to
650 * be performed atomically on the returned map. Additionally, {@code size} and {@code
651 * containsValue} are implemented as bulk read operations, and thus may fail to observe concurrent
652 * writes.
653 *
654 * @param computingFunction the function used to compute new values
655 * @return a serializable concurrent map having the requested features
656 * @deprecated Caching functionality in {@code MapMaker} is being moved to
657 * {@link com.google.common.cache.CacheBuilder}, with {@link #makeComputingMap} being replaced
658 * by {@link com.google.common.cache.CacheBuilder#build}. Note that uses of
659 * {@link #makeComputingMap} with {@code AtomicLong} values can often be migrated to
660 * {@link AtomicLongMap}.
661 * <b>This method is scheduled for deletion in February 2013.</b>
662 *
663 */
664 @Deprecated
665 @Override
666 public <K, V> ConcurrentMap<K, V> makeComputingMap(
667 Function<? super K, ? extends V> computingFunction) {
668 return useNullMap()
669 ? new ComputingMapAdapter<K, V>(this, computingFunction)
670 : new NullComputingConcurrentMap<K, V>(this, computingFunction);
671 }
672
673 /**
674 * Returns a string representation for this MapMaker instance. The exact form of the returned
675 * string is not specificed.
676 */
677 @Override
678 public String toString() {
679 Objects.ToStringHelper s = Objects.toStringHelper(this);
680 if (initialCapacity != UNSET_INT) {
681 s.add("initialCapacity", initialCapacity);
682 }
683 if (concurrencyLevel != UNSET_INT) {
684 s.add("concurrencyLevel", concurrencyLevel);
685 }
686 if (maximumSize != UNSET_INT) {
687 s.add("maximumSize", maximumSize);
688 }
689 if (expireAfterWriteNanos != UNSET_INT) {
690 s.add("expireAfterWrite", expireAfterWriteNanos + "ns");
691 }
692 if (expireAfterAccessNanos != UNSET_INT) {
693 s.add("expireAfterAccess", expireAfterAccessNanos + "ns");
694 }
695 if (keyStrength != null) {
696 s.add("keyStrength", Ascii.toLowerCase(keyStrength.toString()));
697 }
698 if (valueStrength != null) {
699 s.add("valueStrength", Ascii.toLowerCase(valueStrength.toString()));
700 }
701 if (keyEquivalence != null) {
702 s.addValue("keyEquivalence");
703 }
704 if (valueEquivalence != null) {
705 s.addValue("valueEquivalence");
706 }
707 if (removalListener != null) {
708 s.addValue("removalListener");
709 }
710 return s.toString();
711 }
712
713 /**
714 * An object that can receive a notification when an entry is removed from a map. The removal
715 * resulting in notification could have occured to an entry being manually removed or replaced, or
716 * due to eviction resulting from timed expiration, exceeding a maximum size, or garbage
717 * collection.
718 *
719 * <p>An instance may be called concurrently by multiple threads to process different entries.
720 * Implementations of this interface should avoid performing blocking calls or synchronizing on
721 * shared resources.
722 *
723 * @param <K> the most general type of keys this listener can listen for; for
724 * example {@code Object} if any key is acceptable
725 * @param <V> the most general type of values this listener can listen for; for
726 * example {@code Object} if any key is acceptable
727 */
728 interface RemovalListener<K, V> {
729 /**
730 * Notifies the listener that a removal occurred at some point in the past.
731 */
732 void onRemoval(RemovalNotification<K, V> notification);
733 }
734
735 /**
736 * A notification of the removal of a single entry. The key or value may be null if it was already
737 * garbage collected.
738 *
739 * <p>Like other {@code Map.Entry} instances associated with MapMaker, this class holds strong
740 * references to the key and value, regardless of the type of references the map may be using.
741 */
742 static final class RemovalNotification<K, V> extends ImmutableEntry<K, V> {
743 private static final long serialVersionUID = 0;
744
745 private final RemovalCause cause;
746
747 RemovalNotification(@Nullable K key, @Nullable V value, RemovalCause cause) {
748 super(key, value);
749 this.cause = cause;
750 }
751
752 /**
753 * Returns the cause for which the entry was removed.
754 */
755 public RemovalCause getCause() {
756 return cause;
757 }
758
759 /**
760 * Returns {@code true} if there was an automatic removal due to eviction (the cause is neither
761 * {@link RemovalCause#EXPLICIT} nor {@link RemovalCause#REPLACED}).
762 */
763 public boolean wasEvicted() {
764 return cause.wasEvicted();
765 }
766 }
767
768 /**
769 * The reason why an entry was removed.
770 */
771 enum RemovalCause {
772 /**
773 * The entry was manually removed by the user. This can result from the user invoking
774 * {@link Map#remove}, {@link ConcurrentMap#remove}, or {@link java.util.Iterator#remove}.
775 */
776 EXPLICIT {
777 @Override
778 boolean wasEvicted() {
779 return false;
780 }
781 },
782
783 /**
784 * The entry itself was not actually removed, but its value was replaced by the user. This can
785 * result from the user invoking {@link Map#put}, {@link Map#putAll},
786 * {@link ConcurrentMap#replace(Object, Object)}, or
787 * {@link ConcurrentMap#replace(Object, Object, Object)}.
788 */
789 REPLACED {
790 @Override
791 boolean wasEvicted() {
792 return false;
793 }
794 },
795
796 /**
797 * The entry was removed automatically because its key or value was garbage-collected. This
798 * can occur when using {@link #softKeys}, {@link #softValues}, {@link #weakKeys}, or {@link
799 * #weakValues}.
800 */
801 COLLECTED {
802 @Override
803 boolean wasEvicted() {
804 return true;
805 }
806 },
807
808 /**
809 * The entry's expiration timestamp has passed. This can occur when using {@link
810 * #expireAfterWrite} or {@link #expireAfterAccess}.
811 */
812 EXPIRED {
813 @Override
814 boolean wasEvicted() {
815 return true;
816 }
817 },
818
819 /**
820 * The entry was evicted due to size constraints. This can occur when using {@link
821 * #maximumSize}.
822 */
823 SIZE {
824 @Override
825 boolean wasEvicted() {
826 return true;
827 }
828 };
829
830 /**
831 * Returns {@code true} if there was an automatic removal due to eviction (the cause is neither
832 * {@link #EXPLICIT} nor {@link #REPLACED}).
833 */
834 abstract boolean wasEvicted();
835 }
836
837 /** A map that is always empty and evicts on insertion. */
838 static class NullConcurrentMap<K, V> extends AbstractMap<K, V>
839 implements ConcurrentMap<K, V>, Serializable {
840 private static final long serialVersionUID = 0;
841
842 private final RemovalListener<K, V> removalListener;
843 private final RemovalCause removalCause;
844
845 NullConcurrentMap(MapMaker mapMaker) {
846 removalListener = mapMaker.getRemovalListener();
847 removalCause = mapMaker.nullRemovalCause;
848 }
849
850 // implements ConcurrentMap
851
852 @Override
853 public boolean containsKey(@Nullable Object key) {
854 return false;
855 }
856
857 @Override
858 public boolean containsValue(@Nullable Object value) {
859 return false;
860 }
861
862 @Override
863 public V get(@Nullable Object key) {
864 return null;
865 }
866
867 void notifyRemoval(K key, V value) {
868 RemovalNotification<K, V> notification =
869 new RemovalNotification<K, V>(key, value, removalCause);
870 removalListener.onRemoval(notification);
871 }
872
873 @Override
874 public V put(K key, V value) {
875 checkNotNull(key);
876 checkNotNull(value);
877 notifyRemoval(key, value);
878 return null;
879 }
880
881 @Override
882 public V putIfAbsent(K key, V value) {
883 return put(key, value);
884 }
885
886 @Override
887 public V remove(@Nullable Object key) {
888 return null;
889 }
890
891 @Override
892 public boolean remove(@Nullable Object key, @Nullable Object value) {
893 return false;
894 }
895
896 @Override
897 public V replace(K key, V value) {
898 checkNotNull(key);
899 checkNotNull(value);
900 return null;
901 }
902
903 @Override
904 public boolean replace(K key, @Nullable V oldValue, V newValue) {
905 checkNotNull(key);
906 checkNotNull(newValue);
907 return false;
908 }
909
910 @Override
911 public Set<Entry<K, V>> entrySet() {
912 return Collections.emptySet();
913 }
914 }
915
916 /** Computes on retrieval and evicts the result. */
917 static final class NullComputingConcurrentMap<K, V> extends NullConcurrentMap<K, V> {
918 private static final long serialVersionUID = 0;
919
920 final Function<? super K, ? extends V> computingFunction;
921
922 NullComputingConcurrentMap(
923 MapMaker mapMaker, Function<? super K, ? extends V> computingFunction) {
924 super(mapMaker);
925 this.computingFunction = checkNotNull(computingFunction);
926 }
927
928 @SuppressWarnings("unchecked") // unsafe, which is why Cache is preferred
929 @Override
930 public V get(Object k) {
931 K key = (K) k;
932 V value = compute(key);
933 checkNotNull(value, computingFunction + " returned null for key " + key + ".");
934 notifyRemoval(key, value);
935 return value;
936 }
937
938 private V compute(K key) {
939 checkNotNull(key);
940 try {
941 return computingFunction.apply(key);
942 } catch (ComputationException e) {
943 throw e;
944 } catch (Throwable t) {
945 throw new ComputationException(t);
946 }
947 }
948 }
949
950 }