Source Code Cross Referenced for ReferenceMap.java in  » Inversion-of-Control » guice-1.0 » com » google » inject » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Inversion of Control » guice 1.0 » com.google.inject.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /**
002:         * Copyright (C) 2006 Google Inc.
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:         */package com.google.inject.util;
016:
017:        import static com.google.inject.util.ReferenceType.STRONG;
018:
019:        import java.io.IOException;
020:        import java.io.ObjectInputStream;
021:        import java.io.ObjectOutputStream;
022:        import java.io.Serializable;
023:        import java.lang.ref.Reference;
024:        import java.util.ArrayList;
025:        import java.util.Collection;
026:        import java.util.Collections;
027:        import java.util.HashSet;
028:        import java.util.Map;
029:        import java.util.Set;
030:        import java.util.concurrent.ConcurrentHashMap;
031:        import java.util.concurrent.ConcurrentMap;
032:
033:        /**
034:         * Concurrent hash map that wraps keys and/or values in soft or weak
035:         * references. Does not support null keys or values. Uses identity equality
036:         * for weak and soft keys.
037:         *
038:         * <p>The concurrent semantics of {@link ConcurrentHashMap} combined with the
039:         * fact that the garbage collector can asynchronously reclaim and clean up
040:         * after keys and values at any time can lead to some racy semantics. For
041:         * example, {@link #size()} returns an upper bound on the size, i.e. the actual
042:         * size may be smaller in cases where the key or value has been reclaimed but
043:         * the map entry has not been cleaned up yet.
044:         *
045:         * <p>Another example: If {@link #get(Object)} cannot find an existing entry
046:         * for a key, it will try to create one. This operation is not atomic. One
047:         * thread could {@link #put(Object, Object)} a value between the time another
048:         * thread running {@code get()} checks for an entry and decides to create one.
049:         * In this case, the newly created value will replace the put value in the
050:         * map. Also, two threads running {@code get()} concurrently can potentially
051:         * create duplicate values for a given key.
052:         *
053:         * <p>In other words, this class is great for caching but not atomicity.
054:         *
055:         * @author crazybob@google.com (Bob Lee)
056:         */
057:        @SuppressWarnings("unchecked")
058:        public class ReferenceMap<K, V> implements  Map<K, V>, Serializable {
059:
060:            private static final long serialVersionUID = 0;
061:
062:            transient ConcurrentMap<Object, Object> delegate;
063:
064:            final ReferenceType keyReferenceType;
065:            final ReferenceType valueReferenceType;
066:
067:            /**
068:             * Concurrent hash map that wraps keys and/or values based on specified
069:             * reference types.
070:             *
071:             * @param keyReferenceType key reference type
072:             * @param valueReferenceType value reference type
073:             */
074:            public ReferenceMap(ReferenceType keyReferenceType,
075:                    ReferenceType valueReferenceType) {
076:                ensureNotNull(keyReferenceType, valueReferenceType);
077:
078:                if (keyReferenceType == ReferenceType.PHANTOM
079:                        || valueReferenceType == ReferenceType.PHANTOM) {
080:                    throw new IllegalArgumentException(
081:                            "Phantom references not supported.");
082:                }
083:
084:                this .delegate = new ConcurrentHashMap<Object, Object>();
085:                this .keyReferenceType = keyReferenceType;
086:                this .valueReferenceType = valueReferenceType;
087:            }
088:
089:            V internalGet(K key) {
090:                Object valueReference = delegate
091:                        .get(makeKeyReferenceAware(key));
092:                return valueReference == null ? null
093:                        : (V) dereferenceValue(valueReference);
094:            }
095:
096:            public V get(final Object key) {
097:                ensureNotNull(key);
098:                return internalGet((K) key);
099:            }
100:
101:            V execute(Strategy strategy, K key, V value) {
102:                ensureNotNull(key, value);
103:                Object keyReference = referenceKey(key);
104:                Object valueReference = strategy.execute(this , keyReference,
105:                        referenceValue(keyReference, value));
106:                return valueReference == null ? null
107:                        : (V) dereferenceValue(valueReference);
108:            }
109:
110:            public V put(K key, V value) {
111:                return execute(putStrategy(), key, value);
112:            }
113:
114:            public V remove(Object key) {
115:                ensureNotNull(key);
116:                Object referenceAwareKey = makeKeyReferenceAware(key);
117:                Object valueReference = delegate.remove(referenceAwareKey);
118:                return valueReference == null ? null
119:                        : (V) dereferenceValue(valueReference);
120:            }
121:
122:            public int size() {
123:                return delegate.size();
124:            }
125:
126:            public boolean isEmpty() {
127:                return delegate.isEmpty();
128:            }
129:
130:            public boolean containsKey(Object key) {
131:                ensureNotNull(key);
132:                Object referenceAwareKey = makeKeyReferenceAware(key);
133:                return delegate.containsKey(referenceAwareKey);
134:            }
135:
136:            public boolean containsValue(Object value) {
137:                ensureNotNull(value);
138:                for (Object valueReference : delegate.values()) {
139:                    if (value.equals(dereferenceValue(valueReference))) {
140:                        return true;
141:                    }
142:                }
143:                return false;
144:            }
145:
146:            public void putAll(Map<? extends K, ? extends V> t) {
147:                for (Map.Entry<? extends K, ? extends V> entry : t.entrySet()) {
148:                    put(entry.getKey(), entry.getValue());
149:                }
150:            }
151:
152:            public void clear() {
153:                delegate.clear();
154:            }
155:
156:            /**
157:             * Returns an unmodifiable set view of the keys in this map. As this method
158:             * creates a defensive copy, the performance is O(n).
159:             */
160:            public Set<K> keySet() {
161:                return Collections.unmodifiableSet(dereferenceKeySet(delegate
162:                        .keySet()));
163:            }
164:
165:            /**
166:             * Returns an unmodifiable set view of the values in this map. As this
167:             * method creates a defensive copy, the performance is O(n).
168:             */
169:            public Collection<V> values() {
170:                return Collections
171:                        .unmodifiableCollection(dereferenceValues(delegate
172:                                .values()));
173:            }
174:
175:            public V putIfAbsent(K key, V value) {
176:                // TODO (crazybob) if the value has been gc'ed but the entry hasn't been
177:                // cleaned up yet, this put will fail.
178:                return execute(putIfAbsentStrategy(), key, value);
179:            }
180:
181:            public boolean remove(Object key, Object value) {
182:                ensureNotNull(key, value);
183:                Object referenceAwareKey = makeKeyReferenceAware(key);
184:                Object referenceAwareValue = makeValueReferenceAware(value);
185:                return delegate.remove(referenceAwareKey, referenceAwareValue);
186:            }
187:
188:            public boolean replace(K key, V oldValue, V newValue) {
189:                ensureNotNull(key, oldValue, newValue);
190:                Object keyReference = referenceKey(key);
191:
192:                Object referenceAwareOldValue = makeValueReferenceAware(oldValue);
193:                return delegate.replace(keyReference, referenceAwareOldValue,
194:                        referenceValue(keyReference, newValue));
195:            }
196:
197:            public V replace(K key, V value) {
198:                // TODO (crazybob) if the value has been gc'ed but the entry hasn't been
199:                // cleaned up yet, this will succeed when it probably shouldn't.
200:                return execute(replaceStrategy(), key, value);
201:            }
202:
203:            /**
204:             * Returns an unmodifiable set view of the entries in this map. As this
205:             * method creates a defensive copy, the performance is O(n).
206:             */
207:            public Set<Map.Entry<K, V>> entrySet() {
208:                Set<Map.Entry<K, V>> entrySet = new HashSet<Map.Entry<K, V>>();
209:                for (Map.Entry<Object, Object> entry : delegate.entrySet()) {
210:                    Map.Entry<K, V> dereferenced = dereferenceEntry(entry);
211:                    if (dereferenced != null) {
212:                        entrySet.add(dereferenced);
213:                    }
214:                }
215:                return Collections.unmodifiableSet(entrySet);
216:            }
217:
218:            /**
219:             * Dereferences an entry. Returns null if the key or value has been gc'ed.
220:             */
221:            Entry dereferenceEntry(Map.Entry<Object, Object> entry) {
222:                K key = dereferenceKey(entry.getKey());
223:                V value = dereferenceValue(entry.getValue());
224:                return (key == null || value == null) ? null : new Entry(key,
225:                        value);
226:            }
227:
228:            /**
229:             * Creates a reference for a key.
230:             */
231:            Object referenceKey(K key) {
232:                switch (keyReferenceType) {
233:                case STRONG:
234:                    return key;
235:                case SOFT:
236:                    return new SoftKeyReference(key);
237:                case WEAK:
238:                    return new WeakKeyReference(key);
239:                default:
240:                    throw new AssertionError();
241:                }
242:            }
243:
244:            /**
245:             * Converts a reference to a key.
246:             */
247:            K dereferenceKey(Object o) {
248:                return (K) dereference(keyReferenceType, o);
249:            }
250:
251:            /**
252:             * Converts a reference to a value.
253:             */
254:            V dereferenceValue(Object o) {
255:                return (V) dereference(valueReferenceType, o);
256:            }
257:
258:            /**
259:             * Returns the refererent for reference given its reference type.
260:             */
261:            Object dereference(ReferenceType referenceType, Object reference) {
262:                return referenceType == STRONG ? reference
263:                        : ((Reference) reference).get();
264:            }
265:
266:            /**
267:             * Creates a reference for a value.
268:             */
269:            Object referenceValue(Object keyReference, Object value) {
270:                switch (valueReferenceType) {
271:                case STRONG:
272:                    return value;
273:                case SOFT:
274:                    return new SoftValueReference(keyReference, value);
275:                case WEAK:
276:                    return new WeakValueReference(keyReference, value);
277:                default:
278:                    throw new AssertionError();
279:                }
280:            }
281:
282:            /**
283:             * Dereferences a set of key references.
284:             */
285:            Set<K> dereferenceKeySet(Set keyReferences) {
286:                return keyReferenceType == STRONG ? keyReferences
287:                        : dereferenceCollection(keyReferenceType,
288:                                keyReferences, new HashSet());
289:            }
290:
291:            /**
292:             * Dereferences a collection of value references.
293:             */
294:            Collection<V> dereferenceValues(Collection valueReferences) {
295:                return valueReferenceType == STRONG ? valueReferences
296:                        : dereferenceCollection(valueReferenceType,
297:                                valueReferences, new ArrayList(valueReferences
298:                                        .size()));
299:            }
300:
301:            /**
302:             * Wraps key so it can be compared to a referenced key for equality.
303:             */
304:            Object makeKeyReferenceAware(Object o) {
305:                return keyReferenceType == STRONG ? o
306:                        : new KeyReferenceAwareWrapper(o);
307:            }
308:
309:            /**
310:             * Wraps value so it can be compared to a referenced value for equality.
311:             */
312:            Object makeValueReferenceAware(Object o) {
313:                return valueReferenceType == STRONG ? o
314:                        : new ReferenceAwareWrapper(o);
315:            }
316:
317:            /**
318:             * Dereferences elements in {@code in} using
319:             * {@code referenceType} and puts them in {@code out}. Returns
320:             * {@code out}.
321:             */
322:            <T extends Collection<Object>> T dereferenceCollection(
323:                    ReferenceType referenceType, T in, T out) {
324:                for (Object reference : in) {
325:                    out.add(dereference(referenceType, reference));
326:                }
327:                return out;
328:            }
329:
330:            /**
331:             * Marker interface to differentiate external and internal references.
332:             */
333:            interface InternalReference {
334:            }
335:
336:            static int keyHashCode(Object key) {
337:                return System.identityHashCode(key);
338:            }
339:
340:            /**
341:             * Tests weak and soft references for identity equality. Compares references
342:             * to other references and wrappers. If o is a reference, this returns true
343:             * if r == o or if r and o reference the same non null object. If o is a
344:             * wrapper, this returns true if r's referent is identical to the wrapped
345:             * object.
346:             */
347:            static boolean referenceEquals(Reference r, Object o) {
348:                // compare reference to reference.
349:                if (o instanceof  InternalReference) {
350:                    // are they the same reference? used in cleanup.
351:                    if (o == r) {
352:                        return true;
353:                    }
354:
355:                    // do they reference identical values? used in conditional puts.
356:                    Object referent = ((Reference) o).get();
357:                    return referent != null && referent == r.get();
358:                }
359:
360:                // is the wrapped object identical to the referent? used in lookups.
361:                return ((ReferenceAwareWrapper) o).unwrap() == r.get();
362:            }
363:
364:            /**
365:             * Big hack. Used to compare keys and values to referenced keys and values
366:             * without creating more references.
367:             */
368:            static class ReferenceAwareWrapper {
369:
370:                final Object wrapped;
371:
372:                ReferenceAwareWrapper(Object wrapped) {
373:                    this .wrapped = wrapped;
374:                }
375:
376:                Object unwrap() {
377:                    return wrapped;
378:                }
379:
380:                public int hashCode() {
381:                    return wrapped.hashCode();
382:                }
383:
384:                public boolean equals(Object obj) {
385:                    // defer to reference's equals() logic.
386:                    return obj.equals(this );
387:                }
388:            }
389:
390:            /**
391:             * Used for keys. Overrides hash code to use identity hash code.
392:             */
393:            static class KeyReferenceAwareWrapper extends ReferenceAwareWrapper {
394:
395:                public KeyReferenceAwareWrapper(Object wrapped) {
396:                    super (wrapped);
397:                }
398:
399:                public int hashCode() {
400:                    return System.identityHashCode(wrapped);
401:                }
402:            }
403:
404:            class SoftKeyReference extends FinalizableSoftReference<Object>
405:                    implements  InternalReference {
406:
407:                final int hashCode;
408:
409:                public SoftKeyReference(Object key) {
410:                    super (key);
411:                    this .hashCode = keyHashCode(key);
412:                }
413:
414:                public void finalizeReferent() {
415:                    delegate.remove(this );
416:                }
417:
418:                @Override
419:                public int hashCode() {
420:                    return this .hashCode;
421:                }
422:
423:                @Override
424:                public boolean equals(Object o) {
425:                    return referenceEquals(this , o);
426:                }
427:            }
428:
429:            class WeakKeyReference extends FinalizableWeakReference<Object>
430:                    implements  InternalReference {
431:
432:                final int hashCode;
433:
434:                public WeakKeyReference(Object key) {
435:                    super (key);
436:                    this .hashCode = keyHashCode(key);
437:                }
438:
439:                public void finalizeReferent() {
440:                    delegate.remove(this );
441:                }
442:
443:                @Override
444:                public int hashCode() {
445:                    return this .hashCode;
446:                }
447:
448:                @Override
449:                public boolean equals(Object o) {
450:                    return referenceEquals(this , o);
451:                }
452:            }
453:
454:            class SoftValueReference extends FinalizableSoftReference<Object>
455:                    implements  InternalReference {
456:
457:                final Object keyReference;
458:
459:                public SoftValueReference(Object keyReference, Object value) {
460:                    super (value);
461:                    this .keyReference = keyReference;
462:                }
463:
464:                public void finalizeReferent() {
465:                    delegate.remove(keyReference, this );
466:                }
467:
468:                @Override
469:                public boolean equals(Object obj) {
470:                    return referenceEquals(this , obj);
471:                }
472:            }
473:
474:            class WeakValueReference extends FinalizableWeakReference<Object>
475:                    implements  InternalReference {
476:
477:                final Object keyReference;
478:
479:                public WeakValueReference(Object keyReference, Object value) {
480:                    super (value);
481:                    this .keyReference = keyReference;
482:                }
483:
484:                public void finalizeReferent() {
485:                    delegate.remove(keyReference, this );
486:                }
487:
488:                @Override
489:                public boolean equals(Object obj) {
490:                    return referenceEquals(this , obj);
491:                }
492:            }
493:
494:            protected interface Strategy {
495:                public Object execute(ReferenceMap map, Object keyReference,
496:                        Object valueReference);
497:            }
498:
499:            protected Strategy putStrategy() {
500:                return PutStrategy.PUT;
501:            }
502:
503:            protected Strategy putIfAbsentStrategy() {
504:                return PutStrategy.PUT_IF_ABSENT;
505:            }
506:
507:            protected Strategy replaceStrategy() {
508:                return PutStrategy.REPLACE;
509:            }
510:
511:            protected enum PutStrategy implements  Strategy {
512:                PUT {
513:                    public Object execute(ReferenceMap map,
514:                            Object keyReference, Object valueReference) {
515:                        return map.delegate.put(keyReference, valueReference);
516:                    }
517:                },
518:
519:                REPLACE {
520:                    public Object execute(ReferenceMap map,
521:                            Object keyReference, Object valueReference) {
522:                        return map.delegate.replace(keyReference,
523:                                valueReference);
524:                    }
525:                },
526:
527:                PUT_IF_ABSENT {
528:                    public Object execute(ReferenceMap map,
529:                            Object keyReference, Object valueReference) {
530:                        return map.delegate.putIfAbsent(keyReference,
531:                                valueReference);
532:                    }
533:                };
534:            };
535:
536:            private static PutStrategy defaultPutStrategy;
537:
538:            protected PutStrategy getPutStrategy() {
539:                return defaultPutStrategy;
540:            }
541:
542:            class Entry implements  Map.Entry<K, V> {
543:
544:                final K key;
545:                final V value;
546:
547:                public Entry(K key, V value) {
548:                    this .key = key;
549:                    this .value = value;
550:                }
551:
552:                public K getKey() {
553:                    return this .key;
554:                }
555:
556:                public V getValue() {
557:                    return this .value;
558:                }
559:
560:                public V setValue(V value) {
561:                    return put(key, value);
562:                }
563:
564:                public int hashCode() {
565:                    return key.hashCode() * 31 + value.hashCode();
566:                }
567:
568:                public boolean equals(Object o) {
569:                    if (!(o instanceof  ReferenceMap.Entry)) {
570:                        return false;
571:                    }
572:
573:                    Entry entry = (Entry) o;
574:                    return key.equals(entry.key) && value.equals(entry.value);
575:                }
576:
577:                public String toString() {
578:                    return key + "=" + value;
579:                }
580:            }
581:
582:            static void ensureNotNull(Object o) {
583:                if (o == null) {
584:                    throw new NullPointerException();
585:                }
586:            }
587:
588:            static void ensureNotNull(Object... array) {
589:                for (int i = 0; i < array.length; i++) {
590:                    if (array[i] == null) {
591:                        throw new NullPointerException("Argument #" + i
592:                                + " is null.");
593:                    }
594:                }
595:            }
596:
597:            private void writeObject(ObjectOutputStream out) throws IOException {
598:                out.defaultWriteObject();
599:                out.writeInt(size());
600:                for (Map.Entry<Object, Object> entry : delegate.entrySet()) {
601:                    Object key = dereferenceKey(entry.getKey());
602:                    Object value = dereferenceValue(entry.getValue());
603:
604:                    // don't persist gc'ed entries.
605:                    if (key != null && value != null) {
606:                        out.writeObject(key);
607:                        out.writeObject(value);
608:                    }
609:                }
610:                out.writeObject(null);
611:            }
612:
613:            private void readObject(ObjectInputStream in) throws IOException,
614:                    ClassNotFoundException {
615:                in.defaultReadObject();
616:                int size = in.readInt();
617:                this .delegate = new ConcurrentHashMap<Object, Object>(size);
618:                while (true) {
619:                    K key = (K) in.readObject();
620:                    if (key == null) {
621:                        break;
622:                    }
623:                    V value = (V) in.readObject();
624:                    put(key, value);
625:                }
626:            }
627:
628:        }
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