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Comparing jsr166/src/main/java/util/concurrent/ConcurrentHashMap.java (file contents):
Revision 1.24 by dl, Fri Oct 10 23:51:28 2003 UTC vs.
Revision 1.72 by dl, Sat May 28 13:31:22 2005 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3	<	* Expert Group and released to the public domain. Use, modify, and
4	<	* redistribute this code in any way without acknowledgement.
3	>	* Expert Group and released to the public domain, as explained at
4	>	* http://creativecommons.org/licenses/publicdomain
5		*/
6
7		package java.util.concurrent;
#	Line 17 | Line 17 | import java.io.ObjectOutputStream;
17		* adjustable expected concurrency for updates. This class obeys the
18		* same functional specification as {@link java.util.Hashtable}, and
19		* includes versions of methods corresponding to each method of
20	<	* <tt>Hashtable</tt> . However, even though all operations are
20	>	* <tt>Hashtable</tt>. However, even though all operations are
21		* thread-safe, retrieval operations do <em>not</em> entail locking,
22		* and there is <em>not</em> any support for locking the entire table
23		* in a way that prevents all access.  This class is fully
24		* interoperable with <tt>Hashtable</tt> in programs that rely on its
25		* thread safety but not on its synchronization details.
26		*
27	<	* <p> Retrieval operations (including <tt>get</tt>) ordinarily
28	<	* overlap with update operations (including <tt>put</tt> and
29	<	* <tt>remove</tt>). Retrievals reflect the results of the most
30	<	* recently <em>completed</em> update operations holding upon their
31	<	* onset.  For aggregate operations such as <tt>putAll</tt> and
32	<	* <tt>clear</tt>, concurrent retrievals may reflect insertion or
27	>	* <p> Retrieval operations (including <tt>get</tt>) generally do not
28	>	* block, so may overlap with update operations (including
29	>	* <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results
30	>	* of the most recently <em>completed</em> update operations holding
31	>	* upon their onset.  For aggregate operations such as <tt>putAll</tt>
32	>	* and <tt>clear</tt>, concurrent retrievals may reflect insertion or
33		* removal of only some entries.  Similarly, Iterators and
34		* Enumerations return elements reflecting the state of the hash table
35		* at some point at or since the creation of the iterator/enumeration.
36	<	* They do <em>not</em> throw <tt>ConcurrentModificationException</tt>.
37	<	* However, Iterators are designed to be used by only one thread at a
38	<	* time.
36	>	* They do <em>not</em> throw {@link ConcurrentModificationException}.
37	>	* However, iterators are designed to be used by only one thread at a time.
38		*
39		* <p> The allowed concurrency among update operations is guided by
40		* the optional <tt>concurrencyLevel</tt> constructor argument
41	<	* (default 16), which is used as a hint for internal sizing.  The
41	>	* (default <tt>16</tt>), which is used as a hint for internal sizing.  The
42		* table is internally partitioned to try to permit the indicated
43		* number of concurrent updates without contention. Because placement
44		* in hash tables is essentially random, the actual concurrency will
45		* vary.  Ideally, you should choose a value to accommodate as many
46	<	* threads as will ever concurrently access the table. Using a
46	>	* threads as will ever concurrently modify the table. Using a
47		* significantly higher value than you need can waste space and time,
48		* and a significantly lower value can lead to thread contention. But
49		* overestimates and underestimates within an order of magnitude do
50	<	* not usually have much noticeable impact.
50	>	* not usually have much noticeable impact. A value of one is
51	>	* appropriate when it is known that only one thread will modify and
52	>	* all others will only read. Also, resizing this or any other kind of
53	>	* hash table is a relatively slow operation, so, when possible, it is
54	>	* a good idea to provide estimates of expected table sizes in
55	>	* constructors.
56		*
57	<	* <p>This class implements all of the <em>optional</em> methods
58	<	* of the {@link Map} and {@link Iterator} interfaces.
57	>	* <p>This class and its views and iterators implement all of the
58	>	* <em>optional</em> methods of the {@link Map} and {@link Iterator}
59	>	* interfaces.
60		*
61	<	* <p> Like {@link java.util.Hashtable} but unlike {@link
62	<	* java.util.HashMap}, this class does NOT allow <tt>null</tt> to be
63	<	* used as a key or value.
61	>	* <p> Like {@link Hashtable} but unlike {@link HashMap}, this class
62	>	* does <em>not</em> allow <tt>null</tt> to be used as a key or value.
63	>	*
64	>	* <p>This class is a member of the
65	>	* <a href="{@docRoot}/../guide/collections/index.html">
66	>	* Java Collections Framework</a>.
67		*
68		* @since 1.5
69		* @author Doug Lea
70	+	* @param <K> the type of keys maintained by this map
71	+	* @param <V> the type of mapped values
72		*/
73		public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
74	<	implements ConcurrentMap<K, V>, Cloneable, Serializable {
74	>	implements ConcurrentMap<K, V>, Serializable {
75		private static final long serialVersionUID = 7249069246763182397L;
76
77		/*
#	Line 72 | Line 82 | public class ConcurrentHashMap<K, V> ext
82		/* ---------------- Constants -------------- */
83
84		/**
85	<	* The default initial number of table slots for this table.
86	<	* Used when not otherwise specified in constructor.
85	>	* The default initial capacity for this table,
86	>	* used when not otherwise specified in a constructor.
87	>	*/
88	>	static final int DEFAULT_INITIAL_CAPACITY = 16;
89	>
90	>	/**
91	>	* The default load factor for this table, used when not
92	>	* otherwise specified in a constructor.
93	>	*/
94	>	static final float DEFAULT_LOAD_FACTOR = 0.75f;
95	>
96	>	/**
97	>	* The default concurrency level for this table, used when not
98	>	* otherwise specified in a constructor.
99		*/
100	<	private static int DEFAULT_INITIAL_CAPACITY = 16;
100	>	static final int DEFAULT_CONCURRENCY_LEVEL = 16;
101
102		/**
103		* The maximum capacity, used if a higher value is implicitly
104		* specified by either of the constructors with arguments.  MUST
105	<	* be a power of two <= 1<<30 to ensure that entries are indexible
105	>	* be a power of two <= 1<<30 to ensure that entries are indexable
106		* using ints.
107		*/
108	<	static final int MAXIMUM_CAPACITY = 1 << 30;
108	>	static final int MAXIMUM_CAPACITY = 1 << 30;
109
110		/**
111	<	* The default load factor for this table.  Used when not
112	<	* otherwise specified in constructor.
111	>	* The maximum number of segments to allow; used to bound
112	>	* constructor arguments.
113		*/
114	<	static final float DEFAULT_LOAD_FACTOR = 0.75f;
93	<
94	<	/**
95	<	* The default number of concurrency control segments.
96	<	**/
97	<	private static final int DEFAULT_SEGMENTS = 16;
114	>	static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
115
116		/**
117	<	* The maximum number of segments to allow; used to bound ctor arguments.
117	>	* Number of unsynchronized retries in size and containsValue
118	>	* methods before resorting to locking. This is used to avoid
119	>	* unbounded retries if tables undergo continuous modification
120	>	* which would make it impossible to obtain an accurate result.
121		*/
122	<	private static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
122	>	static final int RETRIES_BEFORE_LOCK = 2;
123
124		/* ---------------- Fields -------------- */
125
126		/**
127		* Mask value for indexing into segments. The upper bits of a
128		* key's hash code are used to choose the segment.
129	<	**/
130	<	private final int segmentMask;
129	>	*/
130	>	final int segmentMask;
131
132		/**
133		* Shift value for indexing within segments.
134	<	**/
135	<	private final int segmentShift;
134	>	*/
135	>	final int segmentShift;
136
137		/**
138		* The segments, each of which is a specialized hash table
139		*/
140	<	private final Segment[] segments;
140	>	final Segment<K,V>[] segments;
141
142	<	private transient Set<K> keySet;
143	<	private transient Set<Map.Entry<K,V>> entrySet;
144	<	private transient Collection<V> values;
142	>	transient Set<K> keySet;
143	>	transient Set<Map.Entry<K,V>> entrySet;
144	>	transient Collection<V> values;
145
146		/* ---------------- Small Utilities -------------- */
147
148		/**
149	<	* Return a hash code for non-null Object x.
150	<	* Uses the same hash code spreader as most other j.u hash tables.
149	>	* Returns a hash code for non-null Object x.
150	>	* Uses the same hash code spreader as most other java.util hash tables.
151		* @param x the object serving as a key
152		* @return the hash code
153		*/
154	<	private static int hash(Object x) {
154	>	static int hash(Object x) {
155		int h = x.hashCode();
156		h += ~(h << 9);
157		h ^=  (h >>> 14);
#	Line 141 | Line 161 | public class ConcurrentHashMap<K, V> ext
161		}
162
163		/**
164	<	* Return the segment that should be used for key with given hash
164	>	* Returns the segment that should be used for key with given hash
165	>	* @param hash the hash code for the key
166	>	* @return the segment
167		*/
168	<	private Segment<K,V> segmentFor(int hash) {
169	<	return (Segment<K,V>) segments[(hash >>> segmentShift) & segmentMask];
168	>	final Segment<K,V> segmentFor(int hash) {
169	>	return segments[(hash >>> segmentShift) & segmentMask];
170		}
171
172		/* ---------------- Inner Classes -------------- */
173
174		/**
175	+	* ConcurrentHashMap list entry. Note that this is never exported
176	+	* out as a user-visible Map.Entry.
177	+	*
178	+	* Because the value field is volatile, not final, it is legal wrt
179	+	* the Java Memory Model for an unsynchronized reader to see null
180	+	* instead of initial value when read via a data race.  Although a
181	+	* reordering leading to this is not likely to ever actually
182	+	* occur, the Segment.readValueUnderLock method is used as a
183	+	* backup in case a null (pre-initialized) value is ever seen in
184	+	* an unsynchronized access method.
185	+	*/
186	+	static final class HashEntry<K,V> {
187	+	final K key;
188	+	final int hash;
189	+	volatile V value;
190	+	final HashEntry<K,V> next;
191	+
192	+	HashEntry(K key, int hash, HashEntry<K,V> next, V value) {
193	+	this.key = key;
194	+	this.hash = hash;
195	+	this.next = next;
196	+	this.value = value;
197	+	}
198	+
199	+	@SuppressWarnings("unchecked")
200	+	static final <K,V> HashEntry<K,V>[] newArray(int i) {
201	+	return new HashEntry[i];
202	+	}
203	+	}
204	+
205	+	/**
206		* Segments are specialized versions of hash tables.  This
207		* subclasses from ReentrantLock opportunistically, just to
208		* simplify some locking and avoid separate construction.
209	<	**/
210	<	private static final class Segment<K,V> extends ReentrantLock implements Serializable {
209	>	*/
210	>	static final class Segment<K,V> extends ReentrantLock implements Serializable {
211		/*
212		* Segments maintain a table of entry lists that are ALWAYS
213		* kept in a consistent state, so can be read without locking.
#	Line 167 | Line 220 | public class ConcurrentHashMap<K, V> ext
220		* is less than two for the default load factor threshold.)
221		*
222		* Read operations can thus proceed without locking, but rely
223	<	* on a memory barrier to ensure that completed write
224	<	* operations performed by other threads are
225	<	* noticed. Conveniently, the "count" field, tracking the
226	<	* number of elements, can also serve as the volatile variable
227	<	* providing proper read/write barriers. This is convenient
228	<	* because this field needs to be read in many read operations
176	<	* anyway.
223	>	* on selected uses of volatiles to ensure that completed
224	>	* write operations performed by other threads are
225	>	* noticed. For most purposes, the "count" field, tracking the
226	>	* number of elements, serves as that volatile variable
227	>	* ensuring visibility.  This is convenient because this field
228	>	* needs to be read in many read operations anyway:
229		*
230	<	* Implementors note. The basic rules for all this are:
179	<	*
180	<	*   - All unsynchronized read operations must first read the
230	>	*   - All (unsynchronized) read operations must first read the
231		*     "count" field, and should not look at table entries if
232		*     it is 0.
233		*
234	<	*   - All synchronized write operations should write to
235	<	*     the "count" field after updating. The operations must not
236	<	*     take any action that could even momentarily cause
237	<	*     a concurrent read operation to see inconsistent
238	<	*     data. This is made easier by the nature of the read
239	<	*     operations in Map. For example, no operation
234	>	*   - All (synchronized) write operations should write to
235	>	*     the "count" field after structurally changing any bin.
236	>	*     The operations must not take any action that could even
237	>	*     momentarily cause a concurrent read operation to see
238	>	*     inconsistent data. This is made easier by the nature of
239	>	*     the read operations in Map. For example, no operation
240		*     can reveal that the table has grown but the threshold
241		*     has not yet been updated, so there are no atomicity
242		*     requirements for this with respect to reads.
243		*
244	<	* As a guide, all critical volatile reads and writes are marked
245	<	* in code comments.
244	>	* As a guide, all critical volatile reads and writes to the
245	>	* count field are marked in code comments.
246		*/
247
248		private static final long serialVersionUID = 2249069246763182397L;
249
250		/**
251		* The number of elements in this segment's region.
252	<	**/
252	>	*/
253		transient volatile int count;
254
255		/**
256	<	* Number of updates; used for checking lack of modifications
257	<	* in bulk-read methods.
256	>	* Number of updates that alter the size of the table. This is
257	>	* used during bulk-read methods to make sure they see a
258	>	* consistent snapshot: If modCounts change during a traversal
259	>	* of segments computing size or checking containsValue, then
260	>	* we might have an inconsistent view of state so (usually)
261	>	* must retry.
262		*/
263		transient int modCount;
264
265		/**
266		* The table is rehashed when its size exceeds this threshold.
267	<	* (The value of this field is always (int)(capacity *
268	<	* loadFactor).)
267	>	* (The value of this field is always <tt>(int)(capacity *
268	>	* loadFactor)</tt>.)
269		*/
270	<	private transient int threshold;
270	>	transient int threshold;
271
272		/**
273	<	* The per-segment table
274	<	*/
221	<	transient HashEntry[] table;
273	>	* The per-segment table. */
274	>	transient volatile HashEntry<K,V>[] table;
275
276		/**
277		* The load factor for the hash table.  Even though this value
#	Line 226 | Line 279 | public class ConcurrentHashMap<K, V> ext
279		* links to outer object.
280		* @serial
281		*/
282	<	private final float loadFactor;
282	>	final float loadFactor;
283
284		Segment(int initialCapacity, float lf) {
285		loadFactor = lf;
286	<	setTable(new HashEntry[initialCapacity]);
286	>	setTable(HashEntry.<K,V>newArray(initialCapacity));
287	>	}
288	>
289	>	@SuppressWarnings("unchecked")
290	>	static final <K,V> Segment<K,V>[] newArray(int i) {
291	>	return new Segment[i];
292		}
293
294		/**
295	<	* Set table to new HashEntry array.
295	>	* Sets table to new HashEntry array.
296		* Call only while holding lock or in constructor.
297	<	**/
298	<	private void setTable(HashEntry[] newTable) {
241	<	table = newTable;
297	>	*/
298	>	void setTable(HashEntry<K,V>[] newTable) {
299		threshold = (int)(newTable.length * loadFactor);
300	<	count = count; // write-volatile
300	>	table = newTable;
301	>	}
302	>
303	>	/**
304	>	* Returns properly casted first entry of bin for given hash.
305	>	*/
306	>	HashEntry<K,V> getFirst(int hash) {
307	>	HashEntry<K,V>[] tab = table;
308	>	return tab[hash & (tab.length - 1)];
309	>	}
310	>
311	>	/**
312	>	* Reads value field of an entry under lock. Called if value
313	>	* field ever appears to be null. This is possible only if a
314	>	* compiler happens to reorder a HashEntry initialization with
315	>	* its table assignment, which is legal under memory model
316	>	* but is not known to ever occur.
317	>	*/
318	>	V readValueUnderLock(HashEntry<K,V> e) {
319	>	lock();
320	>	try {
321	>	return e.value;
322	>	} finally {
323	>	unlock();
324	>	}
325		}
326
327		/* Specialized implementations of map methods */
328
329	<	V get(K key, int hash) {
329	>	V get(Object key, int hash) {
330		if (count != 0) { // read-volatile
331	<	HashEntry[] tab = table;
251	<	int index = hash & (tab.length - 1);
252	<	HashEntry<K,V> e = (HashEntry<K,V>) tab[index];
331	>	HashEntry<K,V> e = getFirst(hash);
332		while (e != null) {
333	<	if (e.hash == hash && key.equals(e.key))
334	<	return e.value;
333	>	if (e.hash == hash && key.equals(e.key)) {
334	>	V v = e.value;
335	>	if (v != null)
336	>	return v;
337	>	return readValueUnderLock(e); // recheck
338	>	}
339		e = e.next;
340		}
341		}
#	Line 261 | Line 344 | public class ConcurrentHashMap<K, V> ext
344
345		boolean containsKey(Object key, int hash) {
346		if (count != 0) { // read-volatile
347	<	HashEntry[] tab = table;
265	<	int index = hash & (tab.length - 1);
266	<	HashEntry<K,V> e = (HashEntry<K,V>) tab[index];
347	>	HashEntry<K,V> e = getFirst(hash);
348		while (e != null) {
349		if (e.hash == hash && key.equals(e.key))
350		return true;
#	Line 275 | Line 356 | public class ConcurrentHashMap<K, V> ext
356
357		boolean containsValue(Object value) {
358		if (count != 0) { // read-volatile
359	<	HashEntry[] tab = table;
359	>	HashEntry<K,V>[] tab = table;
360		int len = tab.length;
361	<	for (int i = 0 ; i < len; i++)
362	<	for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i] ; e != null ; e = e.next)
363	<	if (value.equals(e.value))
361	>	for (int i = 0 ; i < len; i++) {
362	>	for (HashEntry<K,V> e = tab[i]; e != null; e = e.next) {
363	>	V v = e.value;
364	>	if (v == null) // recheck
365	>	v = readValueUnderLock(e);
366	>	if (value.equals(v))
367		return true;
368	+	}
369	+	}
370		}
371		return false;
372		}
373
374	+	boolean replace(K key, int hash, V oldValue, V newValue) {
375	+	lock();
376	+	try {
377	+	HashEntry<K,V> e = getFirst(hash);
378	+	while (e != null && (e.hash != hash || !key.equals(e.key)))
379	+	e = e.next;
380	+
381	+	boolean replaced = false;
382	+	if (e != null && oldValue.equals(e.value)) {
383	+	replaced = true;
384	+	e.value = newValue;
385	+	}
386	+	return replaced;
387	+	} finally {
388	+	unlock();
389	+	}
390	+	}
391	+
392	+	V replace(K key, int hash, V newValue) {
393	+	lock();
394	+	try {
395	+	HashEntry<K,V> e = getFirst(hash);
396	+	while (e != null && (e.hash != hash || !key.equals(e.key)))
397	+	e = e.next;
398	+
399	+	V oldValue = null;
400	+	if (e != null) {
401	+	oldValue = e.value;
402	+	e.value = newValue;
403	+	}
404	+	return oldValue;
405	+	} finally {
406	+	unlock();
407	+	}
408	+	}
409	+
410	+
411		V put(K key, int hash, V value, boolean onlyIfAbsent) {
412		lock();
413		try {
414		int c = count;
415	<	HashEntry[] tab = table;
415	>	if (c++ > threshold) // ensure capacity
416	>	rehash();
417	>	HashEntry<K,V>[] tab = table;
418		int index = hash & (tab.length - 1);
419	<	HashEntry<K,V> first = (HashEntry<K,V>) tab[index];
419	>	HashEntry<K,V> first = tab[index];
420	>	HashEntry<K,V> e = first;
421	>	while (e != null && (e.hash != hash || !key.equals(e.key)))
422	>	e = e.next;
423
424	<	for (HashEntry<K,V> e = first; e != null; e = (HashEntry<K,V>) e.next) {
425	<	if (e.hash == hash && key.equals(e.key)) {
426	<	V oldValue = e.value;
427	<	if (!onlyIfAbsent)
428	<	e.value = value;
301	<	++modCount;
302	<	count = c; // write-volatile
303	<	return oldValue;
304	<	}
424	>	V oldValue;
425	>	if (e != null) {
426	>	oldValue = e.value;
427	>	if (!onlyIfAbsent)
428	>	e.value = value;
429		}
430	<
431	<	tab[index] = new HashEntry<K,V>(hash, key, value, first);
432	<	++modCount;
433	<	++c;
434	<	count = c; // write-volatile
435	<	if (c > threshold)
436	<	setTable(rehash(tab));
313	<	return null;
430	>	else {
431	>	oldValue = null;
432	>	++modCount;
433	>	tab[index] = new HashEntry<K,V>(key, hash, first, value);
434	>	count = c; // write-volatile
435	>	}
436	>	return oldValue;
437		} finally {
438		unlock();
439		}
440		}
441
442	<	private HashEntry[] rehash(HashEntry[] oldTable) {
442	>	void rehash() {
443	>	HashEntry<K,V>[] oldTable = table;
444		int oldCapacity = oldTable.length;
445		if (oldCapacity >= MAXIMUM_CAPACITY)
446	<	return oldTable;
446	>	return;
447
448		/*
449		* Reclassify nodes in each list to new Map.  Because we are
#	Line 328 | Line 452 | public class ConcurrentHashMap<K, V> ext
452		* offset. We eliminate unnecessary node creation by catching
453		* cases where old nodes can be reused because their next
454		* fields won't change. Statistically, at the default
455	<	* threshhold, only about one-sixth of them need cloning when
455	>	* threshold, only about one-sixth of them need cloning when
456		* a table doubles. The nodes they replace will be garbage
457		* collectable as soon as they are no longer referenced by any
458		* reader thread that may be in the midst of traversing table
459		* right now.
460		*/
461
462	<	HashEntry[] newTable = new HashEntry[oldCapacity << 1];
462	>	HashEntry<K,V>[] newTable = HashEntry.newArray(oldCapacity<<1);
463	>	threshold = (int)(newTable.length * loadFactor);
464		int sizeMask = newTable.length - 1;
465		for (int i = 0; i < oldCapacity ; i++) {
466		// We need to guarantee that any existing reads of old Map can
467		//  proceed. So we cannot yet null out each bin.
468	<	HashEntry<K,V> e = (HashEntry<K,V>)oldTable[i];
468	>	HashEntry<K,V> e = oldTable[i];
469
470		if (e != null) {
471		HashEntry<K,V> next = e.next;
#	Line 368 | Line 493 | public class ConcurrentHashMap<K, V> ext
493		// Clone all remaining nodes
494		for (HashEntry<K,V> p = e; p != lastRun; p = p.next) {
495		int k = p.hash & sizeMask;
496	<	newTable[k] = new HashEntry<K,V>(p.hash,
497	<	p.key,
498	<	p.value,
374	<	(HashEntry<K,V>) newTable[k]);
496	>	HashEntry<K,V> n = newTable[k];
497	>	newTable[k] = new HashEntry<K,V>(p.key, p.hash,
498	>	n, p.value);
499		}
500		}
501		}
502		}
503	<	return newTable;
503	>	table = newTable;
504		}
505
506		/**
#	Line 385 | Line 509 | public class ConcurrentHashMap<K, V> ext
509		V remove(Object key, int hash, Object value) {
510		lock();
511		try {
512	<	int c = count;
513	<	HashEntry[] tab = table;
512	>	int c = count - 1;
513	>	HashEntry<K,V>[] tab = table;
514		int index = hash & (tab.length - 1);
515	<	HashEntry<K,V> first = (HashEntry<K,V>)tab[index];
392	<
515	>	HashEntry<K,V> first = tab[index];
516		HashEntry<K,V> e = first;
517	<	for (;;) {
395	<	if (e == null)
396	<	return null;
397	<	if (e.hash == hash && key.equals(e.key))
398	<	break;
517	>	while (e != null && (e.hash != hash || !key.equals(e.key)))
518		e = e.next;
400	–	}
519
520	<	V oldValue = e.value;
521	<	if (value != null && !value.equals(oldValue))
522	<	return null;
523	<
524	<	// All entries following removed node can stay in list, but
525	<	// all preceeding ones need to be cloned.
526	<	HashEntry<K,V> newFirst = e.next;
527	<	for (HashEntry<K,V> p = first; p != e; p = p.next)
528	<	newFirst = new HashEntry<K,V>(p.hash, p.key,
529	<	p.value, newFirst);
530	<	tab[index] = newFirst;
531	<	++modCount;
532	<	count = c-1; // write-volatile
520	>	V oldValue = null;
521	>	if (e != null) {
522	>	V v = e.value;
523	>	if (value == null || value.equals(v)) {
524	>	oldValue = v;
525	>	// All entries following removed node can stay
526	>	// in list, but all preceding ones need to be
527	>	// cloned.
528	>	++modCount;
529	>	HashEntry<K,V> newFirst = e.next;
530	>	for (HashEntry<K,V> p = first; p != e; p = p.next)
531	>	newFirst = new HashEntry<K,V>(p.key, p.hash,
532	>	newFirst, p.value);
533	>	tab[index] = newFirst;
534	>	count = c; // write-volatile
535	>	}
536	>	}
537		return oldValue;
538		} finally {
539		unlock();
#	Line 419 | Line 541 | public class ConcurrentHashMap<K, V> ext
541		}
542
543		void clear() {
544	<	lock();
545	<	try {
546	<	HashEntry[] tab = table;
547	<	for (int i = 0; i < tab.length ; i++)
548	<	tab[i] = null;
549	<	++modCount;
550	<	count = 0; // write-volatile
551	<	} finally {
552	<	unlock();
544	>	if (count != 0) {
545	>	lock();
546	>	try {
547	>	HashEntry<K,V>[] tab = table;
548	>	for (int i = 0; i < tab.length ; i++)
549	>	tab[i] = null;
550	>	++modCount;
551	>	count = 0; // write-volatile
552	>	} finally {
553	>	unlock();
554	>	}
555		}
556		}
557		}
558
435	–	/**
436	–	* ConcurrentHashMap list entry.
437	–	*/
438	–	private static class HashEntry<K,V> implements Entry<K,V> {
439	–	private final K key;
440	–	private V value;
441	–	private final int hash;
442	–	private final HashEntry<K,V> next;
443	–
444	–	HashEntry(int hash, K key, V value, HashEntry<K,V> next) {
445	–	this.value = value;
446	–	this.hash = hash;
447	–	this.key = key;
448	–	this.next = next;
449	–	}
450	–
451	–	public K getKey() {
452	–	return key;
453	–	}
454	–
455	–	public V getValue() {
456	–	return value;
457	–	}
458	–
459	–	public V setValue(V newValue) {
460	–	// We aren't required to, and don't provide any
461	–	// visibility barriers for setting value.
462	–	if (newValue == null)
463	–	throw new NullPointerException();
464	–	V oldValue = this.value;
465	–	this.value = newValue;
466	–	return oldValue;
467	–	}
468	–
469	–	public boolean equals(Object o) {
470	–	if (!(o instanceof Entry))
471	–	return false;
472	–	Entry<K,V> e = (Entry<K,V>)o;
473	–	return (key.equals(e.getKey()) && value.equals(e.getValue()));
474	–	}
475	–
476	–	public int hashCode() {
477	–	return  key.hashCode() ^ value.hashCode();
478	–	}
479	–
480	–	public String toString() {
481	–	return key + "=" + value;
482	–	}
483	–	}
559
560
561		/* ---------------- Public operations -------------- */
562
563		/**
564	<	* Constructs a new, empty map with the specified initial
565	<	* capacity and the specified load factor.
564	>	* Creates a new, empty map with the specified initial
565	>	* capacity, load factor and concurrency level.
566		*
567		* @param initialCapacity the initial capacity. The implementation
568		* performs internal sizing to accommodate this many elements.
569		* @param loadFactor  the load factor threshold, used to control resizing.
570	+	* Resizing may be performed when the average number of elements per
571	+	* bin exceeds this threshold.
572		* @param concurrencyLevel the estimated number of concurrently
573		* updating threads. The implementation performs internal sizing
574	<	* to try to accommodate this many threads.
574	>	* to try to accommodate this many threads.
575		* @throws IllegalArgumentException if the initial capacity is
576		* negative or the load factor or concurrencyLevel are
577		* nonpositive.
#	Line 516 | Line 593 | public class ConcurrentHashMap<K, V> ext
593		}
594		segmentShift = 32 - sshift;
595		segmentMask = ssize - 1;
596	<	this.segments = new Segment[ssize];
596	>	this.segments = Segment.newArray(ssize);
597
598		if (initialCapacity > MAXIMUM_CAPACITY)
599		initialCapacity = MAXIMUM_CAPACITY;
#	Line 532 | Line 609 | public class ConcurrentHashMap<K, V> ext
609		}
610
611		/**
612	<	* Constructs a new, empty map with the specified initial
613	<	* capacity,  and with default load factor and concurrencyLevel.
612	>	* Creates a new, empty map with the specified initial capacity
613	>	* and load factor and with the default concurrencyLevel
614	>	* (<tt>16</tt>).
615		*
616		* @param initialCapacity The implementation performs internal
617		* sizing to accommodate this many elements.
618	+	* @param loadFactor  the load factor threshold, used to control resizing.
619	+	* Resizing may be performed when the average number of elements per
620	+	* bin exceeds this threshold.
621	+	* @throws IllegalArgumentException if the initial capacity of
622	+	* elements is negative or the load factor is nonpositive
623	+	*/
624	+	public ConcurrentHashMap(int initialCapacity, float loadFactor) {
625	+	this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
626	+	}
627	+
628	+	/**
629	+	* Creates a new, empty map with the specified initial capacity,
630	+	* and with default load factor (<tt>0.75f</tt>)
631	+	* and concurrencyLevel (<tt>16</tt>).
632	+	*
633	+	* @param initialCapacity the initial capacity. The implementation
634	+	* performs internal sizing to accommodate this many elements.
635		* @throws IllegalArgumentException if the initial capacity of
636		* elements is negative.
637		*/
638		public ConcurrentHashMap(int initialCapacity) {
639	<	this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
639	>	this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
640		}
641
642		/**
643	<	* Constructs a new, empty map with a default initial capacity,
644	<	* load factor, and concurrencyLevel.
643	>	* Creates a new, empty map with a default initial capacity
644	>	* (<tt>16</tt>), load factor
645	>	* (<tt>0.75f</tt>), and concurrencyLevel
646	>	* (<tt>16</tt>).
647		*/
648		public ConcurrentHashMap() {
649	<	this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
649	>	this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
650		}
651
652		/**
653	<	* Constructs a new map with the same mappings as the given map.  The
654	<	* map is created with a capacity of twice the number of mappings in
655	<	* the given map or 11 (whichever is greater), and a default load factor.
653	>	* Creates a new map with the same mappings as the given map.  The
654	>	* map is created with a capacity of 1.5 times the number of
655	>	* mappings in the given map or <tt>16</tt>
656	>	* (whichever is greater), and a default load factor
657	>	* (<tt>0.75f</tt>) and concurrencyLevel
658	>	* (<tt>16</tt>).
659	>	* @param m the map
660		*/
661	<	public <A extends K, B extends V> ConcurrentHashMap(Map<A,B> t) {
662	<	this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1,
663	<	11),
664	<	DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
665	<	putAll(t);
661	>	public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
662	>	this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
663	>	DEFAULT_INITIAL_CAPACITY),
664	>	DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
665	>	putAll(m);
666		}
667
668	<	// inherit Map javadoc
668	>	/**
669	>	* Returns <tt>true</tt> if this map contains no key-value mappings.
670	>	*
671	>	* @return <tt>true</tt> if this map contains no key-value mappings
672	>	*/
673		public boolean isEmpty() {
674	+	final Segment<K,V>[] segments = this.segments;
675		/*
676	<	* We need to keep track of per-segment modCounts to avoid ABA
676	>	* We keep track of per-segment modCounts to avoid ABA
677		* problems in which an element in one segment was added and
678		* in another removed during traversal, in which case the
679		* table was never actually empty at any point. Note the
#	Line 580 | Line 686 | public class ConcurrentHashMap<K, V> ext
686		for (int i = 0; i < segments.length; ++i) {
687		if (segments[i].count != 0)
688		return false;
689	<	else
689	>	else
690		mcsum += mc[i] = segments[i].modCount;
691		}
692		// If mcsum happens to be zero, then we know we got a snapshot
#	Line 589 | Line 695 | public class ConcurrentHashMap<K, V> ext
695		if (mcsum != 0) {
696		for (int i = 0; i < segments.length; ++i) {
697		if (segments[i].count != 0 ||
698	<	mc[i] != segments[i].modCount)
698	>	mc[i] != segments[i].modCount)
699		return false;
700		}
701		}
702		return true;
703		}
704
705	<	// inherit Map javadoc
705	>	/**
706	>	* Returns the number of key-value mappings in this map.  If the
707	>	* map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
708	>	* <tt>Integer.MAX_VALUE</tt>.
709	>	*
710	>	* @return the number of key-value mappings in this map
711	>	*/
712		public int size() {
713	+	final Segment<K,V>[] segments = this.segments;
714	+	long sum = 0;
715	+	long check = 0;
716		int[] mc = new int[segments.length];
717	<	for (;;) {
718	<	long sum = 0;
717	>	// Try a few times to get accurate count. On failure due to
718	>	// continuous async changes in table, resort to locking.
719	>	for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
720	>	check = 0;
721	>	sum = 0;
722		int mcsum = 0;
723		for (int i = 0; i < segments.length; ++i) {
724		sum += segments[i].count;
725		mcsum += mc[i] = segments[i].modCount;
726		}
609	–	int check = 0;
727		if (mcsum != 0) {
728		for (int i = 0; i < segments.length; ++i) {
729		check += segments[i].count;
#	Line 616 | Line 733 | public class ConcurrentHashMap<K, V> ext
733		}
734		}
735		}
736	<	if (check == sum) {
737	<	if (sum > Integer.MAX_VALUE)
738	<	return Integer.MAX_VALUE;
739	<	else
740	<	return (int)sum;
741	<	}
736	>	if (check == sum)
737	>	break;
738	>	}
739	>	if (check != sum) { // Resort to locking all segments
740	>	sum = 0;
741	>	for (int i = 0; i < segments.length; ++i)
742	>	segments[i].lock();
743	>	for (int i = 0; i < segments.length; ++i)
744	>	sum += segments[i].count;
745	>	for (int i = 0; i < segments.length; ++i)
746	>	segments[i].unlock();
747		}
748	+	if (sum > Integer.MAX_VALUE)
749	+	return Integer.MAX_VALUE;
750	+	else
751	+	return (int)sum;
752		}
753
628	–
754		/**
755	<	* Returns the value to which the specified key is mapped in this table.
755	>	* Returns the value to which this map maps the specified key, or
756	>	* <tt>null</tt> if the map contains no mapping for the key.
757		*
758	<	* @param   key   a key in the table.
759	<	* @return  the value to which the key is mapped in this table;
760	<	*          <tt>null</tt> if the key is not mapped to any value in
761	<	*          this table.
636	<	* @throws  NullPointerException  if the key is
637	<	*               <tt>null</tt>.
758	>	* @param key key whose associated value is to be returned
759	>	* @return the value associated with <tt>key</tt> in this map, or
760	>	*         <tt>null</tt> if there is no mapping for <tt>key</tt>
761	>	* @throws NullPointerException if the specified key is null
762		*/
763		public V get(Object key) {
764		int hash = hash(key); // throws NullPointerException if key null
765	<	return segmentFor(hash).get((K) key, hash);
765	>	return segmentFor(hash).get(key, hash);
766		}
767
768		/**
769		* Tests if the specified object is a key in this table.
770		*
771	<	* @param   key   possible key.
772	<	* @return  <tt>true</tt> if and only if the specified object
773	<	*          is a key in this table, as determined by the
774	<	*          <tt>equals</tt> method; <tt>false</tt> otherwise.
775	<	* @throws  NullPointerException  if the key is
652	<	*               <tt>null</tt>.
771	>	* @param  key   possible key
772	>	* @return <tt>true</tt> if and only if the specified object
773	>	*         is a key in this table, as determined by the
774	>	*         <tt>equals</tt> method; <tt>false</tt> otherwise.
775	>	* @throws NullPointerException if the specified key is null
776		*/
777		public boolean containsKey(Object key) {
778		int hash = hash(key); // throws NullPointerException if key null
#	Line 662 | Line 785 | public class ConcurrentHashMap<K, V> ext
785		* traversal of the hash table, and so is much slower than
786		* method <tt>containsKey</tt>.
787		*
788	<	* @param value value whose presence in this map is to be tested.
788	>	* @param value value whose presence in this map is to be tested
789		* @return <tt>true</tt> if this map maps one or more keys to the
790	<	* specified value.
791	<	* @throws  NullPointerException  if the value is <tt>null</tt>.
790	>	*         specified value
791	>	* @throws NullPointerException if the specified value is null
792		*/
793		public boolean containsValue(Object value) {
794		if (value == null)
795		throw new NullPointerException();
796
797	+	// See explanation of modCount use above
798	+
799	+	final Segment<K,V>[] segments = this.segments;
800		int[] mc = new int[segments.length];
801	<	for (;;) {
801	>
802	>	// Try a few times without locking
803	>	for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
804		int sum = 0;
805		int mcsum = 0;
806		for (int i = 0; i < segments.length; ++i) {
#	Line 694 | Line 822 | public class ConcurrentHashMap<K, V> ext
822		if (cleanSweep)
823		return false;
824		}
825	+	// Resort to locking all segments
826	+	for (int i = 0; i < segments.length; ++i)
827	+	segments[i].lock();
828	+	boolean found = false;
829	+	try {
830	+	for (int i = 0; i < segments.length; ++i) {
831	+	if (segments[i].containsValue(value)) {
832	+	found = true;
833	+	break;
834	+	}
835	+	}
836	+	} finally {
837	+	for (int i = 0; i < segments.length; ++i)
838	+	segments[i].unlock();
839	+	}
840	+	return found;
841		}
842
843		/**
844		* Legacy method testing if some key maps into the specified value
845		* in this table.  This method is identical in functionality to
846	<	* {@link #containsValue}, and  exists solely to ensure
846	>	* {@link #containsValue}, and exists solely to ensure
847		* full compatibility with class {@link java.util.Hashtable},
848		* which supported this method prior to introduction of the
849		* Java Collections framework.
850
851	<	* @param      value   a value to search for.
852	<	* @return     <tt>true</tt> if and only if some key maps to the
853	<	*             <tt>value</tt> argument in this table as
854	<	*             determined by the <tt>equals</tt> method;
855	<	*             <tt>false</tt> otherwise.
856	<	* @throws  NullPointerException  if the value is <tt>null</tt>.
851	>	* @param  value a value to search for
852	>	* @return <tt>true</tt> if and only if some key maps to the
853	>	*         <tt>value</tt> argument in this table as
854	>	*         determined by the <tt>equals</tt> method;
855	>	*         <tt>false</tt> otherwise
856	>	* @throws NullPointerException if the specified value is null
857		*/
858		public boolean contains(Object value) {
859		return containsValue(value);
#	Line 718 | Line 862 | public class ConcurrentHashMap<K, V> ext
862		/**
863		* Maps the specified <tt>key</tt> to the specified
864		* <tt>value</tt> in this table. Neither the key nor the
865	<	* value can be <tt>null</tt>. <p>
865	>	* value can be <tt>null</tt>.
866		*
867	<	* The value can be retrieved by calling the <tt>get</tt> method
867	>	* <p> The value can be retrieved by calling the <tt>get</tt> method
868		* with a key that is equal to the original key.
869		*
870	<	* @param      key     the table key.
871	<	* @param      value   the value.
872	<	* @return     the previous value of the specified key in this table,
873	<	*             or <tt>null</tt> if it did not have one.
874	<	* @throws  NullPointerException  if the key or value is
731	<	*               <tt>null</tt>.
870	>	* @param key key with which the specified value is to be associated
871	>	* @param value value to be associated with the specified key
872	>	* @return the previous value associated with <tt>key</tt>, or
873	>	*         <tt>null</tt> if there was no mapping for <tt>key</tt>
874	>	* @throws NullPointerException if the specified key or value is null
875		*/
876		public V put(K key, V value) {
877		if (value == null)
#	Line 738 | Line 881 | public class ConcurrentHashMap<K, V> ext
881		}
882
883		/**
884	<	* If the specified key is not already associated
742	<	* with a value, associate it with the given value.
743	<	* This is equivalent to
744	<	* <pre>
745	<	*   if (!map.containsKey(key))
746	<	*      return map.put(key, value);
747	<	*   else
748	<	*      return map.get(key);
749	<	* </pre>
750	<	* Except that the action is performed atomically.
751	<	* @param key key with which the specified value is to be associated.
752	<	* @param value value to be associated with the specified key.
753	<	* @return previous value associated with specified key, or <tt>null</tt>
754	<	*         if there was no mapping for key.  A <tt>null</tt> return can
755	<	*         also indicate that the map previously associated <tt>null</tt>
756	<	*         with the specified key, if the implementation supports
757	<	*         <tt>null</tt> values.
758	<	*
759	<	* @throws UnsupportedOperationException if the <tt>put</tt> operation is
760	<	*            not supported by this map.
761	<	* @throws ClassCastException if the class of the specified key or value
762	<	*            prevents it from being stored in this map.
763	<	* @throws NullPointerException if the specified key or value is
764	<	*            <tt>null</tt>.
884	>	* {@inheritDoc}
885		*
886	<	**/
886	>	* @return the previous value associated with the specified key,
887	>	*         or <tt>null</tt> if there was no mapping for the key
888	>	* @throws NullPointerException if the specified key or value is null
889	>	*/
890		public V putIfAbsent(K key, V value) {
891		if (value == null)
892		throw new NullPointerException();
#	Line 771 | Line 894 | public class ConcurrentHashMap<K, V> ext
894		return segmentFor(hash).put(key, hash, value, true);
895		}
896
774	–
897		/**
898		* Copies all of the mappings from the specified map to this one.
777	–	*
899		* These mappings replace any mappings that this map had for any of the
900	<	* keys currently in the specified Map.
900	>	* keys currently in the specified map.
901		*
902	<	* @param t Mappings to be stored in this map.
902	>	* @param m mappings to be stored in this map
903		*/
904	<	public void putAll(Map<? extends K, ? extends V> t) {
905	<	for (Iterator<Map.Entry<? extends K, ? extends V>> it = (Iterator<Map.Entry<? extends K, ? extends V>>) t.entrySet().iterator(); it.hasNext(); ) {
904	>	public void putAll(Map<? extends K, ? extends V> m) {
905	>	for (Iterator<? extends Map.Entry<? extends K, ? extends V>> it = (Iterator<? extends Map.Entry<? extends K, ? extends V>>) m.entrySet().iterator(); it.hasNext(); ) {
906		Entry<? extends K, ? extends V> e = it.next();
907		put(e.getKey(), e.getValue());
908		}
909		}
910
911		/**
912	<	* Removes the key (and its corresponding value) from this
913	<	* table. This method does nothing if the key is not in the table.
912	>	* Removes the key (and its corresponding value) from this map.
913	>	* This method does nothing if the key is not in the map.
914		*
915	<	* @param   key   the key that needs to be removed.
916	<	* @return  the value to which the key had been mapped in this table,
917	<	*          or <tt>null</tt> if the key did not have a mapping.
918	<	* @throws  NullPointerException  if the key is
798	<	*               <tt>null</tt>.
915	>	* @param  key the key that needs to be removed
916	>	* @return the previous value associated with <tt>key</tt>, or
917	>	*         <tt>null</tt> if there was no mapping for <tt>key</tt>.
918	>	* @throws NullPointerException if the specified key is null
919		*/
920		public V remove(Object key) {
921		int hash = hash(key);
#	Line 803 | Line 923 | public class ConcurrentHashMap<K, V> ext
923		}
924
925		/**
926	<	* Remove entry for key only if currently mapped to given value.
927	<	* Acts as
928	<	* <pre>
809	<	*  if (map.get(key).equals(value)) {
810	<	*     map.remove(key);
811	<	*     return true;
812	<	* } else return false;
813	<	* </pre>
814	<	* except that the action is performed atomically.
815	<	* @param key key with which the specified value is associated.
816	<	* @param value value associated with the specified key.
817	<	* @return true if the value was removed
818	<	* @throws NullPointerException if the specified key is
819	<	*            <tt>null</tt>.
926	>	* {@inheritDoc}
927	>	*
928	>	* @throws NullPointerException if the specified key is null
929		*/
930		public boolean remove(Object key, Object value) {
931	+	if (value == null)
932	+	return false;
933		int hash = hash(key);
934		return segmentFor(hash).remove(key, hash, value) != null;
935		}
936
937		/**
938	<	* Removes all mappings from this map.
938	>	* {@inheritDoc}
939	>	*
940	>	* @throws NullPointerException if any of the arguments are null
941		*/
942	<	public void clear() {
943	<	for (int i = 0; i < segments.length; ++i)
944	<	segments[i].clear();
942	>	public boolean replace(K key, V oldValue, V newValue) {
943	>	if (oldValue == null || newValue == null)
944	>	throw new NullPointerException();
945	>	int hash = hash(key);
946	>	return segmentFor(hash).replace(key, hash, oldValue, newValue);
947		}
948
949	+	/**
950	+	* {@inheritDoc}
951	+	*
952	+	* @return the previous value associated with the specified key,
953	+	*         or <tt>null</tt> if there was no mapping for the key
954	+	* @throws NullPointerException if the specified key or value is null
955	+	*/
956	+	public V replace(K key, V value) {
957	+	if (value == null)
958	+	throw new NullPointerException();
959	+	int hash = hash(key);
960	+	return segmentFor(hash).replace(key, hash, value);
961	+	}
962
963		/**
964	<	* Returns a shallow copy of this
965	<	* <tt>ConcurrentHashMap</tt> instance: the keys and
966	<	* values themselves are not cloned.
967	<	*
968	<	* @return a shallow copy of this map.
841	<	*/
842	<	public Object clone() {
843	<	// We cannot call super.clone, since it would share final
844	<	// segments array, and there's no way to reassign finals.
845	<
846	<	float lf = segments[0].loadFactor;
847	<	int segs = segments.length;
848	<	int cap = (int)(size() / lf);
849	<	if (cap < segs) cap = segs;
850	<	ConcurrentHashMap<K,V> t = new ConcurrentHashMap<K,V>(cap, lf, segs);
851	<	t.putAll(this);
852	<	return t;
964	>	* Removes all of the mappings from this map.
965	>	*/
966	>	public void clear() {
967	>	for (int i = 0; i < segments.length; ++i)
968	>	segments[i].clear();
969		}
970
971		/**
972	<	* Returns a set view of the keys contained in this map.  The set is
973	<	* backed by the map, so changes to the map are reflected in the set, and
974	<	* vice-versa.  The set supports element removal, which removes the
975	<	* corresponding mapping from this map, via the <tt>Iterator.remove</tt>,
976	<	* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and
977	<	* <tt>clear</tt> operations.  It does not support the <tt>add</tt> or
972	>	* Returns a {@link Set} view of the keys contained in this map.
973	>	* The set is backed by the map, so changes to the map are
974	>	* reflected in the set, and vice-versa.  The set supports element
975	>	* removal, which removes the corresponding mapping from this map,
976	>	* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
977	>	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
978	>	* operations.  It does not support the <tt>add</tt> or
979		* <tt>addAll</tt> operations.
980	<	* The returned <tt>iterator</tt> is a "weakly consistent" iterator that
981	<	* will never throw {@link java.util.ConcurrentModificationException},
980	>	*
981	>	* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
982	>	* that will never throw {@link ConcurrentModificationException},
983		* and guarantees to traverse elements as they existed upon
984		* construction of the iterator, and may (but is not guaranteed to)
985		* reflect any modifications subsequent to construction.
868	–	*
869	–	* @return a set view of the keys contained in this map.
986		*/
987		public Set<K> keySet() {
988		Set<K> ks = keySet;
989		return (ks != null) ? ks : (keySet = new KeySet());
990		}
991
876	–
992		/**
993	<	* Returns a collection view of the values contained in this map.  The
994	<	* collection is backed by the map, so changes to the map are reflected in
995	<	* the collection, and vice-versa.  The collection supports element
996	<	* removal, which removes the corresponding mapping from this map, via the
997	<	* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
998	<	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations.
999	<	* It does not support the <tt>add</tt> or <tt>addAll</tt> operations.
1000	<	* The returned <tt>iterator</tt> is a "weakly consistent" iterator that
1001	<	* will never throw {@link java.util.ConcurrentModificationException},
993	>	* Returns a {@link Collection} view of the values contained in this map.
994	>	* The collection is backed by the map, so changes to the map are
995	>	* reflected in the collection, and vice-versa.  The collection
996	>	* supports element removal, which removes the corresponding
997	>	* mapping from this map, via the <tt>Iterator.remove</tt>,
998	>	* <tt>Collection.remove</tt>, <tt>removeAll</tt>,
999	>	* <tt>retainAll</tt>, and <tt>clear</tt> operations.  It does not
1000	>	* support the <tt>add</tt> or <tt>addAll</tt> operations.
1001	>	*
1002	>	* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
1003	>	* that will never throw {@link ConcurrentModificationException},
1004		* and guarantees to traverse elements as they existed upon
1005		* construction of the iterator, and may (but is not guaranteed to)
1006		* reflect any modifications subsequent to construction.
890	–	*
891	–	* @return a collection view of the values contained in this map.
1007		*/
1008		public Collection<V> values() {
1009		Collection<V> vs = values;
1010		return (vs != null) ? vs : (values = new Values());
1011		}
1012
898	–
1013		/**
1014	<	* Returns a collection view of the mappings contained in this map.  Each
1015	<	* element in the returned collection is a <tt>Map.Entry</tt>.  The
1016	<	* collection is backed by the map, so changes to the map are reflected in
1017	<	* the collection, and vice-versa.  The collection supports element
1018	<	* removal, which removes the corresponding mapping from the map, via the
1019	<	* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
1020	<	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations.
1021	<	* It does not support the <tt>add</tt> or <tt>addAll</tt> operations.
1022	<	* The returned <tt>iterator</tt> is a "weakly consistent" iterator that
1023	<	* will never throw {@link java.util.ConcurrentModificationException},
1014	>	* Returns a {@link Set} view of the mappings contained in this map.
1015	>	* The set is backed by the map, so changes to the map are
1016	>	* reflected in the set, and vice-versa.  The set supports element
1017	>	* removal, which removes the corresponding mapping from the map,
1018	>	* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
1019	>	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
1020	>	* operations.  It does not support the <tt>add</tt> or
1021	>	* <tt>addAll</tt> operations.
1022	>	*
1023	>	* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
1024	>	* that will never throw {@link ConcurrentModificationException},
1025		* and guarantees to traverse elements as they existed upon
1026		* construction of the iterator, and may (but is not guaranteed to)
1027		* reflect any modifications subsequent to construction.
913	–	*
914	–	* @return a collection view of the mappings contained in this map.
1028		*/
1029		public Set<Map.Entry<K,V>> entrySet() {
1030		Set<Map.Entry<K,V>> es = entrySet;
1031	<	return (es != null) ? es : (entrySet = (Set<Map.Entry<K,V>>) (Set) new EntrySet());
1031	>	return (es != null) ? es : (entrySet = new EntrySet());
1032		}
1033
921	–
1034		/**
1035		* Returns an enumeration of the keys in this table.
1036		*
1037	<	* @return  an enumeration of the keys in this table.
1038	<	* @see     #keySet
1037	>	* @return an enumeration of the keys in this table
1038	>	* @see #keySet
1039		*/
1040		public Enumeration<K> keys() {
1041		return new KeyIterator();
#	Line 931 | Line 1043 | public class ConcurrentHashMap<K, V> ext
1043
1044		/**
1045		* Returns an enumeration of the values in this table.
934	–	* Use the Enumeration methods on the returned object to fetch the elements
935	–	* sequentially.
1046		*
1047	<	* @return  an enumeration of the values in this table.
1048	<	* @see     #values
1047	>	* @return an enumeration of the values in this table
1048	>	* @see #values
1049		*/
1050		public Enumeration<V> elements() {
1051		return new ValueIterator();
#	Line 943 | Line 1053 | public class ConcurrentHashMap<K, V> ext
1053
1054		/* ---------------- Iterator Support -------------- */
1055
1056	<	private abstract class HashIterator {
1057	<	private int nextSegmentIndex;
1058	<	private int nextTableIndex;
1059	<	private HashEntry[] currentTable;
1060	<	private HashEntry<K, V> nextEntry;
1061	<	private HashEntry<K, V> lastReturned;
1056	>	abstract class HashIterator {
1057	>	int nextSegmentIndex;
1058	>	int nextTableIndex;
1059	>	HashEntry<K,V>[] currentTable;
1060	>	HashEntry<K, V> nextEntry;
1061	>	HashEntry<K, V> lastReturned;
1062
1063	<	private HashIterator() {
1063	>	HashIterator() {
1064		nextSegmentIndex = segments.length - 1;
1065		nextTableIndex = -1;
1066		advance();
#	Line 958 | Line 1068 | public class ConcurrentHashMap<K, V> ext
1068
1069		public boolean hasMoreElements() { return hasNext(); }
1070
1071	<	private void advance() {
1071	>	final void advance() {
1072		if (nextEntry != null && (nextEntry = nextEntry.next) != null)
1073		return;
1074
1075		while (nextTableIndex >= 0) {
1076	<	if ( (nextEntry = (HashEntry<K,V>)currentTable[nextTableIndex--]) != null)
1076	>	if ( (nextEntry = currentTable[nextTableIndex--]) != null)
1077		return;
1078		}
1079
1080		while (nextSegmentIndex >= 0) {
1081	<	Segment<K,V> seg = (Segment<K,V>)segments[nextSegmentIndex--];
1081	>	Segment<K,V> seg = segments[nextSegmentIndex--];
1082		if (seg.count != 0) {
1083		currentTable = seg.table;
1084		for (int j = currentTable.length - 1; j >= 0; --j) {
1085	<	if ( (nextEntry = (HashEntry<K,V>)currentTable[j]) != null) {
1085	>	if ( (nextEntry = currentTable[j]) != null) {
1086		nextTableIndex = j - 1;
1087		return;
1088		}
#	Line 999 | Line 1109 | public class ConcurrentHashMap<K, V> ext
1109		}
1110		}
1111
1112	<	private class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> {
1112	>	final class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> {
1113		public K next() { return super.nextEntry().key; }
1114		public K nextElement() { return super.nextEntry().key; }
1115		}
1116
1117	<	private class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> {
1117	>	final class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> {
1118		public V next() { return super.nextEntry().value; }
1119		public V nextElement() { return super.nextEntry().value; }
1120		}
1121
1122	<	private class EntryIterator extends HashIterator implements Iterator<Entry<K,V>> {
1123	<	public Map.Entry<K,V> next() { return super.nextEntry(); }
1122	>
1123	>
1124	>	/**
1125	>	* Entry iterator. Exported Entry objects must write-through
1126	>	* changes in setValue, even if the nodes have been cloned. So we
1127	>	* cannot return internal HashEntry objects. Instead, the iterator
1128	>	* itself acts as a forwarding pseudo-entry.
1129	>	*/
1130	>	final class EntryIterator extends HashIterator implements Map.Entry<K,V>, Iterator<Entry<K,V>> {
1131	>	public Map.Entry<K,V> next() {
1132	>	nextEntry();
1133	>	return this;
1134	>	}
1135	>
1136	>	public K getKey() {
1137	>	if (lastReturned == null)
1138	>	throw new IllegalStateException("Entry was removed");
1139	>	return lastReturned.key;
1140	>	}
1141	>
1142	>	public V getValue() {
1143	>	if (lastReturned == null)
1144	>	throw new IllegalStateException("Entry was removed");
1145	>	return ConcurrentHashMap.this.get(lastReturned.key);
1146	>	}
1147	>
1148	>	public V setValue(V value) {
1149	>	if (lastReturned == null)
1150	>	throw new IllegalStateException("Entry was removed");
1151	>	return ConcurrentHashMap.this.put(lastReturned.key, value);
1152	>	}
1153	>
1154	>	public boolean equals(Object o) {
1155	>	// If not acting as entry, just use default.
1156	>	if (lastReturned == null)
1157	>	return super.equals(o);
1158	>	if (!(o instanceof Map.Entry))
1159	>	return false;
1160	>	Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1161	>	return eq(getKey(), e.getKey()) && eq(getValue(), e.getValue());
1162	>	}
1163	>
1164	>	public int hashCode() {
1165	>	// If not acting as entry, just use default.
1166	>	if (lastReturned == null)
1167	>	return super.hashCode();
1168	>
1169	>	Object k = getKey();
1170	>	Object v = getValue();
1171	>	return ((k == null) ? 0 : k.hashCode()) ^
1172	>	((v == null) ? 0 : v.hashCode());
1173	>	}
1174	>
1175	>	public String toString() {
1176	>	// If not acting as entry, just use default.
1177	>	if (lastReturned == null)
1178	>	return super.toString();
1179	>	else
1180	>	return getKey() + "=" + getValue();
1181	>	}
1182	>
1183	>	boolean eq(Object o1, Object o2) {
1184	>	return (o1 == null ? o2 == null : o1.equals(o2));
1185	>	}
1186	>
1187		}
1188
1189	<	private class KeySet extends AbstractSet<K> {
1189	>	final class KeySet extends AbstractSet<K> {
1190		public Iterator<K> iterator() {
1191		return new KeyIterator();
1192		}
#	Line 1029 | Line 1202 | public class ConcurrentHashMap<K, V> ext
1202		public void clear() {
1203		ConcurrentHashMap.this.clear();
1204		}
1205	+	public Object[] toArray() {
1206	+	Collection<K> c = new ArrayList<K>();
1207	+	for (Iterator<K> i = iterator(); i.hasNext(); )
1208	+	c.add(i.next());
1209	+	return c.toArray();
1210	+	}
1211	+	public <T> T[] toArray(T[] a) {
1212	+	Collection<K> c = new ArrayList<K>();
1213	+	for (Iterator<K> i = iterator(); i.hasNext(); )
1214	+	c.add(i.next());
1215	+	return c.toArray(a);
1216	+	}
1217		}
1218
1219	<	private class Values extends AbstractCollection<V> {
1219	>	final class Values extends AbstractCollection<V> {
1220		public Iterator<V> iterator() {
1221		return new ValueIterator();
1222		}
#	Line 1044 | Line 1229 | public class ConcurrentHashMap<K, V> ext
1229		public void clear() {
1230		ConcurrentHashMap.this.clear();
1231		}
1232	+	public Object[] toArray() {
1233	+	Collection<V> c = new ArrayList<V>();
1234	+	for (Iterator<V> i = iterator(); i.hasNext(); )
1235	+	c.add(i.next());
1236	+	return c.toArray();
1237	+	}
1238	+	public <T> T[] toArray(T[] a) {
1239	+	Collection<V> c = new ArrayList<V>();
1240	+	for (Iterator<V> i = iterator(); i.hasNext(); )
1241	+	c.add(i.next());
1242	+	return c.toArray(a);
1243	+	}
1244		}
1245
1246	<	private class EntrySet extends AbstractSet<Map.Entry<K,V>> {
1246	>	final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
1247		public Iterator<Map.Entry<K,V>> iterator() {
1248		return new EntryIterator();
1249		}
1250		public boolean contains(Object o) {
1251		if (!(o instanceof Map.Entry))
1252		return false;
1253	<	Map.Entry<K,V> e = (Map.Entry<K,V>)o;
1253	>	Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1254		V v = ConcurrentHashMap.this.get(e.getKey());
1255		return v != null && v.equals(e.getValue());
1256		}
1257		public boolean remove(Object o) {
1258		if (!(o instanceof Map.Entry))
1259		return false;
1260	<	Map.Entry<K,V> e = (Map.Entry<K,V>)o;
1260	>	Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1261		return ConcurrentHashMap.this.remove(e.getKey(), e.getValue());
1262		}
1263		public int size() {
#	Line 1069 | Line 1266 | public class ConcurrentHashMap<K, V> ext
1266		public void clear() {
1267		ConcurrentHashMap.this.clear();
1268		}
1269	+	public Object[] toArray() {
1270	+	// Since we don't ordinarily have distinct Entry objects, we
1271	+	// must pack elements using exportable SimpleEntry
1272	+	Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>(size());
1273	+	for (Iterator<Map.Entry<K,V>> i = iterator(); i.hasNext(); )
1274	+	c.add(new AbstractMap.SimpleEntry<K,V>(i.next()));
1275	+	return c.toArray();
1276	+	}
1277	+	public <T> T[] toArray(T[] a) {
1278	+	Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>(size());
1279	+	for (Iterator<Map.Entry<K,V>> i = iterator(); i.hasNext(); )
1280	+	c.add(new AbstractMap.SimpleEntry<K,V>(i.next()));
1281	+	return c.toArray(a);
1282	+	}
1283	+
1284		}
1285
1286		/* ---------------- Serialization Support -------------- */
1287
1288		/**
1289	<	* Save the state of the <tt>ConcurrentHashMap</tt>
1290	<	* instance to a stream (i.e.,
1079	<	* serialize it).
1289	>	* Save the state of the <tt>ConcurrentHashMap</tt> instance to a
1290	>	* stream (i.e., serialize it).
1291		* @param s the stream
1292		* @serialData
1293		* the key (Object) and value (Object)
#	Line 1087 | Line 1298 | public class ConcurrentHashMap<K, V> ext
1298		s.defaultWriteObject();
1299
1300		for (int k = 0; k < segments.length; ++k) {
1301	<	Segment<K,V> seg = (Segment<K,V>)segments[k];
1301	>	Segment<K,V> seg = segments[k];
1302		seg.lock();
1303		try {
1304	<	HashEntry[] tab = seg.table;
1304	>	HashEntry<K,V>[] tab = seg.table;
1305		for (int i = 0; i < tab.length; ++i) {
1306	<	for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i]; e != null; e = e.next) {
1306	>	for (HashEntry<K,V> e = tab[i]; e != null; e = e.next) {
1307		s.writeObject(e.key);
1308		s.writeObject(e.value);
1309		}
#	Line 1106 | Line 1317 | public class ConcurrentHashMap<K, V> ext
1317		}
1318
1319		/**
1320	<	* Reconstitute the <tt>ConcurrentHashMap</tt>
1321	<	* instance from a stream (i.e.,
1111	<	* deserialize it).
1320	>	* Reconstitute the <tt>ConcurrentHashMap</tt> instance from a
1321	>	* stream (i.e., deserialize it).
1322		* @param s the stream
1323		*/
1324		private void readObject(java.io.ObjectInputStream s)
#	Line 1117 | Line 1327 | public class ConcurrentHashMap<K, V> ext
1327
1328		// Initialize each segment to be minimally sized, and let grow.
1329		for (int i = 0; i < segments.length; ++i) {
1330	<	segments[i].setTable(new HashEntry[1]);
1330	>	segments[i].setTable((HashEntry<K,V>[])HashEntry.newArray(1));
1331		}
1332
1333		// Read the keys and values, and put the mappings in the table
#	Line 1130 | Line 1340 | public class ConcurrentHashMap<K, V> ext
1340		}
1341		}
1342		}
1133	–

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