[ViewVC] Diff of: jsr166/jsr166/src/main/java/util/concurrent/ConcurrentHashMap.java

Comparing jsr166/src/main/java/util/concurrent/ConcurrentHashMap.java (file contents):
Revision 1.54 by dl, Fri Dec 31 13:00:39 2004 UTC vs.
Revision 1.112 by jsr166, Fri Jun 3 02:28:05 2011 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, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package java.util.concurrent;
#	Line 33 \| Line 33 \| import java.io.ObjectOutputStream;
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
37	<	* {@link ConcurrentModificationException}. However, iterators are
38	<	* designed to be used by only one thread at a 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
#	Line 59 \| Line 58 \| import java.io.ObjectOutputStream;
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
64	<	* 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">
65	>	* <a href="{@docRoot}/../technotes/guides/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
71	>	* @param <V> the type of mapped values
72		*/
73		public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
74		implements ConcurrentMap<K, V>, Serializable {
#	Line 78 \| Line 76 \| public class ConcurrentHashMap<K, V> ext
76
77		/*
78		* The basic strategy is to subdivide the table among Segments,
79	<	* each of which itself is a concurrently readable hash table.
79	>	* each of which itself is a concurrently readable hash table. To
80	>	* reduce footprint, all but one segments are constructed only
81	>	* when first needed (see ensureSegment). To maintain visibility
82	>	* in the presence of lazy construction, accesses to segments as
83	>	* well as elements of segment's table must use volatile access,
84	>	* which is done via Unsafe within methods segmentAt etc
85	>	* below. These provide the functionality of AtomicReferenceArrays
86	>	* but reduce the levels of indirection. Additionally,
87	>	* volatile-writes of table elements and entry "next" fields
88	>	* within locked operations use the cheaper "lazySet" forms of
89	>	* writes (via putOrderedObject) because these writes are always
90	>	* followed by lock releases that maintain sequential consistency
91	>	* of table updates.
92	>	*
93	>	* Historical note: The previous version of this class relied
94	>	* heavily on "final" fields, which avoided some volatile reads at
95	>	* the expense of a large initial footprint. Some remnants of
96	>	* that design (including forced construction of segment 0) exist
97	>	* to ensure serialization compatibility.
98		*/
99
100		/* ---------------- Constants -------------- */
101
102		/**
103	<	* The default initial number of table slots for this table.
104	<	* Used when not otherwise specified in constructor.
103	>	* The default initial capacity for this table,
104	>	* used when not otherwise specified in a constructor.
105	>	*/
106	>	static final int DEFAULT_INITIAL_CAPACITY = 16;
107	>
108	>	/**
109	>	* The default load factor for this table, used when not
110	>	* otherwise specified in a constructor.
111		*/
112	<	static int DEFAULT_INITIAL_CAPACITY = 16;
112	>	static final float DEFAULT_LOAD_FACTOR = 0.75f;
113	>
114	>	/**
115	>	* The default concurrency level for this table, used when not
116	>	* otherwise specified in a constructor.
117	>	*/
118	>	static final int DEFAULT_CONCURRENCY_LEVEL = 16;
119
120		/**
121		* The maximum capacity, used if a higher value is implicitly
122		* specified by either of the constructors with arguments. MUST
123	<	* be a power of two <= 1<<30 to ensure that entries are indexible
123	>	* be a power of two <= 1<<30 to ensure that entries are indexable
124		* using ints.
125		*/
126	<	static final int MAXIMUM_CAPACITY = 1 << 30;
126	>	static final int MAXIMUM_CAPACITY = 1 << 30;
127
128		/**
129	<	* The default load factor for this table. Used when not
130	<	* otherwise specified in constructor.
129	>	* The minimum capacity for per-segment tables. Must be a power
130	>	* of two, at least two to avoid immediate resizing on next use
131	>	* after lazy construction.
132		*/
133	<	static final float DEFAULT_LOAD_FACTOR = 0.75f;
105	<
106	<	/**
107	<	* The default number of concurrency control segments.
108	<	**/
109	<	static final int DEFAULT_SEGMENTS = 16;
133	>	static final int MIN_SEGMENT_TABLE_CAPACITY = 2;
134
135		/**
136		* The maximum number of segments to allow; used to bound
137	<	* constructor arguments.
137	>	* constructor arguments. Must be power of two less than 1 << 24.
138		*/
139		static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
140
#	Line 127 \| Line 151 \| public class ConcurrentHashMap<K, V> ext
151		/**
152		* Mask value for indexing into segments. The upper bits of a
153		* key's hash code are used to choose the segment.
154	<	**/
154	>	*/
155		final int segmentMask;
156
157		/**
158		* Shift value for indexing within segments.
159	<	**/
159	>	*/
160		final int segmentShift;
161
162		/**
163	<	* The segments, each of which is a specialized hash table
163	>	* The segments, each of which is a specialized hash table.
164		*/
165	<	final Segment[] segments;
165	>	final Segment<K,V>[] segments;
166
167		transient Set<K> keySet;
168		transient Set<Map.Entry<K,V>> entrySet;
169		transient Collection<V> values;
170
147	–	/* ---------------- Small Utilities -------------- */
148	–
149	–	/**
150	–	* Returns a hash code for non-null Object x.
151	–	* Uses the same hash code spreader as most other java.util hash tables.
152	–	* @param x the object serving as a key
153	–	* @return the hash code
154	–	*/
155	–	static int hash(Object x) {
156	–	int h = x.hashCode();
157	–	h += ~(h << 9);
158	–	h ^= (h >>> 14);
159	–	h += (h << 4);
160	–	h ^= (h >>> 10);
161	–	return h;
162	–	}
163	–
164	–	/**
165	–	* Returns the segment that should be used for key with given hash
166	–	* @param hash the hash code for the key
167	–	* @return the segment
168	–	*/
169	–	final Segment<K,V> segmentFor(int hash) {
170	–	return (Segment<K,V>) segments[(hash >>> segmentShift) & segmentMask];
171	–	}
172	–
173	–	/* ---------------- Inner Classes -------------- */
174	–
171		/**
172		* ConcurrentHashMap list entry. Note that this is never exported
173	<	* out as a user-visible Map.Entry.
178	<	*
179	<	* Because the value field is volatile, not final, it is legal wrt
180	<	* the Java Memory Model for an unsynchronized reader to see null
181	<	* instead of initial value when read via a data race. Although a
182	<	* reordering leading to this is not likely to ever actually
183	<	* occur, the Segment.readValueUnderLock method is used as a
184	<	* backup in case a null (pre-initialized) value is ever seen in
185	<	* an unsynchronized access method.
173	>	* out as a user-visible Map.Entry.
174		*/
175		static final class HashEntry<K,V> {
188	–	final K key;
176		final int hash;
177	+	final K key;
178		volatile V value;
179	<	final HashEntry<K,V> next;
179	>	volatile HashEntry<K,V> next;
180
181	<	HashEntry(K key, int hash, HashEntry<K,V> next, V value) {
194	<	this.key = key;
181	>	HashEntry(int hash, K key, V value, HashEntry<K,V> next) {
182		this.hash = hash;
183	<	this.next = next;
183	>	this.key = key;
184		this.value = value;
185	+	this.next = next;
186	+	}
187	+
188	+	/**
189	+	* Sets next field with volatile write semantics. (See above
190	+	* about use of putOrderedObject.)
191	+	*/
192	+	final void setNext(HashEntry<K,V> n) {
193	+	UNSAFE.putOrderedObject(this, nextOffset, n);
194	+	}
195	+
196	+	// Unsafe mechanics
197	+	static final sun.misc.Unsafe UNSAFE;
198	+	static final long nextOffset;
199	+	static {
200	+	try {
201	+	UNSAFE = sun.misc.Unsafe.getUnsafe();
202	+	Class<?> k = HashEntry.class;
203	+	nextOffset = UNSAFE.objectFieldOffset
204	+	(k.getDeclaredField("next"));
205	+	} catch (Exception e) {
206	+	throw new Error(e);
207	+	}
208		}
209		}
210
211		/**
212	+	* Gets the ith element of given table (if nonnull) with volatile
213	+	* read semantics. Note: This is manually integrated into a few
214	+	* performance-sensitive methods to reduce call overhead.
215	+	*/
216	+	@SuppressWarnings("unchecked")
217	+	static final <K,V> HashEntry<K,V> entryAt(HashEntry<K,V>[] tab, int i) {
218	+	return (tab == null) ? null :
219	+	(HashEntry<K,V>) UNSAFE.getObjectVolatile
220	+	(tab, ((long)i << TSHIFT) + TBASE);
221	+	}
222	+
223	+	/**
224	+	* Sets the ith element of given table, with volatile write
225	+	* semantics. (See above about use of putOrderedObject.)
226	+	*/
227	+	static final <K,V> void setEntryAt(HashEntry<K,V>[] tab, int i,
228	+	HashEntry<K,V> e) {
229	+	UNSAFE.putOrderedObject(tab, ((long)i << TSHIFT) + TBASE, e);
230	+	}
231	+
232	+	/**
233	+	* Applies a supplemental hash function to a given hashCode, which
234	+	* defends against poor quality hash functions. This is critical
235	+	* because ConcurrentHashMap uses power-of-two length hash tables,
236	+	* that otherwise encounter collisions for hashCodes that do not
237	+	* differ in lower or upper bits.
238	+	*/
239	+	private static int hash(int h) {
240	+	// Spread bits to regularize both segment and index locations,
241	+	// using variant of single-word Wang/Jenkins hash.
242	+	h += (h << 15) ^ 0xffffcd7d;
243	+	h ^= (h >>> 10);
244	+	h += (h << 3);
245	+	h ^= (h >>> 6);
246	+	h += (h << 2) + (h << 14);
247	+	return h ^ (h >>> 16);
248	+	}
249	+
250	+	/**
251		* Segments are specialized versions of hash tables. This
252		* subclasses from ReentrantLock opportunistically, just to
253		* simplify some locking and avoid separate construction.
254	<	**/
254	>	*/
255		static final class Segment<K,V> extends ReentrantLock implements Serializable {
256		/*
257	<	* Segments maintain a table of entry lists that are ALWAYS
258	<	* kept in a consistent state, so can be read without locking.
259	<	* Next fields of nodes are immutable (final). All list
260	<	* additions are performed at the front of each bin. This
261	<	* makes it easy to check changes, and also fast to traverse.
262	<	* When nodes would otherwise be changed, new nodes are
214	<	* created to replace them. This works well for hash tables
215	<	* since the bin lists tend to be short. (The average length
216	<	* is less than two for the default load factor threshold.)
217	<	*
218	<	* Read operations can thus proceed without locking, but rely
219	<	* on selected uses of volatiles to ensure that completed
220	<	* write operations performed by other threads are
221	<	* noticed. For most purposes, the "count" field, tracking the
222	<	* number of elements, serves as that volatile variable
223	<	* ensuring visibility. This is convenient because this field
224	<	* needs to be read in many read operations anyway:
225	<	*
226	<	* - All (unsynchronized) read operations must first read the
227	<	* "count" field, and should not look at table entries if
228	<	* it is 0.
257	>	* Segments maintain a table of entry lists that are always
258	>	* kept in a consistent state, so can be read (via volatile
259	>	* reads of segments and tables) without locking. This
260	>	* requires replicating nodes when necessary during table
261	>	* resizing, so the old lists can be traversed by readers
262	>	* still using old version of table.
263		*
264	<	* - All (synchronized) write operations should write to
265	<	* the "count" field after structurally changing any bin.
266	<	* The operations must not take any action that could even
267	<	* momentarily cause a concurrent read operation to see
268	<	* inconsistent data. This is made easier by the nature of
269	<	* the read operations in Map. For example, no operation
270	<	* can reveal that the table has grown but the threshold
271	<	* has not yet been updated, so there are no atomicity
272	<	* requirements for this with respect to reads.
273	<	*
274	<	* As a guide, all critical volatile reads and writes to the
275	<	* count field are marked in code comments.
264	>	* This class defines only mutative methods requiring locking.
265	>	* Except as noted, the methods of this class perform the
266	>	* per-segment versions of ConcurrentHashMap methods. (Other
267	>	* methods are integrated directly into ConcurrentHashMap
268	>	* methods.) These mutative methods use a form of controlled
269	>	* spinning on contention via methods scanAndLock and
270	>	* scanAndLockForPut. These intersperse tryLocks with
271	>	* traversals to locate nodes. The main benefit is to absorb
272	>	* cache misses (which are very common for hash tables) while
273	>	* obtaining locks so that traversal is faster once
274	>	* acquired. We do not actually use the found nodes since they
275	>	* must be re-acquired under lock anyway to ensure sequential
276	>	* consistency of updates (and in any case may be undetectably
277	>	* stale), but they will normally be much faster to re-locate.
278	>	* Also, scanAndLockForPut speculatively creates a fresh node
279	>	* to use in put if no node is found.
280		*/
281
282		private static final long serialVersionUID = 2249069246763182397L;
283
284		/**
285	<	* The number of elements in this segment's region.
286	<	**/
287	<	transient volatile int count;
285	>	* The maximum number of times to tryLock in a prescan before
286	>	* possibly blocking on acquire in preparation for a locked
287	>	* segment operation. On multiprocessors, using a bounded
288	>	* number of retries maintains cache acquired while locating
289	>	* nodes.
290	>	*/
291	>	static final int MAX_SCAN_RETRIES =
292	>	Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1;
293
294		/**
295	<	* Number of updates that alter the size of the table. This is
296	<	* used during bulk-read methods to make sure they see a
254	<	* consistent snapshot: If modCounts change during a traversal
255	<	* of segments computing size or checking containsValue, then
256	<	* we might have an inconsistent view of state so (usually)
257	<	* must retry.
295	>	* The per-segment table. Elements are accessed via
296	>	* entryAt/setEntryAt providing volatile semantics.
297		*/
298	<	transient int modCount;
298	>	transient volatile HashEntry<K,V>[] table;
299
300		/**
301	<	* The table is rehashed when its size exceeds this threshold.
302	<	* (The value of this field is always (int)(capacity *
264	<	* loadFactor).)
301	>	* The number of elements. Accessed only either within locks
302	>	* or among other volatile reads that maintain visibility.
303		*/
304	<	transient int threshold;
304	>	transient int count;
305
306		/**
307	<	* The per-segment table. Declared as a raw type, casted
308	<	* to HashEntry<K,V> on each use.
307	>	* The total number of mutative operations in this segment.
308	>	* Even though this may overflows 32 bits, it provides
309	>	* sufficient accuracy for stability checks in CHM isEmpty()
310	>	* and size() methods. Accessed only either within locks or
311	>	* among other volatile reads that maintain visibility.
312		*/
313	<	transient volatile HashEntry[] table;
313	>	transient int modCount;
314	>
315	>	/**
316	>	* The table is rehashed when its size exceeds this threshold.
317	>	* (The value of this field is always <tt>(int)(capacity *
318	>	* loadFactor)</tt>.)
319	>	*/
320	>	transient int threshold;
321
322		/**
323		* The load factor for the hash table. Even though this value
#	Line 279 \| Line 327 \| public class ConcurrentHashMap<K, V> ext
327		*/
328		final float loadFactor;
329
330	<	Segment(int initialCapacity, float lf) {
331	<	loadFactor = lf;
332	<	setTable(new HashEntry[initialCapacity]);
330	>	Segment(float lf, int threshold, HashEntry<K,V>[] tab) {
331	>	this.loadFactor = lf;
332	>	this.threshold = threshold;
333	>	this.table = tab;
334		}
335
336	<	/**
337	<	* Set table to new HashEntry array.
338	<	* Call only while holding lock or in constructor.
339	<	**/
291	<	void setTable(HashEntry[] newTable) {
292	<	threshold = (int)(newTable.length * loadFactor);
293	<	table = newTable;
294	<	}
295	<
296	<	/**
297	<	* Return properly casted first entry of bin for given hash
298	<	*/
299	<	HashEntry<K,V> getFirst(int hash) {
300	<	HashEntry[] tab = table;
301	<	return (HashEntry<K,V>) tab[hash & (tab.length - 1)];
302	<	}
303	<
304	<	/**
305	<	* Read value field of an entry under lock. Called if value
306	<	* field ever appears to be null. This is possible only if a
307	<	* compiler happens to reorder a HashEntry initialization with
308	<	* its table assignment, which is legal under memory model
309	<	* but is not known to ever occur.
310	<	*/
311	<	V readValueUnderLock(HashEntry<K,V> e) {
312	<	lock();
336	>	final V put(K key, int hash, V value, boolean onlyIfAbsent) {
337	>	HashEntry<K,V> node = tryLock() ? null :
338	>	scanAndLockForPut(key, hash, value);
339	>	V oldValue;
340		try {
341	<	return e.value;
342	<	} finally {
343	<	unlock();
344	<	}
345	<	}
346	<
347	<	/* Specialized implementations of map methods */
348	<
349	<	V get(Object key, int hash) {
350	<	if (count != 0) { // read-volatile
351	<	HashEntry<K,V> e = getFirst(hash);
352	<	while (e != null) {
353	<	if (e.hash == hash && key.equals(e.key)) {
354	<	V v = e.value;
355	<	if (v != null)
356	<	return v;
330	<	return readValueUnderLock(e); // recheck
341	>	HashEntry<K,V>[] tab = table;
342	>	int index = (tab.length - 1) & hash;
343	>	HashEntry<K,V> first = entryAt(tab, index);
344	>	for (HashEntry<K,V> e = first;;) {
345	>	if (e != null) {
346	>	K k;
347	>	if ((k = e.key) == key \|\|
348	>	(e.hash == hash && key.equals(k))) {
349	>	oldValue = e.value;
350	>	if (!onlyIfAbsent) {
351	>	e.value = value;
352	>	++modCount;
353	>	}
354	>	break;
355	>	}
356	>	e = e.next;
357		}
358	<	e = e.next;
359	<	}
360	<	}
361	<	return null;
362	<	}
363	<
364	<	boolean containsKey(Object key, int hash) {
365	<	if (count != 0) { // read-volatile
366	<	HashEntry<K,V> e = getFirst(hash);
367	<	while (e != null) {
368	<	if (e.hash == hash && key.equals(e.key))
369	<	return true;
370	<	e = e.next;
371	<	}
346	<	}
347	<	return false;
348	<	}
349	<
350	<	boolean containsValue(Object value) {
351	<	if (count != 0) { // read-volatile
352	<	HashEntry[] tab = table;
353	<	int len = tab.length;
354	<	for (int i = 0 ; i < len; i++) {
355	<	for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i];
356	<	e != null ;
357	<	e = e.next) {
358	<	V v = e.value;
359	<	if (v == null) // recheck
360	<	v = readValueUnderLock(e);
361	<	if (value.equals(v))
362	<	return true;
358	>	else {
359	>	if (node != null)
360	>	node.setNext(first);
361	>	else
362	>	node = new HashEntry<K,V>(hash, key, value, first);
363	>	int c = count + 1;
364	>	if (c > threshold && tab.length < MAXIMUM_CAPACITY)
365	>	rehash(node);
366	>	else
367	>	setEntryAt(tab, index, node);
368	>	++modCount;
369	>	count = c;
370	>	oldValue = null;
371	>	break;
372		}
373		}
365	–	}
366	–	return false;
367	–	}
368	–
369	–	boolean replace(K key, int hash, V oldValue, V newValue) {
370	–	lock();
371	–	try {
372	–	HashEntry<K,V> e = getFirst(hash);
373	–	while (e != null && (e.hash != hash \|\| !key.equals(e.key)))
374	–	e = e.next;
375	–
376	–	boolean replaced = false;
377	–	if (e != null && oldValue.equals(e.value)) {
378	–	replaced = true;
379	–	e.value = newValue;
380	–	}
381	–	return replaced;
374		} finally {
375		unlock();
376		}
377	+	return oldValue;
378		}
379
380	<	V replace(K key, int hash, V newValue) {
381	<	lock();
382	<	try {
383	<	HashEntry<K,V> e = getFirst(hash);
384	<	while (e != null && (e.hash != hash \|\| !key.equals(e.key)))
385	<	e = e.next;
393	<
394	<	V oldValue = null;
395	<	if (e != null) {
396	<	oldValue = e.value;
397	<	e.value = newValue;
398	<	}
399	<	return oldValue;
400	<	} finally {
401	<	unlock();
402	<	}
403	<	}
404	<
405	<
406	<	V put(K key, int hash, V value, boolean onlyIfAbsent) {
407	<	lock();
408	<	try {
409	<	int c = count;
410	<	if (c++ > threshold) // ensure capacity
411	<	rehash();
412	<	HashEntry[] tab = table;
413	<	int index = hash & (tab.length - 1);
414	<	HashEntry<K,V> first = (HashEntry<K,V>) tab[index];
415	<	HashEntry<K,V> e = first;
416	<	while (e != null && (e.hash != hash \|\| !key.equals(e.key)))
417	<	e = e.next;
418	<
419	<	V oldValue;
420	<	if (e != null) {
421	<	oldValue = e.value;
422	<	if (!onlyIfAbsent)
423	<	e.value = value;
424	<	}
425	<	else {
426	<	oldValue = null;
427	<	++modCount;
428	<	tab[index] = new HashEntry<K,V>(key, hash, first, value);
429	<	count = c; // write-volatile
430	<	}
431	<	return oldValue;
432	<	} finally {
433	<	unlock();
434	<	}
435	<	}
436	<
437	<	void rehash() {
438	<	HashEntry[] oldTable = table;
439	<	int oldCapacity = oldTable.length;
440	<	if (oldCapacity >= MAXIMUM_CAPACITY)
441	<	return;
442	<
380	>	/**
381	>	* Doubles size of table and repacks entries, also adding the
382	>	* given node to new table
383	>	*/
384	>	@SuppressWarnings("unchecked")
385	>	private void rehash(HashEntry<K,V> node) {
386		/*
387	<	* Reclassify nodes in each list to new Map. Because we are
388	<	* using power-of-two expansion, the elements from each bin
389	<	* must either stay at same index, or move with a power of two
390	<	* offset. We eliminate unnecessary node creation by catching
391	<	* cases where old nodes can be reused because their next
392	<	* fields won't change. Statistically, at the default
393	<	* threshold, only about one-sixth of them need cloning when
394	<	* a table doubles. The nodes they replace will be garbage
395	<	* collectable as soon as they are no longer referenced by any
396	<	* reader thread that may be in the midst of traversing table
397	<	* right now.
387	>	* Reclassify nodes in each list to new table. Because we
388	>	* are using power-of-two expansion, the elements from
389	>	* each bin must either stay at same index, or move with a
390	>	* power of two offset. We eliminate unnecessary node
391	>	* creation by catching cases where old nodes can be
392	>	* reused because their next fields won't change.
393	>	* Statistically, at the default threshold, only about
394	>	* one-sixth of them need cloning when a table
395	>	* doubles. The nodes they replace will be garbage
396	>	* collectable as soon as they are no longer referenced by
397	>	* any reader thread that may be in the midst of
398	>	* concurrently traversing table. Entry accesses use plain
399	>	* array indexing because they are followed by volatile
400	>	* table write.
401		*/
402	<
403	<	HashEntry[] newTable = new HashEntry[oldCapacity << 1];
404	<	threshold = (int)(newTable.length * loadFactor);
405	<	int sizeMask = newTable.length - 1;
402	>	HashEntry<K,V>[] oldTable = table;
403	>	int oldCapacity = oldTable.length;
404	>	int newCapacity = oldCapacity << 1;
405	>	threshold = (int)(newCapacity * loadFactor);
406	>	HashEntry<K,V>[] newTable =
407	>	(HashEntry<K,V>[]) new HashEntry<?,?>[newCapacity];
408	>	int sizeMask = newCapacity - 1;
409		for (int i = 0; i < oldCapacity ; i++) {
410	<	// We need to guarantee that any existing reads of old Map can
462	<	// proceed. So we cannot yet null out each bin.
463	<	HashEntry<K,V> e = (HashEntry<K,V>)oldTable[i];
464	<
410	>	HashEntry<K,V> e = oldTable[i];
411		if (e != null) {
412		HashEntry<K,V> next = e.next;
413		int idx = e.hash & sizeMask;
414	<
469	<	// Single node on list
470	<	if (next == null)
414	>	if (next == null) // Single node on list
415		newTable[idx] = e;
416	<
473	<	else {
474	<	// Reuse trailing consecutive sequence at same slot
416	>	else { // Reuse consecutive sequence at same slot
417		HashEntry<K,V> lastRun = e;
418		int lastIdx = idx;
419		for (HashEntry<K,V> last = next;
#	Line 484 \| Line 426 \| public class ConcurrentHashMap<K, V> ext
426		}
427		}
428		newTable[lastIdx] = lastRun;
429	<
488	<	// Clone all remaining nodes
429	>	// Clone remaining nodes
430		for (HashEntry<K,V> p = e; p != lastRun; p = p.next) {
431	<	int k = p.hash & sizeMask;
432	<	HashEntry<K,V> n = (HashEntry<K,V>)newTable[k];
433	<	newTable[k] = new HashEntry<K,V>(p.key, p.hash,
434	<	n, p.value);
431	>	V v = p.value;
432	>	int h = p.hash;
433	>	int k = h & sizeMask;
434	>	HashEntry<K,V> n = newTable[k];
435	>	newTable[k] = new HashEntry<K,V>(h, p.key, v, n);
436		}
437		}
438		}
439		}
440	+	int nodeIndex = node.hash & sizeMask; // add the new node
441	+	node.setNext(newTable[nodeIndex]);
442	+	newTable[nodeIndex] = node;
443		table = newTable;
444		}
445
446		/**
447	+	* Scans for a node containing given key while trying to
448	+	* acquire lock, creating and returning one if not found. Upon
449	+	* return, guarantees that lock is held. Unlike in most
450	+	* methods, calls to method equals are not screened: Since
451	+	* traversal speed doesn't matter, we might as well help warm
452	+	* up the associated code and accesses as well.
453	+	*
454	+	* @return a new node if key not found, else null
455	+	*/
456	+	private HashEntry<K,V> scanAndLockForPut(K key, int hash, V value) {
457	+	HashEntry<K,V> first = entryForHash(this, hash);
458	+	HashEntry<K,V> e = first;
459	+	HashEntry<K,V> node = null;
460	+	int retries = -1; // negative while locating node
461	+	while (!tryLock()) {
462	+	HashEntry<K,V> f; // to recheck first below
463	+	if (retries < 0) {
464	+	if (e == null) {
465	+	if (node == null) // speculatively create node
466	+	node = new HashEntry<K,V>(hash, key, value, null);
467	+	retries = 0;
468	+	}
469	+	else if (key.equals(e.key))
470	+	retries = 0;
471	+	else
472	+	e = e.next;
473	+	}
474	+	else if (++retries > MAX_SCAN_RETRIES) {
475	+	lock();
476	+	break;
477	+	}
478	+	else if ((retries & 1) == 0 &&
479	+	(f = entryForHash(this, hash)) != first) {
480	+	e = first = f; // re-traverse if entry changed
481	+	retries = -1;
482	+	}
483	+	}
484	+	return node;
485	+	}
486	+
487	+	/**
488	+	* Scans for a node containing the given key while trying to
489	+	* acquire lock for a remove or replace operation. Upon
490	+	* return, guarantees that lock is held. Note that we must
491	+	* lock even if the key is not found, to ensure sequential
492	+	* consistency of updates.
493	+	*/
494	+	private void scanAndLock(Object key, int hash) {
495	+	// similar to but simpler than scanAndLockForPut
496	+	HashEntry<K,V> first = entryForHash(this, hash);
497	+	HashEntry<K,V> e = first;
498	+	int retries = -1;
499	+	while (!tryLock()) {
500	+	HashEntry<K,V> f;
501	+	if (retries < 0) {
502	+	if (e == null \|\| key.equals(e.key))
503	+	retries = 0;
504	+	else
505	+	e = e.next;
506	+	}
507	+	else if (++retries > MAX_SCAN_RETRIES) {
508	+	lock();
509	+	break;
510	+	}
511	+	else if ((retries & 1) == 0 &&
512	+	(f = entryForHash(this, hash)) != first) {
513	+	e = first = f;
514	+	retries = -1;
515	+	}
516	+	}
517	+	}
518	+
519	+	/**
520		* Remove; match on key only if value null, else match both.
521		*/
522	<	V remove(Object key, int hash, Object value) {
523	<	lock();
522	>	final V remove(Object key, int hash, Object value) {
523	>	if (!tryLock())
524	>	scanAndLock(key, hash);
525	>	V oldValue = null;
526		try {
527	<	int c = count - 1;
528	<	HashEntry[] tab = table;
529	<	int index = hash & (tab.length - 1);
530	<	HashEntry<K,V> first = (HashEntry<K,V>)tab[index];
531	<	HashEntry<K,V> e = first;
532	<	while (e != null && (e.hash != hash \|\| !key.equals(e.key)))
533	<	e = e.next;
527	>	HashEntry<K,V>[] tab = table;
528	>	int index = (tab.length - 1) & hash;
529	>	HashEntry<K,V> e = entryAt(tab, index);
530	>	HashEntry<K,V> pred = null;
531	>	while (e != null) {
532	>	K k;
533	>	HashEntry<K,V> next = e.next;
534	>	if ((k = e.key) == key \|\|
535	>	(e.hash == hash && key.equals(k))) {
536	>	V v = e.value;
537	>	if (value == null \|\| value == v \|\| value.equals(v)) {
538	>	if (pred == null)
539	>	setEntryAt(tab, index, next);
540	>	else
541	>	pred.setNext(next);
542	>	++modCount;
543	>	--count;
544	>	oldValue = v;
545	>	}
546	>	break;
547	>	}
548	>	pred = e;
549	>	e = next;
550	>	}
551	>	} finally {
552	>	unlock();
553	>	}
554	>	return oldValue;
555	>	}
556
557	<	V oldValue = null;
558	<	if (e != null) {
559	<	V v = e.value;
560	<	if (value == null \|\| value.equals(v)) {
561	<	oldValue = v;
562	<	// All entries following removed node can stay
563	<	// in list, but all preceding ones need to be
564	<	// cloned.
557	>	final boolean replace(K key, int hash, V oldValue, V newValue) {
558	>	if (!tryLock())
559	>	scanAndLock(key, hash);
560	>	boolean replaced = false;
561	>	try {
562	>	HashEntry<K,V> e;
563	>	for (e = entryForHash(this, hash); e != null; e = e.next) {
564	>	K k;
565	>	if ((k = e.key) == key \|\|
566	>	(e.hash == hash && key.equals(k))) {
567	>	if (oldValue.equals(e.value)) {
568	>	e.value = newValue;
569	>	++modCount;
570	>	replaced = true;
571	>	}
572	>	break;
573	>	}
574	>	}
575	>	} finally {
576	>	unlock();
577	>	}
578	>	return replaced;
579	>	}
580	>
581	>	final V replace(K key, int hash, V value) {
582	>	if (!tryLock())
583	>	scanAndLock(key, hash);
584	>	V oldValue = null;
585	>	try {
586	>	HashEntry<K,V> e;
587	>	for (e = entryForHash(this, hash); e != null; e = e.next) {
588	>	K k;
589	>	if ((k = e.key) == key \|\|
590	>	(e.hash == hash && key.equals(k))) {
591	>	oldValue = e.value;
592	>	e.value = value;
593		++modCount;
594	<	HashEntry<K,V> newFirst = e.next;
525	<	for (HashEntry<K,V> p = first; p != e; p = p.next)
526	<	newFirst = new HashEntry<K,V>(p.key, p.hash,
527	<	newFirst, p.value);
528	<	tab[index] = newFirst;
529	<	count = c; // write-volatile
594	>	break;
595		}
596		}
597	<	return oldValue;
597	>	} finally {
598	>	unlock();
599	>	}
600	>	return oldValue;
601	>	}
602	>
603	>	final void clear() {
604	>	lock();
605	>	try {
606	>	HashEntry<K,V>[] tab = table;
607	>	for (int i = 0; i < tab.length ; i++)
608	>	setEntryAt(tab, i, null);
609	>	++modCount;
610	>	count = 0;
611		} finally {
612		unlock();
613		}
614		}
615	+	}
616	+
617	+	// Accessing segments
618
619	<	void clear() {
620	<	if (count != 0) {
621	<	lock();
622	<	try {
623	<	HashEntry[] tab = table;
624	<	for (int i = 0; i < tab.length ; i++)
625	<	tab[i] = null;
626	<	++modCount;
627	<	count = 0; // write-volatile
628	<	} finally {
629	<	unlock();
619	>	/**
620	>	* Gets the jth element of given segment array (if nonnull) with
621	>	* volatile element access semantics via Unsafe. (The null check
622	>	* can trigger harmlessly only during deserialization.) Note:
623	>	* because each element of segments array is set only once (using
624	>	* fully ordered writes), some performance-sensitive methods rely
625	>	* on this method only as a recheck upon null reads.
626	>	*/
627	>	@SuppressWarnings("unchecked")
628	>	static final <K,V> Segment<K,V> segmentAt(Segment<K,V>[] ss, int j) {
629	>	long u = (j << SSHIFT) + SBASE;
630	>	return ss == null ? null :
631	>	(Segment<K,V>) UNSAFE.getObjectVolatile(ss, u);
632	>	}
633	>
634	>	/**
635	>	* Returns the segment for the given index, creating it and
636	>	* recording in segment table (via CAS) if not already present.
637	>	*
638	>	* @param k the index
639	>	* @return the segment
640	>	*/
641	>	@SuppressWarnings("unchecked")
642	>	private Segment<K,V> ensureSegment(int k) {
643	>	final Segment<K,V>[] ss = this.segments;
644	>	long u = (k << SSHIFT) + SBASE; // raw offset
645	>	Segment<K,V> seg;
646	>	if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) == null) {
647	>	Segment<K,V> proto = ss[0]; // use segment 0 as prototype
648	>	int cap = proto.table.length;
649	>	float lf = proto.loadFactor;
650	>	int threshold = (int)(cap * lf);
651	>	HashEntry<K,V>[] tab = (HashEntry<K,V>[])new HashEntry<?,?>[cap];
652	>	if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u))
653	>	== null) { // recheck
654	>	Segment<K,V> s = new Segment<K,V>(lf, threshold, tab);
655	>	while ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u))
656	>	== null) {
657	>	if (UNSAFE.compareAndSwapObject(ss, u, null, seg = s))
658	>	break;
659		}
660		}
661		}
662	+	return seg;
663		}
664
665	+	// Hash-based segment and entry accesses
666
667	+	/**
668	+	* Gets the segment for the given hash code.
669	+	*/
670	+	@SuppressWarnings("unchecked")
671	+	private Segment<K,V> segmentForHash(int h) {
672	+	long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
673	+	return (Segment<K,V>) UNSAFE.getObjectVolatile(segments, u);
674	+	}
675	+
676	+	/**
677	+	* Gets the table entry for the given segment and hash code.
678	+	*/
679	+	@SuppressWarnings("unchecked")
680	+	static final <K,V> HashEntry<K,V> entryForHash(Segment<K,V> seg, int h) {
681	+	HashEntry<K,V>[] tab;
682	+	return (seg == null \|\| (tab = seg.table) == null) ? null :
683	+	(HashEntry<K,V>) UNSAFE.getObjectVolatile
684	+	(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
685	+	}
686
687		/* ---------------- Public operations -------------- */
688
689		/**
690		* Creates a new, empty map with the specified initial
691	<	* capacity and the specified load factor.
691	>	* capacity, load factor and concurrency level.
692		*
693		* @param initialCapacity the initial capacity. The implementation
694		* performs internal sizing to accommodate this many elements.
695		* @param loadFactor the load factor threshold, used to control resizing.
696	+	* Resizing may be performed when the average number of elements per
697	+	* bin exceeds this threshold.
698		* @param concurrencyLevel the estimated number of concurrently
699		* updating threads. The implementation performs internal sizing
700	<	* to try to accommodate this many threads.
700	>	* to try to accommodate this many threads.
701		* @throws IllegalArgumentException if the initial capacity is
702		* negative or the load factor or concurrencyLevel are
703		* nonpositive.
704		*/
705	+	@SuppressWarnings("unchecked")
706		public ConcurrentHashMap(int initialCapacity,
707		float loadFactor, int concurrencyLevel) {
708		if (!(loadFactor > 0) \|\| initialCapacity < 0 \|\| concurrencyLevel <= 0)
709		throw new IllegalArgumentException();
576	–
710		if (concurrencyLevel > MAX_SEGMENTS)
711		concurrencyLevel = MAX_SEGMENTS;
579	–
712		// Find power-of-two sizes best matching arguments
713		int sshift = 0;
714		int ssize = 1;
#	Line 584 \| Line 716 \| public class ConcurrentHashMap<K, V> ext
716		++sshift;
717		ssize <<= 1;
718		}
719	<	segmentShift = 32 - sshift;
720	<	segmentMask = ssize - 1;
589	<	this.segments = new Segment[ssize];
590	<
719	>	this.segmentShift = 32 - sshift;
720	>	this.segmentMask = ssize - 1;
721		if (initialCapacity > MAXIMUM_CAPACITY)
722		initialCapacity = MAXIMUM_CAPACITY;
723		int c = initialCapacity / ssize;
724		if (c * ssize < initialCapacity)
725		++c;
726	<	int cap = 1;
726	>	int cap = MIN_SEGMENT_TABLE_CAPACITY;
727		while (cap < c)
728		cap <<= 1;
729	<
730	<	for (int i = 0; i < this.segments.length; ++i)
731	<	this.segments[i] = new Segment<K,V>(cap, loadFactor);
729	>	// create segments and segments[0]
730	>	Segment<K,V> s0 =
731	>	new Segment<K,V>(loadFactor, (int)(cap * loadFactor),
732	>	(HashEntry<K,V>[])new HashEntry<?,?>[cap]);
733	>	Segment<K,V>[] ss = (Segment<K,V>[])new Segment<?,?>[ssize];
734	>	UNSAFE.putOrderedObject(ss, SBASE, s0); // ordered write of segments[0]
735	>	this.segments = ss;
736		}
737
738		/**
739	<	* Creates a new, empty map with the specified initial
740	<	* capacity, and with default load factor and concurrencyLevel.
739	>	* Creates a new, empty map with the specified initial capacity
740	>	* and load factor and with the default concurrencyLevel (16).
741		*
742		* @param initialCapacity The implementation performs internal
743		* sizing to accommodate this many elements.
744	+	* @param loadFactor the load factor threshold, used to control resizing.
745	+	* Resizing may be performed when the average number of elements per
746	+	* bin exceeds this threshold.
747	+	* @throws IllegalArgumentException if the initial capacity of
748	+	* elements is negative or the load factor is nonpositive
749	+	*
750	+	* @since 1.6
751	+	*/
752	+	public ConcurrentHashMap(int initialCapacity, float loadFactor) {
753	+	this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
754	+	}
755	+
756	+	/**
757	+	* Creates a new, empty map with the specified initial capacity,
758	+	* and with default load factor (0.75) and concurrencyLevel (16).
759	+	*
760	+	* @param initialCapacity the initial capacity. The implementation
761	+	* performs internal sizing to accommodate this many elements.
762		* @throws IllegalArgumentException if the initial capacity of
763		* elements is negative.
764		*/
765		public ConcurrentHashMap(int initialCapacity) {
766	<	this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
766	>	this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
767		}
768
769		/**
770	<	* Creates a new, empty map with a default initial capacity,
771	<	* load factor, and concurrencyLevel.
770	>	* Creates a new, empty map with a default initial capacity (16),
771	>	* load factor (0.75) and concurrencyLevel (16).
772		*/
773		public ConcurrentHashMap() {
774	<	this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
774	>	this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
775		}
776
777		/**
778	<	* Creates a new map with the same mappings as the given map. The
779	<	* map is created with a capacity of twice the number of mappings in
780	<	* the given map or 11 (whichever is greater), and a default load factor
781	<	* and concurrencyLevel.
782	<	* @param t the map
778	>	* Creates a new map with the same mappings as the given map.
779	>	* The map is created with a capacity of 1.5 times the number
780	>	* of mappings in the given map or 16 (whichever is greater),
781	>	* and a default load factor (0.75) and concurrencyLevel (16).
782	>	*
783	>	* @param m the map
784		*/
785	<	public ConcurrentHashMap(Map<? extends K, ? extends V> t) {
786	<	this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1,
787	<	11),
788	<	DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
789	<	putAll(t);
785	>	public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
786	>	this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
787	>	DEFAULT_INITIAL_CAPACITY),
788	>	DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
789	>	putAll(m);
790		}
791
792	<	// inherit Map javadoc
792	>	/**
793	>	* Returns <tt>true</tt> if this map contains no key-value mappings.
794	>	*
795	>	* @return <tt>true</tt> if this map contains no key-value mappings
796	>	*/
797		public boolean isEmpty() {
641	–	final Segment[] segments = this.segments;
798		/*
799	<	* We keep track of per-segment modCounts to avoid ABA
800	<	* problems in which an element in one segment was added and
801	<	* in another removed during traversal, in which case the
802	<	* table was never actually empty at any point. Note the
803	<	* similar use of modCounts in the size() and containsValue()
804	<	* methods, which are the only other methods also susceptible
805	<	* to ABA problems.
799	>	* Sum per-segment modCounts to avoid mis-reporting when
800	>	* elements are concurrently added and removed in one segment
801	>	* while checking another, in which case the table was never
802	>	* actually empty at any point. (The sum ensures accuracy up
803	>	* through at least 1<<31 per-segment modifications before
804	>	* recheck.) Methods size() and containsValue() use similar
805	>	* constructions for stability checks.
806		*/
807	<	int[] mc = new int[segments.length];
808	<	int mcsum = 0;
809	<	for (int i = 0; i < segments.length; ++i) {
810	<	if (segments[i].count != 0)
811	<	return false;
812	<	else
657	<	mcsum += mc[i] = segments[i].modCount;
658	<	}
659	<	// If mcsum happens to be zero, then we know we got a snapshot
660	<	// before any modifications at all were made. This is
661	<	// probably common enough to bother tracking.
662	<	if (mcsum != 0) {
663	<	for (int i = 0; i < segments.length; ++i) {
664	<	if (segments[i].count != 0 \|\|
665	<	mc[i] != segments[i].modCount)
807	>	long sum = 0L;
808	>	final Segment<K,V>[] segments = this.segments;
809	>	for (int j = 0; j < segments.length; ++j) {
810	>	Segment<K,V> seg = segmentAt(segments, j);
811	>	if (seg != null) {
812	>	if (seg.count != 0)
813		return false;
814	+	sum += seg.modCount;
815		}
816		}
817	+	if (sum != 0L) { // recheck unless no modifications
818	+	for (int j = 0; j < segments.length; ++j) {
819	+	Segment<K,V> seg = segmentAt(segments, j);
820	+	if (seg != null) {
821	+	if (seg.count != 0)
822	+	return false;
823	+	sum -= seg.modCount;
824	+	}
825	+	}
826	+	if (sum != 0L)
827	+	return false;
828	+	}
829		return true;
830		}
831
832	<	// inherit Map javadoc
832	>	/**
833	>	* Returns the number of key-value mappings in this map. If the
834	>	* map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
835	>	* <tt>Integer.MAX_VALUE</tt>.
836	>	*
837	>	* @return the number of key-value mappings in this map
838	>	*/
839		public int size() {
674	–	final Segment[] segments = this.segments;
675	–	long sum = 0;
676	–	long check = 0;
677	–	int[] mc = new int[segments.length];
840		// Try a few times to get accurate count. On failure due to
841		// continuous async changes in table, resort to locking.
842	<	for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
843	<	check = 0;
844	<	sum = 0;
845	<	int mcsum = 0;
846	<	for (int i = 0; i < segments.length; ++i) {
847	<	sum += segments[i].count;
848	<	mcsum += mc[i] = segments[i].modCount;
849	<	}
850	<	if (mcsum != 0) {
851	<	for (int i = 0; i < segments.length; ++i) {
852	<	check += segments[i].count;
853	<	if (mc[i] != segments[i].modCount) {
692	<	check = -1; // force retry
693	<	break;
694	<	}
842	>	final Segment<K,V>[] segments = this.segments;
843	>	final int segmentCount = segments.length;
844	>
845	>	long previousSum = 0L;
846	>	for (int retries = -1; retries < RETRIES_BEFORE_LOCK; retries++) {
847	>	long sum = 0L; // sum of modCounts
848	>	long size = 0L;
849	>	for (int i = 0; i < segmentCount; i++) {
850	>	Segment<K,V> segment = segmentAt(segments, i);
851	>	if (segment != null) {
852	>	sum += segment.modCount;
853	>	size += segment.count;
854		}
855		}
856	<	if (check == sum)
857	<	break;
856	>	if (sum == previousSum)
857	>	return ((size >>> 31) == 0) ? (int) size : Integer.MAX_VALUE;
858	>	previousSum = sum;
859		}
700	–	if (check != sum) { // Resort to locking all segments
701	–	sum = 0;
702	–	for (int i = 0; i < segments.length; ++i)
703	–	segments[i].lock();
704	–	for (int i = 0; i < segments.length; ++i)
705	–	sum += segments[i].count;
706	–	for (int i = 0; i < segments.length; ++i)
707	–	segments[i].unlock();
708	–	}
709	–	if (sum > Integer.MAX_VALUE)
710	–	return Integer.MAX_VALUE;
711	–	else
712	–	return (int)sum;
713	–	}
860
861	+	long size = 0L;
862	+	for (int i = 0; i < segmentCount; i++) {
863	+	Segment<K,V> segment = ensureSegment(i);
864	+	segment.lock();
865	+	size += segment.count;
866	+	}
867	+	for (int i = 0; i < segmentCount; i++)
868	+	segments[i].unlock();
869	+	return ((size >>> 31) == 0) ? (int) size : Integer.MAX_VALUE;
870	+	}
871
872		/**
873	<	* Returns the value to which the specified key is mapped in this table.
874	<	*
875	<	* @param key a key in the table.
876	<	* @return the value to which the key is mapped in this table;
877	<	* <tt>null</tt> if the key is not mapped to any value in
878	<	* this table.
879	<	* @throws NullPointerException if the key is
880	<	* <tt>null</tt>.
873	>	* Returns the value to which the specified key is mapped,
874	>	* or {@code null} if this map contains no mapping for the key.
875	>	*
876	>	* <p>More formally, if this map contains a mapping from a key
877	>	* {@code k} to a value {@code v} such that {@code key.equals(k)},
878	>	* then this method returns {@code v}; otherwise it returns
879	>	* {@code null}. (There can be at most one such mapping.)
880	>	*
881	>	* @throws NullPointerException if the specified key is null
882		*/
883		public V get(Object key) {
884	<	int hash = hash(key); // throws NullPointerException if key null
885	<	return segmentFor(hash).get(key, hash);
884	>	Segment<K,V> s; // manually integrate access methods to reduce overhead
885	>	HashEntry<K,V>[] tab;
886	>	int h = hash(key.hashCode());
887	>	long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
888	>	if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null &&
889	>	(tab = s.table) != null) {
890	>	for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile
891	>	(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
892	>	e != null; e = e.next) {
893	>	K k;
894	>	if ((k = e.key) == key \|\| (e.hash == h && key.equals(k)))
895	>	return e.value;
896	>	}
897	>	}
898	>	return null;
899		}
900
901		/**
902		* Tests if the specified object is a key in this table.
903		*
904	<	* @param key possible key.
905	<	* @return <tt>true</tt> if and only if the specified object
906	<	* is a key in this table, as determined by the
907	<	* <tt>equals</tt> method; <tt>false</tt> otherwise.
908	<	* @throws NullPointerException if the key is
739	<	* <tt>null</tt>.
904	>	* @param key possible key
905	>	* @return <tt>true</tt> if and only if the specified object
906	>	* is a key in this table, as determined by the
907	>	* <tt>equals</tt> method; <tt>false</tt> otherwise.
908	>	* @throws NullPointerException if the specified key is null
909		*/
910	+	@SuppressWarnings("unchecked")
911		public boolean containsKey(Object key) {
912	<	int hash = hash(key); // throws NullPointerException if key null
913	<	return segmentFor(hash).containsKey(key, hash);
912	>	Segment<K,V> s; // same as get() except no need for volatile value read
913	>	HashEntry<K,V>[] tab;
914	>	int h = hash(key.hashCode());
915	>	long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
916	>	if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null &&
917	>	(tab = s.table) != null) {
918	>	for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile
919	>	(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
920	>	e != null; e = e.next) {
921	>	K k;
922	>	if ((k = e.key) == key \|\| (e.hash == h && key.equals(k)))
923	>	return true;
924	>	}
925	>	}
926	>	return false;
927		}
928
929		/**
#	Line 749 \| Line 932 \| public class ConcurrentHashMap<K, V> ext
932		* traversal of the hash table, and so is much slower than
933		* method <tt>containsKey</tt>.
934		*
935	<	* @param value value whose presence in this map is to be tested.
935	>	* @param value value whose presence in this map is to be tested
936		* @return <tt>true</tt> if this map maps one or more keys to the
937	<	* specified value.
938	<	* @throws NullPointerException if the value is <tt>null</tt>.
937	>	* specified value
938	>	* @throws NullPointerException if the specified value is null
939		*/
940		public boolean containsValue(Object value) {
941	+	// Same idea as size()
942		if (value == null)
943		throw new NullPointerException();
944	<
945	<	// See explanation of modCount use above
946	<
763	<	final Segment[] segments = this.segments;
764	<	int[] mc = new int[segments.length];
765	<
766	<	// Try a few times without locking
767	<	for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
768	<	int sum = 0;
769	<	int mcsum = 0;
770	<	for (int i = 0; i < segments.length; ++i) {
771	<	int c = segments[i].count;
772	<	mcsum += mc[i] = segments[i].modCount;
773	<	if (segments[i].containsValue(value))
774	<	return true;
775	<	}
776	<	boolean cleanSweep = true;
777	<	if (mcsum != 0) {
778	<	for (int i = 0; i < segments.length; ++i) {
779	<	int c = segments[i].count;
780	<	if (mc[i] != segments[i].modCount) {
781	<	cleanSweep = false;
782	<	break;
783	<	}
784	<	}
785	<	}
786	<	if (cleanSweep)
787	<	return false;
788	<	}
789	<	// Resort to locking all segments
790	<	for (int i = 0; i < segments.length; ++i)
791	<	segments[i].lock();
792	<	boolean found = false;
944	>	final Segment<K,V>[] segments = this.segments;
945	>	long previousSum = 0L;
946	>	int lockCount = 0;
947		try {
948	<	for (int i = 0; i < segments.length; ++i) {
949	<	if (segments[i].containsValue(value)) {
950	<	found = true;
951	<	break;
948	>	for (int retries = -1; ; retries++) {
949	>	long sum = 0L; // sum of modCounts
950	>	for (int j = 0; j < segments.length; j++) {
951	>	Segment<K,V> segment;
952	>	if (retries == RETRIES_BEFORE_LOCK) {
953	>	segment = ensureSegment(j);
954	>	segment.lock();
955	>	lockCount++;
956	>	} else {
957	>	segment = segmentAt(segments, j);
958	>	if (segment == null)
959	>	continue;
960	>	}
961	>	HashEntry<K,V>[] tab = segment.table;
962	>	if (tab != null) {
963	>	for (int i = 0 ; i < tab.length; i++) {
964	>	HashEntry<K,V> e;
965	>	for (e = entryAt(tab, i); e != null; e = e.next) {
966	>	V v = e.value;
967	>	if (v != null && value.equals(v))
968	>	return true;
969	>	}
970	>	}
971	>	sum += segment.modCount;
972	>	}
973		}
974	+	if ((retries >= 0 && sum == previousSum) \|\| lockCount > 0)
975	+	return false;
976	+	previousSum = sum;
977		}
978		} finally {
979	<	for (int i = 0; i < segments.length; ++i)
980	<	segments[i].unlock();
979	>	for (int j = 0; j < lockCount; j++)
980	>	segments[j].unlock();
981		}
804	–	return found;
982		}
983
984		/**
985		* Legacy method testing if some key maps into the specified value
986		* in this table. This method is identical in functionality to
987	<	* {@link #containsValue}, and exists solely to ensure
987	>	* {@link #containsValue}, and exists solely to ensure
988		* full compatibility with class {@link java.util.Hashtable},
989		* which supported this method prior to introduction of the
990		* Java Collections framework.
991	<
992	<	* @param value a value to search for.
993	<	* @return <tt>true</tt> if and only if some key maps to the
994	<	* <tt>value</tt> argument in this table as
995	<	* determined by the <tt>equals</tt> method;
996	<	* <tt>false</tt> otherwise.
997	<	* @throws NullPointerException if the value is <tt>null</tt>.
991	>	*
992	>	* @param value a value to search for
993	>	* @return <tt>true</tt> if and only if some key maps to the
994	>	* <tt>value</tt> argument in this table as
995	>	* determined by the <tt>equals</tt> method;
996	>	* <tt>false</tt> otherwise
997	>	* @throws NullPointerException if the specified value is null
998		*/
999		public boolean contains(Object value) {
1000		return containsValue(value);
1001		}
1002
1003		/**
1004	<	* Maps the specified <tt>key</tt> to the specified
1005	<	* <tt>value</tt> in this table. Neither the key nor the
829	<	* value can be <tt>null</tt>.
1004	>	* Maps the specified key to the specified value in this table.
1005	>	* Neither the key nor the value can be null.
1006		*
1007		* <p> The value can be retrieved by calling the <tt>get</tt> method
1008		* with a key that is equal to the original key.
1009		*
1010	<	* @param key the table key.
1011	<	* @param value the value.
1012	<	* @return the previous value of the specified key in this table,
1013	<	* or <tt>null</tt> if it did not have one.
1014	<	* @throws NullPointerException if the key or value is
839	<	* <tt>null</tt>.
1010	>	* @param key key with which the specified value is to be associated
1011	>	* @param value value to be associated with the specified key
1012	>	* @return the previous value associated with <tt>key</tt>, or
1013	>	* <tt>null</tt> if there was no mapping for <tt>key</tt>
1014	>	* @throws NullPointerException if the specified key or value is null
1015		*/
1016	+	@SuppressWarnings("unchecked")
1017		public V put(K key, V value) {
1018	+	Segment<K,V> s;
1019		if (value == null)
1020		throw new NullPointerException();
1021	<	int hash = hash(key);
1022	<	return segmentFor(hash).put(key, hash, value, false);
1021	>	int hash = hash(key.hashCode());
1022	>	int j = (hash >>> segmentShift) & segmentMask;
1023	>	if ((s = (Segment<K,V>)UNSAFE.getObject // nonvolatile; recheck
1024	>	(segments, (j << SSHIFT) + SBASE)) == null) // in ensureSegment
1025	>	s = ensureSegment(j);
1026	>	return s.put(key, hash, value, false);
1027		}
1028
1029		/**
1030	<	* If the specified key is not already associated
1031	<	* with a value, associate it with the given value.
1032	<	* This is equivalent to
1033	<	* <pre>
1034	<	* if (!map.containsKey(key))
854	<	* return map.put(key, value);
855	<	* else
856	<	* return map.get(key);
857	<	* </pre>
858	<	* Except that the action is performed atomically.
859	<	* @param key key with which the specified value is to be associated.
860	<	* @param value value to be associated with the specified key.
861	<	* @return previous value associated with specified key, or <tt>null</tt>
862	<	* if there was no mapping for key.
863	<	* @throws NullPointerException if the specified key or value is
864	<	* <tt>null</tt>.
1030	>	* {@inheritDoc}
1031	>	*
1032	>	* @return the previous value associated with the specified key,
1033	>	* or <tt>null</tt> if there was no mapping for the key
1034	>	* @throws NullPointerException if the specified key or value is null
1035		*/
1036	+	@SuppressWarnings("unchecked")
1037		public V putIfAbsent(K key, V value) {
1038	+	Segment<K,V> s;
1039		if (value == null)
1040		throw new NullPointerException();
1041	<	int hash = hash(key);
1042	<	return segmentFor(hash).put(key, hash, value, true);
1041	>	int hash = hash(key.hashCode());
1042	>	int j = (hash >>> segmentShift) & segmentMask;
1043	>	if ((s = (Segment<K,V>)UNSAFE.getObject
1044	>	(segments, (j << SSHIFT) + SBASE)) == null)
1045	>	s = ensureSegment(j);
1046	>	return s.put(key, hash, value, true);
1047		}
1048
873	–
1049		/**
1050		* Copies all of the mappings from the specified map to this one.
876	–	*
1051		* These mappings replace any mappings that this map had for any of the
1052	<	* keys currently in the specified Map.
1052	>	* keys currently in the specified map.
1053		*
1054	<	* @param t Mappings to be stored in this map.
1054	>	* @param m mappings to be stored in this map
1055		*/
1056	<	public void putAll(Map<? extends K, ? extends V> t) {
1057	<	for (Iterator<? extends Map.Entry<? extends K, ? extends V>> it = (Iterator<? extends Map.Entry<? extends K, ? extends V>>) t.entrySet().iterator(); it.hasNext(); ) {
884	<	Entry<? extends K, ? extends V> e = it.next();
1056	>	public void putAll(Map<? extends K, ? extends V> m) {
1057	>	for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
1058		put(e.getKey(), e.getValue());
886	–	}
1059		}
1060
1061		/**
1062	<	* Removes the key (and its corresponding value) from this
1063	<	* table. This method does nothing if the key is not in the table.
1062	>	* Removes the key (and its corresponding value) from this map.
1063	>	* This method does nothing if the key is not in the map.
1064		*
1065	<	* @param key the key that needs to be removed.
1066	<	* @return the value to which the key had been mapped in this table,
1067	<	* or <tt>null</tt> if the key did not have a mapping.
1068	<	* @throws NullPointerException if the key is
897	<	* <tt>null</tt>.
1065	>	* @param key the key that needs to be removed
1066	>	* @return the previous value associated with <tt>key</tt>, or
1067	>	* <tt>null</tt> if there was no mapping for <tt>key</tt>
1068	>	* @throws NullPointerException if the specified key is null
1069		*/
1070		public V remove(Object key) {
1071	<	int hash = hash(key);
1072	<	return segmentFor(hash).remove(key, hash, null);
1071	>	int hash = hash(key.hashCode());
1072	>	Segment<K,V> s = segmentForHash(hash);
1073	>	return s == null ? null : s.remove(key, hash, null);
1074		}
1075
1076		/**
1077	<	* Remove entry for key only if currently mapped to given value.
1078	<	* Acts as
1079	<	* <pre>
908	<	* if (map.get(key).equals(value)) {
909	<	* map.remove(key);
910	<	* return true;
911	<	* } else return false;
912	<	* </pre>
913	<	* except that the action is performed atomically.
914	<	* @param key key with which the specified value is associated.
915	<	* @param value value associated with the specified key.
916	<	* @return true if the value was removed
917	<	* @throws NullPointerException if the specified key is
918	<	* <tt>null</tt>.
1077	>	* {@inheritDoc}
1078	>	*
1079	>	* @throws NullPointerException if the specified key is null
1080		*/
1081		public boolean remove(Object key, Object value) {
1082	<	int hash = hash(key);
1083	<	return segmentFor(hash).remove(key, hash, value) != null;
1082	>	int hash = hash(key.hashCode());
1083	>	Segment<K,V> s;
1084	>	return value != null && (s = segmentForHash(hash)) != null &&
1085	>	s.remove(key, hash, value) != null;
1086		}
1087
925	–
1088		/**
1089	<	* Replace entry for key only if currently mapped to given value.
1090	<	* Acts as
1091	<	* <pre>
930	<	* if (map.get(key).equals(oldValue)) {
931	<	* map.put(key, newValue);
932	<	* return true;
933	<	* } else return false;
934	<	* </pre>
935	<	* except that the action is performed atomically.
936	<	* @param key key with which the specified value is associated.
937	<	* @param oldValue value expected to be associated with the specified key.
938	<	* @param newValue value to be associated with the specified key.
939	<	* @return true if the value was replaced
940	<	* @throws NullPointerException if the specified key or values are
941	<	* <tt>null</tt>.
1089	>	* {@inheritDoc}
1090	>	*
1091	>	* @throws NullPointerException if any of the arguments are null
1092		*/
1093		public boolean replace(K key, V oldValue, V newValue) {
1094	+	int hash = hash(key.hashCode());
1095		if (oldValue == null \|\| newValue == null)
1096		throw new NullPointerException();
1097	<	int hash = hash(key);
1098	<	return segmentFor(hash).replace(key, hash, oldValue, newValue);
1097	>	Segment<K,V> s = segmentForHash(hash);
1098	>	return s != null && s.replace(key, hash, oldValue, newValue);
1099		}
1100
1101		/**
1102	<	* Replace entry for key only if currently mapped to some value.
1103	<	* Acts as
1104	<	* <pre>
1105	<	* if ((map.containsKey(key)) {
1106	<	* return map.put(key, value);
956	<	* } else return null;
957	<	* </pre>
958	<	* except that the action is performed atomically.
959	<	* @param key key with which the specified value is associated.
960	<	* @param value value to be associated with the specified key.
961	<	* @return previous value associated with specified key, or <tt>null</tt>
962	<	* if there was no mapping for key.
963	<	* @throws NullPointerException if the specified key or value is
964	<	* <tt>null</tt>.
1102	>	* {@inheritDoc}
1103	>	*
1104	>	* @return the previous value associated with the specified key,
1105	>	* or <tt>null</tt> if there was no mapping for the key
1106	>	* @throws NullPointerException if the specified key or value is null
1107		*/
1108		public V replace(K key, V value) {
1109	+	int hash = hash(key.hashCode());
1110		if (value == null)
1111		throw new NullPointerException();
1112	<	int hash = hash(key);
1113	<	return segmentFor(hash).replace(key, hash, value);
1112	>	Segment<K,V> s = segmentForHash(hash);
1113	>	return s == null ? null : s.replace(key, hash, value);
1114		}
1115
973	–
1116		/**
1117	<	* Removes all mappings from this map.
1117	>	* Removes all of the mappings from this map.
1118		*/
1119		public void clear() {
1120	<	for (int i = 0; i < segments.length; ++i)
1121	<	segments[i].clear();
1120	>	final Segment<K,V>[] segments = this.segments;
1121	>	for (int j = 0; j < segments.length; ++j) {
1122	>	Segment<K,V> s = segmentAt(segments, j);
1123	>	if (s != null)
1124	>	s.clear();
1125	>	}
1126		}
1127
1128		/**
1129	<	* Returns a set view of the keys contained in this map. The set is
1130	<	* backed by the map, so changes to the map are reflected in the set, and
1131	<	* vice-versa. The set supports element removal, which removes the
1132	<	* corresponding mapping from this map, via the <tt>Iterator.remove</tt>,
1133	<	* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and
1134	<	* <tt>clear</tt> operations. It does not support the <tt>add</tt> or
1129	>	* Returns a {@link Set} view of the keys contained in this map.
1130	>	* The set is backed by the map, so changes to the map are
1131	>	* reflected in the set, and vice-versa. The set supports element
1132	>	* removal, which removes the corresponding mapping from this map,
1133	>	* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
1134	>	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
1135	>	* operations. It does not support the <tt>add</tt> or
1136		* <tt>addAll</tt> operations.
1137	<	* The view's returned <tt>iterator</tt> is a "weakly consistent" iterator that
1138	<	* will never throw {@link java.util.ConcurrentModificationException},
1137	>	*
1138	>	* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
1139	>	* that will never throw {@link ConcurrentModificationException},
1140		* and guarantees to traverse elements as they existed upon
1141		* construction of the iterator, and may (but is not guaranteed to)
1142		* reflect any modifications subsequent to construction.
995	–	*
996	–	* @return a set view of the keys contained in this map.
1143		*/
1144		public Set<K> keySet() {
1145		Set<K> ks = keySet;
1146		return (ks != null) ? ks : (keySet = new KeySet());
1147		}
1148
1003	–
1149		/**
1150	<	* Returns a collection view of the values contained in this map. The
1151	<	* collection is backed by the map, so changes to the map are reflected in
1152	<	* the collection, and vice-versa. The collection supports element
1153	<	* removal, which removes the corresponding mapping from this map, via the
1154	<	* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
1155	<	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations.
1156	<	* It does not support the <tt>add</tt> or <tt>addAll</tt> operations.
1157	<	* The view's returned <tt>iterator</tt> is a "weakly consistent" iterator that
1158	<	* will never throw {@link java.util.ConcurrentModificationException},
1150	>	* Returns a {@link Collection} view of the values contained in this map.
1151	>	* The collection is backed by the map, so changes to the map are
1152	>	* reflected in the collection, and vice-versa. The collection
1153	>	* supports element removal, which removes the corresponding
1154	>	* mapping from this map, via the <tt>Iterator.remove</tt>,
1155	>	* <tt>Collection.remove</tt>, <tt>removeAll</tt>,
1156	>	* <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not
1157	>	* support the <tt>add</tt> or <tt>addAll</tt> operations.
1158	>	*
1159	>	* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
1160	>	* that will never throw {@link ConcurrentModificationException},
1161		* and guarantees to traverse elements as they existed upon
1162		* construction of the iterator, and may (but is not guaranteed to)
1163		* reflect any modifications subsequent to construction.
1017	–	*
1018	–	* @return a collection view of the values contained in this map.
1164		*/
1165		public Collection<V> values() {
1166		Collection<V> vs = values;
1167		return (vs != null) ? vs : (values = new Values());
1168		}
1169
1025	–
1170		/**
1171	<	* Returns a collection view of the mappings contained in this map. Each
1172	<	* element in the returned collection is a <tt>Map.Entry</tt>. The
1173	<	* collection is backed by the map, so changes to the map are reflected in
1174	<	* the collection, and vice-versa. The collection supports element
1175	<	* removal, which removes the corresponding mapping from the map, via the
1176	<	* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
1177	<	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations.
1178	<	* It does not support the <tt>add</tt> or <tt>addAll</tt> operations.
1179	<	* The view's returned <tt>iterator</tt> is a "weakly consistent" iterator that
1180	<	* will never throw {@link java.util.ConcurrentModificationException},
1171	>	* Returns a {@link Set} view of the mappings contained in this map.
1172	>	* The set is backed by the map, so changes to the map are
1173	>	* reflected in the set, and vice-versa. The set supports element
1174	>	* removal, which removes the corresponding mapping from the map,
1175	>	* via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
1176	>	* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
1177	>	* operations. It does not support the <tt>add</tt> or
1178	>	* <tt>addAll</tt> operations.
1179	>	*
1180	>	* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
1181	>	* that will never throw {@link ConcurrentModificationException},
1182		* and guarantees to traverse elements as they existed upon
1183		* construction of the iterator, and may (but is not guaranteed to)
1184		* reflect any modifications subsequent to construction.
1040	–	*
1041	–	* @return a collection view of the mappings contained in this map.
1185		*/
1186		public Set<Map.Entry<K,V>> entrySet() {
1187		Set<Map.Entry<K,V>> es = entrySet;
1188	<	return (es != null) ? es : (entrySet = (Set<Map.Entry<K,V>>) (Set) new EntrySet());
1188	>	return (es != null) ? es : (entrySet = new EntrySet());
1189		}
1190
1048	–
1191		/**
1192		* Returns an enumeration of the keys in this table.
1193		*
1194	<	* @return an enumeration of the keys in this table.
1195	<	* @see #keySet
1194	>	* @return an enumeration of the keys in this table
1195	>	* @see #keySet()
1196		*/
1197		public Enumeration<K> keys() {
1198		return new KeyIterator();
#	Line 1059 \| Line 1201 \| public class ConcurrentHashMap<K, V> ext
1201		/**
1202		* Returns an enumeration of the values in this table.
1203		*
1204	<	* @return an enumeration of the values in this table.
1205	<	* @see #values
1204	>	* @return an enumeration of the values in this table
1205	>	* @see #values()
1206		*/
1207		public Enumeration<V> elements() {
1208		return new ValueIterator();
#	Line 1071 \| Line 1213 \| public class ConcurrentHashMap<K, V> ext
1213		abstract class HashIterator {
1214		int nextSegmentIndex;
1215		int nextTableIndex;
1216	<	HashEntry[] currentTable;
1216	>	HashEntry<K,V>[] currentTable;
1217		HashEntry<K, V> nextEntry;
1218		HashEntry<K, V> lastReturned;
1219
#	Line 1081 \| Line 1223 \| public class ConcurrentHashMap<K, V> ext
1223		advance();
1224		}
1225
1226	<	public boolean hasMoreElements() { return hasNext(); }
1227	<
1226	>	/**
1227	>	* Sets nextEntry to first node of next non-empty table
1228	>	* (in backwards order, to simplify checks).
1229	>	*/
1230		final void advance() {
1231	<	if (nextEntry != null && (nextEntry = nextEntry.next) != null)
1232	<	return;
1233	<
1234	<	while (nextTableIndex >= 0) {
1235	<	if ( (nextEntry = (HashEntry<K,V>)currentTable[nextTableIndex--]) != null)
1236	<	return;
1237	<	}
1238	<
1239	<	while (nextSegmentIndex >= 0) {
1240	<	Segment<K,V> seg = (Segment<K,V>)segments[nextSegmentIndex--];
1097	<	if (seg.count != 0) {
1098	<	currentTable = seg.table;
1099	<	for (int j = currentTable.length - 1; j >= 0; --j) {
1100	<	if ( (nextEntry = (HashEntry<K,V>)currentTable[j]) != null) {
1101	<	nextTableIndex = j - 1;
1102	<	return;
1103	<	}
1104	<	}
1231	>	for (;;) {
1232	>	if (nextTableIndex >= 0) {
1233	>	if ((nextEntry = entryAt(currentTable,
1234	>	nextTableIndex--)) != null)
1235	>	break;
1236	>	}
1237	>	else if (nextSegmentIndex >= 0) {
1238	>	Segment<K,V> seg = segmentAt(segments, nextSegmentIndex--);
1239	>	if (seg != null && (currentTable = seg.table) != null)
1240	>	nextTableIndex = currentTable.length - 1;
1241		}
1242	+	else
1243	+	break;
1244		}
1245		}
1246
1247	<	public boolean hasNext() { return nextEntry != null; }
1248	<
1249	<	HashEntry<K,V> nextEntry() {
1112	<	if (nextEntry == null)
1247	>	final HashEntry<K,V> nextEntry() {
1248	>	HashEntry<K,V> e = nextEntry;
1249	>	if (e == null)
1250		throw new NoSuchElementException();
1251	<	lastReturned = nextEntry;
1252	<	advance();
1253	<	return lastReturned;
1251	>	lastReturned = e; // cannot assign until after null check
1252	>	if ((nextEntry = e.next) == null)
1253	>	advance();
1254	>	return e;
1255		}
1256
1257	<	public void remove() {
1257	>	public final boolean hasNext() { return nextEntry != null; }
1258	>	public final boolean hasMoreElements() { return nextEntry != null; }
1259	>
1260	>	public final void remove() {
1261		if (lastReturned == null)
1262		throw new IllegalStateException();
1263		ConcurrentHashMap.this.remove(lastReturned.key);
#	Line 1124 \| Line 1265 \| public class ConcurrentHashMap<K, V> ext
1265		}
1266		}
1267
1268	<	final class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> {
1269	<	public K next() { return super.nextEntry().key; }
1270	<	public K nextElement() { return super.nextEntry().key; }
1271	<	}
1272	<
1273	<	final class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> {
1274	<	public V next() { return super.nextEntry().value; }
1275	<	public V nextElement() { return super.nextEntry().value; }
1268	>	final class KeyIterator
1269	>	extends HashIterator
1270	>	implements Iterator<K>, Enumeration<K>
1271	>	{
1272	>	public final K next() { return super.nextEntry().key; }
1273	>	public final K nextElement() { return super.nextEntry().key; }
1274	>	}
1275	>
1276	>	final class ValueIterator
1277	>	extends HashIterator
1278	>	implements Iterator<V>, Enumeration<V>
1279	>	{
1280	>	public final V next() { return super.nextEntry().value; }
1281	>	public final V nextElement() { return super.nextEntry().value; }
1282		}
1283
1137	–
1138	–
1284		/**
1285	<	* Entry iterator. Exported Entry objects must write-through
1286	<	* changes in setValue, even if the nodes have been cloned. So we
1287	<	* cannot return internal HashEntry objects. Instead, the iterator
1288	<	* itself acts as a forwarding pseudo-entry.
1289	<	*/
1290	<	final class EntryIterator extends HashIterator implements Map.Entry<K,V>, Iterator<Entry<K,V>> {
1291	<	public Map.Entry<K,V> next() {
1292	<	nextEntry();
1148	<	return this;
1149	<	}
1150	<
1151	<	public K getKey() {
1152	<	if (lastReturned == null)
1153	<	throw new IllegalStateException("Entry was removed");
1154	<	return lastReturned.key;
1155	<	}
1156	<
1157	<	public V getValue() {
1158	<	if (lastReturned == null)
1159	<	throw new IllegalStateException("Entry was removed");
1160	<	return ConcurrentHashMap.this.get(lastReturned.key);
1285	>	* Custom Entry class used by EntryIterator.next(), that relays
1286	>	* setValue changes to the underlying map.
1287	>	*/
1288	>	final class WriteThroughEntry
1289	>	extends AbstractMap.SimpleEntry<K,V>
1290	>	{
1291	>	WriteThroughEntry(K k, V v) {
1292	>	super(k,v);
1293		}
1294
1295	+	/**
1296	+	* Sets our entry's value and writes through to the map. The
1297	+	* value to return is somewhat arbitrary here. Since a
1298	+	* WriteThroughEntry does not necessarily track asynchronous
1299	+	* changes, the most recent "previous" value could be
1300	+	* different from what we return (or could even have been
1301	+	* removed in which case the put will re-establish). We do not
1302	+	* and cannot guarantee more.
1303	+	*/
1304		public V setValue(V value) {
1305	<	if (lastReturned == null)
1306	<	throw new IllegalStateException("Entry was removed");
1307	<	return ConcurrentHashMap.this.put(lastReturned.key, value);
1308	<	}
1168	<
1169	<	public boolean equals(Object o) {
1170	<	// If not acting as entry, just use default.
1171	<	if (lastReturned == null)
1172	<	return super.equals(o);
1173	<	if (!(o instanceof Map.Entry))
1174	<	return false;
1175	<	Map.Entry e = (Map.Entry)o;
1176	<	return eq(getKey(), e.getKey()) && eq(getValue(), e.getValue());
1177	<	}
1178	<
1179	<	public int hashCode() {
1180	<	// If not acting as entry, just use default.
1181	<	if (lastReturned == null)
1182	<	return super.hashCode();
1183	<
1184	<	Object k = getKey();
1185	<	Object v = getValue();
1186	<	return ((k == null) ? 0 : k.hashCode()) ^
1187	<	((v == null) ? 0 : v.hashCode());
1188	<	}
1189	<
1190	<	public String toString() {
1191	<	// If not acting as entry, just use default.
1192	<	if (lastReturned == null)
1193	<	return super.toString();
1194	<	else
1195	<	return getKey() + "=" + getValue();
1305	>	if (value == null) throw new NullPointerException();
1306	>	V v = super.setValue(value);
1307	>	ConcurrentHashMap.this.put(getKey(), value);
1308	>	return v;
1309		}
1310	+	}
1311
1312	<	boolean eq(Object o1, Object o2) {
1313	<	return (o1 == null ? o2 == null : o1.equals(o2));
1312	>	final class EntryIterator
1313	>	extends HashIterator
1314	>	implements Iterator<Entry<K,V>>
1315	>	{
1316	>	public Map.Entry<K,V> next() {
1317	>	HashEntry<K,V> e = super.nextEntry();
1318	>	return new WriteThroughEntry(e.key, e.value);
1319		}
1201	–
1320		}
1321
1322		final class KeySet extends AbstractSet<K> {
#	Line 1208 \| Line 1326 \| public class ConcurrentHashMap<K, V> ext
1326		public int size() {
1327		return ConcurrentHashMap.this.size();
1328		}
1329	+	public boolean isEmpty() {
1330	+	return ConcurrentHashMap.this.isEmpty();
1331	+	}
1332		public boolean contains(Object o) {
1333		return ConcurrentHashMap.this.containsKey(o);
1334		}
#	Line 1217 \| Line 1338 \| public class ConcurrentHashMap<K, V> ext
1338		public void clear() {
1339		ConcurrentHashMap.this.clear();
1340		}
1220	–	public Object[] toArray() {
1221	–	Collection<K> c = new ArrayList<K>();
1222	–	for (Iterator<K> i = iterator(); i.hasNext(); )
1223	–	c.add(i.next());
1224	–	return c.toArray();
1225	–	}
1226	–	public <T> T[] toArray(T[] a) {
1227	–	Collection<K> c = new ArrayList<K>();
1228	–	for (Iterator<K> i = iterator(); i.hasNext(); )
1229	–	c.add(i.next());
1230	–	return c.toArray(a);
1231	–	}
1341		}
1342
1343		final class Values extends AbstractCollection<V> {
#	Line 1238 \| Line 1347 \| public class ConcurrentHashMap<K, V> ext
1347		public int size() {
1348		return ConcurrentHashMap.this.size();
1349		}
1350	+	public boolean isEmpty() {
1351	+	return ConcurrentHashMap.this.isEmpty();
1352	+	}
1353		public boolean contains(Object o) {
1354		return ConcurrentHashMap.this.containsValue(o);
1355		}
1356		public void clear() {
1357		ConcurrentHashMap.this.clear();
1358		}
1247	–	public Object[] toArray() {
1248	–	Collection<V> c = new ArrayList<V>();
1249	–	for (Iterator<V> i = iterator(); i.hasNext(); )
1250	–	c.add(i.next());
1251	–	return c.toArray();
1252	–	}
1253	–	public <T> T[] toArray(T[] a) {
1254	–	Collection<V> c = new ArrayList<V>();
1255	–	for (Iterator<V> i = iterator(); i.hasNext(); )
1256	–	c.add(i.next());
1257	–	return c.toArray(a);
1258	–	}
1359		}
1360
1361		final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
#	Line 1265 \| Line 1365 \| public class ConcurrentHashMap<K, V> ext
1365		public boolean contains(Object o) {
1366		if (!(o instanceof Map.Entry))
1367		return false;
1368	<	Map.Entry<K,V> e = (Map.Entry<K,V>)o;
1368	>	Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1369		V v = ConcurrentHashMap.this.get(e.getKey());
1370		return v != null && v.equals(e.getValue());
1371		}
1372		public boolean remove(Object o) {
1373		if (!(o instanceof Map.Entry))
1374		return false;
1375	<	Map.Entry<K,V> e = (Map.Entry<K,V>)o;
1375	>	Map.Entry<?,?> e = (Map.Entry<?,?>)o;
1376		return ConcurrentHashMap.this.remove(e.getKey(), e.getValue());
1377		}
1378		public int size() {
1379		return ConcurrentHashMap.this.size();
1380		}
1381	+	public boolean isEmpty() {
1382	+	return ConcurrentHashMap.this.isEmpty();
1383	+	}
1384		public void clear() {
1385		ConcurrentHashMap.this.clear();
1386		}
1284	–	public Object[] toArray() {
1285	–	// Since we don't ordinarily have distinct Entry objects, we
1286	–	// must pack elements using exportable SimpleEntry
1287	–	Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>(size());
1288	–	for (Iterator<Map.Entry<K,V>> i = iterator(); i.hasNext(); )
1289	–	c.add(new AbstractMap.SimpleEntry<K,V>(i.next()));
1290	–	return c.toArray();
1291	–	}
1292	–	public <T> T[] toArray(T[] a) {
1293	–	Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>(size());
1294	–	for (Iterator<Map.Entry<K,V>> i = iterator(); i.hasNext(); )
1295	–	c.add(new AbstractMap.SimpleEntry<K,V>(i.next()));
1296	–	return c.toArray(a);
1297	–	}
1298	–
1387		}
1388
1389		/* ---------------- Serialization Support -------------- */
1390
1391		/**
1392	<	* Save the state of the <tt>ConcurrentHashMap</tt>
1393	<	* instance to a stream (i.e.,
1306	<	* serialize it).
1392	>	* Saves the state of the <tt>ConcurrentHashMap</tt> instance to a
1393	>	* stream (i.e., serializes it).
1394		* @param s the stream
1395		* @serialData
1396		* the key (Object) and value (Object)
1397		* for each key-value mapping, followed by a null pair.
1398		* The key-value mappings are emitted in no particular order.
1399		*/
1400	<	private void writeObject(java.io.ObjectOutputStream s) throws IOException {
1400	>	private void writeObject(java.io.ObjectOutputStream s) throws IOException {
1401	>	// force all segments for serialization compatibility
1402	>	for (int k = 0; k < segments.length; ++k)
1403	>	ensureSegment(k);
1404		s.defaultWriteObject();
1405
1406	+	final Segment<K,V>[] segments = this.segments;
1407		for (int k = 0; k < segments.length; ++k) {
1408	<	Segment<K,V> seg = (Segment<K,V>)segments[k];
1408	>	Segment<K,V> seg = segmentAt(segments, k);
1409		seg.lock();
1410		try {
1411	<	HashEntry[] tab = seg.table;
1411	>	HashEntry<K,V>[] tab = seg.table;
1412		for (int i = 0; i < tab.length; ++i) {
1413	<	for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i]; e != null; e = e.next) {
1413	>	HashEntry<K,V> e;
1414	>	for (e = entryAt(tab, i); e != null; e = e.next) {
1415		s.writeObject(e.key);
1416		s.writeObject(e.value);
1417		}
#	Line 1333 \| Line 1425 \| public class ConcurrentHashMap<K, V> ext
1425		}
1426
1427		/**
1428	<	* Reconstitute the <tt>ConcurrentHashMap</tt>
1429	<	* instance from a stream (i.e.,
1338	<	* deserialize it).
1428	>	* Reconstitutes the <tt>ConcurrentHashMap</tt> instance from a
1429	>	* stream (i.e., deserializes it).
1430		* @param s the stream
1431		*/
1432	+	@SuppressWarnings("unchecked")
1433		private void readObject(java.io.ObjectInputStream s)
1434	<	throws IOException, ClassNotFoundException {
1434	>	throws IOException, ClassNotFoundException {
1435		s.defaultReadObject();
1436
1437	<	// Initialize each segment to be minimally sized, and let grow.
1438	<	for (int i = 0; i < segments.length; ++i) {
1439	<	segments[i].setTable(new HashEntry[1]);
1437	>	// Re-initialize segments to be minimally sized, and let grow.
1438	>	int cap = MIN_SEGMENT_TABLE_CAPACITY;
1439	>	final Segment<K,V>[] segments = this.segments;
1440	>	for (int k = 0; k < segments.length; ++k) {
1441	>	Segment<K,V> seg = segments[k];
1442	>	if (seg != null) {
1443	>	seg.threshold = (int)(cap * seg.loadFactor);
1444	>	seg.table = (HashEntry<K,V>[]) new HashEntry<?,?>[cap];
1445	>	}
1446		}
1447
1448		// Read the keys and values, and put the mappings in the table
#	Line 1356 \| Line 1454 \| public class ConcurrentHashMap<K, V> ext
1454		put(key, value);
1455		}
1456		}
1359	–	}
1457
1458	+	// Unsafe mechanics
1459	+	private static final sun.misc.Unsafe UNSAFE;
1460	+	private static final long SBASE;
1461	+	private static final int SSHIFT;
1462	+	private static final long TBASE;
1463	+	private static final int TSHIFT;
1464	+
1465	+	static {
1466	+	int ss, ts;
1467	+	try {
1468	+	UNSAFE = sun.misc.Unsafe.getUnsafe();
1469	+	Class<?> tc = HashEntry[].class;
1470	+	Class<?> sc = Segment[].class;
1471	+	TBASE = UNSAFE.arrayBaseOffset(tc);
1472	+	SBASE = UNSAFE.arrayBaseOffset(sc);
1473	+	ts = UNSAFE.arrayIndexScale(tc);
1474	+	ss = UNSAFE.arrayIndexScale(sc);
1475	+	} catch (Exception e) {
1476	+	throw new Error(e);
1477	+	}
1478	+	if ((ss & (ss-1)) != 0 \|\| (ts & (ts-1)) != 0)
1479	+	throw new Error("data type scale not a power of two");
1480	+	SSHIFT = 31 - Integer.numberOfLeadingZeros(ss);
1481	+	TSHIFT = 31 - Integer.numberOfLeadingZeros(ts);
1482	+	}
1483	+
1484	+	}

Diff Legend

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+Removed lines
-+
+Added lines
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+Changed lines
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+Changed lines

Comparing jsr166/src/main/java/util/concurrent/ConcurrentHashMap.java (file contents): Revision 1.54 by dl, Fri Dec 31 13:00:39 2004 UTC vs. Revision 1.112 by jsr166, Fri Jun 3 02:28:05 2011 UTC

Diff Legend

Comparing jsr166/src/main/java/util/concurrent/ConcurrentHashMap.java (file contents):
Revision 1.54 by dl, Fri Dec 31 13:00:39 2004 UTC vs.
Revision 1.112 by jsr166, Fri Jun 3 02:28:05 2011 UTC