ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

root/jsr166/jsr166/src/main/java/util/concurrent/ConcurrentHashMap.java

Comparing jsr166/src/main/java/util/concurrent/ConcurrentHashMap.java (file contents):
Revision 1.75 by jsr166, Thu Jun 16 02:17:07 2005 UTC vs.
Revision 1.115 by jsr166, Fri Dec 2 14:28:17 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;
8		import java.util.concurrent.locks.*;
9		import java.util.*;
10		import java.io.Serializable;
11	–	import java.io.IOException;
12	–	import java.io.ObjectInputStream;
13	–	import java.io.ObjectOutputStream;
11
12		/**
13		* A hash table supporting full concurrency of retrievals and
#	Line 62 | Line 59 | import java.io.ObjectOutputStream;
59		* does <em>not</em> allow <tt>null</tt> to be used as a key or value.
60		*
61		* <p>This class is a member of the
62	<	* <a href="{@docRoot}/../guide/collections/index.html">
62	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
63		* Java Collections Framework</a>.
64		*
65		* @since 1.5
#	Line 76 | Line 73 | public class ConcurrentHashMap<K, V> ext
73
74		/*
75		* The basic strategy is to subdivide the table among Segments,
76	<	* each of which itself is a concurrently readable hash table.
76	>	* each of which itself is a concurrently readable hash table.  To
77	>	* reduce footprint, all but one segments are constructed only
78	>	* when first needed (see ensureSegment). To maintain visibility
79	>	* in the presence of lazy construction, accesses to segments as
80	>	* well as elements of segment's table must use volatile access,
81	>	* which is done via Unsafe within methods segmentAt etc
82	>	* below. These provide the functionality of AtomicReferenceArrays
83	>	* but reduce the levels of indirection. Additionally,
84	>	* volatile-writes of table elements and entry "next" fields
85	>	* within locked operations use the cheaper "lazySet" forms of
86	>	* writes (via putOrderedObject) because these writes are always
87	>	* followed by lock releases that maintain sequential consistency
88	>	* of table updates.
89	>	*
90	>	* Historical note: The previous version of this class relied
91	>	* heavily on "final" fields, which avoided some volatile reads at
92	>	* the expense of a large initial footprint.  Some remnants of
93	>	* that design (including forced construction of segment 0) exist
94	>	* to ensure serialization compatibility.
95		*/
96
97		/* ---------------- Constants -------------- */
#	Line 108 | Line 123 | public class ConcurrentHashMap<K, V> ext
123		static final int MAXIMUM_CAPACITY = 1 << 30;
124
125		/**
126	+	* The minimum capacity for per-segment tables.  Must be a power
127	+	* of two, at least two to avoid immediate resizing on next use
128	+	* after lazy construction.
129	+	*/
130	+	static final int MIN_SEGMENT_TABLE_CAPACITY = 2;
131	+
132	+	/**
133		* The maximum number of segments to allow; used to bound
134	<	* constructor arguments.
134	>	* constructor arguments. Must be power of two less than 1 << 24.
135		*/
136		static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
137
#	Line 135 | Line 157 | public class ConcurrentHashMap<K, V> ext
157		final int segmentShift;
158
159		/**
160	<	* The segments, each of which is a specialized hash table
160	>	* The segments, each of which is a specialized hash table.
161		*/
162		final Segment<K,V>[] segments;
163
#	Line 143 | Line 165 | public class ConcurrentHashMap<K, V> ext
165		transient Set<Map.Entry<K,V>> entrySet;
166		transient Collection<V> values;
167
146	–	/* ---------------- Small Utilities -------------- */
147	–
148	–	/**
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	–	static int hash(Object x) {
155	–	int h = x.hashCode();
156	–	h += ~(h << 9);
157	–	h ^=  (h >>> 14);
158	–	h +=  (h << 4);
159	–	h ^=  (h >>> 10);
160	–	return h;
161	–	}
162	–
163	–	/**
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	–	final Segment<K,V> segmentFor(int hash) {
169	–	return segments[(hash >>> segmentShift) & segmentMask];
170	–	}
171	–
172	–	/* ---------------- Inner Classes -------------- */
173	–
168		/**
169		* ConcurrentHashMap list entry. Note that this is never exported
170		* 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.
171		*/
172		static final class HashEntry<K,V> {
187	–	final K key;
173		final int hash;
174	+	final K key;
175		volatile V value;
176	<	final HashEntry<K,V> next;
176	>	volatile HashEntry<K,V> next;
177
178	<	HashEntry(K key, int hash, HashEntry<K,V> next, V value) {
193	<	this.key = key;
178	>	HashEntry(int hash, K key, V value, HashEntry<K,V> next) {
179		this.hash = hash;
180	<	this.next = next;
180	>	this.key = key;
181		this.value = value;
182	+	this.next = next;
183	+	}
184	+
185	+	/**
186	+	* Sets next field with volatile write semantics.  (See above
187	+	* about use of putOrderedObject.)
188	+	*/
189	+	final void setNext(HashEntry<K,V> n) {
190	+	UNSAFE.putOrderedObject(this, nextOffset, n);
191		}
192
193	<	@SuppressWarnings("unchecked")
194	<	static final <K,V> HashEntry<K,V>[] newArray(int i) {
195	<	return new HashEntry[i];
196	<	}
193	>	// Unsafe mechanics
194	>	static final sun.misc.Unsafe UNSAFE;
195	>	static final long nextOffset;
196	>	static {
197	>	try {
198	>	UNSAFE = sun.misc.Unsafe.getUnsafe();
199	>	Class<?> k = HashEntry.class;
200	>	nextOffset = UNSAFE.objectFieldOffset
201	>	(k.getDeclaredField("next"));
202	>	} catch (Exception e) {
203	>	throw new Error(e);
204	>	}
205	>	}
206	>	}
207	>
208	>	/**
209	>	* Gets the ith element of given table (if nonnull) with volatile
210	>	* read semantics. Note: This is manually integrated into a few
211	>	* performance-sensitive methods to reduce call overhead.
212	>	*/
213	>	@SuppressWarnings("unchecked")
214	>	static final <K,V> HashEntry<K,V> entryAt(HashEntry<K,V>[] tab, int i) {
215	>	return (tab == null) ? null :
216	>	(HashEntry<K,V>) UNSAFE.getObjectVolatile
217	>	(tab, ((long)i << TSHIFT) + TBASE);
218	>	}
219	>
220	>	/**
221	>	* Sets the ith element of given table, with volatile write
222	>	* semantics. (See above about use of putOrderedObject.)
223	>	*/
224	>	static final <K,V> void setEntryAt(HashEntry<K,V>[] tab, int i,
225	>	HashEntry<K,V> e) {
226	>	UNSAFE.putOrderedObject(tab, ((long)i << TSHIFT) + TBASE, e);
227	>	}
228	>
229	>	/**
230	>	* Applies a supplemental hash function to a given hashCode, which
231	>	* defends against poor quality hash functions.  This is critical
232	>	* because ConcurrentHashMap uses power-of-two length hash tables,
233	>	* that otherwise encounter collisions for hashCodes that do not
234	>	* differ in lower or upper bits.
235	>	*/
236	>	private static int hash(int h) {
237	>	// Spread bits to regularize both segment and index locations,
238	>	// using variant of single-word Wang/Jenkins hash.
239	>	h += (h <<  15) ^ 0xffffcd7d;
240	>	h ^= (h >>> 10);
241	>	h += (h <<   3);
242	>	h ^= (h >>>  6);
243	>	h += (h <<   2) + (h << 14);
244	>	return h ^ (h >>> 16);
245		}
246
247		/**
#	Line 209 | Line 251 | public class ConcurrentHashMap<K, V> ext
251		*/
252		static final class Segment<K,V> extends ReentrantLock implements Serializable {
253		/*
254	<	* Segments maintain a table of entry lists that are ALWAYS
255	<	* kept in a consistent state, so can be read without locking.
256	<	* Next fields of nodes are immutable (final).  All list
257	<	* additions are performed at the front of each bin. This
258	<	* makes it easy to check changes, and also fast to traverse.
259	<	* When nodes would otherwise be changed, new nodes are
218	<	* created to replace them. This works well for hash tables
219	<	* since the bin lists tend to be short. (The average length
220	<	* is less than two for the default load factor threshold.)
221	<	*
222	<	* Read operations can thus proceed without locking, but rely
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	<	*   - 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 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.
254	>	* Segments maintain a table of entry lists that are always
255	>	* kept in a consistent state, so can be read (via volatile
256	>	* reads of segments and tables) without locking.  This
257	>	* requires replicating nodes when necessary during table
258	>	* resizing, so the old lists can be traversed by readers
259	>	* still using old version of table.
260		*
261	<	* As a guide, all critical volatile reads and writes to the
262	<	* count field are marked in code comments.
261	>	* This class defines only mutative methods requiring locking.
262	>	* Except as noted, the methods of this class perform the
263	>	* per-segment versions of ConcurrentHashMap methods.  (Other
264	>	* methods are integrated directly into ConcurrentHashMap
265	>	* methods.) These mutative methods use a form of controlled
266	>	* spinning on contention via methods scanAndLock and
267	>	* scanAndLockForPut. These intersperse tryLocks with
268	>	* traversals to locate nodes.  The main benefit is to absorb
269	>	* cache misses (which are very common for hash tables) while
270	>	* obtaining locks so that traversal is faster once
271	>	* acquired. We do not actually use the found nodes since they
272	>	* must be re-acquired under lock anyway to ensure sequential
273	>	* consistency of updates (and in any case may be undetectably
274	>	* stale), but they will normally be much faster to re-locate.
275	>	* Also, scanAndLockForPut speculatively creates a fresh node
276	>	* to use in put if no node is found.
277		*/
278
279		private static final long serialVersionUID = 2249069246763182397L;
280
281		/**
282	<	* The number of elements in this segment's region.
282	>	* The maximum number of times to tryLock in a prescan before
283	>	* possibly blocking on acquire in preparation for a locked
284	>	* segment operation. On multiprocessors, using a bounded
285	>	* number of retries maintains cache acquired while locating
286	>	* nodes.
287		*/
288	<	transient volatile int count;
288	>	static final int MAX_SCAN_RETRIES =
289	>	Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1;
290
291		/**
292	<	* Number of updates that alter the size of the table. This is
293	<	* used during bulk-read methods to make sure they see a
294	<	* consistent snapshot: If modCounts change during a traversal
295	<	* of segments computing size or checking containsValue, then
296	<	* we might have an inconsistent view of state so (usually)
297	<	* must retry.
292	>	* The per-segment table. Elements are accessed via
293	>	* entryAt/setEntryAt providing volatile semantics.
294	>	*/
295	>	transient volatile HashEntry<K,V>[] table;
296	>
297	>	/**
298	>	* The number of elements. Accessed only either within locks
299	>	* or among other volatile reads that maintain visibility.
300	>	*/
301	>	transient int count;
302	>
303	>	/**
304	>	* The total number of mutative operations in this segment.
305	>	* Even though this may overflows 32 bits, it provides
306	>	* sufficient accuracy for stability checks in CHM isEmpty()
307	>	* and size() methods.  Accessed only either within locks or
308	>	* among other volatile reads that maintain visibility.
309		*/
310		transient int modCount;
311
#	Line 270 | Line 317 | public class ConcurrentHashMap<K, V> ext
317		transient int threshold;
318
319		/**
273	–	* The per-segment table.
274	–	*/
275	–	transient volatile HashEntry<K,V>[] table;
276	–
277	–	/**
320		* The load factor for the hash table.  Even though this value
321		* is same for all segments, it is replicated to avoid needing
322		* links to outer object.
#	Line 282 | Line 324 | public class ConcurrentHashMap<K, V> ext
324		*/
325		final float loadFactor;
326
327	<	Segment(int initialCapacity, float lf) {
328	<	loadFactor = lf;
329	<	setTable(HashEntry.<K,V>newArray(initialCapacity));
330	<	}
289	<
290	<	@SuppressWarnings("unchecked")
291	<	static final <K,V> Segment<K,V>[] newArray(int i) {
292	<	return new Segment[i];
293	<	}
294	<
295	<	/**
296	<	* Sets table to new HashEntry array.
297	<	* Call only while holding lock or in constructor.
298	<	*/
299	<	void setTable(HashEntry<K,V>[] newTable) {
300	<	threshold = (int)(newTable.length * loadFactor);
301	<	table = newTable;
302	<	}
303	<
304	<	/**
305	<	* Returns properly casted first entry of bin for given hash.
306	<	*/
307	<	HashEntry<K,V> getFirst(int hash) {
308	<	HashEntry<K,V>[] tab = table;
309	<	return tab[hash & (tab.length - 1)];
327	>	Segment(float lf, int threshold, HashEntry<K,V>[] tab) {
328	>	this.loadFactor = lf;
329	>	this.threshold = threshold;
330	>	this.table = tab;
331		}
332
333	<	/**
334	<	* Reads value field of an entry under lock. Called if value
335	<	* field ever appears to be null. This is possible only if a
336	<	* compiler happens to reorder a HashEntry initialization with
316	<	* its table assignment, which is legal under memory model
317	<	* but is not known to ever occur.
318	<	*/
319	<	V readValueUnderLock(HashEntry<K,V> e) {
320	<	lock();
333	>	final V put(K key, int hash, V value, boolean onlyIfAbsent) {
334	>	HashEntry<K,V> node = tryLock() ? null :
335	>	scanAndLockForPut(key, hash, value);
336	>	V oldValue;
337		try {
322	–	return e.value;
323	–	} finally {
324	–	unlock();
325	–	}
326	–	}
327	–
328	–	/* Specialized implementations of map methods */
329	–
330	–	V get(Object key, int hash) {
331	–	if (count != 0) { // read-volatile
332	–	HashEntry<K,V> e = getFirst(hash);
333	–	while (e != null) {
334	–	if (e.hash == hash && key.equals(e.key)) {
335	–	V v = e.value;
336	–	if (v != null)
337	–	return v;
338	–	return readValueUnderLock(e); // recheck
339	–	}
340	–	e = e.next;
341	–	}
342	–	}
343	–	return null;
344	–	}
345	–
346	–	boolean containsKey(Object key, int hash) {
347	–	if (count != 0) { // read-volatile
348	–	HashEntry<K,V> e = getFirst(hash);
349	–	while (e != null) {
350	–	if (e.hash == hash && key.equals(e.key))
351	–	return true;
352	–	e = e.next;
353	–	}
354	–	}
355	–	return false;
356	–	}
357	–
358	–	boolean containsValue(Object value) {
359	–	if (count != 0) { // read-volatile
338		HashEntry<K,V>[] tab = table;
339	<	int len = tab.length;
340	<	for (int i = 0 ; i < len; i++) {
341	<	for (HashEntry<K,V> e = tab[i]; e != null; e = e.next) {
342	<	V v = e.value;
343	<	if (v == null) // recheck
344	<	v = readValueUnderLock(e);
345	<	if (value.equals(v))
346	<	return true;
339	>	int index = (tab.length - 1) & hash;
340	>	HashEntry<K,V> first = entryAt(tab, index);
341	>	for (HashEntry<K,V> e = first;;) {
342	>	if (e != null) {
343	>	K k;
344	>	if ((k = e.key) == key ||
345	>	(e.hash == hash && key.equals(k))) {
346	>	oldValue = e.value;
347	>	if (!onlyIfAbsent) {
348	>	e.value = value;
349	>	++modCount;
350	>	}
351	>	break;
352	>	}
353	>	e = e.next;
354	>	}
355	>	else {
356	>	if (node != null)
357	>	node.setNext(first);
358	>	else
359	>	node = new HashEntry<K,V>(hash, key, value, first);
360	>	int c = count + 1;
361	>	if (c > threshold && tab.length < MAXIMUM_CAPACITY)
362	>	rehash(node);
363	>	else
364	>	setEntryAt(tab, index, node);
365	>	++modCount;
366	>	count = c;
367	>	oldValue = null;
368	>	break;
369		}
370		}
371	–	}
372	–	return false;
373	–	}
374	–
375	–	boolean replace(K key, int hash, V oldValue, V newValue) {
376	–	lock();
377	–	try {
378	–	HashEntry<K,V> e = getFirst(hash);
379	–	while (e != null && (e.hash != hash || !key.equals(e.key)))
380	–	e = e.next;
381	–
382	–	boolean replaced = false;
383	–	if (e != null && oldValue.equals(e.value)) {
384	–	replaced = true;
385	–	e.value = newValue;
386	–	}
387	–	return replaced;
388	–	} finally {
389	–	unlock();
390	–	}
391	–	}
392	–
393	–	V replace(K key, int hash, V newValue) {
394	–	lock();
395	–	try {
396	–	HashEntry<K,V> e = getFirst(hash);
397	–	while (e != null && (e.hash != hash || !key.equals(e.key)))
398	–	e = e.next;
399	–
400	–	V oldValue = null;
401	–	if (e != null) {
402	–	oldValue = e.value;
403	–	e.value = newValue;
404	–	}
405	–	return oldValue;
406	–	} finally {
407	–	unlock();
408	–	}
409	–	}
410	–
411	–
412	–	V put(K key, int hash, V value, boolean onlyIfAbsent) {
413	–	lock();
414	–	try {
415	–	int c = count;
416	–	if (c++ > threshold) // ensure capacity
417	–	rehash();
418	–	HashEntry<K,V>[] tab = table;
419	–	int index = hash & (tab.length - 1);
420	–	HashEntry<K,V> first = tab[index];
421	–	HashEntry<K,V> e = first;
422	–	while (e != null && (e.hash != hash || !key.equals(e.key)))
423	–	e = e.next;
424	–
425	–	V oldValue;
426	–	if (e != null) {
427	–	oldValue = e.value;
428	–	if (!onlyIfAbsent)
429	–	e.value = value;
430	–	}
431	–	else {
432	–	oldValue = null;
433	–	++modCount;
434	–	tab[index] = new HashEntry<K,V>(key, hash, first, value);
435	–	count = c; // write-volatile
436	–	}
437	–	return oldValue;
371		} finally {
372		unlock();
373		}
374	+	return oldValue;
375		}
376
377	<	void rehash() {
378	<	HashEntry<K,V>[] oldTable = table;
379	<	int oldCapacity = oldTable.length;
380	<	if (oldCapacity >= MAXIMUM_CAPACITY)
381	<	return;
382	<
377	>	/**
378	>	* Doubles size of table and repacks entries, also adding the
379	>	* given node to new table
380	>	*/
381	>	@SuppressWarnings("unchecked")
382	>	private void rehash(HashEntry<K,V> node) {
383		/*
384	<	* Reclassify nodes in each list to new Map.  Because we are
385	<	* using power-of-two expansion, the elements from each bin
386	<	* must either stay at same index, or move with a power of two
387	<	* offset. We eliminate unnecessary node creation by catching
388	<	* cases where old nodes can be reused because their next
389	<	* fields won't change. Statistically, at the default
390	<	* threshold, only about one-sixth of them need cloning when
391	<	* a table doubles. The nodes they replace will be garbage
392	<	* collectable as soon as they are no longer referenced by any
393	<	* reader thread that may be in the midst of traversing table
394	<	* right now.
384	>	* Reclassify nodes in each list to new table.  Because we
385	>	* are using power-of-two expansion, the elements from
386	>	* each bin must either stay at same index, or move with a
387	>	* power of two offset. We eliminate unnecessary node
388	>	* creation by catching cases where old nodes can be
389	>	* reused because their next fields won't change.
390	>	* Statistically, at the default threshold, only about
391	>	* one-sixth of them need cloning when a table
392	>	* doubles. The nodes they replace will be garbage
393	>	* collectable as soon as they are no longer referenced by
394	>	* any reader thread that may be in the midst of
395	>	* concurrently traversing table. Entry accesses use plain
396	>	* array indexing because they are followed by volatile
397	>	* table write.
398		*/
399	<
400	<	HashEntry<K,V>[] newTable = HashEntry.newArray(oldCapacity<<1);
401	<	threshold = (int)(newTable.length * loadFactor);
402	<	int sizeMask = newTable.length - 1;
399	>	HashEntry<K,V>[] oldTable = table;
400	>	int oldCapacity = oldTable.length;
401	>	int newCapacity = oldCapacity << 1;
402	>	threshold = (int)(newCapacity * loadFactor);
403	>	HashEntry<K,V>[] newTable =
404	>	(HashEntry<K,V>[]) new HashEntry<?,?>[newCapacity];
405	>	int sizeMask = newCapacity - 1;
406		for (int i = 0; i < oldCapacity ; i++) {
467	–	// We need to guarantee that any existing reads of old Map can
468	–	//  proceed. So we cannot yet null out each bin.
407		HashEntry<K,V> e = oldTable[i];
470	–
408		if (e != null) {
409		HashEntry<K,V> next = e.next;
410		int idx = e.hash & sizeMask;
411	<
475	<	//  Single node on list
476	<	if (next == null)
411	>	if (next == null)   //  Single node on list
412		newTable[idx] = e;
413	<
479	<	else {
480	<	// Reuse trailing consecutive sequence at same slot
413	>	else { // Reuse consecutive sequence at same slot
414		HashEntry<K,V> lastRun = e;
415		int lastIdx = idx;
416		for (HashEntry<K,V> last = next;
#	Line 490 | Line 423 | public class ConcurrentHashMap<K, V> ext
423		}
424		}
425		newTable[lastIdx] = lastRun;
426	<
494	<	// Clone all remaining nodes
426	>	// Clone remaining nodes
427		for (HashEntry<K,V> p = e; p != lastRun; p = p.next) {
428	<	int k = p.hash & sizeMask;
428	>	V v = p.value;
429	>	int h = p.hash;
430	>	int k = h & sizeMask;
431		HashEntry<K,V> n = newTable[k];
432	<	newTable[k] = new HashEntry<K,V>(p.key, p.hash,
499	<	n, p.value);
432	>	newTable[k] = new HashEntry<K,V>(h, p.key, v, n);
433		}
434		}
435		}
436		}
437	+	int nodeIndex = node.hash & sizeMask; // add the new node
438	+	node.setNext(newTable[nodeIndex]);
439	+	newTable[nodeIndex] = node;
440		table = newTable;
441		}
442
443		/**
444	+	* Scans for a node containing given key while trying to
445	+	* acquire lock, creating and returning one if not found. Upon
446	+	* return, guarantees that lock is held. Unlike in most
447	+	* methods, calls to method equals are not screened: Since
448	+	* traversal speed doesn't matter, we might as well help warm
449	+	* up the associated code and accesses as well.
450	+	*
451	+	* @return a new node if key not found, else null
452	+	*/
453	+	private HashEntry<K,V> scanAndLockForPut(K key, int hash, V value) {
454	+	HashEntry<K,V> first = entryForHash(this, hash);
455	+	HashEntry<K,V> e = first;
456	+	HashEntry<K,V> node = null;
457	+	int retries = -1; // negative while locating node
458	+	while (!tryLock()) {
459	+	HashEntry<K,V> f; // to recheck first below
460	+	if (retries < 0) {
461	+	if (e == null) {
462	+	if (node == null) // speculatively create node
463	+	node = new HashEntry<K,V>(hash, key, value, null);
464	+	retries = 0;
465	+	}
466	+	else if (key.equals(e.key))
467	+	retries = 0;
468	+	else
469	+	e = e.next;
470	+	}
471	+	else if (++retries > MAX_SCAN_RETRIES) {
472	+	lock();
473	+	break;
474	+	}
475	+	else if ((retries & 1) == 0 &&
476	+	(f = entryForHash(this, hash)) != first) {
477	+	e = first = f; // re-traverse if entry changed
478	+	retries = -1;
479	+	}
480	+	}
481	+	return node;
482	+	}
483	+
484	+	/**
485	+	* Scans for a node containing the given key while trying to
486	+	* acquire lock for a remove or replace operation. Upon
487	+	* return, guarantees that lock is held.  Note that we must
488	+	* lock even if the key is not found, to ensure sequential
489	+	* consistency of updates.
490	+	*/
491	+	private void scanAndLock(Object key, int hash) {
492	+	// similar to but simpler than scanAndLockForPut
493	+	HashEntry<K,V> first = entryForHash(this, hash);
494	+	HashEntry<K,V> e = first;
495	+	int retries = -1;
496	+	while (!tryLock()) {
497	+	HashEntry<K,V> f;
498	+	if (retries < 0) {
499	+	if (e == null || key.equals(e.key))
500	+	retries = 0;
501	+	else
502	+	e = e.next;
503	+	}
504	+	else if (++retries > MAX_SCAN_RETRIES) {
505	+	lock();
506	+	break;
507	+	}
508	+	else if ((retries & 1) == 0 &&
509	+	(f = entryForHash(this, hash)) != first) {
510	+	e = first = f;
511	+	retries = -1;
512	+	}
513	+	}
514	+	}
515	+
516	+	/**
517		* Remove; match on key only if value null, else match both.
518		*/
519	<	V remove(Object key, int hash, Object value) {
520	<	lock();
519	>	final V remove(Object key, int hash, Object value) {
520	>	if (!tryLock())
521	>	scanAndLock(key, hash);
522	>	V oldValue = null;
523		try {
513	–	int c = count - 1;
524		HashEntry<K,V>[] tab = table;
525	<	int index = hash & (tab.length - 1);
526	<	HashEntry<K,V> first = tab[index];
527	<	HashEntry<K,V> e = first;
528	<	while (e != null && (e.hash != hash || !key.equals(e.key)))
529	<	e = e.next;
525	>	int index = (tab.length - 1) & hash;
526	>	HashEntry<K,V> e = entryAt(tab, index);
527	>	HashEntry<K,V> pred = null;
528	>	while (e != null) {
529	>	K k;
530	>	HashEntry<K,V> next = e.next;
531	>	if ((k = e.key) == key ||
532	>	(e.hash == hash && key.equals(k))) {
533	>	V v = e.value;
534	>	if (value == null || value == v || value.equals(v)) {
535	>	if (pred == null)
536	>	setEntryAt(tab, index, next);
537	>	else
538	>	pred.setNext(next);
539	>	++modCount;
540	>	--count;
541	>	oldValue = v;
542	>	}
543	>	break;
544	>	}
545	>	pred = e;
546	>	e = next;
547	>	}
548	>	} finally {
549	>	unlock();
550	>	}
551	>	return oldValue;
552	>	}
553
554	<	V oldValue = null;
555	<	if (e != null) {
556	<	V v = e.value;
557	<	if (value == null || value.equals(v)) {
558	<	oldValue = v;
559	<	// All entries following removed node can stay
560	<	// in list, but all preceding ones need to be
561	<	// cloned.
554	>	final boolean replace(K key, int hash, V oldValue, V newValue) {
555	>	if (!tryLock())
556	>	scanAndLock(key, hash);
557	>	boolean replaced = false;
558	>	try {
559	>	HashEntry<K,V> e;
560	>	for (e = entryForHash(this, hash); e != null; e = e.next) {
561	>	K k;
562	>	if ((k = e.key) == key ||
563	>	(e.hash == hash && key.equals(k))) {
564	>	if (oldValue.equals(e.value)) {
565	>	e.value = newValue;
566	>	++modCount;
567	>	replaced = true;
568	>	}
569	>	break;
570	>	}
571	>	}
572	>	} finally {
573	>	unlock();
574	>	}
575	>	return replaced;
576	>	}
577	>
578	>	final V replace(K key, int hash, V value) {
579	>	if (!tryLock())
580	>	scanAndLock(key, hash);
581	>	V oldValue = null;
582	>	try {
583	>	HashEntry<K,V> e;
584	>	for (e = entryForHash(this, hash); e != null; e = e.next) {
585	>	K k;
586	>	if ((k = e.key) == key ||
587	>	(e.hash == hash && key.equals(k))) {
588	>	oldValue = e.value;
589	>	e.value = value;
590		++modCount;
591	<	HashEntry<K,V> newFirst = e.next;
531	<	for (HashEntry<K,V> p = first; p != e; p = p.next)
532	<	newFirst = new HashEntry<K,V>(p.key, p.hash,
533	<	newFirst, p.value);
534	<	tab[index] = newFirst;
535	<	count = c; // write-volatile
591	>	break;
592		}
593		}
538	–	return oldValue;
594		} finally {
595		unlock();
596		}
597	+	return oldValue;
598		}
599
600	<	void clear() {
601	<	if (count != 0) {
602	<	lock();
603	<	try {
604	<	HashEntry<K,V>[] tab = table;
605	<	for (int i = 0; i < tab.length ; i++)
606	<	tab[i] = null;
607	<	++modCount;
608	<	count = 0; // write-volatile
609	<	} finally {
610	<	unlock();
600	>	final void clear() {
601	>	lock();
602	>	try {
603	>	HashEntry<K,V>[] tab = table;
604	>	for (int i = 0; i < tab.length ; i++)
605	>	setEntryAt(tab, i, null);
606	>	++modCount;
607	>	count = 0;
608	>	} finally {
609	>	unlock();
610	>	}
611	>	}
612	>	}
613	>
614	>	// Accessing segments
615	>
616	>	/**
617	>	* Gets the jth element of given segment array (if nonnull) with
618	>	* volatile element access semantics via Unsafe. (The null check
619	>	* can trigger harmlessly only during deserialization.) Note:
620	>	* because each element of segments array is set only once (using
621	>	* fully ordered writes), some performance-sensitive methods rely
622	>	* on this method only as a recheck upon null reads.
623	>	*/
624	>	@SuppressWarnings("unchecked")
625	>	static final <K,V> Segment<K,V> segmentAt(Segment<K,V>[] ss, int j) {
626	>	long u = (j << SSHIFT) + SBASE;
627	>	return ss == null ? null :
628	>	(Segment<K,V>) UNSAFE.getObjectVolatile(ss, u);
629	>	}
630	>
631	>	/**
632	>	* Returns the segment for the given index, creating it and
633	>	* recording in segment table (via CAS) if not already present.
634	>	*
635	>	* @param k the index
636	>	* @return the segment
637	>	*/
638	>	@SuppressWarnings("unchecked")
639	>	private Segment<K,V> ensureSegment(int k) {
640	>	final Segment<K,V>[] ss = this.segments;
641	>	long u = (k << SSHIFT) + SBASE; // raw offset
642	>	Segment<K,V> seg;
643	>	if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) == null) {
644	>	Segment<K,V> proto = ss[0]; // use segment 0 as prototype
645	>	int cap = proto.table.length;
646	>	float lf = proto.loadFactor;
647	>	int threshold = (int)(cap * lf);
648	>	HashEntry<K,V>[] tab = (HashEntry<K,V>[])new HashEntry<?,?>[cap];
649	>	if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u))
650	>	== null) { // recheck
651	>	Segment<K,V> s = new Segment<K,V>(lf, threshold, tab);
652	>	while ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u))
653	>	== null) {
654	>	if (UNSAFE.compareAndSwapObject(ss, u, null, seg = s))
655	>	break;
656		}
657		}
658		}
659	+	return seg;
660		}
661
662	+	// Hash-based segment and entry accesses
663	+
664	+	/**
665	+	* Gets the segment for the given hash code.
666	+	*/
667	+	@SuppressWarnings("unchecked")
668	+	private Segment<K,V> segmentForHash(int h) {
669	+	long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
670	+	return (Segment<K,V>) UNSAFE.getObjectVolatile(segments, u);
671	+	}
672
673	+	/**
674	+	* Gets the table entry for the given segment and hash code.
675	+	*/
676	+	@SuppressWarnings("unchecked")
677	+	static final <K,V> HashEntry<K,V> entryForHash(Segment<K,V> seg, int h) {
678	+	HashEntry<K,V>[] tab;
679	+	return (seg == null || (tab = seg.table) == null) ? null :
680	+	(HashEntry<K,V>) UNSAFE.getObjectVolatile
681	+	(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
682	+	}
683
684		/* ---------------- Public operations -------------- */
685
#	Line 577 | Line 699 | public class ConcurrentHashMap<K, V> ext
699		* negative or the load factor or concurrencyLevel are
700		* nonpositive.
701		*/
702	+	@SuppressWarnings("unchecked")
703		public ConcurrentHashMap(int initialCapacity,
704		float loadFactor, int concurrencyLevel) {
705		if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)
706		throw new IllegalArgumentException();
584	–
707		if (concurrencyLevel > MAX_SEGMENTS)
708		concurrencyLevel = MAX_SEGMENTS;
587	–
709		// Find power-of-two sizes best matching arguments
710		int sshift = 0;
711		int ssize = 1;
#	Line 592 | Line 713 | public class ConcurrentHashMap<K, V> ext
713		++sshift;
714		ssize <<= 1;
715		}
716	<	segmentShift = 32 - sshift;
717	<	segmentMask = ssize - 1;
597	<	this.segments = Segment.newArray(ssize);
598	<
716	>	this.segmentShift = 32 - sshift;
717	>	this.segmentMask = ssize - 1;
718		if (initialCapacity > MAXIMUM_CAPACITY)
719		initialCapacity = MAXIMUM_CAPACITY;
720		int c = initialCapacity / ssize;
721		if (c * ssize < initialCapacity)
722		++c;
723	<	int cap = 1;
723	>	int cap = MIN_SEGMENT_TABLE_CAPACITY;
724		while (cap < c)
725		cap <<= 1;
726	<
727	<	for (int i = 0; i < this.segments.length; ++i)
728	<	this.segments[i] = new Segment<K,V>(cap, loadFactor);
726	>	// create segments and segments[0]
727	>	Segment<K,V> s0 =
728	>	new Segment<K,V>(loadFactor, (int)(cap * loadFactor),
729	>	(HashEntry<K,V>[])new HashEntry<?,?>[cap]);
730	>	Segment<K,V>[] ss = (Segment<K,V>[])new Segment<?,?>[ssize];
731	>	UNSAFE.putOrderedObject(ss, SBASE, s0); // ordered write of segments[0]
732	>	this.segments = ss;
733		}
734
735		/**
736		* Creates a new, empty map with the specified initial capacity
737	<	* and load factor and with the default concurrencyLevel
615	<	* (<tt>16</tt>).
737	>	* and load factor and with the default concurrencyLevel (16).
738		*
739		* @param initialCapacity The implementation performs internal
740		* sizing to accommodate this many elements.
#	Line 621 | Line 743 | public class ConcurrentHashMap<K, V> ext
743		* bin exceeds this threshold.
744		* @throws IllegalArgumentException if the initial capacity of
745		* elements is negative or the load factor is nonpositive
746	+	*
747	+	* @since 1.6
748		*/
749		public ConcurrentHashMap(int initialCapacity, float loadFactor) {
750		this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
#	Line 628 | Line 752 | public class ConcurrentHashMap<K, V> ext
752
753		/**
754		* Creates a new, empty map with the specified initial capacity,
755	<	* and with default load factor (<tt>0.75f</tt>)
632	<	* and concurrencyLevel (<tt>16</tt>).
755	>	* and with default load factor (0.75) and concurrencyLevel (16).
756		*
757		* @param initialCapacity the initial capacity. The implementation
758		* performs internal sizing to accommodate this many elements.
#	Line 641 | Line 764 | public class ConcurrentHashMap<K, V> ext
764		}
765
766		/**
767	<	* Creates a new, empty map with a default initial capacity
768	<	* (<tt>16</tt>), load factor
646	<	* (<tt>0.75f</tt>), and concurrencyLevel
647	<	* (<tt>16</tt>).
767	>	* Creates a new, empty map with a default initial capacity (16),
768	>	* load factor (0.75) and concurrencyLevel (16).
769		*/
770		public ConcurrentHashMap() {
771		this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
772		}
773
774		/**
775	<	* Creates a new map with the same mappings as the given map.  The
776	<	* map is created with a capacity of 1.5 times the number of
777	<	* mappings in the given map or <tt>16</tt>
778	<	* (whichever is greater), and a default load factor
779	<	* (<tt>0.75f</tt>) and concurrencyLevel
659	<	* (<tt>16</tt>).
775	>	* Creates a new map with the same mappings as the given map.
776	>	* The map is created with a capacity of 1.5 times the number
777	>	* of mappings in the given map or 16 (whichever is greater),
778	>	* and a default load factor (0.75) and concurrencyLevel (16).
779	>	*
780		* @param m the map
781		*/
782		public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
#	Line 672 | Line 792 | public class ConcurrentHashMap<K, V> ext
792		* @return <tt>true</tt> if this map contains no key-value mappings
793		*/
794		public boolean isEmpty() {
675	–	final Segment<K,V>[] segments = this.segments;
795		/*
796	<	* We keep track of per-segment modCounts to avoid ABA
797	<	* problems in which an element in one segment was added and
798	<	* in another removed during traversal, in which case the
799	<	* table was never actually empty at any point. Note the
800	<	* similar use of modCounts in the size() and containsValue()
801	<	* methods, which are the only other methods also susceptible
802	<	* to ABA problems.
796	>	* Sum per-segment modCounts to avoid mis-reporting when
797	>	* elements are concurrently added and removed in one segment
798	>	* while checking another, in which case the table was never
799	>	* actually empty at any point. (The sum ensures accuracy up
800	>	* through at least 1<<31 per-segment modifications before
801	>	* recheck.)  Methods size() and containsValue() use similar
802	>	* constructions for stability checks.
803		*/
804	<	int[] mc = new int[segments.length];
805	<	int mcsum = 0;
806	<	for (int i = 0; i < segments.length; ++i) {
807	<	if (segments[i].count != 0)
808	<	return false;
809	<	else
691	<	mcsum += mc[i] = segments[i].modCount;
692	<	}
693	<	// If mcsum happens to be zero, then we know we got a snapshot
694	<	// before any modifications at all were made.  This is
695	<	// probably common enough to bother tracking.
696	<	if (mcsum != 0) {
697	<	for (int i = 0; i < segments.length; ++i) {
698	<	if (segments[i].count != 0 ||
699	<	mc[i] != segments[i].modCount)
804	>	long sum = 0L;
805	>	final Segment<K,V>[] segments = this.segments;
806	>	for (int j = 0; j < segments.length; ++j) {
807	>	Segment<K,V> seg = segmentAt(segments, j);
808	>	if (seg != null) {
809	>	if (seg.count != 0)
810		return false;
811	+	sum += seg.modCount;
812		}
813		}
814	+	if (sum != 0L) { // recheck unless no modifications
815	+	for (int j = 0; j < segments.length; ++j) {
816	+	Segment<K,V> seg = segmentAt(segments, j);
817	+	if (seg != null) {
818	+	if (seg.count != 0)
819	+	return false;
820	+	sum -= seg.modCount;
821	+	}
822	+	}
823	+	if (sum != 0L)
824	+	return false;
825	+	}
826		return true;
827		}
828
#	Line 711 | Line 834 | public class ConcurrentHashMap<K, V> ext
834		* @return the number of key-value mappings in this map
835		*/
836		public int size() {
714	–	final Segment<K,V>[] segments = this.segments;
715	–	long sum = 0;
716	–	long check = 0;
717	–	int[] mc = new int[segments.length];
837		// Try a few times to get accurate count. On failure due to
838		// continuous async changes in table, resort to locking.
839	<	for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
840	<	check = 0;
841	<	sum = 0;
842	<	int mcsum = 0;
843	<	for (int i = 0; i < segments.length; ++i) {
844	<	sum += segments[i].count;
845	<	mcsum += mc[i] = segments[i].modCount;
846	<	}
847	<	if (mcsum != 0) {
848	<	for (int i = 0; i < segments.length; ++i) {
849	<	check += segments[i].count;
850	<	if (mc[i] != segments[i].modCount) {
732	<	check = -1; // force retry
733	<	break;
734	<	}
839	>	final Segment<K,V>[] segments = this.segments;
840	>	final int segmentCount = segments.length;
841	>
842	>	long previousSum = 0L;
843	>	for (int retries = -1; retries < RETRIES_BEFORE_LOCK; retries++) {
844	>	long sum = 0L;    // sum of modCounts
845	>	long size = 0L;
846	>	for (int i = 0; i < segmentCount; i++) {
847	>	Segment<K,V> segment = segmentAt(segments, i);
848	>	if (segment != null) {
849	>	sum += segment.modCount;
850	>	size += segment.count;
851		}
852		}
853	<	if (check == sum)
854	<	break;
853	>	if (sum == previousSum)
854	>	return ((size >>> 31) == 0) ? (int) size : Integer.MAX_VALUE;
855	>	previousSum = sum;
856		}
857	<	if (check != sum) { // Resort to locking all segments
858	<	sum = 0;
859	<	for (int i = 0; i < segments.length; ++i)
860	<	segments[i].lock();
861	<	for (int i = 0; i < segments.length; ++i)
862	<	sum += segments[i].count;
863	<	for (int i = 0; i < segments.length; ++i)
864	<	segments[i].unlock();
865	<	}
866	<	if (sum > Integer.MAX_VALUE)
750	<	return Integer.MAX_VALUE;
751	<	else
752	<	return (int)sum;
857	>
858	>	long size = 0L;
859	>	for (int i = 0; i < segmentCount; i++) {
860	>	Segment<K,V> segment = ensureSegment(i);
861	>	segment.lock();
862	>	size += segment.count;
863	>	}
864	>	for (int i = 0; i < segmentCount; i++)
865	>	segments[i].unlock();
866	>	return ((size >>> 31) == 0) ? (int) size : Integer.MAX_VALUE;
867		}
868
869		/**
870	<	* Returns the value to which this map maps the specified key, or
871	<	* <tt>null</tt> if the map contains no mapping for the key.
872	<	*
873	<	* @param key key whose associated value is to be returned
874	<	* @return the value associated with <tt>key</tt> in this map, or
875	<	*         <tt>null</tt> if there is no mapping for <tt>key</tt>
870	>	* Returns the value to which the specified key is mapped,
871	>	* or {@code null} if this map contains no mapping for the key.
872	>	*
873	>	* <p>More formally, if this map contains a mapping from a key
874	>	* {@code k} to a value {@code v} such that {@code key.equals(k)},
875	>	* then this method returns {@code v}; otherwise it returns
876	>	* {@code null}.  (There can be at most one such mapping.)
877	>	*
878		* @throws NullPointerException if the specified key is null
879		*/
880	+	@SuppressWarnings("unchecked")
881		public V get(Object key) {
882	<	int hash = hash(key); // throws NullPointerException if key null
883	<	return segmentFor(hash).get(key, hash);
882	>	Segment<K,V> s; // manually integrate access methods to reduce overhead
883	>	HashEntry<K,V>[] tab;
884	>	int h = hash(key.hashCode());
885	>	long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
886	>	if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null &&
887	>	(tab = s.table) != null) {
888	>	for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile
889	>	(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
890	>	e != null; e = e.next) {
891	>	K k;
892	>	if ((k = e.key) == key || (e.hash == h && key.equals(k)))
893	>	return e.value;
894	>	}
895	>	}
896	>	return null;
897		}
898
899		/**
#	Line 775 | Line 905 | public class ConcurrentHashMap<K, V> ext
905		*         <tt>equals</tt> method; <tt>false</tt> otherwise.
906		* @throws NullPointerException if the specified key is null
907		*/
908	+	@SuppressWarnings("unchecked")
909		public boolean containsKey(Object key) {
910	<	int hash = hash(key); // throws NullPointerException if key null
911	<	return segmentFor(hash).containsKey(key, hash);
910	>	Segment<K,V> s; // same as get() except no need for volatile value read
911	>	HashEntry<K,V>[] tab;
912	>	int h = hash(key.hashCode());
913	>	long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
914	>	if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null &&
915	>	(tab = s.table) != null) {
916	>	for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile
917	>	(tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
918	>	e != null; e = e.next) {
919	>	K k;
920	>	if ((k = e.key) == key || (e.hash == h && key.equals(k)))
921	>	return true;
922	>	}
923	>	}
924	>	return false;
925		}
926
927		/**
#	Line 792 | Line 936 | public class ConcurrentHashMap<K, V> ext
936		* @throws NullPointerException if the specified value is null
937		*/
938		public boolean containsValue(Object value) {
939	+	// Same idea as size()
940		if (value == null)
941		throw new NullPointerException();
797	–
798	–	// See explanation of modCount use above
799	–
942		final Segment<K,V>[] segments = this.segments;
943	<	int[] mc = new int[segments.length];
944	<
803	<	// Try a few times without locking
804	<	for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
805	<	int sum = 0;
806	<	int mcsum = 0;
807	<	for (int i = 0; i < segments.length; ++i) {
808	<	int c = segments[i].count;
809	<	mcsum += mc[i] = segments[i].modCount;
810	<	if (segments[i].containsValue(value))
811	<	return true;
812	<	}
813	<	boolean cleanSweep = true;
814	<	if (mcsum != 0) {
815	<	for (int i = 0; i < segments.length; ++i) {
816	<	int c = segments[i].count;
817	<	if (mc[i] != segments[i].modCount) {
818	<	cleanSweep = false;
819	<	break;
820	<	}
821	<	}
822	<	}
823	<	if (cleanSweep)
824	<	return false;
825	<	}
826	<	// Resort to locking all segments
827	<	for (int i = 0; i < segments.length; ++i)
828	<	segments[i].lock();
829	<	boolean found = false;
943	>	long previousSum = 0L;
944	>	int lockCount = 0;
945		try {
946	<	for (int i = 0; i < segments.length; ++i) {
947	<	if (segments[i].containsValue(value)) {
948	<	found = true;
949	<	break;
946	>	for (int retries = -1; ; retries++) {
947	>	long sum = 0L;    // sum of modCounts
948	>	for (int j = 0; j < segments.length; j++) {
949	>	Segment<K,V> segment;
950	>	if (retries == RETRIES_BEFORE_LOCK) {
951	>	segment = ensureSegment(j);
952	>	segment.lock();
953	>	lockCount++;
954	>	} else {
955	>	segment = segmentAt(segments, j);
956	>	if (segment == null)
957	>	continue;
958	>	}
959	>	HashEntry<K,V>[] tab = segment.table;
960	>	if (tab != null) {
961	>	for (int i = 0 ; i < tab.length; i++) {
962	>	HashEntry<K,V> e;
963	>	for (e = entryAt(tab, i); e != null; e = e.next) {
964	>	V v = e.value;
965	>	if (v != null && value.equals(v))
966	>	return true;
967	>	}
968	>	}
969	>	sum += segment.modCount;
970	>	}
971		}
972	+	if ((retries >= 0 && sum == previousSum) || lockCount > 0)
973	+	return false;
974	+	previousSum = sum;
975		}
976		} finally {
977	<	for (int i = 0; i < segments.length; ++i)
978	<	segments[i].unlock();
977	>	for (int j = 0; j < lockCount; j++)
978	>	segments[j].unlock();
979		}
841	–	return found;
980		}
981
982		/**
#	Line 848 | Line 986 | public class ConcurrentHashMap<K, V> ext
986		* full compatibility with class {@link java.util.Hashtable},
987		* which supported this method prior to introduction of the
988		* Java Collections framework.
989	<
989	>	*
990		* @param  value a value to search for
991		* @return <tt>true</tt> if and only if some key maps to the
992		*         <tt>value</tt> argument in this table as
#	Line 873 | Line 1011 | public class ConcurrentHashMap<K, V> ext
1011		*         <tt>null</tt> if there was no mapping for <tt>key</tt>
1012		* @throws NullPointerException if the specified key or value is null
1013		*/
1014	+	@SuppressWarnings("unchecked")
1015		public V put(K key, V value) {
1016	+	Segment<K,V> s;
1017		if (value == null)
1018		throw new NullPointerException();
1019	<	int hash = hash(key);
1020	<	return segmentFor(hash).put(key, hash, value, false);
1019	>	int hash = hash(key.hashCode());
1020	>	int j = (hash >>> segmentShift) & segmentMask;
1021	>	if ((s = (Segment<K,V>)UNSAFE.getObject          // nonvolatile; recheck
1022	>	(segments, (j << SSHIFT) + SBASE)) == null) //  in ensureSegment
1023	>	s = ensureSegment(j);
1024	>	return s.put(key, hash, value, false);
1025		}
1026
1027		/**
#	Line 887 | Line 1031 | public class ConcurrentHashMap<K, V> ext
1031		*         or <tt>null</tt> if there was no mapping for the key
1032		* @throws NullPointerException if the specified key or value is null
1033		*/
1034	+	@SuppressWarnings("unchecked")
1035		public V putIfAbsent(K key, V value) {
1036	+	Segment<K,V> s;
1037		if (value == null)
1038		throw new NullPointerException();
1039	<	int hash = hash(key);
1040	<	return segmentFor(hash).put(key, hash, value, true);
1039	>	int hash = hash(key.hashCode());
1040	>	int j = (hash >>> segmentShift) & segmentMask;
1041	>	if ((s = (Segment<K,V>)UNSAFE.getObject
1042	>	(segments, (j << SSHIFT) + SBASE)) == null)
1043	>	s = ensureSegment(j);
1044	>	return s.put(key, hash, value, true);
1045		}
1046
1047		/**
#	Line 902 | Line 1052 | public class ConcurrentHashMap<K, V> ext
1052		* @param m mappings to be stored in this map
1053		*/
1054		public void putAll(Map<? extends K, ? extends V> m) {
1055	<	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();
1055	>	for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
1056		put(e.getKey(), e.getValue());
908	–	}
1057		}
1058
1059		/**
#	Line 914 | Line 1062 | public class ConcurrentHashMap<K, V> ext
1062		*
1063		* @param  key the key that needs to be removed
1064		* @return the previous value associated with <tt>key</tt>, or
1065	<	*         <tt>null</tt> if there was no mapping for <tt>key</tt>.
1065	>	*         <tt>null</tt> if there was no mapping for <tt>key</tt>
1066		* @throws NullPointerException if the specified key is null
1067		*/
1068		public V remove(Object key) {
1069	<	int hash = hash(key);
1070	<	return segmentFor(hash).remove(key, hash, null);
1069	>	int hash = hash(key.hashCode());
1070	>	Segment<K,V> s = segmentForHash(hash);
1071	>	return s == null ? null : s.remove(key, hash, null);
1072		}
1073
1074		/**
#	Line 928 | Line 1077 | public class ConcurrentHashMap<K, V> ext
1077		* @throws NullPointerException if the specified key is null
1078		*/
1079		public boolean remove(Object key, Object value) {
1080	<	if (value == null)
1081	<	return false;
1082	<	int hash = hash(key);
1083	<	return segmentFor(hash).remove(key, hash, value) != null;
1080	>	int hash = hash(key.hashCode());
1081	>	Segment<K,V> s;
1082	>	return value != null && (s = segmentForHash(hash)) != null &&
1083	>	s.remove(key, hash, value) != null;
1084		}
1085
1086		/**
#	Line 940 | Line 1089 | public class ConcurrentHashMap<K, V> ext
1089		* @throws NullPointerException if any of the arguments are null
1090		*/
1091		public boolean replace(K key, V oldValue, V newValue) {
1092	+	int hash = hash(key.hashCode());
1093		if (oldValue == null || newValue == null)
1094		throw new NullPointerException();
1095	<	int hash = hash(key);
1096	<	return segmentFor(hash).replace(key, hash, oldValue, newValue);
1095	>	Segment<K,V> s = segmentForHash(hash);
1096	>	return s != null && s.replace(key, hash, oldValue, newValue);
1097		}
1098
1099		/**
#	Line 954 | Line 1104 | public class ConcurrentHashMap<K, V> ext
1104		* @throws NullPointerException if the specified key or value is null
1105		*/
1106		public V replace(K key, V value) {
1107	+	int hash = hash(key.hashCode());
1108		if (value == null)
1109		throw new NullPointerException();
1110	<	int hash = hash(key);
1111	<	return segmentFor(hash).replace(key, hash, value);
1110	>	Segment<K,V> s = segmentForHash(hash);
1111	>	return s == null ? null : s.replace(key, hash, value);
1112		}
1113
1114		/**
1115		* Removes all of the mappings from this map.
1116		*/
1117		public void clear() {
1118	<	for (int i = 0; i < segments.length; ++i)
1119	<	segments[i].clear();
1118	>	final Segment<K,V>[] segments = this.segments;
1119	>	for (int j = 0; j < segments.length; ++j) {
1120	>	Segment<K,V> s = segmentAt(segments, j);
1121	>	if (s != null)
1122	>	s.clear();
1123	>	}
1124		}
1125
1126		/**
#	Line 1035 | Line 1190 | public class ConcurrentHashMap<K, V> ext
1190		* Returns an enumeration of the keys in this table.
1191		*
1192		* @return an enumeration of the keys in this table
1193	<	* @see #keySet
1193	>	* @see #keySet()
1194		*/
1195		public Enumeration<K> keys() {
1196		return new KeyIterator();
#	Line 1045 | Line 1200 | public class ConcurrentHashMap<K, V> ext
1200		* Returns an enumeration of the values in this table.
1201		*
1202		* @return an enumeration of the values in this table
1203	<	* @see #values
1203	>	* @see #values()
1204		*/
1205		public Enumeration<V> elements() {
1206		return new ValueIterator();
#	Line 1066 | Line 1221 | public class ConcurrentHashMap<K, V> ext
1221		advance();
1222		}
1223
1224	<	public boolean hasMoreElements() { return hasNext(); }
1225	<
1224	>	/**
1225	>	* Sets nextEntry to first node of next non-empty table
1226	>	* (in backwards order, to simplify checks).
1227	>	*/
1228		final void advance() {
1229	<	if (nextEntry != null && (nextEntry = nextEntry.next) != null)
1230	<	return;
1231	<
1232	<	while (nextTableIndex >= 0) {
1233	<	if ( (nextEntry = currentTable[nextTableIndex--]) != null)
1234	<	return;
1235	<	}
1236	<
1237	<	while (nextSegmentIndex >= 0) {
1238	<	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 = currentTable[j]) != null) {
1086	<	nextTableIndex = j - 1;
1087	<	return;
1088	<	}
1089	<	}
1229	>	for (;;) {
1230	>	if (nextTableIndex >= 0) {
1231	>	if ((nextEntry = entryAt(currentTable,
1232	>	nextTableIndex--)) != null)
1233	>	break;
1234	>	}
1235	>	else if (nextSegmentIndex >= 0) {
1236	>	Segment<K,V> seg = segmentAt(segments, nextSegmentIndex--);
1237	>	if (seg != null && (currentTable = seg.table) != null)
1238	>	nextTableIndex = currentTable.length - 1;
1239		}
1240	+	else
1241	+	break;
1242		}
1243		}
1244
1245	<	public boolean hasNext() { return nextEntry != null; }
1246	<
1247	<	HashEntry<K,V> nextEntry() {
1097	<	if (nextEntry == null)
1245	>	final HashEntry<K,V> nextEntry() {
1246	>	HashEntry<K,V> e = nextEntry;
1247	>	if (e == null)
1248		throw new NoSuchElementException();
1249	<	lastReturned = nextEntry;
1250	<	advance();
1251	<	return lastReturned;
1249	>	lastReturned = e; // cannot assign until after null check
1250	>	if ((nextEntry = e.next) == null)
1251	>	advance();
1252	>	return e;
1253		}
1254
1255	<	public void remove() {
1255	>	public final boolean hasNext() { return nextEntry != null; }
1256	>	public final boolean hasMoreElements() { return nextEntry != null; }
1257	>
1258	>	public final void remove() {
1259		if (lastReturned == null)
1260		throw new IllegalStateException();
1261		ConcurrentHashMap.this.remove(lastReturned.key);
#	Line 1109 | Line 1263 | public class ConcurrentHashMap<K, V> ext
1263		}
1264		}
1265
1266	<	final class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> {
1267	<	public K next() { return super.nextEntry().key; }
1268	<	public K nextElement() { return super.nextEntry().key; }
1266	>	final class KeyIterator
1267	>	extends HashIterator
1268	>	implements Iterator<K>, Enumeration<K>
1269	>	{
1270	>	public final K next()        { return super.nextEntry().key; }
1271	>	public final K nextElement() { return super.nextEntry().key; }
1272		}
1273
1274	<	final class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> {
1275	<	public V next() { return super.nextEntry().value; }
1276	<	public V nextElement() { return super.nextEntry().value; }
1274	>	final class ValueIterator
1275	>	extends HashIterator
1276	>	implements Iterator<V>, Enumeration<V>
1277	>	{
1278	>	public final V next()        { return super.nextEntry().value; }
1279	>	public final V nextElement() { return super.nextEntry().value; }
1280		}
1281
1122	–
1123	–
1282		/**
1283	<	* Entry iterator. Exported Entry objects must write-through
1284	<	* 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.
1283	>	* Custom Entry class used by EntryIterator.next(), that relays
1284	>	* setValue changes to the underlying map.
1285		*/
1286	<	final class EntryIterator extends HashIterator implements Map.Entry<K,V>, Iterator<Entry<K,V>> {
1287	<	public Map.Entry<K,V> next() {
1288	<	nextEntry();
1289	<	return this;
1134	<	}
1286	>	final class WriteThroughEntry
1287	>	extends AbstractMap.SimpleEntry<K,V>
1288	>	{
1289	>	static final long serialVersionUID = 7249069246763182397L;
1290
1291	<	public K getKey() {
1292	<	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);
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	<	}
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();
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		}
1186	–
1320		}
1321
1322		final class KeySet extends AbstractSet<K> {
#	Line 1193 | 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 1202 | Line 1338 | public class ConcurrentHashMap<K, V> ext
1338		public void clear() {
1339		ConcurrentHashMap.this.clear();
1340		}
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	–	}
1341		}
1342
1343		final class Values extends AbstractCollection<V> {
#	Line 1223 | 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		}
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	–	}
1359		}
1360
1361		final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
#	Line 1263 | Line 1378 | public class ConcurrentHashMap<K, V> ext
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		}
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	–
1387		}
1388
1389		/* ---------------- Serialization Support -------------- */
1390
1391		/**
1392	<	* Save the state of the <tt>ConcurrentHashMap</tt> instance to a
1393	<	* stream (i.e., 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)
1401	>	throws java.io.IOException {
1402	>	// force all segments for serialization compatibility
1403	>	for (int k = 0; k < segments.length; ++k)
1404	>	ensureSegment(k);
1405		s.defaultWriteObject();
1406
1407	+	final Segment<K,V>[] segments = this.segments;
1408		for (int k = 0; k < segments.length; ++k) {
1409	<	Segment<K,V> seg = segments[k];
1409	>	Segment<K,V> seg = segmentAt(segments, k);
1410		seg.lock();
1411		try {
1412		HashEntry<K,V>[] tab = seg.table;
1413		for (int i = 0; i < tab.length; ++i) {
1414	<	for (HashEntry<K,V> e = tab[i]; e != null; e = e.next) {
1414	>	HashEntry<K,V> e;
1415	>	for (e = entryAt(tab, i); e != null; e = e.next) {
1416		s.writeObject(e.key);
1417		s.writeObject(e.value);
1418		}
#	Line 1317 | Line 1426 | public class ConcurrentHashMap<K, V> ext
1426		}
1427
1428		/**
1429	<	* Reconstitute the <tt>ConcurrentHashMap</tt> instance from a
1430	<	* stream (i.e., deserialize it).
1429	>	* Reconstitutes the <tt>ConcurrentHashMap</tt> instance from a
1430	>	* stream (i.e., deserializes it).
1431		* @param s the stream
1432		*/
1433	+	@SuppressWarnings("unchecked")
1434		private void readObject(java.io.ObjectInputStream s)
1435	<	throws IOException, ClassNotFoundException  {
1435	>	throws java.io.IOException, ClassNotFoundException {
1436		s.defaultReadObject();
1437
1438	<	// Initialize each segment to be minimally sized, and let grow.
1439	<	for (int i = 0; i < segments.length; ++i) {
1440	<	segments[i].setTable(new HashEntry[1]);
1438	>	// Re-initialize segments to be minimally sized, and let grow.
1439	>	int cap = MIN_SEGMENT_TABLE_CAPACITY;
1440	>	final Segment<K,V>[] segments = this.segments;
1441	>	for (int k = 0; k < segments.length; ++k) {
1442	>	Segment<K,V> seg = segments[k];
1443	>	if (seg != null) {
1444	>	seg.threshold = (int)(cap * seg.loadFactor);
1445	>	seg.table = (HashEntry<K,V>[]) new HashEntry<?,?>[cap];
1446	>	}
1447		}
1448
1449		// Read the keys and values, and put the mappings in the table
#	Line 1339 | Line 1455 | public class ConcurrentHashMap<K, V> ext
1455		put(key, value);
1456		}
1457		}
1458	+
1459	+	// Unsafe mechanics
1460	+	private static final sun.misc.Unsafe UNSAFE;
1461	+	private static final long SBASE;
1462	+	private static final int SSHIFT;
1463	+	private static final long TBASE;
1464	+	private static final int TSHIFT;
1465	+
1466	+	static {
1467	+	int ss, ts;
1468	+	try {
1469	+	UNSAFE = sun.misc.Unsafe.getUnsafe();
1470	+	Class<?> tc = HashEntry[].class;
1471	+	Class<?> sc = Segment[].class;
1472	+	TBASE = UNSAFE.arrayBaseOffset(tc);
1473	+	SBASE = UNSAFE.arrayBaseOffset(sc);
1474	+	ts = UNSAFE.arrayIndexScale(tc);
1475	+	ss = UNSAFE.arrayIndexScale(sc);
1476	+	} catch (Exception e) {
1477	+	throw new Error(e);
1478	+	}
1479	+	if ((ss & (ss-1)) != 0 || (ts & (ts-1)) != 0)
1480	+	throw new Error("data type scale not a power of two");
1481	+	SSHIFT = 31 - Integer.numberOfLeadingZeros(ss);
1482	+	TSHIFT = 31 - Integer.numberOfLeadingZeros(ts);
1483	+	}
1484	+
1485		}

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines