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Comparing jsr166/src/main/java/util/concurrent/ConcurrentHashMap.java (file contents):
Revision 1.44 by dl, Mon Feb 9 13:28:47 2004 UTC vs.
Revision 1.45 by dl, Sat Apr 10 14:21:45 2004 UTC

#	Line 49 | Line 49 | import java.io.ObjectOutputStream;
49		* and a significantly lower value can lead to thread contention. But
50		* overestimates and underestimates within an order of magnitude do
51		* not usually have much noticeable impact. A value of one is
52	<	* appropriate when it is known that only one thread will modify
53	<	* and all others will only read.
52	>	* appropriate when it is known that only one thread will modify and
53	>	* all others will only read. Also, resizing this or any other kind of
54	>	* hash table is a relatively slow operation, so, when possible, it is
55	>	* a good idea to provide estimates of expected table sizes in
56	>	* constructors.
57		*
58	<	* <p>This class implements all of the <em>optional</em> methods
59	<	* of the {@link Map} and {@link Iterator} interfaces.
58	>	* <p>This class and its views and iterators implement all of the
59	>	* <em>optional</em> methods of the {@link Map} and {@link Iterator}
60	>	* interfaces.
61		*
62		* <p> Like {@link java.util.Hashtable} but unlike {@link
63		* java.util.HashMap}, this class does NOT allow <tt>null</tt> to be
#	Line 178 | Line 182 | public class ConcurrentHashMap<K, V> ext
182		* is less than two for the default load factor threshold.)
183		*
184		* Read operations can thus proceed without locking, but rely
185	<	* on a memory barrier to ensure that completed write
186	<	* operations performed by other threads are
187	<	* noticed. Conveniently, the "count" field, tracking the
188	<	* number of elements, can also serve as the volatile variable
189	<	* providing proper read/write barriers. This is convenient
190	<	* because this field needs to be read in many read operations
187	<	* anyway.
185	>	* on selected uses of volatiles to ensure that completed
186	>	* write operations performed by other threads are
187	>	* noticed. For most purposes, the "count" field, tracking the
188	>	* number of elements, serves as that volatile variable
189	>	* ensuring visibility.  This is convenient because this field
190	>	* needs to be read in many read operations anyway:
191		*
192	<	* Implementors note. The basic rules for all this are:
190	<	*
191	<	*   - All unsynchronized read operations must first read the
192	>	*   - All (unsynchronized) read operations must first read the
193		*     "count" field, and should not look at table entries if
194		*     it is 0.
195		*
196	<	*   - All synchronized write operations should write to
197	<	*     the "count" field after updating. The operations must not
198	<	*     take any action that could even momentarily cause
199	<	*     a concurrent read operation to see inconsistent
200	<	*     data. This is made easier by the nature of the read
201	<	*     operations in Map. For example, no operation
196	>	*   - All (synchronized) write operations should write to
197	>	*     the "count" field after structurally changing any bin.
198	>	*     The operations must not take any action that could even
199	>	*     momentarily cause a concurrent read operation to see
200	>	*     inconsistent data. This is made easier by the nature of
201	>	*     the read operations in Map. For example, no operation
202		*     can reveal that the table has grown but the threshold
203		*     has not yet been updated, so there are no atomicity
204		*     requirements for this with respect to reads.
205		*
206	<	* As a guide, all critical volatile reads and writes are marked
207	<	* in code comments.
206	>	* As a guide, all critical volatile reads and writes to the
207	>	* count field are marked in code comments.
208		*/
209
210		private static final long serialVersionUID = 2249069246763182397L;
#	Line 214 | Line 215 | public class ConcurrentHashMap<K, V> ext
215		transient volatile int count;
216
217		/**
218	<	* Number of updates; used for checking lack of modifications
219	<	* in bulk-read methods.
218	>	* Number of updates that alter the size of the table. This is
219	>	* used during bulk-read methods to make sure they see a
220	>	* consistent snapshot: If modCounts change during a traversal
221	>	* of segments computing size or checking contatinsValue, then
222	>	* we might have an inconsistent view of state so (usually)
223	>	* must retry.
224		*/
225		transient int modCount;
226
#	Line 227 | Line 232 | public class ConcurrentHashMap<K, V> ext
232		transient int threshold;
233
234		/**
235	<	* The per-segment table
235	>	* The per-segment table. Declared as a raw type, casted
236	>	* to HashEntry<K,V> on each use.
237		*/
238	<	transient HashEntry[] table;
238	>	transient volatile HashEntry[] table;
239
240		/**
241		* The load factor for the hash table.  Even though this value
#	Line 249 | Line 255 | public class ConcurrentHashMap<K, V> ext
255		* Call only while holding lock or in constructor.
256		**/
257		void setTable(HashEntry[] newTable) {
252	–	table = newTable;
258		threshold = (int)(newTable.length * loadFactor);
259	<	count = count; // write-volatile
259	>	table = newTable;
260	>	}
261	>
262	>	/**
263	>	* Return properly casted first entry of bin for given hash
264	>	*/
265	>	HashEntry<K,V> getFirst(int hash) {
266	>	HashEntry[] tab = table;
267	>	return (HashEntry<K,V>) tab[hash & (tab.length - 1)];
268	>	}
269	>
270	>	/**
271	>	* Read value field of an entry under lock. Called if value
272	>	* field ever appears to be null. This is possible only if a
273	>	* compiler happens to reorder a HashEntry initialization with
274	>	* its table assignment, which is legal under memory model
275	>	* but is not known to ever occur.
276	>	*/
277	>	V readValueUnderLock(HashEntry<K,V> e) {
278	>	lock();
279	>	try {
280	>	return e.value;
281	>	} finally {
282	>	unlock();
283	>	}
284		}
285
286		/* Specialized implementations of map methods */
287
288		V get(Object key, int hash) {
289		if (count != 0) { // read-volatile
290	<	HashEntry[] tab = table;
262	<	int index = hash & (tab.length - 1);
263	<	HashEntry<K,V> e = (HashEntry<K,V>) tab[index];
290	>	HashEntry<K,V> e = getFirst(hash);
291		while (e != null) {
292	<	if (e.hash == hash && key.equals(e.key))
293	<	return e.value;
292	>	if (e.hash == hash && key.equals(e.key)) {
293	>	V v = e.value;
294	>	if (v != null)
295	>	return v;
296	>	return readValueUnderLock(e); // recheck
297	>	}
298		e = e.next;
299		}
300		}
#	Line 272 | Line 303 | public class ConcurrentHashMap<K, V> ext
303
304		boolean containsKey(Object key, int hash) {
305		if (count != 0) { // read-volatile
306	<	HashEntry[] tab = table;
276	<	int index = hash & (tab.length - 1);
277	<	HashEntry<K,V> e = (HashEntry<K,V>) tab[index];
306	>	HashEntry<K,V> e = getFirst(hash);
307		while (e != null) {
308		if (e.hash == hash && key.equals(e.key))
309		return true;
#	Line 288 | Line 317 | public class ConcurrentHashMap<K, V> ext
317		if (count != 0) { // read-volatile
318		HashEntry[] tab = table;
319		int len = tab.length;
320	<	for (int i = 0 ; i < len; i++)
321	<	for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i] ; e != null ; e = e.next)
322	<	if (value.equals(e.value))
320	>	for (int i = 0 ; i < len; i++) {
321	>	for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i];
322	>	e != null ;
323	>	e = e.next) {
324	>	V v = e.value;
325	>	if (v == null) // recheck
326	>	v = readValueUnderLock(e);
327	>	if (value.equals(v))
328		return true;
329	+	}
330	+	}
331		}
332		return false;
333		}
#	Line 299 | Line 335 | public class ConcurrentHashMap<K, V> ext
335		boolean replace(K key, int hash, V oldValue, V newValue) {
336		lock();
337		try {
338	<	int c = count;
339	<	HashEntry[] tab = table;
304	<	int index = hash & (tab.length - 1);
305	<	HashEntry<K,V> first = (HashEntry<K,V>) tab[index];
306	<	HashEntry<K,V> e = first;
307	<	for (;;) {
308	<	if (e == null)
309	<	return false;
310	<	if (e.hash == hash && key.equals(e.key))
311	<	break;
338	>	HashEntry<K,V> e = getFirst(hash);
339	>	while (e != null && (e.hash != hash || !key.equals(e.key)))
340		e = e.next;
313	–	}
341
342	<	V v = e.value;
343	<	if (v == null || !oldValue.equals(v))
344	<	return false;
345	<
346	<	e.value = newValue;
347	<	count = c; // write-volatile
321	<	return true;
322	<
342	>	boolean replaced = false;
343	>	if (e != null && oldValue.equals(e.value)) {
344	>	replaced = true;
345	>	e.value = newValue;
346	>	}
347	>	return replaced;
348		} finally {
349		unlock();
350		}
#	Line 328 | Line 353 | public class ConcurrentHashMap<K, V> ext
353		V replace(K key, int hash, V newValue) {
354		lock();
355		try {
356	<	int c = count;
357	<	HashEntry[] tab = table;
333	<	int index = hash & (tab.length - 1);
334	<	HashEntry<K,V> first = (HashEntry<K,V>) tab[index];
335	<	HashEntry<K,V> e = first;
336	<	for (;;) {
337	<	if (e == null)
338	<	return null;
339	<	if (e.hash == hash && key.equals(e.key))
340	<	break;
356	>	HashEntry<K,V> e = getFirst(hash);
357	>	while (e != null && (e.hash != hash || !key.equals(e.key)))
358		e = e.next;
342	–	}
359
360	<	V v = e.value;
361	<	e.value = newValue;
362	<	count = c; // write-volatile
363	<	return v;
364	<
360	>	V oldValue = null;
361	>	if (e != null) {
362	>	oldValue = e.value;
363	>	e.value = newValue;
364	>	}
365	>	return oldValue;
366		} finally {
367		unlock();
368		}
#	Line 356 | Line 373 | public class ConcurrentHashMap<K, V> ext
373		lock();
374		try {
375		int c = count;
376	+	if (c++ > threshold) // ensure capacity
377	+	rehash();
378		HashEntry[] tab = table;
379		int index = hash & (tab.length - 1);
380		HashEntry<K,V> first = (HashEntry<K,V>) tab[index];
381	+	HashEntry<K,V> e = first;
382	+	while (e != null && (e.hash != hash || !key.equals(e.key)))
383	+	e = e.next;
384
385	<	for (HashEntry<K,V> e = first; e != null; e = (HashEntry<K,V>) e.next) {
386	<	if (e.hash == hash && key.equals(e.key)) {
387	<	V oldValue = e.value;
388	<	if (!onlyIfAbsent)
389	<	e.value = value;
368	<	++modCount;
369	<	count = c; // write-volatile
370	<	return oldValue;
371	<	}
385	>	V oldValue;
386	>	if (e != null) {
387	>	oldValue = e.value;
388	>	if (!onlyIfAbsent)
389	>	e.value = value;
390		}
391	<
392	<	tab[index] = new HashEntry<K,V>(hash, key, value, first);
393	<	++modCount;
394	<	++c;
395	<	count = c; // write-volatile
396	<	if (c > threshold)
397	<	setTable(rehash(tab));
380	<	return null;
391	>	else {
392	>	oldValue = null;
393	>	++modCount;
394	>	tab[index] = new HashEntry<K,V>(key, hash, first, value);
395	>	count = c; // write-volatile
396	>	}
397	>	return oldValue;
398		} finally {
399		unlock();
400		}
401		}
402
403	<	HashEntry[] rehash(HashEntry[] oldTable) {
403	>	void rehash() {
404	>	HashEntry[] oldTable = table;
405		int oldCapacity = oldTable.length;
406		if (oldCapacity >= MAXIMUM_CAPACITY)
407	<	return oldTable;
407	>	return;
408
409		/*
410		* Reclassify nodes in each list to new Map.  Because we are
#	Line 403 | Line 421 | public class ConcurrentHashMap<K, V> ext
421		*/
422
423		HashEntry[] newTable = new HashEntry[oldCapacity << 1];
424	+	threshold = (int)(newTable.length * loadFactor);
425		int sizeMask = newTable.length - 1;
426		for (int i = 0; i < oldCapacity ; i++) {
427		// We need to guarantee that any existing reads of old Map can
#	Line 435 | Line 454 | public class ConcurrentHashMap<K, V> ext
454		// Clone all remaining nodes
455		for (HashEntry<K,V> p = e; p != lastRun; p = p.next) {
456		int k = p.hash & sizeMask;
457	<	newTable[k] = new HashEntry<K,V>(p.hash,
458	<	p.key,
459	<	p.value,
441	<	(HashEntry<K,V>) newTable[k]);
457	>	HashEntry<K,V> n = (HashEntry<K,V>)newTable[k];
458	>	newTable[k] = new HashEntry<K,V>(p.key, p.hash,
459	>	n, p.value);
460		}
461		}
462		}
463		}
464	<	return newTable;
464	>	table = newTable;
465		}
466
467		/**
#	Line 452 | Line 470 | public class ConcurrentHashMap<K, V> ext
470		V remove(Object key, int hash, Object value) {
471		lock();
472		try {
473	<	int c = count;
473	>	int c = count - 1;
474		HashEntry[] tab = table;
475		int index = hash & (tab.length - 1);
476		HashEntry<K,V> first = (HashEntry<K,V>)tab[index];
459	–
477		HashEntry<K,V> e = first;
478	<	for (;;) {
462	<	if (e == null)
463	<	return null;
464	<	if (e.hash == hash && key.equals(e.key))
465	<	break;
478	>	while (e != null && (e.hash != hash || !key.equals(e.key)))
479		e = e.next;
467	–	}
480
481	<	V oldValue = e.value;
482	<	if (value != null && !value.equals(oldValue))
483	<	return null;
484	<
485	<	// All entries following removed node can stay in list, but
486	<	// all preceding ones need to be cloned.
487	<	HashEntry<K,V> newFirst = e.next;
488	<	for (HashEntry<K,V> p = first; p != e; p = p.next)
489	<	newFirst = new HashEntry<K,V>(p.hash, p.key,
490	<	p.value, newFirst);
491	<	tab[index] = newFirst;
492	<	++modCount;
493	<	count = c-1; // write-volatile
481	>	V oldValue = null;
482	>	if (e != null) {
483	>	V v = e.value;
484	>	if (value == null || value.equals(v)) {
485	>	oldValue = v;
486	>	// All entries following removed node can stay
487	>	// in list, but all preceding ones need to be
488	>	// cloned.
489	>	++modCount;
490	>	HashEntry<K,V> newFirst = e.next;
491	>	for (HashEntry<K,V> p = first; p != e; p = p.next)
492	>	newFirst = new HashEntry<K,V>(p.key, p.hash,
493	>	newFirst, p.value);
494	>	tab[index] = newFirst;
495	>	count = c; // write-volatile
496	>	}
497	>	}
498		return oldValue;
499		} finally {
500		unlock();
#	Line 486 | Line 502 | public class ConcurrentHashMap<K, V> ext
502		}
503
504		void clear() {
505	<	lock();
506	<	try {
507	<	HashEntry[] tab = table;
508	<	for (int i = 0; i < tab.length ; i++)
509	<	tab[i] = null;
510	<	++modCount;
511	<	count = 0; // write-volatile
512	<	} finally {
513	<	unlock();
505	>	if (count != 0) {
506	>	lock();
507	>	try {
508	>	HashEntry[] tab = table;
509	>	for (int i = 0; i < tab.length ; i++)
510	>	tab[i] = null;
511	>	++modCount;
512	>	count = 0; // write-volatile
513	>	} finally {
514	>	unlock();
515	>	}
516		}
517		}
518		}
#	Line 505 | Line 523 | public class ConcurrentHashMap<K, V> ext
523		*/
524		static final class HashEntry<K,V> {
525		final K key;
508	–	V value;
526		final int hash;
527	+	volatile V value;
528		final HashEntry<K,V> next;
529
530	<	HashEntry(int hash, K key, V value, HashEntry<K,V> next) {
513	<	this.value = value;
514	<	this.hash = hash;
530	>	HashEntry(K key, int hash, HashEntry<K,V> next, V value) {
531		this.key = key;
532	+	this.hash = hash;
533		this.next = next;
534	+	this.value = value;
535		}
536		}
537
#	Line 604 | Line 622 | public class ConcurrentHashMap<K, V> ext
622		public boolean isEmpty() {
623		final Segment[] segments = this.segments;
624		/*
625	<	* We need to keep track of per-segment modCounts to avoid ABA
625	>	* We keep track of per-segment modCounts to avoid ABA
626		* problems in which an element in one segment was added and
627		* in another removed during traversal, in which case the
628		* table was never actually empty at any point. Note the
#	Line 636 | Line 654 | public class ConcurrentHashMap<K, V> ext
654		// inherit Map javadoc
655		public int size() {
656		final Segment[] segments = this.segments;
657	+	long sum = 0;
658	+	long check = 0;
659		int[] mc = new int[segments.length];
660	<	for (;;) {
661	<	long sum = 0;
660	>	// Try at most twice to get accurate count. On failure due to
661	>	// continuous async changes in table, resort to locking.
662	>	for (int k = 0; k < 2; ++k) {
663	>	check = 0;
664	>	sum = 0;
665		int mcsum = 0;
666		for (int i = 0; i < segments.length; ++i) {
667		sum += segments[i].count;
668		mcsum += mc[i] = segments[i].modCount;
669		}
647	–	int check = 0;
670		if (mcsum != 0) {
671		for (int i = 0; i < segments.length; ++i) {
672		check += segments[i].count;
#	Line 654 | Line 676 | public class ConcurrentHashMap<K, V> ext
676		}
677		}
678		}
679	<	if (check == sum) {
680	<	if (sum > Integer.MAX_VALUE)
681	<	return Integer.MAX_VALUE;
682	<	else
683	<	return (int)sum;
684	<	}
679	>	if (check == sum)
680	>	break;
681	>	}
682	>	if (check != sum) { // Resort to locking all segments
683	>	sum = 0;
684	>	for (int i = 0; i < segments.length; ++i)
685	>	segments[i].lock();
686	>	for (int i = 0; i < segments.length; ++i)
687	>	sum += segments[i].count;
688	>	for (int i = 0; i < segments.length; ++i)
689	>	segments[i].unlock();
690		}
691	+	if (sum > Integer.MAX_VALUE)
692	+	return Integer.MAX_VALUE;
693	+	else
694	+	return (int)sum;
695		}
696
697
#	Line 708 | Line 739 | public class ConcurrentHashMap<K, V> ext
739		public boolean containsValue(Object value) {
740		if (value == null)
741		throw new NullPointerException();
742	+
743	+	// See explanation of modCount use above
744
745		final Segment[] segments = this.segments;
746		int[] mc = new int[segments.length];
747	<	for (;;) {
747	>
748	>	// Try at most twice without locking
749	>	for (int k = 0; k < 2; ++k) {
750		int sum = 0;
751		int mcsum = 0;
752		for (int i = 0; i < segments.length; ++i) {
#	Line 733 | Line 768 | public class ConcurrentHashMap<K, V> ext
768		if (cleanSweep)
769		return false;
770		}
771	+	// Resort to locking all segments
772	+	for (int i = 0; i < segments.length; ++i)
773	+	segments[i].lock();
774	+	boolean found = false;
775	+	try {
776	+	for (int i = 0; i < segments.length; ++i) {
777	+	if (segments[i].containsValue(value)) {
778	+	found = true;
779	+	break;
780	+	}
781	+	}
782	+	} finally {
783	+	for (int i = 0; i < segments.length; ++i)
784	+	segments[i].unlock();
785	+	}
786	+	return found;
787		}
788
789		/**

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