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root/jsr166/jsr166/src/jsr166y/LinkedTransferQueue.java

Comparing jsr166/src/jsr166y/LinkedTransferQueue.java (file contents):
Revision 1.18 by jsr166, Mon Jul 20 22:26:03 2009 UTC vs.
Revision 1.44 by jsr166, Tue Aug 4 20:32:16 2009 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	+
9		import java.util.concurrent.*;
10	<	import java.util.concurrent.locks.*;
11	<	import java.util.concurrent.atomic.*;
12	<	import java.util.*;
13	<	import java.io.*;
14	<	import sun.misc.Unsafe;
15	<	import java.lang.reflect.*;
10	>
11	>	import java.util.AbstractQueue;
12	>	import java.util.Collection;
13	>	import java.util.ConcurrentModificationException;
14	>	import java.util.Iterator;
15	>	import java.util.NoSuchElementException;
16	>	import java.util.Queue;
17	>	import java.util.concurrent.locks.LockSupport;
18	>	import java.util.concurrent.atomic.AtomicReference;
19
20		/**
21	<	* An unbounded {@linkplain TransferQueue} based on linked nodes.
21	>	* An unbounded {@link TransferQueue} based on linked nodes.
22		* This queue orders elements FIFO (first-in-first-out) with respect
23		* to any given producer.  The <em>head</em> of the queue is that
24		* element that has been on the queue the longest time for some
#	Line 44 | Line 48 | import java.lang.reflect.*;
48		* @since 1.7
49		* @author Doug Lea
50		* @param <E> the type of elements held in this collection
47	–	*
51		*/
52		public class LinkedTransferQueue<E> extends AbstractQueue<E>
53		implements TransferQueue<E>, java.io.Serializable {
#	Line 81 | Line 84 | public class LinkedTransferQueue<E> exte
84		* seems not to vary with number of CPUs (beyond 2) so is just
85		* a constant.
86		*/
87	<	static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
87	>	static final int maxTimedSpins = (NCPUS < 2) ? 0 : 32;
88
89		/**
90		* The number of times to spin before blocking in untimed waits.
#	Line 103 | Line 106 | public class LinkedTransferQueue<E> exte
106		* garbage retention. Similarly, setting the next field to this is
107		* used as sentinel that node is off list.
108		*/
109	<	static final class QNode extends AtomicReference<Object> {
110	<	volatile QNode next;
109	>	static final class Node<E> extends AtomicReference<Object> {
110	>	volatile Node<E> next;
111		volatile Thread waiter;       // to control park/unpark
112		final boolean isData;
113	<	QNode(Object item, boolean isData) {
113	>
114	>	Node(E item, boolean isData) {
115		super(item);
116		this.isData = isData;
117		}
118
119	<	static final AtomicReferenceFieldUpdater<QNode, QNode>
120	<	nextUpdater = AtomicReferenceFieldUpdater.newUpdater
121	<	(QNode.class, QNode.class, "next");
119	>	// Unsafe mechanics
120	>
121	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
122	>	private static final long nextOffset =
123	>	objectFieldOffset(UNSAFE, "next", Node.class);
124
125	<	final boolean casNext(QNode cmp, QNode val) {
126	<	return nextUpdater.compareAndSet(this, cmp, val);
125	>	final boolean casNext(Node<E> cmp, Node<E> val) {
126	>	return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val);
127		}
128
129		final void clearNext() {
130	<	nextUpdater.lazySet(this, this);
130	>	UNSAFE.putOrderedObject(this, nextOffset, this);
131		}
132
133	+	/**
134	+	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
135	+	* Replace with a simple call to Unsafe.getUnsafe when integrating
136	+	* into a jdk.
137	+	*
138	+	* @return a sun.misc.Unsafe
139	+	*/
140	+	private static sun.misc.Unsafe getUnsafe() {
141	+	try {
142	+	return sun.misc.Unsafe.getUnsafe();
143	+	} catch (SecurityException se) {
144	+	try {
145	+	return java.security.AccessController.doPrivileged
146	+	(new java.security
147	+	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
148	+	public sun.misc.Unsafe run() throws Exception {
149	+	java.lang.reflect.Field f = sun.misc
150	+	.Unsafe.class.getDeclaredField("theUnsafe");
151	+	f.setAccessible(true);
152	+	return (sun.misc.Unsafe) f.get(null);
153	+	}});
154	+	} catch (java.security.PrivilegedActionException e) {
155	+	throw new RuntimeException("Could not initialize intrinsics",
156	+	e.getCause());
157	+	}
158	+	}
159	+	}
160	+
161	+	private static final long serialVersionUID = -3375979862319811754L;
162		}
163
164		/**
#	Line 135 | Line 170 | public class LinkedTransferQueue<E> exte
170		// enough padding for 64bytes with 4byte refs
171		Object p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe;
172		PaddedAtomicReference(T r) { super(r); }
173	+	private static final long serialVersionUID = 8170090609809740854L;
174		}
175
176
177		/** head of the queue */
178	<	private transient final PaddedAtomicReference<QNode> head;
178	>	private transient final PaddedAtomicReference<Node<E>> head;
179	>
180		/** tail of the queue */
181	<	private transient final PaddedAtomicReference<QNode> tail;
181	>	private transient final PaddedAtomicReference<Node<E>> tail;
182
183		/**
184		* Reference to a cancelled node that might not yet have been
185		* unlinked from queue because it was the last inserted node
186		* when it cancelled.
187		*/
188	<	private transient final PaddedAtomicReference<QNode> cleanMe;
188	>	private transient final PaddedAtomicReference<Node<E>> cleanMe;
189
190		/**
191		* Tries to cas nh as new head; if successful, unlink
192		* old head's next node to avoid garbage retention.
193		*/
194	<	private boolean advanceHead(QNode h, QNode nh) {
194	>	private boolean advanceHead(Node<E> h, Node<E> nh) {
195		if (h == head.get() && head.compareAndSet(h, nh)) {
196		h.clearNext(); // forget old next
197		return true;
#	Line 172 | Line 209 | public class LinkedTransferQueue<E> exte
209		* @param nanos timeout in nanosecs, used only if mode is TIMEOUT
210		* @return an item, or null on failure
211		*/
212	<	private Object xfer(Object e, int mode, long nanos) {
212	>	private E xfer(E e, int mode, long nanos) {
213		boolean isData = (e != null);
214	<	QNode s = null;
215	<	final PaddedAtomicReference<QNode> head = this.head;
216	<	final PaddedAtomicReference<QNode> tail = this.tail;
214	>	Node<E> s = null;
215	>	final PaddedAtomicReference<Node<E>> head = this.head;
216	>	final PaddedAtomicReference<Node<E>> tail = this.tail;
217
218		for (;;) {
219	<	QNode t = tail.get();
220	<	QNode h = head.get();
219	>	Node<E> t = tail.get();
220	>	Node<E> h = head.get();
221
222	<	if (t != null && (t == h || t.isData == isData)) {
222	>	if (t == h || t.isData == isData) {
223		if (s == null)
224	<	s = new QNode(e, isData);
225	<	QNode last = t.next;
224	>	s = new Node<E>(e, isData);
225	>	Node<E> last = t.next;
226		if (last != null) {
227		if (t == tail.get())
228		tail.compareAndSet(t, last);
#	Line 194 | Line 231 | public class LinkedTransferQueue<E> exte
231		tail.compareAndSet(t, s);
232		return awaitFulfill(t, s, e, mode, nanos);
233		}
234	<	}
235	<
199	<	else if (h != null) {
200	<	QNode first = h.next;
234	>	} else {
235	>	Node<E> first = h.next;
236		if (t == tail.get() && first != null &&
237		advanceHead(h, first)) {
238		Object x = first.get();
239		if (x != first && first.compareAndSet(x, e)) {
240		LockSupport.unpark(first.waiter);
241	<	return isData? e : x;
241	>	return isData ? e : (E) x;
242		}
243		}
244		}
#	Line 215 | Line 250 | public class LinkedTransferQueue<E> exte
250		* Version of xfer for poll() and tryTransfer, which
251		* simplifies control paths both here and in xfer.
252		*/
253	<	private Object fulfill(Object e) {
253	>	private E fulfill(E e) {
254		boolean isData = (e != null);
255	<	final PaddedAtomicReference<QNode> head = this.head;
256	<	final PaddedAtomicReference<QNode> tail = this.tail;
255	>	final PaddedAtomicReference<Node<E>> head = this.head;
256	>	final PaddedAtomicReference<Node<E>> tail = this.tail;
257
258		for (;;) {
259	<	QNode t = tail.get();
260	<	QNode h = head.get();
259	>	Node<E> t = tail.get();
260	>	Node<E> h = head.get();
261
262	<	if (t != null && (t == h || t.isData == isData)) {
263	<	QNode last = t.next;
262	>	if (t == h || t.isData == isData) {
263	>	Node<E> last = t.next;
264		if (t == tail.get()) {
265		if (last != null)
266		tail.compareAndSet(t, last);
267		else
268		return null;
269		}
270	<	}
271	<	else if (h != null) {
237	<	QNode first = h.next;
270	>	} else {
271	>	Node<E> first = h.next;
272		if (t == tail.get() &&
273		first != null &&
274		advanceHead(h, first)) {
275		Object x = first.get();
276		if (x != first && first.compareAndSet(x, e)) {
277		LockSupport.unpark(first.waiter);
278	<	return isData? e : x;
278	>	return isData ? e : (E) x;
279		}
280		}
281		}
#	Line 257 | Line 291 | public class LinkedTransferQueue<E> exte
291		* @param e the comparison value for checking match
292		* @param mode mode
293		* @param nanos timeout value
294	<	* @return matched item, or s if cancelled
294	>	* @return matched item, or null if cancelled
295		*/
296	<	private Object awaitFulfill(QNode pred, QNode s, Object e,
297	<	int mode, long nanos) {
296	>	private E awaitFulfill(Node<E> pred, Node<E> s, E e,
297	>	int mode, long nanos) {
298		if (mode == NOWAIT)
299		return null;
300
301	<	long lastTime = (mode == TIMEOUT)? System.nanoTime() : 0;
301	>	long lastTime = (mode == TIMEOUT) ? System.nanoTime() : 0;
302		Thread w = Thread.currentThread();
303		int spins = -1; // set to desired spin count below
304		for (;;) {
#	Line 279 | Line 313 | public class LinkedTransferQueue<E> exte
313		}
314		else if (x != null) {
315		s.set(s);             // avoid garbage retention
316	<	return x;
316	>	return (E) x;
317		}
318		else
319		return e;
#	Line 294 | Line 328 | public class LinkedTransferQueue<E> exte
328		}
329		}
330		if (spins < 0) {
331	<	QNode h = head.get(); // only spin if at head
332	<	spins = ((h != null && h.next == s) ?
333	<	(mode == TIMEOUT?
334	<	maxTimedSpins : maxUntimedSpins) : 0);
331	>	Node<E> h = head.get(); // only spin if at head
332	>	spins = ((h.next != s) ? 0 :
333	>	(mode == TIMEOUT) ? maxTimedSpins :
334	>	maxUntimedSpins);
335		}
336		if (spins > 0)
337		--spins;
#	Line 319 | Line 353 | public class LinkedTransferQueue<E> exte
353		/**
354		* Returns validated tail for use in cleaning methods.
355		*/
356	<	private QNode getValidatedTail() {
356	>	private Node<E> getValidatedTail() {
357		for (;;) {
358	<	QNode h = head.get();
359	<	QNode first = h.next;
360	<	if (first != null && first.next == first) { // help advance
358	>	Node<E> h = head.get();
359	>	Node<E> first = h.next;
360	>	if (first != null && first.get() == first) { // help advance
361		advanceHead(h, first);
362		continue;
363		}
364	<	QNode t = tail.get();
365	<	QNode last = t.next;
364	>	Node<E> t = tail.get();
365	>	Node<E> last = t.next;
366		if (t == tail.get()) {
367		if (last != null)
368		tail.compareAndSet(t, last); // help advance
#	Line 344 | Line 378 | public class LinkedTransferQueue<E> exte
378		* @param pred predecessor of cancelled node
379		* @param s the cancelled node
380		*/
381	<	private void clean(QNode pred, QNode s) {
381	>	private void clean(Node<E> pred, Node<E> s) {
382		Thread w = s.waiter;
383		if (w != null) {             // Wake up thread
384		s.waiter = null;
#	Line 364 | Line 398 | public class LinkedTransferQueue<E> exte
398		* processed, so this always terminates.
399		*/
400		while (pred.next == s) {
401	<	QNode oldpred = reclean();  // First, help get rid of cleanMe
402	<	QNode t = getValidatedTail();
401	>	Node<E> oldpred = reclean();  // First, help get rid of cleanMe
402	>	Node<E> t = getValidatedTail();
403		if (s != t) {               // If not tail, try to unsplice
404	<	QNode sn = s.next;      // s.next == s means s already off list
404	>	Node<E> sn = s.next;      // s.next == s means s already off list
405		if (sn == s || pred.casNext(s, sn))
406		break;
407		}
#	Line 383 | Line 417 | public class LinkedTransferQueue<E> exte
417		*
418		* @return current cleanMe node (or null)
419		*/
420	<	private QNode reclean() {
420	>	private Node<E> reclean() {
421		/*
422		* cleanMe is, or at one time was, predecessor of cancelled
423		* node s that was the tail so could not be unspliced.  If s
#	Line 395 | Line 429 | public class LinkedTransferQueue<E> exte
429		* This can loop only due to contention on casNext or
430		* clearing cleanMe.
431		*/
432	<	QNode pred;
432	>	Node<E> pred;
433		while ((pred = cleanMe.get()) != null) {
434	<	QNode t = getValidatedTail();
435	<	QNode s = pred.next;
434	>	Node<E> t = getValidatedTail();
435	>	Node<E> s = pred.next;
436		if (s != t) {
437	<	QNode sn;
437	>	Node<E> sn;
438		if (s == null || s == pred || s.get() != s ||
439		(sn = s.next) == s || pred.casNext(s, sn))
440		cleanMe.compareAndSet(pred, null);
#	Line 415 | Line 449 | public class LinkedTransferQueue<E> exte
449		* Creates an initially empty {@code LinkedTransferQueue}.
450		*/
451		public LinkedTransferQueue() {
452	<	QNode dummy = new QNode(null, false);
453	<	head = new PaddedAtomicReference<QNode>(dummy);
454	<	tail = new PaddedAtomicReference<QNode>(dummy);
455	<	cleanMe = new PaddedAtomicReference<QNode>(null);
452	>	Node<E> dummy = new Node<E>(null, false);
453	>	head = new PaddedAtomicReference<Node<E>>(dummy);
454	>	tail = new PaddedAtomicReference<Node<E>>(dummy);
455	>	cleanMe = new PaddedAtomicReference<Node<E>>(null);
456		}
457
458		/**
#	Line 435 | Line 469 | public class LinkedTransferQueue<E> exte
469		addAll(c);
470		}
471
472	<	public void put(E e) throws InterruptedException {
473	<	if (e == null) throw new NullPointerException();
474	<	if (Thread.interrupted()) throw new InterruptedException();
475	<	xfer(e, NOWAIT, 0);
472	>	/**
473	>	* Inserts the specified element at the tail of this queue.
474	>	* As the queue is unbounded, this method will never block.
475	>	*
476	>	* @throws NullPointerException if the specified element is null
477	>	*/
478	>	public void put(E e) {
479	>	offer(e);
480		}
481
482	<	public boolean offer(E e, long timeout, TimeUnit unit)
483	<	throws InterruptedException {
484	<	if (e == null) throw new NullPointerException();
485	<	if (Thread.interrupted()) throw new InterruptedException();
486	<	xfer(e, NOWAIT, 0);
487	<	return true;
482	>	/**
483	>	* Inserts the specified element at the tail of this queue.
484	>	* As the queue is unbounded, this method will never block or
485	>	* return {@code false}.
486	>	*
487	>	* @return {@code true} (as specified by
488	>	*  {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
489	>	* @throws NullPointerException if the specified element is null
490	>	*/
491	>	public boolean offer(E e, long timeout, TimeUnit unit) {
492	>	return offer(e);
493		}
494
495	+	/**
496	+	* Inserts the specified element at the tail of this queue.
497	+	* As the queue is unbounded, this method will never return {@code false}.
498	+	*
499	+	* @return {@code true} (as specified by
500	+	*         {@link BlockingQueue#offer(Object) BlockingQueue.offer})
501	+	* @throws NullPointerException if the specified element is null
502	+	*/
503		public boolean offer(E e) {
504		if (e == null) throw new NullPointerException();
505		xfer(e, NOWAIT, 0);
506		return true;
507		}
508
509	+	/**
510	+	* Inserts the specified element at the tail of this queue.
511	+	* As the queue is unbounded, this method will never throw
512	+	* {@link IllegalStateException} or return {@code false}.
513	+	*
514	+	* @return {@code true} (as specified by {@link Collection#add})
515	+	* @throws NullPointerException if the specified element is null
516	+	*/
517		public boolean add(E e) {
518	+	return offer(e);
519	+	}
520	+
521	+	/**
522	+	* Transfers the element to a waiting consumer immediately, if possible.
523	+	*
524	+	* <p>More precisely, transfers the specified element immediately
525	+	* if there exists a consumer already waiting to receive it (in
526	+	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
527	+	* otherwise returning {@code false} without enqueuing the element.
528	+	*
529	+	* @throws NullPointerException if the specified element is null
530	+	*/
531	+	public boolean tryTransfer(E e) {
532		if (e == null) throw new NullPointerException();
533	<	xfer(e, NOWAIT, 0);
461	<	return true;
533	>	return fulfill(e) != null;
534		}
535
536	+	/**
537	+	* Transfers the element to a consumer, waiting if necessary to do so.
538	+	*
539	+	* <p>More precisely, transfers the specified element immediately
540	+	* if there exists a consumer already waiting to receive it (in
541	+	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
542	+	* else inserts the specified element at the tail of this queue
543	+	* and waits until the element is received by a consumer.
544	+	*
545	+	* @throws NullPointerException if the specified element is null
546	+	*/
547		public void transfer(E e) throws InterruptedException {
548		if (e == null) throw new NullPointerException();
549		if (xfer(e, WAIT, 0) == null) {
#	Line 469 | Line 552 | public class LinkedTransferQueue<E> exte
552		}
553		}
554
555	+	/**
556	+	* Transfers the element to a consumer if it is possible to do so
557	+	* before the timeout elapses.
558	+	*
559	+	* <p>More precisely, transfers the specified element immediately
560	+	* if there exists a consumer already waiting to receive it (in
561	+	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
562	+	* else inserts the specified element at the tail of this queue
563	+	* and waits until the element is received by a consumer,
564	+	* returning {@code false} if the specified wait time elapses
565	+	* before the element can be transferred.
566	+	*
567	+	* @throws NullPointerException if the specified element is null
568	+	*/
569		public boolean tryTransfer(E e, long timeout, TimeUnit unit)
570		throws InterruptedException {
571		if (e == null) throw new NullPointerException();
#	Line 479 | Line 576 | public class LinkedTransferQueue<E> exte
576		throw new InterruptedException();
577		}
578
482	–	public boolean tryTransfer(E e) {
483	–	if (e == null) throw new NullPointerException();
484	–	return fulfill(e) != null;
485	–	}
486	–
579		public E take() throws InterruptedException {
580	<	Object e = xfer(null, WAIT, 0);
580	>	E e = xfer(null, WAIT, 0);
581		if (e != null)
582	<	return (E)e;
582	>	return e;
583		Thread.interrupted();
584		throw new InterruptedException();
585		}
586
587		public E poll(long timeout, TimeUnit unit) throws InterruptedException {
588	<	Object e = xfer(null, TIMEOUT, unit.toNanos(timeout));
588	>	E e = xfer(null, TIMEOUT, unit.toNanos(timeout));
589		if (e != null || !Thread.interrupted())
590	<	return (E)e;
590	>	return e;
591		throw new InterruptedException();
592		}
593
594		public E poll() {
595	<	return (E)fulfill(null);
595	>	return fulfill(null);
596		}
597
598	+	/**
599	+	* @throws NullPointerException     {@inheritDoc}
600	+	* @throws IllegalArgumentException {@inheritDoc}
601	+	*/
602		public int drainTo(Collection<? super E> c) {
603		if (c == null)
604		throw new NullPointerException();
#	Line 517 | Line 613 | public class LinkedTransferQueue<E> exte
613		return n;
614		}
615
616	+	/**
617	+	* @throws NullPointerException     {@inheritDoc}
618	+	* @throws IllegalArgumentException {@inheritDoc}
619	+	*/
620		public int drainTo(Collection<? super E> c, int maxElements) {
621		if (c == null)
622		throw new NullPointerException();
#	Line 536 | Line 636 | public class LinkedTransferQueue<E> exte
636		/**
637		* Returns head after performing any outstanding helping steps.
638		*/
639	<	private QNode traversalHead() {
639	>	private Node<E> traversalHead() {
640		for (;;) {
641	<	QNode t = tail.get();
642	<	QNode h = head.get();
643	<	if (h != null && t != null) {
644	<	QNode last = t.next;
645	<	QNode first = h.next;
646	<	if (t == tail.get()) {
647	<	if (last != null)
648	<	tail.compareAndSet(t, last);
649	<	else if (first != null) {
650	<	Object x = first.get();
651	<	if (x == first)
552	<	advanceHead(h, first);
553	<	else
554	<	return h;
555	<	}
641	>	Node<E> t = tail.get();
642	>	Node<E> h = head.get();
643	>	Node<E> last = t.next;
644	>	Node<E> first = h.next;
645	>	if (t == tail.get()) {
646	>	if (last != null)
647	>	tail.compareAndSet(t, last);
648	>	else if (first != null) {
649	>	Object x = first.get();
650	>	if (x == first)
651	>	advanceHead(h, first);
652		else
653		return h;
654		}
655	+	else
656	+	return h;
657		}
658		reclean();
659		}
660		}
661
662	<
662	>	/**
663	>	* Returns an iterator over the elements in this queue in proper
664	>	* sequence, from head to tail.
665	>	*
666	>	* <p>The returned iterator is a "weakly consistent" iterator that
667	>	* will never throw
668	>	* {@link ConcurrentModificationException ConcurrentModificationException},
669	>	* and guarantees to traverse elements as they existed upon
670	>	* construction of the iterator, and may (but is not guaranteed
671	>	* to) reflect any modifications subsequent to construction.
672	>	*
673	>	* @return an iterator over the elements in this queue in proper sequence
674	>	*/
675		public Iterator<E> iterator() {
676		return new Itr();
677		}
#	Line 574 | Line 684 | public class LinkedTransferQueue<E> exte
684		* if subsequently removed.
685		*/
686		class Itr implements Iterator<E> {
687	<	QNode next;        // node to return next
688	<	QNode pnext;       // predecessor of next
689	<	QNode snext;       // successor of next
690	<	QNode curr;        // last returned node, for remove()
691	<	QNode pcurr;       // predecessor of curr, for remove()
582	<	E nextItem;        // Cache of next item, once committed to in next
687	>	Node<E> next;        // node to return next
688	>	Node<E> pnext;       // predecessor of next
689	>	Node<E> curr;        // last returned node, for remove()
690	>	Node<E> pcurr;       // predecessor of curr, for remove()
691	>	E nextItem;          // Cache of next item, once committed to in next
692
693		Itr() {
694	<	findNext();
694	>	advance();
695		}
696
697		/**
698	<	* Ensures next points to next valid node, or null if none.
698	>	* Moves to next valid node and returns item to return for
699	>	* next(), or null if no such.
700		*/
701	<	void findNext() {
701	>	private E advance() {
702	>	pcurr = pnext;
703	>	curr = next;
704	>	E item = nextItem;
705	>
706		for (;;) {
707	<	QNode pred = pnext;
708	<	QNode q = next;
709	<	if (pred == null || pred == q) {
596	<	pred = traversalHead();
597	<	q = pred.next;
598	<	}
599	<	if (q == null || !q.isData) {
707	>	pnext = (next == null) ? traversalHead() : next;
708	>	next = pnext.next;
709	>	if (next == pnext) {
710		next = null;
711	<	return;
711	>	continue;  // restart
712		}
713	<	Object x = q.get();
714	<	QNode s = q.next;
715	<	if (x != null && q != x && q != s) {
716	<	nextItem = (E)x;
717	<	snext = s;
718	<	pnext = pred;
609	<	next = q;
610	<	return;
713	>	if (next == null)
714	>	break;
715	>	Object x = next.get();
716	>	if (x != null && x != next) {
717	>	nextItem = (E) x;
718	>	break;
719		}
612	–	pnext = q;
613	–	next = s;
720		}
721	+	return item;
722		}
723
724		public boolean hasNext() {
#	Line 619 | Line 726 | public class LinkedTransferQueue<E> exte
726		}
727
728		public E next() {
729	<	if (next == null) throw new NoSuchElementException();
730	<	pcurr = pnext;
731	<	curr = next;
625	<	pnext = next;
626	<	next = snext;
627	<	E x = nextItem;
628	<	findNext();
629	<	return x;
729	>	if (next == null)
730	>	throw new NoSuchElementException();
731	>	return advance();
732		}
733
734		public void remove() {
735	<	QNode p = curr;
735	>	Node<E> p = curr;
736		if (p == null)
737		throw new IllegalStateException();
738		Object x = p.get();
#	Line 641 | Line 743 | public class LinkedTransferQueue<E> exte
743
744		public E peek() {
745		for (;;) {
746	<	QNode h = traversalHead();
747	<	QNode p = h.next;
746	>	Node<E> h = traversalHead();
747	>	Node<E> p = h.next;
748		if (p == null)
749		return null;
750		Object x = p.get();
#	Line 650 | Line 752 | public class LinkedTransferQueue<E> exte
752		if (!p.isData)
753		return null;
754		if (x != null)
755	<	return (E)x;
755	>	return (E) x;
756		}
757		}
758		}
759
760	+	/**
761	+	* Returns {@code true} if this queue contains no elements.
762	+	*
763	+	* @return {@code true} if this queue contains no elements
764	+	*/
765		public boolean isEmpty() {
766		for (;;) {
767	<	QNode h = traversalHead();
768	<	QNode p = h.next;
767	>	Node<E> h = traversalHead();
768	>	Node<E> p = h.next;
769		if (p == null)
770		return true;
771		Object x = p.get();
#	Line 673 | Line 780 | public class LinkedTransferQueue<E> exte
780
781		public boolean hasWaitingConsumer() {
782		for (;;) {
783	<	QNode h = traversalHead();
784	<	QNode p = h.next;
783	>	Node<E> h = traversalHead();
784	>	Node<E> p = h.next;
785		if (p == null)
786		return false;
787		Object x = p.get();
#	Line 696 | Line 803 | public class LinkedTransferQueue<E> exte
803		* @return the number of elements in this queue
804		*/
805		public int size() {
806	<	int count = 0;
807	<	QNode h = traversalHead();
808	<	for (QNode p = h.next; p != null && p.isData; p = p.next) {
809	<	Object x = p.get();
810	<	if (x != null && x != p) {
811	<	if (++count == Integer.MAX_VALUE) // saturated
806	>	for (;;) {
807	>	int count = 0;
808	>	Node<E> pred = traversalHead();
809	>	for (;;) {
810	>	Node<E> q = pred.next;
811	>	if (q == pred) // restart
812		break;
813	+	if (q == null || !q.isData)
814	+	return count;
815	+	Object x = q.get();
816	+	if (x != null && x != q) {
817	+	if (++count == Integer.MAX_VALUE) // saturated
818	+	return count;
819	+	}
820	+	pred = q;
821		}
822		}
708	–	return count;
823		}
824
825		public int getWaitingConsumerCount() {
826	<	int count = 0;
827	<	QNode h = traversalHead();
828	<	for (QNode p = h.next; p != null && !p.isData; p = p.next) {
829	<	if (p.get() == null) {
830	<	if (++count == Integer.MAX_VALUE)
826	>	// converse of size -- count valid non-data nodes
827	>	for (;;) {
828	>	int count = 0;
829	>	Node<E> pred = traversalHead();
830	>	for (;;) {
831	>	Node<E> q = pred.next;
832	>	if (q == pred) // restart
833		break;
834	+	if (q == null || q.isData)
835	+	return count;
836	+	Object x = q.get();
837	+	if (x == null) {
838	+	if (++count == Integer.MAX_VALUE) // saturated
839	+	return count;
840	+	}
841	+	pred = q;
842		}
843		}
720	–	return count;
721	–	}
722	–
723	–	public int remainingCapacity() {
724	–	return Integer.MAX_VALUE;
844		}
845
846	+	/**
847	+	* Removes a single instance of the specified element from this queue,
848	+	* if it is present.  More formally, removes an element {@code e} such
849	+	* that {@code o.equals(e)}, if this queue contains one or more such
850	+	* elements.
851	+	* Returns {@code true} if this queue contained the specified element
852	+	* (or equivalently, if this queue changed as a result of the call).
853	+	*
854	+	* @param o element to be removed from this queue, if present
855	+	* @return {@code true} if this queue changed as a result of the call
856	+	*/
857		public boolean remove(Object o) {
858		if (o == null)
859		return false;
860		for (;;) {
861	<	QNode pred = traversalHead();
861	>	Node<E> pred = traversalHead();
862		for (;;) {
863	<	QNode q = pred.next;
734	<	if (q == null || !q.isData)
735	<	return false;
863	>	Node<E> q = pred.next;
864		if (q == pred) // restart
865		break;
866	+	if (q == null || !q.isData)
867	+	return false;
868		Object x = q.get();
869		if (x != null && x != q && o.equals(x) &&
870		q.compareAndSet(x, q)) {
#	Line 747 | Line 877 | public class LinkedTransferQueue<E> exte
877		}
878
879		/**
880	+	* Always returns {@code Integer.MAX_VALUE} because a
881	+	* {@code LinkedTransferQueue} is not capacity constrained.
882	+	*
883	+	* @return {@code Integer.MAX_VALUE} (as specified by
884	+	*         {@link BlockingQueue#remainingCapacity()})
885	+	*/
886	+	public int remainingCapacity() {
887	+	return Integer.MAX_VALUE;
888	+	}
889	+
890	+	/**
891		* Save the state to a stream (that is, serialize it).
892		*
893		* @serialData All of the elements (each an {@code E}) in
#	Line 765 | Line 906 | public class LinkedTransferQueue<E> exte
906		/**
907		* Reconstitute the Queue instance from a stream (that is,
908		* deserialize it).
909	+	*
910		* @param s the stream
911		*/
912		private void readObject(java.io.ObjectInputStream s)
#	Line 772 | Line 914 | public class LinkedTransferQueue<E> exte
914		s.defaultReadObject();
915		resetHeadAndTail();
916		for (;;) {
917	<	E item = (E)s.readObject();
917	>	@SuppressWarnings("unchecked") E item = (E) s.readObject();
918		if (item == null)
919		break;
920		else
#	Line 780 | Line 922 | public class LinkedTransferQueue<E> exte
922		}
923		}
924
783	–
925		// Support for resetting head/tail while deserializing
926		private void resetHeadAndTail() {
927	<	QNode dummy = new QNode(null, false);
928	<	_unsafe.putObjectVolatile(this, headOffset,
929	<	new PaddedAtomicReference<QNode>(dummy));
930	<	_unsafe.putObjectVolatile(this, tailOffset,
931	<	new PaddedAtomicReference<QNode>(dummy));
932	<	_unsafe.putObjectVolatile(this, cleanMeOffset,
933	<	new PaddedAtomicReference<QNode>(null));
927	>	Node<E> dummy = new Node<E>(null, false);
928	>	UNSAFE.putObjectVolatile(this, headOffset,
929	>	new PaddedAtomicReference<Node<E>>(dummy));
930	>	UNSAFE.putObjectVolatile(this, tailOffset,
931	>	new PaddedAtomicReference<Node<E>>(dummy));
932	>	UNSAFE.putObjectVolatile(this, cleanMeOffset,
933	>	new PaddedAtomicReference<Node<E>>(null));
934	>	}
935	>
936	>	// Unsafe mechanics
937	>
938	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
939	>	private static final long headOffset =
940	>	objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class);
941	>	private static final long tailOffset =
942	>	objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class);
943	>	private static final long cleanMeOffset =
944	>	objectFieldOffset(UNSAFE, "cleanMe", LinkedTransferQueue.class);
945	>
946	>
947	>	static long objectFieldOffset(sun.misc.Unsafe UNSAFE,
948	>	String field, Class<?> klazz) {
949	>	try {
950	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
951	>	} catch (NoSuchFieldException e) {
952	>	// Convert Exception to corresponding Error
953	>	NoSuchFieldError error = new NoSuchFieldError(field);
954	>	error.initCause(e);
955	>	throw error;
956	>	}
957		}
958
959	<	// Temporary Unsafe mechanics for preliminary release
960	<	private static Unsafe getUnsafe() throws Throwable {
959	>	/**
960	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
961	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
962	>	* into a jdk.
963	>	*
964	>	* @return a sun.misc.Unsafe
965	>	*/
966	>	private static sun.misc.Unsafe getUnsafe() {
967		try {
968	<	return Unsafe.getUnsafe();
968	>	return sun.misc.Unsafe.getUnsafe();
969		} catch (SecurityException se) {
970		try {
971		return java.security.AccessController.doPrivileged
972	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
973	<	public Unsafe run() throws Exception {
974	<	return getUnsafePrivileged();
972	>	(new java.security
973	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
974	>	public sun.misc.Unsafe run() throws Exception {
975	>	java.lang.reflect.Field f = sun.misc
976	>	.Unsafe.class.getDeclaredField("theUnsafe");
977	>	f.setAccessible(true);
978	>	return (sun.misc.Unsafe) f.get(null);
979		}});
980		} catch (java.security.PrivilegedActionException e) {
981	<	throw e.getCause();
981	>	throw new RuntimeException("Could not initialize intrinsics",
982	>	e.getCause());
983		}
984		}
985		}
811	–
812	–	private static Unsafe getUnsafePrivileged()
813	–	throws NoSuchFieldException, IllegalAccessException {
814	–	Field f = Unsafe.class.getDeclaredField("theUnsafe");
815	–	f.setAccessible(true);
816	–	return (Unsafe) f.get(null);
817	–	}
818	–
819	–	private static long fieldOffset(String fieldName)
820	–	throws NoSuchFieldException {
821	–	return _unsafe.objectFieldOffset
822	–	(LinkedTransferQueue.class.getDeclaredField(fieldName));
823	–	}
824	–
825	–	private static final Unsafe _unsafe;
826	–	private static final long headOffset;
827	–	private static final long tailOffset;
828	–	private static final long cleanMeOffset;
829	–	static {
830	–	try {
831	–	_unsafe = getUnsafe();
832	–	headOffset = fieldOffset("head");
833	–	tailOffset = fieldOffset("tail");
834	–	cleanMeOffset = fieldOffset("cleanMe");
835	–	} catch (Throwable e) {
836	–	throw new RuntimeException("Could not initialize intrinsics", e);
837	–	}
838	–	}
839	–
986		}

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