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Comparing jsr166/src/jsr166y/LinkedTransferQueue.java (file contents):
Revision 1.19 by jsr166, Tue Jul 21 00:15:14 2009 UTC vs.
Revision 1.43 by jsr166, Sat Aug 1 21:24:01 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>
116	<	nextUpdater = AtomicReferenceFieldUpdater.newUpdater
117	<	(QNode.class, QNode.class, "next");
119	>	// Unsafe mechanics
120
121	<	final boolean casNext(QNode cmp, QNode val) {
122	<	return nextUpdater.compareAndSet(this, cmp, val);
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(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)) {
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 197 | Line 234 | public class LinkedTransferQueue<E> exte
234		}
235
236		else if (h != null) {
237	<	QNode first = h.next;
237	>	Node<E> first = h.next;
238		if (t == tail.get() && first != null &&
239		advanceHead(h, first)) {
240		Object x = first.get();
241		if (x != first && first.compareAndSet(x, e)) {
242		LockSupport.unpark(first.waiter);
243	<	return isData? e : x;
243	>	return isData ? e : (E) x;
244		}
245		}
246		}
#	Line 215 | Line 252 | public class LinkedTransferQueue<E> exte
252		* Version of xfer for poll() and tryTransfer, which
253		* simplifies control paths both here and in xfer.
254		*/
255	<	private Object fulfill(Object e) {
255	>	private E fulfill(E e) {
256		boolean isData = (e != null);
257	<	final PaddedAtomicReference<QNode> head = this.head;
258	<	final PaddedAtomicReference<QNode> tail = this.tail;
257	>	final PaddedAtomicReference<Node<E>> head = this.head;
258	>	final PaddedAtomicReference<Node<E>> tail = this.tail;
259
260		for (;;) {
261	<	QNode t = tail.get();
262	<	QNode h = head.get();
261	>	Node<E> t = tail.get();
262	>	Node<E> h = head.get();
263
264		if (t != null && (t == h || t.isData == isData)) {
265	<	QNode last = t.next;
265	>	Node<E> last = t.next;
266		if (t == tail.get()) {
267		if (last != null)
268		tail.compareAndSet(t, last);
#	Line 234 | Line 271 | public class LinkedTransferQueue<E> exte
271		}
272		}
273		else if (h != null) {
274	<	QNode first = h.next;
274	>	Node<E> first = h.next;
275		if (t == tail.get() &&
276		first != null &&
277		advanceHead(h, first)) {
278		Object x = first.get();
279		if (x != first && first.compareAndSet(x, e)) {
280		LockSupport.unpark(first.waiter);
281	<	return isData? e : x;
281	>	return isData ? e : (E) x;
282		}
283		}
284		}
#	Line 257 | Line 294 | public class LinkedTransferQueue<E> exte
294		* @param e the comparison value for checking match
295		* @param mode mode
296		* @param nanos timeout value
297	<	* @return matched item, or s if cancelled
297	>	* @return matched item, or null if cancelled
298		*/
299	<	private Object awaitFulfill(QNode pred, QNode s, Object e,
300	<	int mode, long nanos) {
299	>	private E awaitFulfill(Node<E> pred, Node<E> s, E e,
300	>	int mode, long nanos) {
301		if (mode == NOWAIT)
302		return null;
303
304	<	long lastTime = (mode == TIMEOUT)? System.nanoTime() : 0;
304	>	long lastTime = (mode == TIMEOUT) ? System.nanoTime() : 0;
305		Thread w = Thread.currentThread();
306		int spins = -1; // set to desired spin count below
307		for (;;) {
#	Line 279 | Line 316 | public class LinkedTransferQueue<E> exte
316		}
317		else if (x != null) {
318		s.set(s);             // avoid garbage retention
319	<	return x;
319	>	return (E) x;
320		}
321		else
322		return e;
#	Line 294 | Line 331 | public class LinkedTransferQueue<E> exte
331		}
332		}
333		if (spins < 0) {
334	<	QNode h = head.get(); // only spin if at head
334	>	Node<E> h = head.get(); // only spin if at head
335		spins = ((h != null && h.next == s) ?
336	<	(mode == TIMEOUT?
336	>	((mode == TIMEOUT) ?
337		maxTimedSpins : maxUntimedSpins) : 0);
338		}
339		if (spins > 0)
#	Line 319 | Line 356 | public class LinkedTransferQueue<E> exte
356		/**
357		* Returns validated tail for use in cleaning methods.
358		*/
359	<	private QNode getValidatedTail() {
359	>	private Node<E> getValidatedTail() {
360		for (;;) {
361	<	QNode h = head.get();
362	<	QNode first = h.next;
363	<	if (first != null && first.next == first) { // help advance
361	>	Node<E> h = head.get();
362	>	Node<E> first = h.next;
363	>	if (first != null && first.get() == first) { // help advance
364		advanceHead(h, first);
365		continue;
366		}
367	<	QNode t = tail.get();
368	<	QNode last = t.next;
367	>	Node<E> t = tail.get();
368	>	Node<E> last = t.next;
369		if (t == tail.get()) {
370		if (last != null)
371		tail.compareAndSet(t, last); // help advance
#	Line 344 | Line 381 | public class LinkedTransferQueue<E> exte
381		* @param pred predecessor of cancelled node
382		* @param s the cancelled node
383		*/
384	<	private void clean(QNode pred, QNode s) {
384	>	private void clean(Node<E> pred, Node<E> s) {
385		Thread w = s.waiter;
386		if (w != null) {             // Wake up thread
387		s.waiter = null;
#	Line 364 | Line 401 | public class LinkedTransferQueue<E> exte
401		* processed, so this always terminates.
402		*/
403		while (pred.next == s) {
404	<	QNode oldpred = reclean();  // First, help get rid of cleanMe
405	<	QNode t = getValidatedTail();
404	>	Node<E> oldpred = reclean();  // First, help get rid of cleanMe
405	>	Node<E> t = getValidatedTail();
406		if (s != t) {               // If not tail, try to unsplice
407	<	QNode sn = s.next;      // s.next == s means s already off list
407	>	Node<E> sn = s.next;      // s.next == s means s already off list
408		if (sn == s || pred.casNext(s, sn))
409		break;
410		}
#	Line 383 | Line 420 | public class LinkedTransferQueue<E> exte
420		*
421		* @return current cleanMe node (or null)
422		*/
423	<	private QNode reclean() {
423	>	private Node<E> reclean() {
424		/*
425		* cleanMe is, or at one time was, predecessor of cancelled
426		* node s that was the tail so could not be unspliced.  If s
#	Line 395 | Line 432 | public class LinkedTransferQueue<E> exte
432		* This can loop only due to contention on casNext or
433		* clearing cleanMe.
434		*/
435	<	QNode pred;
435	>	Node<E> pred;
436		while ((pred = cleanMe.get()) != null) {
437	<	QNode t = getValidatedTail();
438	<	QNode s = pred.next;
437	>	Node<E> t = getValidatedTail();
438	>	Node<E> s = pred.next;
439		if (s != t) {
440	<	QNode sn;
440	>	Node<E> sn;
441		if (s == null || s == pred || s.get() != s ||
442		(sn = s.next) == s || pred.casNext(s, sn))
443		cleanMe.compareAndSet(pred, null);
#	Line 415 | Line 452 | public class LinkedTransferQueue<E> exte
452		* Creates an initially empty {@code LinkedTransferQueue}.
453		*/
454		public LinkedTransferQueue() {
455	<	QNode dummy = new QNode(null, false);
456	<	head = new PaddedAtomicReference<QNode>(dummy);
457	<	tail = new PaddedAtomicReference<QNode>(dummy);
458	<	cleanMe = new PaddedAtomicReference<QNode>(null);
455	>	Node<E> dummy = new Node<E>(null, false);
456	>	head = new PaddedAtomicReference<Node<E>>(dummy);
457	>	tail = new PaddedAtomicReference<Node<E>>(dummy);
458	>	cleanMe = new PaddedAtomicReference<Node<E>>(null);
459		}
460
461		/**
#	Line 435 | Line 472 | public class LinkedTransferQueue<E> exte
472		addAll(c);
473		}
474
475	<	public void put(E e) throws InterruptedException {
476	<	if (e == null) throw new NullPointerException();
477	<	if (Thread.interrupted()) throw new InterruptedException();
478	<	xfer(e, NOWAIT, 0);
475	>	/**
476	>	* Inserts the specified element at the tail of this queue.
477	>	* As the queue is unbounded, this method will never block.
478	>	*
479	>	* @throws NullPointerException if the specified element is null
480	>	*/
481	>	public void put(E e) {
482	>	offer(e);
483		}
484
485	<	public boolean offer(E e, long timeout, TimeUnit unit)
486	<	throws InterruptedException {
487	<	if (e == null) throw new NullPointerException();
488	<	if (Thread.interrupted()) throw new InterruptedException();
489	<	xfer(e, NOWAIT, 0);
490	<	return true;
485	>	/**
486	>	* Inserts the specified element at the tail of this queue.
487	>	* As the queue is unbounded, this method will never block or
488	>	* return {@code false}.
489	>	*
490	>	* @return {@code true} (as specified by
491	>	*  {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
492	>	* @throws NullPointerException if the specified element is null
493	>	*/
494	>	public boolean offer(E e, long timeout, TimeUnit unit) {
495	>	return offer(e);
496		}
497
498	+	/**
499	+	* Inserts the specified element at the tail of this queue.
500	+	* As the queue is unbounded, this method will never return {@code false}.
501	+	*
502	+	* @return {@code true} (as specified by
503	+	*         {@link BlockingQueue#offer(Object) BlockingQueue.offer})
504	+	* @throws NullPointerException if the specified element is null
505	+	*/
506		public boolean offer(E e) {
507		if (e == null) throw new NullPointerException();
508		xfer(e, NOWAIT, 0);
509		return true;
510		}
511
512	+	/**
513	+	* Inserts the specified element at the tail of this queue.
514	+	* As the queue is unbounded, this method will never throw
515	+	* {@link IllegalStateException} or return {@code false}.
516	+	*
517	+	* @return {@code true} (as specified by {@link Collection#add})
518	+	* @throws NullPointerException if the specified element is null
519	+	*/
520		public boolean add(E e) {
521	+	return offer(e);
522	+	}
523	+
524	+	/**
525	+	* Transfers the element to a waiting consumer immediately, if possible.
526	+	*
527	+	* <p>More precisely, transfers the specified element immediately
528	+	* if there exists a consumer already waiting to receive it (in
529	+	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
530	+	* otherwise returning {@code false} without enqueuing the element.
531	+	*
532	+	* @throws NullPointerException if the specified element is null
533	+	*/
534	+	public boolean tryTransfer(E e) {
535		if (e == null) throw new NullPointerException();
536	<	xfer(e, NOWAIT, 0);
461	<	return true;
536	>	return fulfill(e) != null;
537		}
538
539	+	/**
540	+	* Transfers the element to a consumer, waiting if necessary to do so.
541	+	*
542	+	* <p>More precisely, transfers the specified element immediately
543	+	* if there exists a consumer already waiting to receive it (in
544	+	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
545	+	* else inserts the specified element at the tail of this queue
546	+	* and waits until the element is received by a consumer.
547	+	*
548	+	* @throws NullPointerException if the specified element is null
549	+	*/
550		public void transfer(E e) throws InterruptedException {
551		if (e == null) throw new NullPointerException();
552		if (xfer(e, WAIT, 0) == null) {
#	Line 469 | Line 555 | public class LinkedTransferQueue<E> exte
555		}
556		}
557
558	+	/**
559	+	* Transfers the element to a consumer if it is possible to do so
560	+	* before the timeout elapses.
561	+	*
562	+	* <p>More precisely, transfers the specified element immediately
563	+	* if there exists a consumer already waiting to receive it (in
564	+	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
565	+	* else inserts the specified element at the tail of this queue
566	+	* and waits until the element is received by a consumer,
567	+	* returning {@code false} if the specified wait time elapses
568	+	* before the element can be transferred.
569	+	*
570	+	* @throws NullPointerException if the specified element is null
571	+	*/
572		public boolean tryTransfer(E e, long timeout, TimeUnit unit)
573		throws InterruptedException {
574		if (e == null) throw new NullPointerException();
#	Line 479 | Line 579 | public class LinkedTransferQueue<E> exte
579		throw new InterruptedException();
580		}
581
482	–	public boolean tryTransfer(E e) {
483	–	if (e == null) throw new NullPointerException();
484	–	return fulfill(e) != null;
485	–	}
486	–
582		public E take() throws InterruptedException {
583	<	Object e = xfer(null, WAIT, 0);
583	>	E e = xfer(null, WAIT, 0);
584		if (e != null)
585	<	return (E)e;
585	>	return e;
586		Thread.interrupted();
587		throw new InterruptedException();
588		}
589
590		public E poll(long timeout, TimeUnit unit) throws InterruptedException {
591	<	Object e = xfer(null, TIMEOUT, unit.toNanos(timeout));
591	>	E e = xfer(null, TIMEOUT, unit.toNanos(timeout));
592		if (e != null || !Thread.interrupted())
593	<	return (E)e;
593	>	return e;
594		throw new InterruptedException();
595		}
596
597		public E poll() {
598	<	return (E)fulfill(null);
598	>	return fulfill(null);
599		}
600
601	+	/**
602	+	* @throws NullPointerException     {@inheritDoc}
603	+	* @throws IllegalArgumentException {@inheritDoc}
604	+	*/
605		public int drainTo(Collection<? super E> c) {
606		if (c == null)
607		throw new NullPointerException();
#	Line 517 | Line 616 | public class LinkedTransferQueue<E> exte
616		return n;
617		}
618
619	+	/**
620	+	* @throws NullPointerException     {@inheritDoc}
621	+	* @throws IllegalArgumentException {@inheritDoc}
622	+	*/
623		public int drainTo(Collection<? super E> c, int maxElements) {
624		if (c == null)
625		throw new NullPointerException();
#	Line 536 | Line 639 | public class LinkedTransferQueue<E> exte
639		/**
640		* Returns head after performing any outstanding helping steps.
641		*/
642	<	private QNode traversalHead() {
642	>	private Node<E> traversalHead() {
643		for (;;) {
644	<	QNode t = tail.get();
645	<	QNode h = head.get();
644	>	Node<E> t = tail.get();
645	>	Node<E> h = head.get();
646		if (h != null && t != null) {
647	<	QNode last = t.next;
648	<	QNode first = h.next;
647	>	Node<E> last = t.next;
648	>	Node<E> first = h.next;
649		if (t == tail.get()) {
650		if (last != null)
651		tail.compareAndSet(t, last);
#	Line 561 | Line 664 | public class LinkedTransferQueue<E> exte
664		}
665		}
666
667	<
667	>	/**
668	>	* Returns an iterator over the elements in this queue in proper
669	>	* sequence, from head to tail.
670	>	*
671	>	* <p>The returned iterator is a "weakly consistent" iterator that
672	>	* will never throw
673	>	* {@link ConcurrentModificationException ConcurrentModificationException},
674	>	* and guarantees to traverse elements as they existed upon
675	>	* construction of the iterator, and may (but is not guaranteed
676	>	* to) reflect any modifications subsequent to construction.
677	>	*
678	>	* @return an iterator over the elements in this queue in proper sequence
679	>	*/
680		public Iterator<E> iterator() {
681		return new Itr();
682		}
#	Line 574 | Line 689 | public class LinkedTransferQueue<E> exte
689		* if subsequently removed.
690		*/
691		class Itr implements Iterator<E> {
692	<	QNode next;        // node to return next
693	<	QNode pnext;       // predecessor of next
694	<	QNode snext;       // successor of next
695	<	QNode curr;        // last returned node, for remove()
696	<	QNode pcurr;       // predecessor of curr, for remove()
582	<	E nextItem;        // Cache of next item, once committed to in next
692	>	Node<E> next;        // node to return next
693	>	Node<E> pnext;       // predecessor of next
694	>	Node<E> curr;        // last returned node, for remove()
695	>	Node<E> pcurr;       // predecessor of curr, for remove()
696	>	E nextItem;          // Cache of next item, once committed to in next
697
698		Itr() {
699	<	findNext();
699	>	advance();
700		}
701
702		/**
703	<	* Ensures next points to next valid node, or null if none.
703	>	* Moves to next valid node and returns item to return for
704	>	* next(), or null if no such.
705		*/
706	<	void findNext() {
706	>	private E advance() {
707	>	pcurr = pnext;
708	>	curr = next;
709	>	E item = nextItem;
710	>
711		for (;;) {
712	<	QNode pred = pnext;
713	<	QNode q = next;
714	<	if (pred == null || pred == q) {
596	<	pred = traversalHead();
597	<	q = pred.next;
598	<	}
599	<	if (q == null || !q.isData) {
712	>	pnext = (next == null) ? traversalHead() : next;
713	>	next = pnext.next;
714	>	if (next == pnext) {
715		next = null;
716	<	return;
716	>	continue;  // restart
717		}
718	<	Object x = q.get();
719	<	QNode s = q.next;
720	<	if (x != null && q != x && q != s) {
721	<	nextItem = (E)x;
722	<	snext = s;
723	<	pnext = pred;
609	<	next = q;
610	<	return;
718	>	if (next == null)
719	>	break;
720	>	Object x = next.get();
721	>	if (x != null && x != next) {
722	>	nextItem = (E) x;
723	>	break;
724		}
612	–	pnext = q;
613	–	next = s;
725		}
726	+	return item;
727		}
728
729		public boolean hasNext() {
#	Line 619 | Line 731 | public class LinkedTransferQueue<E> exte
731		}
732
733		public E next() {
734	<	if (next == null) throw new NoSuchElementException();
735	<	pcurr = pnext;
736	<	curr = next;
625	<	pnext = next;
626	<	next = snext;
627	<	E x = nextItem;
628	<	findNext();
629	<	return x;
734	>	if (next == null)
735	>	throw new NoSuchElementException();
736	>	return advance();
737		}
738
739		public void remove() {
740	<	QNode p = curr;
740	>	Node<E> p = curr;
741		if (p == null)
742		throw new IllegalStateException();
743		Object x = p.get();
#	Line 641 | Line 748 | public class LinkedTransferQueue<E> exte
748
749		public E peek() {
750		for (;;) {
751	<	QNode h = traversalHead();
752	<	QNode p = h.next;
751	>	Node<E> h = traversalHead();
752	>	Node<E> p = h.next;
753		if (p == null)
754		return null;
755		Object x = p.get();
#	Line 650 | Line 757 | public class LinkedTransferQueue<E> exte
757		if (!p.isData)
758		return null;
759		if (x != null)
760	<	return (E)x;
760	>	return (E) x;
761		}
762		}
763		}
764
765	+	/**
766	+	* Returns {@code true} if this queue contains no elements.
767	+	*
768	+	* @return {@code true} if this queue contains no elements
769	+	*/
770		public boolean isEmpty() {
771		for (;;) {
772	<	QNode h = traversalHead();
773	<	QNode p = h.next;
772	>	Node<E> h = traversalHead();
773	>	Node<E> p = h.next;
774		if (p == null)
775		return true;
776		Object x = p.get();
#	Line 673 | Line 785 | public class LinkedTransferQueue<E> exte
785
786		public boolean hasWaitingConsumer() {
787		for (;;) {
788	<	QNode h = traversalHead();
789	<	QNode p = h.next;
788	>	Node<E> h = traversalHead();
789	>	Node<E> p = h.next;
790		if (p == null)
791		return false;
792		Object x = p.get();
#	Line 696 | Line 808 | public class LinkedTransferQueue<E> exte
808		* @return the number of elements in this queue
809		*/
810		public int size() {
811	<	int count = 0;
812	<	QNode h = traversalHead();
813	<	for (QNode p = h.next; p != null && p.isData; p = p.next) {
814	<	Object x = p.get();
815	<	if (x != null && x != p) {
816	<	if (++count == Integer.MAX_VALUE) // saturated
811	>	for (;;) {
812	>	int count = 0;
813	>	Node<E> pred = traversalHead();
814	>	for (;;) {
815	>	Node<E> q = pred.next;
816	>	if (q == pred) // restart
817		break;
818	+	if (q == null || !q.isData)
819	+	return count;
820	+	Object x = q.get();
821	+	if (x != null && x != q) {
822	+	if (++count == Integer.MAX_VALUE) // saturated
823	+	return count;
824	+	}
825	+	pred = q;
826		}
827		}
708	–	return count;
828		}
829
830		public int getWaitingConsumerCount() {
831	<	int count = 0;
832	<	QNode h = traversalHead();
833	<	for (QNode p = h.next; p != null && !p.isData; p = p.next) {
834	<	if (p.get() == null) {
835	<	if (++count == Integer.MAX_VALUE)
831	>	// converse of size -- count valid non-data nodes
832	>	for (;;) {
833	>	int count = 0;
834	>	Node<E> pred = traversalHead();
835	>	for (;;) {
836	>	Node<E> q = pred.next;
837	>	if (q == pred) // restart
838		break;
839	+	if (q == null || q.isData)
840	+	return count;
841	+	Object x = q.get();
842	+	if (x == null) {
843	+	if (++count == Integer.MAX_VALUE) // saturated
844	+	return count;
845	+	}
846	+	pred = q;
847		}
848		}
720	–	return count;
721	–	}
722	–
723	–	public int remainingCapacity() {
724	–	return Integer.MAX_VALUE;
849		}
850
851	+	/**
852	+	* Removes a single instance of the specified element from this queue,
853	+	* if it is present.  More formally, removes an element {@code e} such
854	+	* that {@code o.equals(e)}, if this queue contains one or more such
855	+	* elements.
856	+	* Returns {@code true} if this queue contained the specified element
857	+	* (or equivalently, if this queue changed as a result of the call).
858	+	*
859	+	* @param o element to be removed from this queue, if present
860	+	* @return {@code true} if this queue changed as a result of the call
861	+	*/
862		public boolean remove(Object o) {
863		if (o == null)
864		return false;
865		for (;;) {
866	<	QNode pred = traversalHead();
866	>	Node<E> pred = traversalHead();
867		for (;;) {
868	<	QNode q = pred.next;
734	<	if (q == null || !q.isData)
735	<	return false;
868	>	Node<E> q = pred.next;
869		if (q == pred) // restart
870		break;
871	+	if (q == null || !q.isData)
872	+	return false;
873		Object x = q.get();
874		if (x != null && x != q && o.equals(x) &&
875		q.compareAndSet(x, q)) {
#	Line 747 | Line 882 | public class LinkedTransferQueue<E> exte
882		}
883
884		/**
885	+	* Always returns {@code Integer.MAX_VALUE} because a
886	+	* {@code LinkedTransferQueue} is not capacity constrained.
887	+	*
888	+	* @return {@code Integer.MAX_VALUE} (as specified by
889	+	*         {@link BlockingQueue#remainingCapacity()})
890	+	*/
891	+	public int remainingCapacity() {
892	+	return Integer.MAX_VALUE;
893	+	}
894	+
895	+	/**
896		* Save the state to a stream (that is, serialize it).
897		*
898		* @serialData All of the elements (each an {@code E}) in
#	Line 773 | Line 919 | public class LinkedTransferQueue<E> exte
919		s.defaultReadObject();
920		resetHeadAndTail();
921		for (;;) {
922	<	E item = (E)s.readObject();
922	>	@SuppressWarnings("unchecked") E item = (E) s.readObject();
923		if (item == null)
924		break;
925		else
#	Line 781 | Line 927 | public class LinkedTransferQueue<E> exte
927		}
928		}
929
784	–
930		// Support for resetting head/tail while deserializing
931		private void resetHeadAndTail() {
932	<	QNode dummy = new QNode(null, false);
933	<	_unsafe.putObjectVolatile(this, headOffset,
934	<	new PaddedAtomicReference<QNode>(dummy));
935	<	_unsafe.putObjectVolatile(this, tailOffset,
936	<	new PaddedAtomicReference<QNode>(dummy));
937	<	_unsafe.putObjectVolatile(this, cleanMeOffset,
938	<	new PaddedAtomicReference<QNode>(null));
932	>	Node<E> dummy = new Node<E>(null, false);
933	>	UNSAFE.putObjectVolatile(this, headOffset,
934	>	new PaddedAtomicReference<Node<E>>(dummy));
935	>	UNSAFE.putObjectVolatile(this, tailOffset,
936	>	new PaddedAtomicReference<Node<E>>(dummy));
937	>	UNSAFE.putObjectVolatile(this, cleanMeOffset,
938	>	new PaddedAtomicReference<Node<E>>(null));
939	>	}
940	>
941	>	// Unsafe mechanics
942	>
943	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
944	>	private static final long headOffset =
945	>	objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class);
946	>	private static final long tailOffset =
947	>	objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class);
948	>	private static final long cleanMeOffset =
949	>	objectFieldOffset(UNSAFE, "cleanMe", LinkedTransferQueue.class);
950	>
951	>
952	>	static long objectFieldOffset(sun.misc.Unsafe UNSAFE,
953	>	String field, Class<?> klazz) {
954	>	try {
955	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
956	>	} catch (NoSuchFieldException e) {
957	>	// Convert Exception to corresponding Error
958	>	NoSuchFieldError error = new NoSuchFieldError(field);
959	>	error.initCause(e);
960	>	throw error;
961	>	}
962		}
963
964	<	// Temporary Unsafe mechanics for preliminary release
965	<	private static Unsafe getUnsafe() throws Throwable {
964	>	/**
965	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
966	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
967	>	* into a jdk.
968	>	*
969	>	* @return a sun.misc.Unsafe
970	>	*/
971	>	private static sun.misc.Unsafe getUnsafe() {
972		try {
973	<	return Unsafe.getUnsafe();
973	>	return sun.misc.Unsafe.getUnsafe();
974		} catch (SecurityException se) {
975		try {
976		return java.security.AccessController.doPrivileged
977	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
978	<	public Unsafe run() throws Exception {
979	<	return getUnsafePrivileged();
977	>	(new java.security
978	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
979	>	public sun.misc.Unsafe run() throws Exception {
980	>	java.lang.reflect.Field f = sun.misc
981	>	.Unsafe.class.getDeclaredField("theUnsafe");
982	>	f.setAccessible(true);
983	>	return (sun.misc.Unsafe) f.get(null);
984		}});
985		} catch (java.security.PrivilegedActionException e) {
986	<	throw e.getCause();
986	>	throw new RuntimeException("Could not initialize intrinsics",
987	>	e.getCause());
988		}
989		}
990		}
812	–
813	–	private static Unsafe getUnsafePrivileged()
814	–	throws NoSuchFieldException, IllegalAccessException {
815	–	Field f = Unsafe.class.getDeclaredField("theUnsafe");
816	–	f.setAccessible(true);
817	–	return (Unsafe) f.get(null);
818	–	}
819	–
820	–	private static long fieldOffset(String fieldName)
821	–	throws NoSuchFieldException {
822	–	return _unsafe.objectFieldOffset
823	–	(LinkedTransferQueue.class.getDeclaredField(fieldName));
824	–	}
825	–
826	–	private static final Unsafe _unsafe;
827	–	private static final long headOffset;
828	–	private static final long tailOffset;
829	–	private static final long cleanMeOffset;
830	–	static {
831	–	try {
832	–	_unsafe = getUnsafe();
833	–	headOffset = fieldOffset("head");
834	–	tailOffset = fieldOffset("tail");
835	–	cleanMeOffset = fieldOffset("cleanMe");
836	–	} catch (Throwable e) {
837	–	throw new RuntimeException("Could not initialize intrinsics", e);
838	–	}
839	–	}
840	–
991		}

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