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

Comparing jsr166/src/jsr166y/LinkedTransferQueue.java (file contents):
Revision 1.23 by jsr166, Thu Jul 23 23:07:57 2009 UTC vs.
Revision 1.38 by jsr166, Fri Jul 31 14:48:18 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.
#	Line 102 | 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 134 | 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 259 | Line 296 | public class LinkedTransferQueue<E> exte
296		* @param nanos timeout value
297		* @return matched item, or s 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
#	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) ?
337		maxTimedSpins : maxUntimedSpins) : 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;
361	>	Node<E> h = head.get();
362	>	Node<E> first = h.next;
363		if (first != null && first.next == 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 specified element immediately if there exists a
526	+	* consumer already waiting to receive it (in {@link #take} or
527	+	* timed {@link #poll(long,TimeUnit) poll}), otherwise
528	+	* returning {@code false} without enqueuing the element.
529	+	*
530	+	* @throws NullPointerException if the specified element is null
531	+	*/
532	+	public boolean tryTransfer(E e) {
533		if (e == null) throw new NullPointerException();
534	<	xfer(e, NOWAIT, 0);
461	<	return true;
534	>	return fulfill(e) != null;
535		}
536
537	+	/**
538	+	* Inserts the specified element at the tail of this queue,
539	+	* waiting if necessary for the element to be received by a
540	+	* consumer invoking {@code take} or {@code poll}.
541	+	*
542	+	* @throws NullPointerException if the specified element is null
543	+	*/
544		public void transfer(E e) throws InterruptedException {
545		if (e == null) throw new NullPointerException();
546		if (xfer(e, WAIT, 0) == null) {
#	Line 469 | Line 549 | public class LinkedTransferQueue<E> exte
549		}
550		}
551
552	+	/**
553	+	* Inserts the specified element at the tail of this queue,
554	+	* waiting up to the specified wait time if necessary for the
555	+	* element to be received by a consumer invoking {@code take} or
556	+	* {@code poll}.
557	+	*
558	+	* @throws NullPointerException if the specified element is null
559	+	*/
560		public boolean tryTransfer(E e, long timeout, TimeUnit unit)
561		throws InterruptedException {
562		if (e == null) throw new NullPointerException();
#	Line 479 | Line 567 | public class LinkedTransferQueue<E> exte
567		throw new InterruptedException();
568		}
569
482	–	public boolean tryTransfer(E e) {
483	–	if (e == null) throw new NullPointerException();
484	–	return fulfill(e) != null;
485	–	}
486	–
570		public E take() throws InterruptedException {
571	<	Object e = xfer(null, WAIT, 0);
571	>	E e = xfer(null, WAIT, 0);
572		if (e != null)
573	<	return (E) e;
573	>	return e;
574		Thread.interrupted();
575		throw new InterruptedException();
576		}
577
578		public E poll(long timeout, TimeUnit unit) throws InterruptedException {
579	<	Object e = xfer(null, TIMEOUT, unit.toNanos(timeout));
579	>	E e = xfer(null, TIMEOUT, unit.toNanos(timeout));
580		if (e != null || !Thread.interrupted())
581	<	return (E) e;
581	>	return e;
582		throw new InterruptedException();
583		}
584
585		public E poll() {
586	<	return (E) fulfill(null);
586	>	return fulfill(null);
587		}
588
589	+	/**
590	+	* @throws NullPointerException     {@inheritDoc}
591	+	* @throws IllegalArgumentException {@inheritDoc}
592	+	*/
593		public int drainTo(Collection<? super E> c) {
594		if (c == null)
595		throw new NullPointerException();
#	Line 517 | Line 604 | public class LinkedTransferQueue<E> exte
604		return n;
605		}
606
607	+	/**
608	+	* @throws NullPointerException     {@inheritDoc}
609	+	* @throws IllegalArgumentException {@inheritDoc}
610	+	*/
611		public int drainTo(Collection<? super E> c, int maxElements) {
612		if (c == null)
613		throw new NullPointerException();
#	Line 536 | Line 627 | public class LinkedTransferQueue<E> exte
627		/**
628		* Returns head after performing any outstanding helping steps.
629		*/
630	<	private QNode traversalHead() {
630	>	private Node<E> traversalHead() {
631		for (;;) {
632	<	QNode t = tail.get();
633	<	QNode h = head.get();
632	>	Node<E> t = tail.get();
633	>	Node<E> h = head.get();
634		if (h != null && t != null) {
635	<	QNode last = t.next;
636	<	QNode first = h.next;
635	>	Node<E> last = t.next;
636	>	Node<E> first = h.next;
637		if (t == tail.get()) {
638		if (last != null)
639		tail.compareAndSet(t, last);
#	Line 561 | Line 652 | public class LinkedTransferQueue<E> exte
652		}
653		}
654
655	<
655	>	/**
656	>	* Returns an iterator over the elements in this queue in proper
657	>	* sequence, from head to tail.
658	>	*
659	>	* <p>The returned iterator is a "weakly consistent" iterator that
660	>	* will never throw
661	>	* {@link ConcurrentModificationException ConcurrentModificationException},
662	>	* and guarantees to traverse elements as they existed upon
663	>	* construction of the iterator, and may (but is not guaranteed
664	>	* to) reflect any modifications subsequent to construction.
665	>	*
666	>	* @return an iterator over the elements in this queue in proper sequence
667	>	*/
668		public Iterator<E> iterator() {
669		return new Itr();
670		}
#	Line 574 | Line 677 | public class LinkedTransferQueue<E> exte
677		* if subsequently removed.
678		*/
679		class Itr implements Iterator<E> {
680	<	QNode next;        // node to return next
681	<	QNode pnext;       // predecessor of next
682	<	QNode snext;       // successor of next
683	<	QNode curr;        // last returned node, for remove()
684	<	QNode pcurr;       // predecessor of curr, for remove()
582	<	E nextItem;        // Cache of next item, once committed to in next
680	>	Node<E> next;        // node to return next
681	>	Node<E> pnext;       // predecessor of next
682	>	Node<E> curr;        // last returned node, for remove()
683	>	Node<E> pcurr;       // predecessor of curr, for remove()
684	>	E nextItem;          // Cache of next item, once committed to in next
685
686		Itr() {
687	<	findNext();
687	>	advance();
688		}
689
690		/**
691	<	* Ensures next points to next valid node, or null if none.
691	>	* Moves to next valid node and returns item to return for
692	>	* next(), or null if no such.
693		*/
694	<	void findNext() {
694	>	private E advance() {
695	>	pcurr = pnext;
696	>	curr = next;
697	>	E item = nextItem;
698	>
699		for (;;) {
700	<	QNode pred = pnext;
701	<	QNode q = next;
702	<	if (pred == null || pred == q) {
596	<	pred = traversalHead();
597	<	q = pred.next;
598	<	}
599	<	if (q == null || !q.isData) {
700	>	pnext = (next == null) ? traversalHead() : next;
701	>	next = pnext.next;
702	>	if (next == pnext) {
703		next = null;
704	<	return;
704	>	continue;  // restart
705		}
706	<	Object x = q.get();
707	<	QNode s = q.next;
708	<	if (x != null && q != x && q != s) {
706	>	if (next == null)
707	>	break;
708	>	Object x = next.get();
709	>	if (x != null && x != next) {
710		nextItem = (E) x;
711	<	snext = s;
608	<	pnext = pred;
609	<	next = q;
610	<	return;
711	>	break;
712		}
612	–	pnext = q;
613	–	next = s;
713		}
714	+	return item;
715		}
716
717		public boolean hasNext() {
#	Line 619 | Line 719 | public class LinkedTransferQueue<E> exte
719		}
720
721		public E next() {
722	<	if (next == null) throw new NoSuchElementException();
723	<	pcurr = pnext;
724	<	curr = next;
625	<	pnext = next;
626	<	next = snext;
627	<	E x = nextItem;
628	<	findNext();
629	<	return x;
722	>	if (next == null)
723	>	throw new NoSuchElementException();
724	>	return advance();
725		}
726
727		public void remove() {
728	<	QNode p = curr;
728	>	Node<E> p = curr;
729		if (p == null)
730		throw new IllegalStateException();
731		Object x = p.get();
#	Line 641 | Line 736 | public class LinkedTransferQueue<E> exte
736
737		public E peek() {
738		for (;;) {
739	<	QNode h = traversalHead();
740	<	QNode p = h.next;
739	>	Node<E> h = traversalHead();
740	>	Node<E> p = h.next;
741		if (p == null)
742		return null;
743		Object x = p.get();
#	Line 657 | Line 752 | public class LinkedTransferQueue<E> exte
752
753		public boolean isEmpty() {
754		for (;;) {
755	<	QNode h = traversalHead();
756	<	QNode p = h.next;
755	>	Node<E> h = traversalHead();
756	>	Node<E> p = h.next;
757		if (p == null)
758		return true;
759		Object x = p.get();
#	Line 673 | Line 768 | public class LinkedTransferQueue<E> exte
768
769		public boolean hasWaitingConsumer() {
770		for (;;) {
771	<	QNode h = traversalHead();
772	<	QNode p = h.next;
771	>	Node<E> h = traversalHead();
772	>	Node<E> p = h.next;
773		if (p == null)
774		return false;
775		Object x = p.get();
#	Line 696 | Line 791 | public class LinkedTransferQueue<E> exte
791		* @return the number of elements in this queue
792		*/
793		public int size() {
794	<	int count = 0;
795	<	QNode h = traversalHead();
796	<	for (QNode p = h.next; p != null && p.isData; p = p.next) {
797	<	Object x = p.get();
798	<	if (x != null && x != p) {
799	<	if (++count == Integer.MAX_VALUE) // saturated
794	>	for (;;) {
795	>	int count = 0;
796	>	Node<E> pred = traversalHead();
797	>	for (;;) {
798	>	Node<E> q = pred.next;
799	>	if (q == pred) // restart
800		break;
801	+	if (q == null || !q.isData)
802	+	return count;
803	+	Object x = q.get();
804	+	if (x != null && x != q) {
805	+	if (++count == Integer.MAX_VALUE) // saturated
806	+	return count;
807	+	}
808	+	pred = q;
809		}
810		}
708	–	return count;
811		}
812
813		public int getWaitingConsumerCount() {
814	<	int count = 0;
815	<	QNode h = traversalHead();
816	<	for (QNode p = h.next; p != null && !p.isData; p = p.next) {
817	<	if (p.get() == null) {
818	<	if (++count == Integer.MAX_VALUE)
814	>	// converse of size -- count valid non-data nodes
815	>	for (;;) {
816	>	int count = 0;
817	>	Node<E> pred = traversalHead();
818	>	for (;;) {
819	>	Node<E> q = pred.next;
820	>	if (q == pred) // restart
821		break;
822	+	if (q == null || q.isData)
823	+	return count;
824	+	Object x = q.get();
825	+	if (x == null) {
826	+	if (++count == Integer.MAX_VALUE) // saturated
827	+	return count;
828	+	}
829	+	pred = q;
830		}
831		}
720	–	return count;
721	–	}
722	–
723	–	public int remainingCapacity() {
724	–	return Integer.MAX_VALUE;
832		}
833
834		public boolean remove(Object o) {
835		if (o == null)
836		return false;
837		for (;;) {
838	<	QNode pred = traversalHead();
838	>	Node<E> pred = traversalHead();
839		for (;;) {
840	<	QNode q = pred.next;
734	<	if (q == null || !q.isData)
735	<	return false;
840	>	Node<E> q = pred.next;
841		if (q == pred) // restart
842		break;
843	+	if (q == null || !q.isData)
844	+	return false;
845		Object x = q.get();
846		if (x != null && x != q && o.equals(x) &&
847		q.compareAndSet(x, q)) {
#	Line 747 | Line 854 | public class LinkedTransferQueue<E> exte
854		}
855
856		/**
857	+	* Always returns {@code Integer.MAX_VALUE} because a
858	+	* {@code LinkedTransferQueue} is not capacity constrained.
859	+	*
860	+	* @return {@code Integer.MAX_VALUE} (as specified by
861	+	*         {@link BlockingQueue#remainingCapacity()})
862	+	*/
863	+	public int remainingCapacity() {
864	+	return Integer.MAX_VALUE;
865	+	}
866	+
867	+	/**
868		* Save the state to a stream (that is, serialize it).
869		*
870		* @serialData All of the elements (each an {@code E}) in
#	Line 773 | Line 891 | public class LinkedTransferQueue<E> exte
891		s.defaultReadObject();
892		resetHeadAndTail();
893		for (;;) {
894	<	E item = (E) s.readObject();
894	>	@SuppressWarnings("unchecked") E item = (E) s.readObject();
895		if (item == null)
896		break;
897		else
#	Line 781 | Line 899 | public class LinkedTransferQueue<E> exte
899		}
900		}
901
784	–
902		// Support for resetting head/tail while deserializing
903		private void resetHeadAndTail() {
904	<	QNode dummy = new QNode(null, false);
904	>	Node<E> dummy = new Node<E>(null, false);
905		UNSAFE.putObjectVolatile(this, headOffset,
906	<	new PaddedAtomicReference<QNode>(dummy));
906	>	new PaddedAtomicReference<Node<E>>(dummy));
907		UNSAFE.putObjectVolatile(this, tailOffset,
908	<	new PaddedAtomicReference<QNode>(dummy));
908	>	new PaddedAtomicReference<Node<E>>(dummy));
909		UNSAFE.putObjectVolatile(this, cleanMeOffset,
910	<	new PaddedAtomicReference<QNode>(null));
910	>	new PaddedAtomicReference<Node<E>>(null));
911		}
912
913	<	// Temporary Unsafe mechanics for preliminary release
914	<	private static Unsafe getUnsafe() throws Throwable {
913	>	// Unsafe mechanics
914	>
915	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
916	>	private static final long headOffset =
917	>	objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class);
918	>	private static final long tailOffset =
919	>	objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class);
920	>	private static final long cleanMeOffset =
921	>	objectFieldOffset(UNSAFE, "cleanMe", LinkedTransferQueue.class);
922	>
923	>
924	>	static long objectFieldOffset(sun.misc.Unsafe UNSAFE,
925	>	String field, Class<?> klazz) {
926		try {
927	<	return Unsafe.getUnsafe();
927	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
928	>	} catch (NoSuchFieldException e) {
929	>	// Convert Exception to corresponding Error
930	>	NoSuchFieldError error = new NoSuchFieldError(field);
931	>	error.initCause(e);
932	>	throw error;
933	>	}
934	>	}
935	>
936	>	/**
937	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
938	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
939	>	* into a jdk.
940	>	*
941	>	* @return a sun.misc.Unsafe
942	>	*/
943	>	private static sun.misc.Unsafe getUnsafe() {
944	>	try {
945	>	return sun.misc.Unsafe.getUnsafe();
946		} catch (SecurityException se) {
947		try {
948		return java.security.AccessController.doPrivileged
949	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
950	<	public Unsafe run() throws Exception {
951	<	return getUnsafePrivileged();
949	>	(new java.security
950	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
951	>	public sun.misc.Unsafe run() throws Exception {
952	>	java.lang.reflect.Field f = sun.misc
953	>	.Unsafe.class.getDeclaredField("theUnsafe");
954	>	f.setAccessible(true);
955	>	return (sun.misc.Unsafe) f.get(null);
956		}});
957		} catch (java.security.PrivilegedActionException e) {
958	<	throw e.getCause();
958	>	throw new RuntimeException("Could not initialize intrinsics",
959	>	e.getCause());
960		}
961		}
962		}
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	–
963		}

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