ViewVC Help

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

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

Comparing jsr166/src/jsr166y/LinkedTransferQueue.java (file contents):
Revision 1.4 by jsr166, Fri Jul 25 18:10:41 2008 UTC vs.
Revision 1.24 by jsr166, Thu Jul 23 23:23:41 2009 UTC

#	Line 10 | Line 10 | import java.util.concurrent.locks.*;
10		import java.util.concurrent.atomic.*;
11		import java.util.*;
12		import java.io.*;
13	+	import sun.misc.Unsafe;
14	+	import java.lang.reflect.*;
15
16		/**
17		* An unbounded {@linkplain TransferQueue} based on linked nodes.
#	Line 19 | Line 21 | import java.io.*;
21		* producer.  The <em>tail</em> of the queue is that element that has
22		* been on the queue the shortest time for some producer.
23		*
24	<	* <p>Beware that, unlike in most collections, the <tt>size</tt>
24	>	* <p>Beware that, unlike in most collections, the {@code size}
25		* method is <em>NOT</em> a constant-time operation. Because of the
26		* asynchronous nature of these queues, determining the current number
27		* of elements requires a traversal of the elements.
#	Line 42 | Line 44 | import java.io.*;
44		* @since 1.7
45		* @author Doug Lea
46		* @param <E> the type of elements held in this collection
45	–	*
47		*/
48		public class LinkedTransferQueue<E> extends AbstractQueue<E>
49		implements TransferQueue<E>, java.io.Serializable {
50		private static final long serialVersionUID = -3223113410248163686L;
51
52		/*
52	–	* This is still a work in progress...
53	–	*
53		* This class extends the approach used in FIFO-mode
54		* SynchronousQueues. See the internal documentation, as well as
55		* the PPoPP 2006 paper "Scalable Synchronous Queues" by Scherer,
56		* Lea & Scott
57		* (http://www.cs.rice.edu/~wns1/papers/2006-PPoPP-SQ.pdf)
58		*
59	<	* The main extension is to provide different Wait modes
60	<	* for the main "xfer" method that puts or takes items.
61	<	* These don't impact the basic dual-queue logic, but instead
62	<	* control whether or how threads block upon insertion
63	<	* of request or data nodes into the dual queue.
59	>	* The main extension is to provide different Wait modes for the
60	>	* main "xfer" method that puts or takes items.  These don't
61	>	* impact the basic dual-queue logic, but instead control whether
62	>	* or how threads block upon insertion of request or data nodes
63	>	* into the dual queue. It also uses slightly different
64	>	* conventions for tracking whether nodes are off-list or
65	>	* cancelled.
66		*/
67
68		// Wait modes for xfer method
#	Line 79 | Line 80 | public class LinkedTransferQueue<E> exte
80		* seems not to vary with number of CPUs (beyond 2) so is just
81		* a constant.
82		*/
83	<	static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
83	>	static final int maxTimedSpins = (NCPUS < 2) ? 0 : 32;
84
85		/**
86		* The number of times to spin before blocking in untimed waits.
#	Line 94 | Line 95 | public class LinkedTransferQueue<E> exte
95		*/
96		static final long spinForTimeoutThreshold = 1000L;
97
98	<	/**
99	<	* Node class for LinkedTransferQueue. Opportunistically subclasses from
100	<	* AtomicReference to represent item. Uses Object, not E, to allow
101	<	* setting item to "this" after use, to avoid garbage
102	<	* retention. Similarly, setting the next field to this is used as
103	<	* sentinel that node is off list.
98	>	/**
99	>	* Node class for LinkedTransferQueue. Opportunistically
100	>	* subclasses from AtomicReference to represent item. Uses Object,
101	>	* not E, to allow setting item to "this" after use, to avoid
102	>	* garbage retention. Similarly, setting the next field to this is
103	>	* used as sentinel that node is off list.
104		*/
105		static final class QNode extends AtomicReference<Object> {
106		volatile QNode next;
#	Line 114 | Line 115 | public class LinkedTransferQueue<E> exte
115		nextUpdater = AtomicReferenceFieldUpdater.newUpdater
116		(QNode.class, QNode.class, "next");
117
118	<	boolean casNext(QNode cmp, QNode val) {
118	>	final boolean casNext(QNode cmp, QNode val) {
119		return nextUpdater.compareAndSet(this, cmp, val);
120		}
121	+
122	+	final void clearNext() {
123	+	nextUpdater.lazySet(this, this);
124	+	}
125	+
126	+	private static final long serialVersionUID = -3375979862319811754L;
127		}
128
129		/**
#	Line 128 | Line 135 | public class LinkedTransferQueue<E> exte
135		// enough padding for 64bytes with 4byte refs
136		Object p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe;
137		PaddedAtomicReference(T r) { super(r); }
138	+	private static final long serialVersionUID = 8170090609809740854L;
139		}
140
141
142	<	private final QNode dummy = new QNode(null, false);
143	<	private final PaddedAtomicReference<QNode> head =
144	<	new PaddedAtomicReference<QNode>(dummy);
145	<	private final PaddedAtomicReference<QNode> tail =
146	<	new PaddedAtomicReference<QNode>(dummy);
142	>	/** head of the queue */
143	>	private transient final PaddedAtomicReference<QNode> head;
144	>
145	>	/** tail of the queue */
146	>	private transient final PaddedAtomicReference<QNode> tail;
147
148		/**
149		* Reference to a cancelled node that might not yet have been
150		* unlinked from queue because it was the last inserted node
151		* when it cancelled.
152		*/
153	<	private final PaddedAtomicReference<QNode> cleanMe =
146	<	new PaddedAtomicReference<QNode>(null);
153	>	private transient final PaddedAtomicReference<QNode> cleanMe;
154
155		/**
156		* Tries to cas nh as new head; if successful, unlink
#	Line 151 | Line 158 | public class LinkedTransferQueue<E> exte
158		*/
159		private boolean advanceHead(QNode h, QNode nh) {
160		if (h == head.get() && head.compareAndSet(h, nh)) {
161	<	h.next = h; // forget old next
161	>	h.clearNext(); // forget old next
162		return true;
163		}
164		return false;
165		}
166	<
166	>
167		/**
168		* Puts or takes an item. Used for most queue operations (except
169	<	* poll() and tryTransfer())
169	>	* poll() and tryTransfer()). See the similar code in
170	>	* SynchronousQueue for detailed explanation.
171	>	*
172		* @param e the item or if null, signifies that this is a take
173		* @param mode the wait mode: NOWAIT, TIMEOUT, WAIT
174		* @param nanos timeout in nanosecs, used only if mode is TIMEOUT
#	Line 188 | Line 197 | public class LinkedTransferQueue<E> exte
197		return awaitFulfill(t, s, e, mode, nanos);
198		}
199		}
200	<
200	>
201		else if (h != null) {
202		QNode first = h.next;
203	<	if (t == tail.get() && first != null &&
203	>	if (t == tail.get() && first != null &&
204		advanceHead(h, first)) {
205		Object x = first.get();
206		if (x != first && first.compareAndSet(x, e)) {
207		LockSupport.unpark(first.waiter);
208	<	return isData? e : x;
208	>	return isData ? e : x;
209		}
210		}
211		}
#	Line 206 | Line 215 | public class LinkedTransferQueue<E> exte
215
216		/**
217		* Version of xfer for poll() and tryTransfer, which
218	<	* simplifies control paths both here and in xfer
218	>	* simplifies control paths both here and in xfer.
219		*/
220		private Object fulfill(Object e) {
221		boolean isData = (e != null);
#	Line 228 | Line 237 | public class LinkedTransferQueue<E> exte
237		}
238		else if (h != null) {
239		QNode first = h.next;
240	<	if (t == tail.get() &&
240	>	if (t == tail.get() &&
241		first != null &&
242		advanceHead(h, first)) {
243		Object x = first.get();
244		if (x != first && first.compareAndSet(x, e)) {
245		LockSupport.unpark(first.waiter);
246	<	return isData? e : x;
246	>	return isData ? e : x;
247		}
248		}
249		}
#	Line 252 | Line 261 | public class LinkedTransferQueue<E> exte
261		* @param nanos timeout value
262		* @return matched item, or s if cancelled
263		*/
264	<	private Object awaitFulfill(QNode pred, QNode s, Object e,
264	>	private Object awaitFulfill(QNode pred, QNode s, Object e,
265		int mode, long nanos) {
266		if (mode == NOWAIT)
267		return null;
268
269	<	long lastTime = (mode == TIMEOUT)? System.nanoTime() : 0;
269	>	long lastTime = (mode == TIMEOUT) ? System.nanoTime() : 0;
270		Thread w = Thread.currentThread();
271		int spins = -1; // set to desired spin count below
272		for (;;) {
#	Line 266 | Line 275 | public class LinkedTransferQueue<E> exte
275		Object x = s.get();
276		if (x != e) {                 // Node was matched or cancelled
277		advanceHead(pred, s);     // unlink if head
278	<	if (x == s)               // was cancelled
279	<	return clean(pred, s);
280	<	else if (x != null) {
278	>	if (x == s) {             // was cancelled
279	>	clean(pred, s);
280	>	return null;
281	>	}
282	>	else if (x != null) {
283		s.set(s);             // avoid garbage retention
284		return x;
285		}
286		else
287		return e;
288		}
278	–
289		if (mode == TIMEOUT) {
290		long now = System.nanoTime();
291		nanos -= now - lastTime;
#	Line 288 | Line 298 | public class LinkedTransferQueue<E> exte
298		if (spins < 0) {
299		QNode h = head.get(); // only spin if at head
300		spins = ((h != null && h.next == s) ?
301	<	(mode == TIMEOUT?
301	>	((mode == TIMEOUT) ?
302		maxTimedSpins : maxUntimedSpins) : 0);
303		}
304		if (spins > 0)
#	Line 296 | Line 306 | public class LinkedTransferQueue<E> exte
306		else if (s.waiter == null)
307		s.waiter = w;
308		else if (mode != TIMEOUT) {
309	<	//                LockSupport.park(this);
300	<	LockSupport.park(); // allows run on java5
309	>	LockSupport.park(this);
310		s.waiter = null;
311		spins = -1;
312		}
313		else if (nanos > spinForTimeoutThreshold) {
314	<	//                LockSupport.parkNanos(this, nanos);
306	<	LockSupport.parkNanos(nanos);
314	>	LockSupport.parkNanos(this, nanos);
315		s.waiter = null;
316		spins = -1;
317		}
#	Line 311 | Line 319 | public class LinkedTransferQueue<E> exte
319		}
320
321		/**
322	+	* Returns validated tail for use in cleaning methods.
323	+	*/
324	+	private QNode getValidatedTail() {
325	+	for (;;) {
326	+	QNode h = head.get();
327	+	QNode first = h.next;
328	+	if (first != null && first.next == first) { // help advance
329	+	advanceHead(h, first);
330	+	continue;
331	+	}
332	+	QNode t = tail.get();
333	+	QNode last = t.next;
334	+	if (t == tail.get()) {
335	+	if (last != null)
336	+	tail.compareAndSet(t, last); // help advance
337	+	else
338	+	return t;
339	+	}
340	+	}
341	+	}
342	+
343	+	/**
344		* Gets rid of cancelled node s with original predecessor pred.
345	<	* @return null (to simplify use by callers)
345	>	*
346	>	* @param pred predecessor of cancelled node
347	>	* @param s the cancelled node
348		*/
349	<	private Object clean(QNode pred, QNode s) {
349	>	private void clean(QNode pred, QNode s) {
350		Thread w = s.waiter;
351		if (w != null) {             // Wake up thread
352		s.waiter = null;
353		if (w != Thread.currentThread())
354		LockSupport.unpark(w);
355		}
356	<
357	<	for (;;) {
358	<	if (pred.next != s) // already cleaned
359	<	return null;
360	<	QNode h = head.get();
361	<	QNode hn = h.next;   // Absorb cancelled first node as head
362	<	if (hn != null && hn.next == hn) {
363	<	advanceHead(h, hn);
364	<	continue;
365	<	}
366	<	QNode t = tail.get();      // Ensure consistent read for tail
367	<	if (t == h)
368	<	return null;
369	<	QNode tn = t.next;
370	<	if (t != tail.get())
371	<	continue;
372	<	if (tn != null) {          // Help advance tail
341	<	tail.compareAndSet(t, tn);
342	<	continue;
343	<	}
344	<	if (s != t) {             // If not tail, try to unsplice
345	<	QNode sn = s.next;
356	>
357	>	if (pred == null)
358	>	return;
359	>
360	>	/*
361	>	* At any given time, exactly one node on list cannot be
362	>	* deleted -- the last inserted node. To accommodate this, if
363	>	* we cannot delete s, we save its predecessor as "cleanMe",
364	>	* processing the previously saved version first. At least one
365	>	* of node s or the node previously saved can always be
366	>	* processed, so this always terminates.
367	>	*/
368	>	while (pred.next == s) {
369	>	QNode oldpred = reclean();  // First, help get rid of cleanMe
370	>	QNode t = getValidatedTail();
371	>	if (s != t) {               // If not tail, try to unsplice
372	>	QNode sn = s.next;      // s.next == s means s already off list
373		if (sn == s || pred.casNext(s, sn))
374	<	return null;
374	>	break;
375		}
376	<	QNode dp = cleanMe.get();
377	<	if (dp != null) {    // Try unlinking previous cancelled node
378	<	QNode d = dp.next;
352	<	QNode dn;
353	<	if (d == null ||               // d is gone or
354	<	d == dp ||                 // d is off list or
355	<	d.get() != d ||            // d not cancelled or
356	<	(d != t &&                 // d not tail and
357	<	(dn = d.next) != null &&  //   has successor
358	<	dn != d &&                //   that is on list
359	<	dp.casNext(d, dn)))       // d unspliced
360	<	cleanMe.compareAndSet(dp, null);
361	<	if (dp == pred)
362	<	return null;      // s is already saved node
363	<	}
364	<	else if (cleanMe.compareAndSet(null, pred))
365	<	return null;          // Postpone cleaning s
376	>	else if (oldpred == pred || // Already saved
377	>	(oldpred == null && cleanMe.compareAndSet(null, pred)))
378	>	break;                  // Postpone cleaning
379		}
380		}
381	<
381	>
382		/**
383	<	* Creates an initially empty <tt>LinkedTransferQueue</tt>.
383	>	* Tries to unsplice the cancelled node held in cleanMe that was
384	>	* previously uncleanable because it was at tail.
385	>	*
386	>	* @return current cleanMe node (or null)
387	>	*/
388	>	private QNode reclean() {
389	>	/*
390	>	* cleanMe is, or at one time was, predecessor of cancelled
391	>	* node s that was the tail so could not be unspliced.  If s
392	>	* is no longer the tail, try to unsplice if necessary and
393	>	* make cleanMe slot available.  This differs from similar
394	>	* code in clean() because we must check that pred still
395	>	* points to a cancelled node that must be unspliced -- if
396	>	* not, we can (must) clear cleanMe without unsplicing.
397	>	* This can loop only due to contention on casNext or
398	>	* clearing cleanMe.
399	>	*/
400	>	QNode pred;
401	>	while ((pred = cleanMe.get()) != null) {
402	>	QNode t = getValidatedTail();
403	>	QNode s = pred.next;
404	>	if (s != t) {
405	>	QNode sn;
406	>	if (s == null || s == pred || s.get() != s ||
407	>	(sn = s.next) == s || pred.casNext(s, sn))
408	>	cleanMe.compareAndSet(pred, null);
409	>	}
410	>	else // s is still tail; cannot clean
411	>	break;
412	>	}
413	>	return pred;
414	>	}
415	>
416	>	/**
417	>	* Creates an initially empty {@code LinkedTransferQueue}.
418		*/
419		public LinkedTransferQueue() {
420	+	QNode dummy = new QNode(null, false);
421	+	head = new PaddedAtomicReference<QNode>(dummy);
422	+	tail = new PaddedAtomicReference<QNode>(dummy);
423	+	cleanMe = new PaddedAtomicReference<QNode>(null);
424		}
425
426		/**
427	<	* Creates a <tt>LinkedTransferQueue</tt>
427	>	* Creates a {@code LinkedTransferQueue}
428		* initially containing the elements of the given collection,
429		* added in traversal order of the collection's iterator.
430	+	*
431		* @param c the collection of elements to initially contain
432		* @throws NullPointerException if the specified collection or any
433		*         of its elements are null
434		*/
435		public LinkedTransferQueue(Collection<? extends E> c) {
436	+	this();
437		addAll(c);
438		}
439
#	Line 390 | Line 443 | public class LinkedTransferQueue<E> exte
443		xfer(e, NOWAIT, 0);
444		}
445
446	<	public boolean offer(E e, long timeout, TimeUnit unit)
446	>	public boolean offer(E e, long timeout, TimeUnit unit)
447		throws InterruptedException {
448		if (e == null) throw new NullPointerException();
449		if (Thread.interrupted()) throw new InterruptedException();
#	Line 404 | Line 457 | public class LinkedTransferQueue<E> exte
457		return true;
458		}
459
460	+	public boolean add(E e) {
461	+	if (e == null) throw new NullPointerException();
462	+	xfer(e, NOWAIT, 0);
463	+	return true;
464	+	}
465	+
466		public void transfer(E e) throws InterruptedException {
467		if (e == null) throw new NullPointerException();
468		if (xfer(e, WAIT, 0) == null) {
469	<	Thread.interrupted();
469	>	Thread.interrupted();
470		throw new InterruptedException();
471	<	}
471	>	}
472		}
473
474		public boolean tryTransfer(E e, long timeout, TimeUnit unit)
#	Line 430 | Line 489 | public class LinkedTransferQueue<E> exte
489		public E take() throws InterruptedException {
490		Object e = xfer(null, WAIT, 0);
491		if (e != null)
492	<	return (E)e;
493	<	Thread.interrupted();
492	>	return (E) e;
493	>	Thread.interrupted();
494		throw new InterruptedException();
495		}
496
497		public E poll(long timeout, TimeUnit unit) throws InterruptedException {
498		Object e = xfer(null, TIMEOUT, unit.toNanos(timeout));
499		if (e != null || !Thread.interrupted())
500	<	return (E)e;
500	>	return (E) e;
501		throw new InterruptedException();
502		}
503
504		public E poll() {
505	<	return (E)fulfill(null);
505	>	return (E) fulfill(null);
506		}
507
508		public int drainTo(Collection<? super E> c) {
#	Line 477 | Line 536 | public class LinkedTransferQueue<E> exte
536		// Traversal-based methods
537
538		/**
539	<	* Return head after performing any outstanding helping steps
539	>	* Returns head after performing any outstanding helping steps.
540		*/
541		private QNode traversalHead() {
542		for (;;) {
#	Line 487 | Line 546 | public class LinkedTransferQueue<E> exte
546		QNode last = t.next;
547		QNode first = h.next;
548		if (t == tail.get()) {
549	<	if (last != null)
549	>	if (last != null)
550		tail.compareAndSet(t, last);
551		else if (first != null) {
552		Object x = first.get();
553	<	if (x == first)
554	<	advanceHead(h, first);
553	>	if (x == first)
554	>	advanceHead(h, first);
555		else
556		return h;
557		}
#	Line 500 | Line 559 | public class LinkedTransferQueue<E> exte
559		return h;
560		}
561		}
562	+	reclean();
563		}
564		}
565
#	Line 516 | Line 576 | public class LinkedTransferQueue<E> exte
576		* if subsequently removed.
577		*/
578		class Itr implements Iterator<E> {
579	<	QNode nextNode;    // Next node to return next
580	<	QNode currentNode; // last returned node, for remove()
581	<	QNode prevNode;    // predecessor of last returned node
582	<	E nextItem;        // Cache of next item, once commited to in next
583	<
579	>	QNode next;        // node to return next
580	>	QNode pnext;       // predecessor of next
581	>	QNode snext;       // successor of next
582	>	QNode curr;        // last returned node, for remove()
583	>	QNode pcurr;       // predecessor of curr, for remove()
584	>	E nextItem;        // Cache of next item, once committed to in next
585	>
586		Itr() {
587	<	nextNode = traversalHead();
526	<	advance();
587	>	findNext();
588		}
589	<
590	<	E advance() {
591	<	prevNode = currentNode;
592	<	currentNode = nextNode;
593	<	E x = nextItem;
533	<
534	<	QNode p = nextNode.next;
589	>
590	>	/**
591	>	* Ensures next points to next valid node, or null if none.
592	>	*/
593	>	void findNext() {
594		for (;;) {
595	<	if (p == null || !p.isData) {
596	<	nextNode = null;
597	<	nextItem = null;
598	<	return x;
595	>	QNode pred = pnext;
596	>	QNode q = next;
597	>	if (pred == null || pred == q) {
598	>	pred = traversalHead();
599	>	q = pred.next;
600		}
601	<	Object item = p.get();
602	<	if (item != p && item != null) {
603	<	nextNode = p;
604	<	nextItem = (E)item;
605	<	return x;
606	<	}
607	<	prevNode = p;
608	<	p = p.next;
601	>	if (q == null || !q.isData) {
602	>	next = null;
603	>	return;
604	>	}
605	>	Object x = q.get();
606	>	QNode s = q.next;
607	>	if (x != null && q != x && q != s) {
608	>	nextItem = (E) x;
609	>	snext = s;
610	>	pnext = pred;
611	>	next = q;
612	>	return;
613	>	}
614	>	pnext = q;
615	>	next = s;
616		}
617		}
618	<
618	>
619		public boolean hasNext() {
620	<	return nextNode != null;
620	>	return next != null;
621		}
622	<
622	>
623		public E next() {
624	<	if (nextNode == null) throw new NoSuchElementException();
625	<	return advance();
624	>	if (next == null) throw new NoSuchElementException();
625	>	pcurr = pnext;
626	>	curr = next;
627	>	pnext = next;
628	>	next = snext;
629	>	E x = nextItem;
630	>	findNext();
631	>	return x;
632		}
633	<
633	>
634		public void remove() {
635	<	QNode p = currentNode;
636	<	QNode prev = prevNode;
564	<	if (prev == null || p == null)
635	>	QNode p = curr;
636	>	if (p == null)
637		throw new IllegalStateException();
638		Object x = p.get();
639		if (x != null && x != p && p.compareAndSet(x, p))
640	<	clean(prev, p);
640	>	clean(pcurr, p);
641		}
642		}
643
#	Line 580 | Line 652 | public class LinkedTransferQueue<E> exte
652		if (!p.isData)
653		return null;
654		if (x != null)
655	<	return (E)x;
655	>	return (E) x;
656		}
657		}
658		}
#	Line 608 | Line 680 | public class LinkedTransferQueue<E> exte
680		if (p == null)
681		return false;
682		Object x = p.get();
683	<	if (p != x)
683	>	if (p != x)
684		return !p.isData;
685		}
686		}
687	<
687	>
688		/**
689		* Returns the number of elements in this queue.  If this queue
690	<	* contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
691	<	* <tt>Integer.MAX_VALUE</tt>.
690	>	* contains more than {@code Integer.MAX_VALUE} elements, returns
691	>	* {@code Integer.MAX_VALUE}.
692		*
693		* <p>Beware that, unlike in most collections, this method is
694		* <em>NOT</em> a constant-time operation. Because of the
#	Line 630 | Line 702 | public class LinkedTransferQueue<E> exte
702		QNode h = traversalHead();
703		for (QNode p = h.next; p != null && p.isData; p = p.next) {
704		Object x = p.get();
705	<	if (x != null && x != p) {
705	>	if (x != null && x != p) {
706		if (++count == Integer.MAX_VALUE) // saturated
707		break;
708		}
#	Line 654 | Line 726 | public class LinkedTransferQueue<E> exte
726		return Integer.MAX_VALUE;
727		}
728
729	+	public boolean remove(Object o) {
730	+	if (o == null)
731	+	return false;
732	+	for (;;) {
733	+	QNode pred = traversalHead();
734	+	for (;;) {
735	+	QNode q = pred.next;
736	+	if (q == null || !q.isData)
737	+	return false;
738	+	if (q == pred) // restart
739	+	break;
740	+	Object x = q.get();
741	+	if (x != null && x != q && o.equals(x) &&
742	+	q.compareAndSet(x, q)) {
743	+	clean(pred, q);
744	+	return true;
745	+	}
746	+	pred = q;
747	+	}
748	+	}
749	+	}
750	+
751		/**
752		* Save the state to a stream (that is, serialize it).
753		*
754	<	* @serialData All of the elements (each an <tt>E</tt>) in
754	>	* @serialData All of the elements (each an {@code E}) in
755		* the proper order, followed by a null
756		* @param s the stream
757		*/
758		private void writeObject(java.io.ObjectOutputStream s)
759		throws java.io.IOException {
760		s.defaultWriteObject();
761	<	for (Iterator<E> it = iterator(); it.hasNext(); )
762	<	s.writeObject(it.next());
761	>	for (E e : this)
762	>	s.writeObject(e);
763		// Use trailing null as sentinel
764		s.writeObject(null);
765		}
#	Line 673 | Line 767 | public class LinkedTransferQueue<E> exte
767		/**
768		* Reconstitute the Queue instance from a stream (that is,
769		* deserialize it).
770	+	*
771		* @param s the stream
772		*/
773		private void readObject(java.io.ObjectInputStream s)
774		throws java.io.IOException, ClassNotFoundException {
775		s.defaultReadObject();
776	+	resetHeadAndTail();
777		for (;;) {
778	<	E item = (E)s.readObject();
778	>	E item = (E) s.readObject();
779		if (item == null)
780		break;
781		else
782		offer(item);
783		}
784		}
785	+
786	+
787	+	// Support for resetting head/tail while deserializing
788	+	private void resetHeadAndTail() {
789	+	QNode dummy = new QNode(null, false);
790	+	UNSAFE.putObjectVolatile(this, headOffset,
791	+	new PaddedAtomicReference<QNode>(dummy));
792	+	UNSAFE.putObjectVolatile(this, tailOffset,
793	+	new PaddedAtomicReference<QNode>(dummy));
794	+	UNSAFE.putObjectVolatile(this, cleanMeOffset,
795	+	new PaddedAtomicReference<QNode>(null));
796	+	}
797	+
798	+	// Temporary Unsafe mechanics for preliminary release
799	+	private static Unsafe getUnsafe() throws Throwable {
800	+	try {
801	+	return Unsafe.getUnsafe();
802	+	} catch (SecurityException se) {
803	+	try {
804	+	return java.security.AccessController.doPrivileged
805	+	(new java.security.PrivilegedExceptionAction<Unsafe>() {
806	+	public Unsafe run() throws Exception {
807	+	return getUnsafePrivileged();
808	+	}});
809	+	} catch (java.security.PrivilegedActionException e) {
810	+	throw e.getCause();
811	+	}
812	+	}
813	+	}
814	+
815	+	private static Unsafe getUnsafePrivileged()
816	+	throws NoSuchFieldException, IllegalAccessException {
817	+	Field f = Unsafe.class.getDeclaredField("theUnsafe");
818	+	f.setAccessible(true);
819	+	return (Unsafe) f.get(null);
820	+	}
821	+
822	+	private static long fieldOffset(String fieldName)
823	+	throws NoSuchFieldException {
824	+	return UNSAFE.objectFieldOffset
825	+	(LinkedTransferQueue.class.getDeclaredField(fieldName));
826	+	}
827	+
828	+	private static final Unsafe UNSAFE;
829	+	private static final long headOffset;
830	+	private static final long tailOffset;
831	+	private static final long cleanMeOffset;
832	+	static {
833	+	try {
834	+	UNSAFE = getUnsafe();
835	+	headOffset = fieldOffset("head");
836	+	tailOffset = fieldOffset("tail");
837	+	cleanMeOffset = fieldOffset("cleanMe");
838	+	} catch (Throwable e) {
839	+	throw new RuntimeException("Could not initialize intrinsics", e);
840	+	}
841	+	}
842	+
843		}

Diff Legend

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