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

Comparing jsr166/src/jsr166y/LinkedTransferQueue.java (file contents):
Revision 1.24 by jsr166, Thu Jul 23 23:23:41 2009 UTC vs.
Revision 1.27 by jsr166, Sun Jul 26 05:55:34 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.Iterator;
14	>	import java.util.NoSuchElementException;
15	>	import java.util.concurrent.locks.LockSupport;
16	>	import java.util.concurrent.atomic.AtomicReference;
17	>	import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
18
19		/**
20		* An unbounded {@linkplain TransferQueue} based on linked nodes.
#	Line 102 | Line 105 | public class LinkedTransferQueue<E> exte
105		* garbage retention. Similarly, setting the next field to this is
106		* used as sentinel that node is off list.
107		*/
108	<	static final class QNode extends AtomicReference<Object> {
109	<	volatile QNode next;
108	>	static final class Node<E> extends AtomicReference<Object> {
109	>	volatile Node<E> next;
110		volatile Thread waiter;       // to control park/unpark
111		final boolean isData;
112	<	QNode(Object item, boolean isData) {
112	>
113	>	Node(E item, boolean isData) {
114		super(item);
115		this.isData = isData;
116		}
117
118	<	static final AtomicReferenceFieldUpdater<QNode, QNode>
118	>	@SuppressWarnings("rawtypes")
119	>	static final AtomicReferenceFieldUpdater<Node, Node>
120		nextUpdater = AtomicReferenceFieldUpdater.newUpdater
121	<	(QNode.class, QNode.class, "next");
121	>	(Node.class, Node.class, "next");
122
123	<	final boolean casNext(QNode cmp, QNode val) {
123	>	final boolean casNext(Node<E> cmp, Node<E> val) {
124		return nextUpdater.compareAndSet(this, cmp, val);
125		}
126
#	Line 140 | Line 145 | public class LinkedTransferQueue<E> exte
145
146
147		/** head of the queue */
148	<	private transient final PaddedAtomicReference<QNode> head;
148	>	private transient final PaddedAtomicReference<Node<E>> head;
149
150		/** tail of the queue */
151	<	private transient final PaddedAtomicReference<QNode> tail;
151	>	private transient final PaddedAtomicReference<Node<E>> tail;
152
153		/**
154		* Reference to a cancelled node that might not yet have been
155		* unlinked from queue because it was the last inserted node
156		* when it cancelled.
157		*/
158	<	private transient final PaddedAtomicReference<QNode> cleanMe;
158	>	private transient final PaddedAtomicReference<Node<E>> cleanMe;
159
160		/**
161		* Tries to cas nh as new head; if successful, unlink
162		* old head's next node to avoid garbage retention.
163		*/
164	<	private boolean advanceHead(QNode h, QNode nh) {
164	>	private boolean advanceHead(Node<E> h, Node<E> nh) {
165		if (h == head.get() && head.compareAndSet(h, nh)) {
166		h.clearNext(); // forget old next
167		return true;
#	Line 174 | Line 179 | public class LinkedTransferQueue<E> exte
179		* @param nanos timeout in nanosecs, used only if mode is TIMEOUT
180		* @return an item, or null on failure
181		*/
182	<	private Object xfer(Object e, int mode, long nanos) {
182	>	private E xfer(E e, int mode, long nanos) {
183		boolean isData = (e != null);
184	<	QNode s = null;
185	<	final PaddedAtomicReference<QNode> head = this.head;
186	<	final PaddedAtomicReference<QNode> tail = this.tail;
184	>	Node<E> s = null;
185	>	final PaddedAtomicReference<Node<E>> head = this.head;
186	>	final PaddedAtomicReference<Node<E>> tail = this.tail;
187
188		for (;;) {
189	<	QNode t = tail.get();
190	<	QNode h = head.get();
189	>	Node<E> t = tail.get();
190	>	Node<E> h = head.get();
191
192		if (t != null && (t == h || t.isData == isData)) {
193		if (s == null)
194	<	s = new QNode(e, isData);
195	<	QNode last = t.next;
194	>	s = new Node<E>(e, isData);
195	>	Node<E> last = t.next;
196		if (last != null) {
197		if (t == tail.get())
198		tail.compareAndSet(t, last);
#	Line 199 | Line 204 | public class LinkedTransferQueue<E> exte
204		}
205
206		else if (h != null) {
207	<	QNode first = h.next;
207	>	Node<E> first = h.next;
208		if (t == tail.get() && first != null &&
209		advanceHead(h, first)) {
210		Object x = first.get();
211		if (x != first && first.compareAndSet(x, e)) {
212		LockSupport.unpark(first.waiter);
213	<	return isData ? e : x;
213	>	return isData ? e : (E) x;
214		}
215		}
216		}
#	Line 217 | Line 222 | public class LinkedTransferQueue<E> exte
222		* Version of xfer for poll() and tryTransfer, which
223		* simplifies control paths both here and in xfer.
224		*/
225	<	private Object fulfill(Object e) {
225	>	private E fulfill(E e) {
226		boolean isData = (e != null);
227	<	final PaddedAtomicReference<QNode> head = this.head;
228	<	final PaddedAtomicReference<QNode> tail = this.tail;
227	>	final PaddedAtomicReference<Node<E>> head = this.head;
228	>	final PaddedAtomicReference<Node<E>> tail = this.tail;
229
230		for (;;) {
231	<	QNode t = tail.get();
232	<	QNode h = head.get();
231	>	Node<E> t = tail.get();
232	>	Node<E> h = head.get();
233
234		if (t != null && (t == h || t.isData == isData)) {
235	<	QNode last = t.next;
235	>	Node<E> last = t.next;
236		if (t == tail.get()) {
237		if (last != null)
238		tail.compareAndSet(t, last);
#	Line 236 | Line 241 | public class LinkedTransferQueue<E> exte
241		}
242		}
243		else if (h != null) {
244	<	QNode first = h.next;
244	>	Node<E> first = h.next;
245		if (t == tail.get() &&
246		first != null &&
247		advanceHead(h, first)) {
248		Object x = first.get();
249		if (x != first && first.compareAndSet(x, e)) {
250		LockSupport.unpark(first.waiter);
251	<	return isData ? e : x;
251	>	return isData ? e : (E) x;
252		}
253		}
254		}
#	Line 261 | Line 266 | public class LinkedTransferQueue<E> exte
266		* @param nanos timeout value
267		* @return matched item, or s if cancelled
268		*/
269	<	private Object awaitFulfill(QNode pred, QNode s, Object e,
270	<	int mode, long nanos) {
269	>	private E awaitFulfill(Node<E> pred, Node<E> s, E e,
270	>	int mode, long nanos) {
271		if (mode == NOWAIT)
272		return null;
273
#	Line 281 | Line 286 | public class LinkedTransferQueue<E> exte
286		}
287		else if (x != null) {
288		s.set(s);             // avoid garbage retention
289	<	return x;
289	>	return (E) x;
290		}
291		else
292		return e;
#	Line 296 | Line 301 | public class LinkedTransferQueue<E> exte
301		}
302		}
303		if (spins < 0) {
304	<	QNode h = head.get(); // only spin if at head
304	>	Node<E> h = head.get(); // only spin if at head
305		spins = ((h != null && h.next == s) ?
306		((mode == TIMEOUT) ?
307		maxTimedSpins : maxUntimedSpins) : 0);
#	Line 321 | Line 326 | public class LinkedTransferQueue<E> exte
326		/**
327		* Returns validated tail for use in cleaning methods.
328		*/
329	<	private QNode getValidatedTail() {
329	>	private Node<E> getValidatedTail() {
330		for (;;) {
331	<	QNode h = head.get();
332	<	QNode first = h.next;
331	>	Node<E> h = head.get();
332	>	Node<E> first = h.next;
333		if (first != null && first.next == first) { // help advance
334		advanceHead(h, first);
335		continue;
336		}
337	<	QNode t = tail.get();
338	<	QNode last = t.next;
337	>	Node<E> t = tail.get();
338	>	Node<E> last = t.next;
339		if (t == tail.get()) {
340		if (last != null)
341		tail.compareAndSet(t, last); // help advance
#	Line 346 | Line 351 | public class LinkedTransferQueue<E> exte
351		* @param pred predecessor of cancelled node
352		* @param s the cancelled node
353		*/
354	<	private void clean(QNode pred, QNode s) {
354	>	private void clean(Node<E> pred, Node<E> s) {
355		Thread w = s.waiter;
356		if (w != null) {             // Wake up thread
357		s.waiter = null;
#	Line 366 | Line 371 | public class LinkedTransferQueue<E> exte
371		* processed, so this always terminates.
372		*/
373		while (pred.next == s) {
374	<	QNode oldpred = reclean();  // First, help get rid of cleanMe
375	<	QNode t = getValidatedTail();
374	>	Node<E> oldpred = reclean();  // First, help get rid of cleanMe
375	>	Node<E> t = getValidatedTail();
376		if (s != t) {               // If not tail, try to unsplice
377	<	QNode sn = s.next;      // s.next == s means s already off list
377	>	Node<E> sn = s.next;      // s.next == s means s already off list
378		if (sn == s || pred.casNext(s, sn))
379		break;
380		}
#	Line 385 | Line 390 | public class LinkedTransferQueue<E> exte
390		*
391		* @return current cleanMe node (or null)
392		*/
393	<	private QNode reclean() {
393	>	private Node<E> reclean() {
394		/*
395		* cleanMe is, or at one time was, predecessor of cancelled
396		* node s that was the tail so could not be unspliced.  If s
#	Line 397 | Line 402 | public class LinkedTransferQueue<E> exte
402		* This can loop only due to contention on casNext or
403		* clearing cleanMe.
404		*/
405	<	QNode pred;
405	>	Node<E> pred;
406		while ((pred = cleanMe.get()) != null) {
407	<	QNode t = getValidatedTail();
408	<	QNode s = pred.next;
407	>	Node<E> t = getValidatedTail();
408	>	Node<E> s = pred.next;
409		if (s != t) {
410	<	QNode sn;
410	>	Node<E> sn;
411		if (s == null || s == pred || s.get() != s ||
412		(sn = s.next) == s || pred.casNext(s, sn))
413		cleanMe.compareAndSet(pred, null);
#	Line 417 | Line 422 | public class LinkedTransferQueue<E> exte
422		* Creates an initially empty {@code LinkedTransferQueue}.
423		*/
424		public LinkedTransferQueue() {
425	<	QNode dummy = new QNode(null, false);
426	<	head = new PaddedAtomicReference<QNode>(dummy);
427	<	tail = new PaddedAtomicReference<QNode>(dummy);
428	<	cleanMe = new PaddedAtomicReference<QNode>(null);
425	>	Node<E> dummy = new Node<E>(null, false);
426	>	head = new PaddedAtomicReference<Node<E>>(dummy);
427	>	tail = new PaddedAtomicReference<Node<E>>(dummy);
428	>	cleanMe = new PaddedAtomicReference<Node<E>>(null);
429		}
430
431		/**
#	Line 502 | Line 507 | public class LinkedTransferQueue<E> exte
507		}
508
509		public E poll() {
510	<	return (E) fulfill(null);
510	>	return fulfill(null);
511		}
512
513		public int drainTo(Collection<? super E> c) {
#	Line 538 | Line 543 | public class LinkedTransferQueue<E> exte
543		/**
544		* Returns head after performing any outstanding helping steps.
545		*/
546	<	private QNode traversalHead() {
546	>	private Node<E> traversalHead() {
547		for (;;) {
548	<	QNode t = tail.get();
549	<	QNode h = head.get();
548	>	Node<E> t = tail.get();
549	>	Node<E> h = head.get();
550		if (h != null && t != null) {
551	<	QNode last = t.next;
552	<	QNode first = h.next;
551	>	Node<E> last = t.next;
552	>	Node<E> first = h.next;
553		if (t == tail.get()) {
554		if (last != null)
555		tail.compareAndSet(t, last);
#	Line 576 | Line 581 | public class LinkedTransferQueue<E> exte
581		* if subsequently removed.
582		*/
583		class Itr implements Iterator<E> {
584	<	QNode next;        // node to return next
585	<	QNode pnext;       // predecessor of next
586	<	QNode snext;       // successor of next
587	<	QNode curr;        // last returned node, for remove()
588	<	QNode pcurr;       // predecessor of curr, for remove()
584	>	Node<E> next;        // node to return next
585	>	Node<E> pnext;       // predecessor of next
586	>	Node<E> snext;       // successor of next
587	>	Node<E> curr;        // last returned node, for remove()
588	>	Node<E> pcurr;       // predecessor of curr, for remove()
589		E nextItem;        // Cache of next item, once committed to in next
590
591		Itr() {
#	Line 592 | Line 597 | public class LinkedTransferQueue<E> exte
597		*/
598		void findNext() {
599		for (;;) {
600	<	QNode pred = pnext;
601	<	QNode q = next;
600	>	Node<E> pred = pnext;
601	>	Node<E> q = next;
602		if (pred == null || pred == q) {
603		pred = traversalHead();
604		q = pred.next;
#	Line 603 | Line 608 | public class LinkedTransferQueue<E> exte
608		return;
609		}
610		Object x = q.get();
611	<	QNode s = q.next;
611	>	Node<E> s = q.next;
612		if (x != null && q != x && q != s) {
613		nextItem = (E) x;
614		snext = s;
#	Line 632 | Line 637 | public class LinkedTransferQueue<E> exte
637		}
638
639		public void remove() {
640	<	QNode p = curr;
640	>	Node<E> p = curr;
641		if (p == null)
642		throw new IllegalStateException();
643		Object x = p.get();
#	Line 643 | Line 648 | public class LinkedTransferQueue<E> exte
648
649		public E peek() {
650		for (;;) {
651	<	QNode h = traversalHead();
652	<	QNode p = h.next;
651	>	Node<E> h = traversalHead();
652	>	Node<E> p = h.next;
653		if (p == null)
654		return null;
655		Object x = p.get();
#	Line 659 | Line 664 | public class LinkedTransferQueue<E> exte
664
665		public boolean isEmpty() {
666		for (;;) {
667	<	QNode h = traversalHead();
668	<	QNode p = h.next;
667	>	Node<E> h = traversalHead();
668	>	Node<E> p = h.next;
669		if (p == null)
670		return true;
671		Object x = p.get();
#	Line 675 | Line 680 | public class LinkedTransferQueue<E> exte
680
681		public boolean hasWaitingConsumer() {
682		for (;;) {
683	<	QNode h = traversalHead();
684	<	QNode p = h.next;
683	>	Node<E> h = traversalHead();
684	>	Node<E> p = h.next;
685		if (p == null)
686		return false;
687		Object x = p.get();
#	Line 699 | Line 704 | public class LinkedTransferQueue<E> exte
704		*/
705		public int size() {
706		int count = 0;
707	<	QNode h = traversalHead();
708	<	for (QNode p = h.next; p != null && p.isData; p = p.next) {
707	>	Node<E> h = traversalHead();
708	>	for (Node<E> p = h.next; p != null && p.isData; p = p.next) {
709		Object x = p.get();
710		if (x != null && x != p) {
711		if (++count == Integer.MAX_VALUE) // saturated
#	Line 712 | Line 717 | public class LinkedTransferQueue<E> exte
717
718		public int getWaitingConsumerCount() {
719		int count = 0;
720	<	QNode h = traversalHead();
721	<	for (QNode p = h.next; p != null && !p.isData; p = p.next) {
720	>	Node<E> h = traversalHead();
721	>	for (Node<E> p = h.next; p != null && !p.isData; p = p.next) {
722		if (p.get() == null) {
723		if (++count == Integer.MAX_VALUE)
724		break;
#	Line 730 | Line 735 | public class LinkedTransferQueue<E> exte
735		if (o == null)
736		return false;
737		for (;;) {
738	<	QNode pred = traversalHead();
738	>	Node<E> pred = traversalHead();
739		for (;;) {
740	<	QNode q = pred.next;
740	>	Node<E> q = pred.next;
741		if (q == null || !q.isData)
742		return false;
743		if (q == pred) // restart
#	Line 775 | Line 780 | public class LinkedTransferQueue<E> exte
780		s.defaultReadObject();
781		resetHeadAndTail();
782		for (;;) {
783	<	E item = (E) s.readObject();
783	>	@SuppressWarnings("unchecked") E item = (E) s.readObject();
784		if (item == null)
785		break;
786		else
#	Line 783 | Line 788 | public class LinkedTransferQueue<E> exte
788		}
789		}
790
786	–
791		// Support for resetting head/tail while deserializing
792		private void resetHeadAndTail() {
793	<	QNode dummy = new QNode(null, false);
793	>	Node<E> dummy = new Node<E>(null, false);
794		UNSAFE.putObjectVolatile(this, headOffset,
795	<	new PaddedAtomicReference<QNode>(dummy));
795	>	new PaddedAtomicReference<Node<E>>(dummy));
796		UNSAFE.putObjectVolatile(this, tailOffset,
797	<	new PaddedAtomicReference<QNode>(dummy));
797	>	new PaddedAtomicReference<Node<E>>(dummy));
798		UNSAFE.putObjectVolatile(this, cleanMeOffset,
799	<	new PaddedAtomicReference<QNode>(null));
799	>	new PaddedAtomicReference<Node<E>>(null));
800		}
801
802	<	// Temporary Unsafe mechanics for preliminary release
803	<	private static Unsafe getUnsafe() throws Throwable {
802	>	// Unsafe mechanics for jsr166y 3rd party package.
803	>	private static sun.misc.Unsafe getUnsafe() {
804		try {
805	<	return Unsafe.getUnsafe();
805	>	return sun.misc.Unsafe.getUnsafe();
806		} catch (SecurityException se) {
807		try {
808		return java.security.AccessController.doPrivileged
809	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
810	<	public Unsafe run() throws Exception {
811	<	return getUnsafePrivileged();
809	>	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
810	>	public sun.misc.Unsafe run() throws Exception {
811	>	return getUnsafeByReflection();
812		}});
813		} catch (java.security.PrivilegedActionException e) {
814	<	throw e.getCause();
814	>	throw new RuntimeException("Could not initialize intrinsics",
815	>	e.getCause());
816		}
817		}
818		}
819
820	<	private static Unsafe getUnsafePrivileged()
820	>	private static sun.misc.Unsafe getUnsafeByReflection()
821		throws NoSuchFieldException, IllegalAccessException {
822	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
822	>	java.lang.reflect.Field f =
823	>	sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
824		f.setAccessible(true);
825	<	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));
825	>	return (sun.misc.Unsafe) f.get(null);
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 {
828	>	private static long fieldOffset(String fieldName, Class<?> klazz) {
829		try {
830	<	UNSAFE = getUnsafe();
831	<	headOffset = fieldOffset("head");
832	<	tailOffset = fieldOffset("tail");
833	<	cleanMeOffset = fieldOffset("cleanMe");
834	<	} catch (Throwable e) {
835	<	throw new RuntimeException("Could not initialize intrinsics", e);
830	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
831	>	} catch (NoSuchFieldException e) {
832	>	// Convert Exception to Error
833	>	NoSuchFieldError error = new NoSuchFieldError(fieldName);
834	>	error.initCause(e);
835	>	throw error;
836		}
837		}
838
839	+	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
840	+	private static final long headOffset =
841	+	fieldOffset("head", LinkedTransferQueue.class);
842	+	private static final long tailOffset =
843	+	fieldOffset("tail", LinkedTransferQueue.class);
844	+	private static final long cleanMeOffset =
845	+	fieldOffset("cleanMe", LinkedTransferQueue.class);
846	+
847		}

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