361 |
|
* precede or follow CASes use simple relaxed forms. Other |
362 |
|
* cleanups use releasing/lazy writes. |
363 |
|
*/ |
364 |
< |
static final class Node { |
364 |
> |
static final class Node<E> { |
365 |
|
final boolean isData; // false if this is a request node |
366 |
|
volatile Object item; // initially non-null if isData; CASed to match |
367 |
< |
volatile Node next; |
367 |
> |
volatile Node<E> next; |
368 |
|
volatile Thread waiter; // null until waiting |
369 |
|
|
370 |
|
// CAS methods for fields |
371 |
< |
final boolean casNext(Node cmp, Node val) { |
371 |
> |
final boolean casNext(Node<E> cmp, Node<E> val) { |
372 |
|
return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val); |
373 |
|
} |
374 |
|
|
375 |
|
final boolean casItem(Object cmp, Object val) { |
376 |
+ |
assert cmp == null || cmp.getClass() != Node.class; |
377 |
|
return UNSAFE.compareAndSwapObject(this, itemOffset, cmp, val); |
378 |
|
} |
379 |
|
|
381 |
|
* Creates a new node. Uses relaxed write because item can only |
382 |
|
* be seen if followed by CAS. |
383 |
|
*/ |
384 |
< |
Node(Object item, boolean isData) { |
384 |
> |
Node(E item, boolean isData) { |
385 |
|
UNSAFE.putObject(this, itemOffset, item); // relaxed write |
386 |
|
this.isData = isData; |
387 |
|
} |
410 |
|
*/ |
411 |
|
final boolean isMatched() { |
412 |
|
Object x = item; |
413 |
< |
return x == this || (x != null) != isData; |
413 |
> |
return (x == this) || ((x == null) == isData); |
414 |
> |
} |
415 |
> |
|
416 |
> |
/** |
417 |
> |
* Returns true if this is an unmatched request node. |
418 |
> |
*/ |
419 |
> |
final boolean isUnmatchedRequest() { |
420 |
> |
return !isData && item == null; |
421 |
|
} |
422 |
|
|
423 |
|
/** |
435 |
|
* Tries to artificially match a data node -- used by remove. |
436 |
|
*/ |
437 |
|
final boolean tryMatchData() { |
438 |
+ |
assert isData; |
439 |
|
Object x = item; |
440 |
|
if (x != null && x != this && casItem(x, null)) { |
441 |
|
LockSupport.unpark(waiter); |
457 |
|
} |
458 |
|
|
459 |
|
/** head of the queue; null until first enqueue */ |
460 |
< |
private transient volatile Node head; |
460 |
> |
transient volatile Node<E> head; |
461 |
|
|
462 |
|
/** predecessor of dangling unspliceable node */ |
463 |
< |
private transient volatile Node cleanMe; // decl here to reduce contention |
463 |
> |
private transient volatile Node<E> cleanMe; // decl here reduces contention |
464 |
|
|
465 |
|
/** tail of the queue; null until first append */ |
466 |
< |
private transient volatile Node tail; |
466 |
> |
private transient volatile Node<E> tail; |
467 |
|
|
468 |
|
// CAS methods for fields |
469 |
< |
private boolean casTail(Node cmp, Node val) { |
469 |
> |
private boolean casTail(Node<E> cmp, Node<E> val) { |
470 |
|
return UNSAFE.compareAndSwapObject(this, tailOffset, cmp, val); |
471 |
|
} |
472 |
|
|
473 |
< |
private boolean casHead(Node cmp, Node val) { |
473 |
> |
private boolean casHead(Node<E> cmp, Node<E> val) { |
474 |
|
return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val); |
475 |
|
} |
476 |
|
|
477 |
< |
private boolean casCleanMe(Node cmp, Node val) { |
477 |
> |
private boolean casCleanMe(Node<E> cmp, Node<E> val) { |
478 |
|
return UNSAFE.compareAndSwapObject(this, cleanMeOffset, cmp, val); |
479 |
|
} |
480 |
|
|
487 |
|
private static final int SYNC = 2; // for transfer, take |
488 |
|
private static final int TIMEOUT = 3; // for timed poll, tryTransfer |
489 |
|
|
490 |
+ |
@SuppressWarnings("unchecked") |
491 |
+ |
static <E> E cast(Object item) { |
492 |
+ |
assert item == null || item.getClass() != Node.class; |
493 |
+ |
return (E) item; |
494 |
+ |
} |
495 |
+ |
|
496 |
|
/** |
497 |
|
* Implements all queuing methods. See above for explanation. |
498 |
|
* |
503 |
|
* @return an item if matched, else e |
504 |
|
* @throws NullPointerException if haveData mode but e is null |
505 |
|
*/ |
506 |
< |
private Object xfer(Object e, boolean haveData, int how, long nanos) { |
506 |
> |
private E xfer(E e, boolean haveData, int how, long nanos) { |
507 |
|
if (haveData && (e == null)) |
508 |
|
throw new NullPointerException(); |
509 |
< |
Node s = null; // the node to append, if needed |
509 |
> |
Node<E> s = null; // the node to append, if needed |
510 |
|
|
511 |
|
retry: for (;;) { // restart on append race |
512 |
|
|
513 |
< |
for (Node h = head, p = h; p != null;) { // find & match first node |
513 |
> |
for (Node<E> h = head, p = h; p != null;) { |
514 |
> |
// find & match first node |
515 |
|
boolean isData = p.isData; |
516 |
|
Object item = p.item; |
517 |
|
if (item != p && (item != null) == isData) { // unmatched |
518 |
|
if (isData == haveData) // can't match |
519 |
|
break; |
520 |
|
if (p.casItem(item, e)) { // match |
521 |
< |
for (Node q = p; q != h;) { |
522 |
< |
Node n = q.next; // update head by 2 |
521 |
> |
for (Node<E> q = p; q != h;) { |
522 |
> |
Node<E> n = q.next; // update head by 2 |
523 |
|
if (n != null) // unless singleton |
524 |
|
q = n; |
525 |
|
if (head == h && casHead(h, q)) { |
531 |
|
break; // unless slack < 2 |
532 |
|
} |
533 |
|
LockSupport.unpark(p.waiter); |
534 |
< |
return item; |
534 |
> |
return this.<E>cast(item); |
535 |
|
} |
536 |
|
} |
537 |
< |
Node n = p.next; |
537 |
> |
Node<E> n = p.next; |
538 |
|
p = (p != n) ? n : (h = head); // Use head if p offlist |
539 |
|
} |
540 |
|
|
541 |
|
if (how >= ASYNC) { // No matches available |
542 |
|
if (s == null) |
543 |
< |
s = new Node(e, haveData); |
544 |
< |
Node pred = tryAppend(s, haveData); |
543 |
> |
s = new Node<E>(e, haveData); |
544 |
> |
Node<E> pred = tryAppend(s, haveData); |
545 |
|
if (pred == null) |
546 |
|
continue retry; // lost race vs opposite mode |
547 |
|
if (how >= SYNC) |
560 |
|
* different mode, else s's predecessor, or s itself if no |
561 |
|
* predecessor |
562 |
|
*/ |
563 |
< |
private Node tryAppend(Node s, boolean haveData) { |
564 |
< |
for (Node t = tail, p = t;;) { // move p to last node and append |
565 |
< |
Node n, u; // temps for reads of next & tail |
563 |
> |
private Node<E> tryAppend(Node<E> s, boolean haveData) { |
564 |
> |
for (Node<E> t = tail, p = t;;) { // move p to last node and append |
565 |
> |
Node<E> n, u; // temps for reads of next & tail |
566 |
|
if (p == null && (p = head) == null) { |
567 |
|
if (casHead(null, s)) |
568 |
|
return s; // initialize |
598 |
|
* @param nanos timeout value |
599 |
|
* @return matched item, or e if unmatched on interrupt or timeout |
600 |
|
*/ |
601 |
< |
private Object awaitMatch(Node s, Node pred, Object e, |
586 |
< |
int how, long nanos) { |
601 |
> |
private E awaitMatch(Node<E> s, Node<E> pred, E e, int how, long nanos) { |
602 |
|
long lastTime = (how == TIMEOUT) ? System.nanoTime() : 0L; |
603 |
|
Thread w = Thread.currentThread(); |
604 |
|
int spins = -1; // initialized after first item and cancel checks |
607 |
|
for (;;) { |
608 |
|
Object item = s.item; |
609 |
|
if (item != e) { // matched |
610 |
+ |
assert item != s; |
611 |
|
s.forgetContents(); // avoid garbage |
612 |
< |
return item; |
612 |
> |
return this.<E>cast(item); |
613 |
|
} |
614 |
|
if ((w.isInterrupted() || (how == TIMEOUT && nanos <= 0)) && |
615 |
< |
s.casItem(e, s)) { // cancel |
615 |
> |
s.casItem(e, s)) { // cancel |
616 |
|
unsplice(pred, s); |
617 |
|
return e; |
618 |
|
} |
648 |
|
* Returns spin/yield value for a node with given predecessor and |
649 |
|
* data mode. See above for explanation. |
650 |
|
*/ |
651 |
< |
private static int spinsFor(Node pred, boolean haveData) { |
651 |
> |
private static int spinsFor(Node<?> pred, boolean haveData) { |
652 |
|
if (MP && pred != null) { |
653 |
|
if (pred.isData != haveData) // phase change |
654 |
|
return FRONT_SPINS + CHAINED_SPINS; |
665 |
|
* or trailing node; failing on contention. |
666 |
|
*/ |
667 |
|
private void shortenHeadPath() { |
668 |
< |
Node h, hn, p, q; |
668 |
> |
Node<E> h, hn, p, q; |
669 |
|
if ((p = h = head) != null && h.isMatched() && |
670 |
|
(q = hn = h.next) != null) { |
671 |
< |
Node n; |
671 |
> |
Node<E> n; |
672 |
|
while ((n = q.next) != q) { |
673 |
|
if (n == null || !q.isMatched()) { |
674 |
|
if (hn != q && h.next == hn) |
687 |
|
* Returns the first unmatched node of the given mode, or null if |
688 |
|
* none. Used by methods isEmpty, hasWaitingConsumer. |
689 |
|
*/ |
690 |
< |
private Node firstOfMode(boolean data) { |
691 |
< |
for (Node p = head; p != null; ) { |
690 |
> |
private Node<E> firstOfMode(boolean data) { |
691 |
> |
for (Node<E> p = head; p != null; ) { |
692 |
|
if (!p.isMatched()) |
693 |
|
return (p.isData == data) ? p : null; |
694 |
< |
Node n = p.next; |
694 |
> |
Node<E> n = p.next; |
695 |
|
p = (n != p) ? n : head; |
696 |
|
} |
697 |
|
return null; |
699 |
|
|
700 |
|
/** |
701 |
|
* Returns the item in the first unmatched node with isData; or |
702 |
< |
* null if none. Used by peek. |
702 |
> |
* null if none. Used by peek. |
703 |
|
*/ |
704 |
< |
private Object firstDataItem() { |
705 |
< |
for (Node p = head; p != null; ) { |
704 |
> |
private E firstDataItem() { |
705 |
> |
for (Node<E> p = head; p != null; ) { |
706 |
|
boolean isData = p.isData; |
707 |
|
Object item = p.item; |
708 |
|
if (item != p && (item != null) == isData) |
709 |
< |
return isData ? item : null; |
710 |
< |
Node n = p.next; |
709 |
> |
return isData ? this.<E>cast(item) : null; |
710 |
> |
Node<E> n = p.next; |
711 |
|
p = (n != p) ? n : head; |
712 |
|
} |
713 |
|
return null; |
719 |
|
*/ |
720 |
|
private int countOfMode(boolean data) { |
721 |
|
int count = 0; |
722 |
< |
for (Node p = head; p != null; ) { |
722 |
> |
for (Node<E> p = head; p != null; ) { |
723 |
|
if (!p.isMatched()) { |
724 |
|
if (p.isData != data) |
725 |
|
return 0; |
726 |
|
if (++count == Integer.MAX_VALUE) // saturated |
727 |
|
break; |
728 |
|
} |
729 |
< |
Node n = p.next; |
729 |
> |
Node<E> n = p.next; |
730 |
|
if (n != p) |
731 |
|
p = n; |
732 |
|
else { |
738 |
|
} |
739 |
|
|
740 |
|
final class Itr implements Iterator<E> { |
741 |
< |
private Node nextNode; // next node to return item for |
742 |
< |
private Object nextItem; // the corresponding item |
743 |
< |
private Node lastRet; // last returned node, to support remove |
741 |
> |
private Node<E> nextNode; // next node to return item for |
742 |
> |
private E nextItem; // the corresponding item |
743 |
> |
private Node<E> lastRet; // last returned node, to support remove |
744 |
|
|
745 |
|
/** |
746 |
|
* Moves to next node after prev, or first node if prev null. |
747 |
|
*/ |
748 |
< |
private void advance(Node prev) { |
748 |
> |
private void advance(Node<E> prev) { |
749 |
|
lastRet = prev; |
750 |
< |
Node p; |
750 |
> |
Node<E> p; |
751 |
|
if (prev == null || (p = prev.next) == prev) |
752 |
|
p = head; |
753 |
|
while (p != null) { |
754 |
|
Object item = p.item; |
755 |
|
if (p.isData) { |
756 |
|
if (item != null && item != p) { |
757 |
< |
nextItem = item; |
757 |
> |
nextItem = LinkedTransferQueue.this.<E>cast(item); |
758 |
|
nextNode = p; |
759 |
|
return; |
760 |
|
} |
761 |
|
} |
762 |
|
else if (item == null) |
763 |
|
break; |
764 |
< |
Node n = p.next; |
764 |
> |
Node<E> n = p.next; |
765 |
|
p = (n != p) ? n : head; |
766 |
|
} |
767 |
|
nextNode = null; |
776 |
|
} |
777 |
|
|
778 |
|
public final E next() { |
779 |
< |
Node p = nextNode; |
779 |
> |
Node<E> p = nextNode; |
780 |
|
if (p == null) throw new NoSuchElementException(); |
781 |
< |
Object e = nextItem; |
781 |
> |
E e = nextItem; |
782 |
|
advance(p); |
783 |
< |
return (E) e; |
783 |
> |
return e; |
784 |
|
} |
785 |
|
|
786 |
|
public final void remove() { |
787 |
< |
Node p = lastRet; |
787 |
> |
Node<E> p = lastRet; |
788 |
|
if (p == null) throw new IllegalStateException(); |
789 |
|
lastRet = null; |
790 |
< |
findAndRemoveNode(p); |
790 |
> |
findAndRemoveDataNode(p); |
791 |
|
} |
792 |
|
} |
793 |
|
|
800 |
|
* @param pred predecessor of node to be unspliced |
801 |
|
* @param s the node to be unspliced |
802 |
|
*/ |
803 |
< |
private void unsplice(Node pred, Node s) { |
803 |
> |
private void unsplice(Node<E> pred, Node<E> s) { |
804 |
|
s.forgetContents(); // clear unneeded fields |
805 |
|
/* |
806 |
|
* At any given time, exactly one node on list cannot be |
813 |
|
*/ |
814 |
|
if (pred != null && pred != s) { |
815 |
|
while (pred.next == s) { |
816 |
< |
Node oldpred = (cleanMe == null) ? null : reclean(); |
817 |
< |
Node n = s.next; |
816 |
> |
Node<E> oldpred = (cleanMe == null) ? null : reclean(); |
817 |
> |
Node<E> n = s.next; |
818 |
|
if (n != null) { |
819 |
|
if (n != s) |
820 |
|
pred.casNext(s, n); |
833 |
|
* |
834 |
|
* @return current cleanMe node (or null) |
835 |
|
*/ |
836 |
< |
private Node reclean() { |
836 |
> |
private Node<E> reclean() { |
837 |
|
/* |
838 |
|
* cleanMe is, or at one time was, predecessor of a cancelled |
839 |
|
* node s that was the tail so could not be unspliced. If it |
844 |
|
* we can (must) clear cleanMe without unsplicing. This can |
845 |
|
* loop only due to contention. |
846 |
|
*/ |
847 |
< |
Node pred; |
847 |
> |
Node<E> pred; |
848 |
|
while ((pred = cleanMe) != null) { |
849 |
< |
Node s = pred.next; |
850 |
< |
Node n; |
849 |
> |
Node<E> s = pred.next; |
850 |
> |
Node<E> n; |
851 |
|
if (s == null || s == pred || !s.isMatched()) |
852 |
|
casCleanMe(pred, null); // already gone |
853 |
|
else if ((n = s.next) != null) { |
863 |
|
|
864 |
|
/** |
865 |
|
* Main implementation of Iterator.remove(). Find |
866 |
< |
* and unsplice the given node. |
866 |
> |
* and unsplice the given data node. |
867 |
|
*/ |
868 |
< |
final void findAndRemoveNode(Node s) { |
868 |
> |
final void findAndRemoveDataNode(Node<E> s) { |
869 |
> |
assert s.isData; |
870 |
|
if (s.tryMatchData()) { |
871 |
< |
Node pred = null; |
855 |
< |
Node p = head; |
856 |
< |
while (p != null) { |
871 |
> |
for (Node<E> pred = null, p = head; p != null; ) { |
872 |
|
if (p == s) { |
873 |
|
unsplice(pred, p); |
874 |
|
break; |
875 |
|
} |
876 |
< |
if (!p.isData && !p.isMatched()) |
876 |
> |
if (p.isUnmatchedRequest()) |
877 |
|
break; |
878 |
|
pred = p; |
879 |
|
if ((p = p.next) == pred) { // stale |
889 |
|
*/ |
890 |
|
private boolean findAndRemove(Object e) { |
891 |
|
if (e != null) { |
892 |
< |
Node pred = null; |
878 |
< |
Node p = head; |
879 |
< |
while (p != null) { |
892 |
> |
for (Node<E> pred = null, p = head; p != null; ) { |
893 |
|
Object item = p.item; |
894 |
|
if (p.isData) { |
895 |
|
if (item != null && item != p && e.equals(item) && |
901 |
|
else if (item == null) |
902 |
|
break; |
903 |
|
pred = p; |
904 |
< |
if ((p = p.next) == pred) { |
904 |
> |
if ((p = p.next) == pred) { // stale |
905 |
|
pred = null; |
906 |
|
p = head; |
907 |
|
} |
1037 |
|
} |
1038 |
|
|
1039 |
|
public E take() throws InterruptedException { |
1040 |
< |
Object e = xfer(null, false, SYNC, 0); |
1040 |
> |
E e = xfer(null, false, SYNC, 0); |
1041 |
|
if (e != null) |
1042 |
< |
return (E)e; |
1042 |
> |
return e; |
1043 |
|
Thread.interrupted(); |
1044 |
|
throw new InterruptedException(); |
1045 |
|
} |
1046 |
|
|
1047 |
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
1048 |
< |
Object e = xfer(null, false, TIMEOUT, unit.toNanos(timeout)); |
1048 |
> |
E e = xfer(null, false, TIMEOUT, unit.toNanos(timeout)); |
1049 |
|
if (e != null || !Thread.interrupted()) |
1050 |
< |
return (E)e; |
1050 |
> |
return e; |
1051 |
|
throw new InterruptedException(); |
1052 |
|
} |
1053 |
|
|
1054 |
|
public E poll() { |
1055 |
< |
return (E)xfer(null, false, NOW, 0); |
1055 |
> |
return xfer(null, false, NOW, 0); |
1056 |
|
} |
1057 |
|
|
1058 |
|
/** |
1109 |
|
} |
1110 |
|
|
1111 |
|
public E peek() { |
1112 |
< |
return (E) firstDataItem(); |
1112 |
> |
return firstDataItem(); |
1113 |
|
} |
1114 |
|
|
1115 |
|
/** |
1205 |
|
} |
1206 |
|
} |
1207 |
|
|
1195 |
– |
|
1208 |
|
// Unsafe mechanics |
1209 |
|
|
1210 |
|
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1227 |
|
} |
1228 |
|
} |
1229 |
|
|
1230 |
< |
private static sun.misc.Unsafe getUnsafe() { |
1230 |
> |
/** |
1231 |
> |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
1232 |
> |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
1233 |
> |
* into a jdk. |
1234 |
> |
* |
1235 |
> |
* @return a sun.misc.Unsafe |
1236 |
> |
*/ |
1237 |
> |
static sun.misc.Unsafe getUnsafe() { |
1238 |
|
try { |
1239 |
|
return sun.misc.Unsafe.getUnsafe(); |
1240 |
|
} catch (SecurityException se) { |