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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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package jsr166y; |
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import java.util.concurrent.*; |
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import java.util.AbstractQueue; |
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import java.util.Collection; |
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import java.util.ConcurrentModificationException; |
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import java.util.Iterator; |
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import java.util.NoSuchElementException; |
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import java.util.Queue; |
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import java.util.concurrent.TimeUnit; |
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import java.util.concurrent.locks.LockSupport; |
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/** |
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* producer. The <em>tail</em> of the queue is that element that has |
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* been on the queue the shortest time for some producer. |
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* |
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* <p>Beware that, unlike in most collections, the {@code size} |
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* method is <em>NOT</em> a constant-time operation. Because of the |
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* <p>Beware that, unlike in most collections, the {@code size} method |
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* is <em>NOT</em> a constant-time operation. Because of the |
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* asynchronous nature of these queues, determining the current number |
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* of elements requires a traversal of the elements. |
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* of elements requires a traversal of the elements, and so may report |
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* inaccurate results if this collection is modified during traversal. |
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* Additionally, the bulk operations {@code addAll}, |
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* {@code removeAll}, {@code retainAll}, {@code containsAll}, |
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* {@code equals}, and {@code toArray} are <em>not</em> guaranteed |
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* to be performed atomically. For example, an iterator operating |
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* concurrently with an {@code addAll} operation might view only some |
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* of the added elements. |
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* |
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* <p>This class and its iterator implement all of the |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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} |
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final boolean casItem(Object cmp, Object val) { |
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// assert cmp == null || cmp.getClass() != Node.class; |
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// assert cmp == null || cmp.getClass() != Node.class; |
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return UNSAFE.compareAndSwapObject(this, itemOffset, cmp, val); |
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} |
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|
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* Tries to artificially match a data node -- used by remove. |
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*/ |
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final boolean tryMatchData() { |
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// assert isData; |
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// assert isData; |
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Object x = item; |
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if (x != null && x != this && casItem(x, null)) { |
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LockSupport.unpark(waiter); |
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return false; |
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} |
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// Unsafe mechanics |
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private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
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private static final long nextOffset = |
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objectFieldOffset(UNSAFE, "next", Node.class); |
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private static final long itemOffset = |
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objectFieldOffset(UNSAFE, "item", Node.class); |
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private static final long waiterOffset = |
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objectFieldOffset(UNSAFE, "waiter", Node.class); |
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|
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private static final long serialVersionUID = -3375979862319811754L; |
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|
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// Unsafe mechanics |
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private static final sun.misc.Unsafe UNSAFE; |
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private static final long itemOffset; |
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private static final long nextOffset; |
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private static final long waiterOffset; |
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static { |
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try { |
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UNSAFE = getUnsafe(); |
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Class k = Node.class; |
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itemOffset = UNSAFE.objectFieldOffset |
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(k.getDeclaredField("item")); |
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nextOffset = UNSAFE.objectFieldOffset |
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(k.getDeclaredField("next")); |
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waiterOffset = UNSAFE.objectFieldOffset |
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(k.getDeclaredField("waiter")); |
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} catch (Exception e) { |
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throw new Error(e); |
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} |
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} |
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} |
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/** head of the queue; null until first enqueue */ |
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|
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@SuppressWarnings("unchecked") |
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static <E> E cast(Object item) { |
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// assert item == null || item.getClass() != Node.class; |
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// assert item == null || item.getClass() != Node.class; |
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return (E) item; |
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} |
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throw new NullPointerException(); |
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Node s = null; // the node to append, if needed |
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|
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retry: for (;;) { // restart on append race |
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retry: |
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for (;;) { // restart on append race |
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|
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for (Node h = head, p = h; p != null;) { // find & match first node |
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boolean isData = p.isData; |
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if (p.casItem(item, e)) { // match |
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for (Node q = p; q != h;) { |
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Node n = q.next; // update by 2 unless singleton |
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if (head == h && casHead(h, n == null? q : n)) { |
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if (head == h && casHead(h, n == null ? q : n)) { |
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h.forgetNext(); |
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break; |
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} // advance and retry |
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for (;;) { |
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Object item = s.item; |
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if (item != e) { // matched |
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// assert item != s; |
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// assert item != s; |
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s.forgetContents(); // avoid garbage |
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return this.<E>cast(item); |
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} |
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* Moves to next node after prev, or first node if prev null. |
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*/ |
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private void advance(Node prev) { |
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lastPred = lastRet; |
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lastRet = prev; |
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for (Node p = (prev == null) ? head : succ(prev); |
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p != null; p = succ(p)) { |
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Object item = p.item; |
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if (p.isData) { |
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if (item != null && item != p) { |
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nextItem = LinkedTransferQueue.this.<E>cast(item); |
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nextNode = p; |
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/* |
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* To track and avoid buildup of deleted nodes in the face |
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* of calls to both Queue.remove and Itr.remove, we must |
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* include variants of unsplice and sweep upon each |
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* advance: Upon Itr.remove, we may need to catch up links |
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* from lastPred, and upon other removes, we might need to |
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* skip ahead from stale nodes and unsplice deleted ones |
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* found while advancing. |
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*/ |
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|
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Node r, b; // reset lastPred upon possible deletion of lastRet |
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if ((r = lastRet) != null && !r.isMatched()) |
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lastPred = r; // next lastPred is old lastRet |
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else if ((b = lastPred) == null || b.isMatched()) |
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lastPred = null; // at start of list |
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else { |
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Node s, n; // help with removal of lastPred.next |
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while ((s = b.next) != null && |
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s != b && s.isMatched() && |
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(n = s.next) != null && n != s) |
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b.casNext(s, n); |
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} |
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|
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this.lastRet = prev; |
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|
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for (Node p = prev, s, n;;) { |
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s = (p == null) ? head : p.next; |
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if (s == null) |
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break; |
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else if (s == p) { |
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p = null; |
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continue; |
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} |
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Object item = s.item; |
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if (s.isData) { |
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if (item != null && item != s) { |
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nextItem = LinkedTransferQueue.<E>cast(item); |
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nextNode = s; |
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return; |
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} |
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} |
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else if (item == null) |
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break; |
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// assert s.isMatched(); |
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if (p == null) |
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p = s; |
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else if ((n = s.next) == null) |
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break; |
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else if (s == n) |
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p = null; |
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else |
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p.casNext(s, n); |
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} |
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nextNode = null; |
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nextItem = null; |
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} |
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Itr() { |
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} |
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public final void remove() { |
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Node p = lastRet; |
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if (p == null) throw new IllegalStateException(); |
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if (p.tryMatchData()) |
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unsplice(lastPred, p); |
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final Node lastRet = this.lastRet; |
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if (lastRet == null) |
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throw new IllegalStateException(); |
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this.lastRet = null; |
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if (lastRet.tryMatchData()) |
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unsplice(lastPred, lastRet); |
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} |
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} |
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*/ |
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private void sweep() { |
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for (Node p = head, s, n; p != null && (s = p.next) != null; ) { |
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if (p == s) // stale |
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p = head; |
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else if (!s.isMatched()) |
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if (!s.isMatched()) |
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// Unmatched nodes are never self-linked |
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p = s; |
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else if ((n = s.next) == null || s == n) // trailing node is pinned |
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else if ((n = s.next) == null) // trailing node is pinned |
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break; |
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else if (s == n) // stale |
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// No need to also check for p == s, since that implies s == n |
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p = head; |
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else |
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p.casNext(s, n); |
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} |
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* return {@code false}. |
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* |
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* @return {@code true} (as specified by |
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* {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer}) |
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* {@link java.util.concurrent.BlockingQueue#offer(Object,long,TimeUnit) |
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* BlockingQueue.offer}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean offer(E e, long timeout, TimeUnit unit) { |
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* Inserts the specified element at the tail of this queue. |
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* As the queue is unbounded, this method will never return {@code false}. |
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* |
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* @return {@code true} (as specified by |
972 |
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* {@link BlockingQueue#offer(Object) BlockingQueue.offer}) |
1032 |
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* @return {@code true} (as specified by {@link Queue#offer}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean offer(E e) { |
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} |
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/** |
1164 |
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* Returns an iterator over the elements in this queue in proper |
1165 |
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* sequence, from head to tail. |
1164 |
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* Returns an iterator over the elements in this queue in proper sequence. |
1165 |
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* The elements will be returned in order from first (head) to last (tail). |
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* |
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* <p>The returned iterator is a "weakly consistent" iterator that |
1168 |
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* will never throw |
1169 |
< |
* {@link ConcurrentModificationException ConcurrentModificationException}, |
1170 |
< |
* and guarantees to traverse elements as they existed upon |
1171 |
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* construction of the iterator, and may (but is not guaranteed |
1172 |
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* to) reflect any modifications subsequent to construction. |
1168 |
> |
* will never throw {@link java.util.ConcurrentModificationException |
1169 |
> |
* ConcurrentModificationException}, and guarantees to traverse |
1170 |
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* elements as they existed upon construction of the iterator, and |
1171 |
> |
* may (but is not guaranteed to) reflect any modifications |
1172 |
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* subsequent to construction. |
1173 |
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* |
1174 |
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* @return an iterator over the elements in this queue in proper sequence |
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*/ |
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} |
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|
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/** |
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* Returns {@code true} if this queue contains the specified element. |
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* More formally, returns {@code true} if and only if this queue contains |
1239 |
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* at least one element {@code e} such that {@code o.equals(e)}. |
1240 |
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* |
1241 |
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* @param o object to be checked for containment in this queue |
1242 |
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* @return {@code true} if this queue contains the specified element |
1243 |
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*/ |
1244 |
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public boolean contains(Object o) { |
1245 |
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if (o == null) return false; |
1246 |
+ |
for (Node p = head; p != null; p = succ(p)) { |
1247 |
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Object item = p.item; |
1248 |
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if (p.isData) { |
1249 |
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if (item != null && item != p && o.equals(item)) |
1250 |
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return true; |
1251 |
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} |
1252 |
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else if (item == null) |
1253 |
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break; |
1254 |
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} |
1255 |
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return false; |
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} |
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|
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/** |
1259 |
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* Always returns {@code Integer.MAX_VALUE} because a |
1260 |
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* {@code LinkedTransferQueue} is not capacity constrained. |
1261 |
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* |
1262 |
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* @return {@code Integer.MAX_VALUE} (as specified by |
1263 |
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* {@link BlockingQueue#remainingCapacity()}) |
1263 |
> |
* {@link java.util.concurrent.BlockingQueue#remainingCapacity() |
1264 |
> |
* BlockingQueue.remainingCapacity}) |
1265 |
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*/ |
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public int remainingCapacity() { |
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return Integer.MAX_VALUE; |
1303 |
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|
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// Unsafe mechanics |
1305 |
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|
1306 |
< |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1307 |
< |
private static final long headOffset = |
1308 |
< |
objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class); |
1309 |
< |
private static final long tailOffset = |
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objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class); |
1228 |
< |
private static final long sweepVotesOffset = |
1229 |
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objectFieldOffset(UNSAFE, "sweepVotes", LinkedTransferQueue.class); |
1230 |
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|
1231 |
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static long objectFieldOffset(sun.misc.Unsafe UNSAFE, |
1232 |
< |
String field, Class<?> klazz) { |
1306 |
> |
private static final sun.misc.Unsafe UNSAFE; |
1307 |
> |
private static final long headOffset; |
1308 |
> |
private static final long tailOffset; |
1309 |
> |
private static final long sweepVotesOffset; |
1310 |
> |
static { |
1311 |
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try { |
1312 |
< |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1313 |
< |
} catch (NoSuchFieldException e) { |
1314 |
< |
// Convert Exception to corresponding Error |
1315 |
< |
NoSuchFieldError error = new NoSuchFieldError(field); |
1316 |
< |
error.initCause(e); |
1317 |
< |
throw error; |
1312 |
> |
UNSAFE = getUnsafe(); |
1313 |
> |
Class k = LinkedTransferQueue.class; |
1314 |
> |
headOffset = UNSAFE.objectFieldOffset |
1315 |
> |
(k.getDeclaredField("head")); |
1316 |
> |
tailOffset = UNSAFE.objectFieldOffset |
1317 |
> |
(k.getDeclaredField("tail")); |
1318 |
> |
sweepVotesOffset = UNSAFE.objectFieldOffset |
1319 |
> |
(k.getDeclaredField("sweepVotes")); |
1320 |
> |
} catch (Exception e) { |
1321 |
> |
throw new Error(e); |
1322 |
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} |
1323 |
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} |
1324 |
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