http://git-wip-us.apache.org/repos/asf/incubator-ignite/blob/c1e649dc/modules/jdk8-backport/src/main/java/org/jdk8/backport/ConcurrentLinkedDeque8.java
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a/modules/jdk8-backport/src/main/java/org/jdk8/backport/ConcurrentLinkedDeque8.java
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@@ -1,1983 +0,0 @@
-/*
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation. Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-/*
- * This file is available under and governed by the GNU General Public
- * License version 2 only, as published by the Free Software Foundation.
- * However, the following notice accompanied the original version of this
- * file:
- *
- * Written by Doug Lea with assistance from members of JCP JSR-166
- * Expert Group and released to the public domain, as explained at
- * http://creativecommons.org/publicdomain/zero/1.0/
- */
-
-/*
- * Copyright © 1993, 2013, Oracle and/or its affiliates.
- * All rights reserved.
- */
-
-package org.jdk8.backport;
-
-import sun.misc.*;
-
-import java.lang.reflect.*;
-import java.security.*;
-import java.util.*;
-import java.util.Queue;
-
-/**
- * An unbounded concurrent {@linkplain Deque deque} based on linked nodes.
- * Concurrent insertion, removal, and access operations execute safely
- * across multiple threads.
- * A {@code ConcurrentLinkedDeque} is an appropriate choice when
- * many threads will share access to a common collection.
- * Like most other concurrent collection implementations, this class
- * does not permit the use of {@code null} elements.
- *
- * <p>Iterators are <i>weakly consistent</i>, returning elements
- * reflecting the state of the deque at some point at or since the
- * creation of the iterator. They do <em>not</em> throw {@link
- * java.util.ConcurrentModificationException
- * ConcurrentModificationException}, and may proceed concurrently with
- * other operations.
- *
- * <p>Beware that, unlike in most collections, the {@code size} method
- * is <em>NOT</em> a constant-time operation. Because of the
- * asynchronous nature of these deques, determining the current number
- * of elements requires a traversal of the elements, and so may report
- * inaccurate results if this collection is modified during traversal.
- * Additionally, the bulk operations {@code addAll},
- * {@code removeAll}, {@code retainAll}, {@code containsAll},
- * {@code equals}, and {@code toArray} are <em>not</em> guaranteed
- * to be performed atomically. For example, an iterator operating
- * concurrently with an {@code addAll} operation might view only some
- * of the added elements.
- *
- * <p>This class and its iterator implement all of the <em>optional</em>
- * methods of the {@link Deque} and {@link Iterator} interfaces.
- *
- * <p>Memory consistency effects: As with other concurrent collections,
- * actions in a thread prior to placing an object into a
- * {@code ConcurrentLinkedDeque}
- * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
- * actions subsequent to the access or removal of that element from
- * the {@code ConcurrentLinkedDeque} in another thread.
- * <p>
- * Written by Doug Lea and Martin Buchholz with assistance from members of
- * JCP JSR-166 Expert Group and released to the public domain, as explained
- * at http://creativecommons.org/publicdomain/zero/1.0/
- */
-@SuppressWarnings( {"ALL"})
-public class ConcurrentLinkedDeque8<E> extends AbstractCollection<E>
implements Deque<E> {
- /*
- * This is an implementation of a concurrent lock-free deque
- * supporting interior removes but not interior insertions, as
- * required to support the entire Deque interface.
- *
- * We extend the techniques developed for ConcurrentLinkedQueue and
- * LinkedTransferQueue (see the internal docs for those classes).
- * Understanding the ConcurrentLinkedQueue implementation is a
- * prerequisite for understanding the implementation of this class.
- *
- * The data structure is a symmetrical doubly-linked "GC-robust"
- * linked list of nodes. We minimize the number of volatile writes
- * using two techniques: advancing multiple hops with a single CAS
- * and mixing volatile and non-volatile writes of the same memory
- * locations.
- *
- * A node contains the expected E ("item") and links to predecessor
- * ("prev") and successor ("next") nodes:
- *
- * class Node<E> { volatile Node<E> prev, next; volatile E item; }
- *
- * A node p is considered "live" if it contains a non-null item
- * (p.item != null). When an item is CASed to null, the item is
- * atomically logically deleted from the collection.
- *
- * At any time, there is precisely one "first" node with a null
- * prev reference that terminates any chain of prev references
- * starting at a live node. Similarly there is precisely one
- * "last" node terminating any chain of next references starting at
- * a live node. The "first" and "last" nodes may or may not be live.
- * The "first" and "last" nodes are always mutually reachable.
- *
- * A new element is added atomically by CASing the null prev or
- * next reference in the first or last node to a fresh node
- * containing the element. The element's node atomically becomes
- * "live" at that point.
- *
- * A node is considered "active" if it is a live node, or the
- * first or last node. Active nodes cannot be unlinked.
- *
- * A "self-link" is a next or prev reference that is the same node:
- * p.prev == p or p.next == p
- * Self-links are used in the node unlinking process. Active nodes
- * never have self-links.
- *
- * A node p is active if and only if:
- *
- * p.item != null ||
- * (p.prev == null && p.next != p) ||
- * (p.next == null && p.prev != p)
- *
- * The deque object has two node references, "head" and "tail".
- * The head and tail are only approximations to the first and last
- * nodes of the deque. The first node can always be found by
- * following prev pointers from head; likewise for tail. However,
- * it is permissible for head and tail to be referring to deleted
- * nodes that have been unlinked and so may not be reachable from
- * any live node.
- *
- * There are 3 stages of node deletion;
- * "logical deletion", "unlinking", and "gc-unlinking".
- *
- * 1. "logical deletion" by CASing item to null atomically removes
- * the element from the collection, and makes the containing node
- * eligible for unlinking.
- *
- * 2. "unlinking" makes a deleted node unreachable from active
- * nodes, and thus eventually reclaimable by GC. Unlinked nodes
- * may remain reachable indefinitely from an iterator.
- *
- * Physical node unlinking is merely an optimization (albeit a
- * critical one), and so can be performed at our convenience. At
- * any time, the set of live nodes maintained by prev and next
- * links are identical, that is, the live nodes found via next
- * links from the first node is equal to the elements found via
- * prev links from the last node. However, this is not true for
- * nodes that have already been logically deleted - such nodes may
- * be reachable in one direction only.
- *
- * 3. "gc-unlinking" takes unlinking further by making active
- * nodes unreachable from deleted nodes, making it easier for the
- * GC to reclaim future deleted nodes. This step makes the data
- * structure "gc-robust", as first described in detail by Boehm
- * (http://portal.acm.org/citation.cfm?doid=503272.503282).
- *
- * GC-unlinked nodes may remain reachable indefinitely from an
- * iterator, but unlike unlinked nodes, are never reachable from
- * head or tail.
- *
- * Making the data structure GC-robust will eliminate the risk of
- * unbounded memory retention with conservative GCs and is likely
- * to improve performance with generational GCs.
- *
- * When a node is dequeued at either end, e.g. via poll(), we would
- * like to break any references from the node to active nodes. We
- * develop further the use of self-links that was very effective in
- * other concurrent collection classes. The idea is to replace
- * prev and next pointers with special values that are interpreted
- * to mean off-the-list-at-one-end. These are approximations, but
- * good enough to preserve the properties we want in our
- * traversals, e.g. we guarantee that a traversal will never visit
- * the same element twice, but we don't guarantee whether a
- * traversal that runs out of elements will be able to see more
- * elements later after enqueues at that end. Doing gc-unlinking
- * safely is particularly tricky, since any node can be in use
- * indefinitely (for example by an iterator). We must ensure that
- * the nodes pointed at by head/tail never get gc-unlinked, since
- * head/tail are needed to get "back on track" by other nodes that
- * are gc-unlinked. gc-unlinking accounts for much of the
- * implementation complexity.
- *
- * Since neither unlinking nor gc-unlinking are necessary for
- * correctness, there are many implementation choices regarding
- * frequency (eagerness) of these operations. Since volatile
- * reads are likely to be much cheaper than CASes, saving CASes by
- * unlinking multiple adjacent nodes at a time may be a win.
- * gc-unlinking can be performed rarely and still be effective,
- * since it is most important that long chains of deleted nodes
- * are occasionally broken.
- *
- * The actual representation we use is that p.next == p means to
- * goto the first node (which in turn is reached by following prev
- * pointers from head), and p.next == null && p.prev == p means
- * that the iteration is at an end and that p is a (static final)
- * dummy node, NEXT_TERMINATOR, and not the last active node.
- * Finishing the iteration when encountering such a TERMINATOR is
- * good enough for read-only traversals, so such traversals can use
- * p.next == null as the termination condition. When we need to
- * find the last (active) node, for enqueueing a new node, we need
- * to check whether we have reached a TERMINATOR node; if so,
- * restart traversal from tail.
- *
- * The implementation is completely directionally symmetrical,
- * except that most public methods that iterate through the list
- * follow next pointers ("forward" direction).
- *
- * We believe (without full proof) that all single-element deque
- * operations (e.g., addFirst, peekLast, pollLast) are linearizable
- * (see Herlihy and Shavit's book). However, some combinations of
- * operations are known not to be linearizable. In particular,
- * when an addFirst(A) is racing with pollFirst() removing B, it is
- * possible for an observer iterating over the elements to observe
- * A B C and subsequently observe A C, even though no interior
- * removes are ever performed. Nevertheless, iterators behave
- * reasonably, providing the "weakly consistent" guarantees.
- *
- * Empirically, microbenchmarks suggest that this class adds about
- * 40% overhead relative to ConcurrentLinkedQueue, which feels as
- * good as we can hope for.
- */
-
- /**
- * A node from which the first node on list (that is, the unique node p
- * with p.prev == null && p.next != p) can be reached in O(1) time.
- * Invariants:
- * - the first node is always O(1) reachable from head via prev links
- * - all live nodes are reachable from the first node via succ()
- * - head != null
- * - (tmp = head).next != tmp || tmp != head
- * - head is never gc-unlinked (but may be unlinked)
- * Non-invariants:
- * - head.item may or may not be null
- * - head may not be reachable from the first or last node, or from tail
- */
- private volatile Node<E> head;
-
- /**
- * A node from which the last node on list (that is, the unique node p
- * with p.next == null && p.prev != p) can be reached in O(1) time.
- * Invariants:
- * - the last node is always O(1) reachable from tail via next links
- * - all live nodes are reachable from the last node via pred()
- * - tail != null
- * - tail is never gc-unlinked (but may be unlinked)
- * Non-invariants:
- * - tail.item may or may not be null
- * - tail may not be reachable from the first or last node, or from head
- */
- private volatile Node<E> tail;
-
- /** */
- private final LongAdder size = new LongAdder();
-
- /** Previous and next terminators. */
- private static final Node<Object> PREV_TERMINATOR, NEXT_TERMINATOR;
-
- @SuppressWarnings("unchecked")
- Node<E> prevTerminator() {
- return (Node<E>) PREV_TERMINATOR;
- }
-
- @SuppressWarnings("unchecked")
- Node<E> nextTerminator() {
- return (Node<E>) NEXT_TERMINATOR;
- }
-
- /**
- * Internal node element.
- *
- * @param <E> Node item.
- */
- @SuppressWarnings( {"PackageVisibleField", "PackageVisibleInnerClass"})
- public static final class Node<E> {
- volatile Node<E> prev;
- volatile E item;
- volatile Node<E> next;
-
- /**
- * Default constructor for NEXT_TERMINATOR, PREV_TERMINATOR.
- */
- Node() {
- // No-op.
- }
-
- /**
- * Constructs a new node. Uses relaxed write because item can
- * only be seen after publication via casNext or casPrev.
- *
- * @param item Item to initialize.
- */
- Node(E item) {
- UNSAFE.putObject(this, itemOffset, item);
- }
-
- /**
- * @return Item or {@code null} if this node was removed from the
queue.
- */
- public E item() {
- return item;
- }
-
- /**
- * @param cmp Compare value.
- * @param val New value.
- * @return {@code True} if set.
- */
- boolean casItem(E cmp, E val) {
- return UNSAFE.compareAndSwapObject(this, itemOffset, cmp, val);
- }
-
- /**
- * @param val New value.
- */
- void lazySetNext(Node<E> val) {
- UNSAFE.putOrderedObject(this, nextOffset, val);
- }
-
- /**
- * @param cmp Compare value.
- * @param val New value.
- * @return {@code True} if set.
- */
- boolean casNext(Node<E> cmp, Node<E> val) {
- return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val);
- }
-
- /**
- * @param val New value.
- */
- void lazySetPrev(Node<E> val) {
- UNSAFE.putOrderedObject(this, prevOffset, val);
- }
-
- /**
- * @param cmp Compare value.
- * @param val New value.
- * @return {@code True} if set.
- */
- boolean casPrev(Node<E> cmp, Node<E> val) {
- return UNSAFE.compareAndSwapObject(this, prevOffset, cmp, val);
- }
-
- /** Unsafe. */
- private static final Unsafe UNSAFE;
-
- /** Previous field offset. */
- private static final long prevOffset;
-
- /** Item field offset. */
- private static final long itemOffset;
-
- /** Next field offset. */
- private static final long nextOffset;
-
- /**
- * Initialize offsets.
- */
- static {
- try {
- UNSAFE = unsafe();
-
- Class k = Node.class;
-
- prevOffset =
UNSAFE.objectFieldOffset(k.getDeclaredField("prev"));
- itemOffset =
UNSAFE.objectFieldOffset(k.getDeclaredField("item"));
- nextOffset =
UNSAFE.objectFieldOffset(k.getDeclaredField("next"));
- }
- catch (Exception e) {
- throw new Error(e);
- }
- }
- }
-
- /**
- * Links e as first element.
- */
- private void linkFirst(E e) {
- checkNotNull(e);
-
- size.increment();
-
- final Node<E> newNode = new Node<E>(e);
-
- restartFromHead:
- for (;;) {
- for (Node<E> h = head, p = h, q;;) {
- if ((q = p.prev) != null && (q = (p = q).prev) != null)
- // Check for head updates every other hop.
- // If p == q, we are sure to follow head instead.
- p = (h != (h = head)) ? h : q;
- else if (p.next == p) // PREV_TERMINATOR
- continue restartFromHead;
- else {
- // p is first node
- newNode.lazySetNext(p); // CAS piggyback.
-
- if (p.casPrev(null, newNode)) {
- // Successful CAS is the linearization point
- // for e to become an element of this deque,
- // and for newNode to become "live".
- if (p != h) // hop two nodes at a time
- casHead(h, newNode); // Failure is OK.
-
- return;
- }
- // Lost CAS race to another thread; re-read prev
- }
- }
- }
- }
-
- /**
- * Same as {@link #linkFirst(Object)}, but returns new {@link Node}.
- *
- * @param e Element to link.
- * @return New node.
- */
- private Node<E> linkFirstx(E e) {
- checkNotNull(e);
-
- size.increment();
-
- final Node<E> newNode = new Node<E>(e);
-
- restartFromHead:
- for (;;) {
- for (Node<E> h = head, p = h, q;;) {
- if ((q = p.prev) != null && (q = (p = q).prev) != null)
- // Check for head updates every other hop.
- // If p == q, we are sure to follow head instead.
- p = (h != (h = head)) ? h : q;
- else if (p.next == p) // PREV_TERMINATOR
- continue restartFromHead;
- else {
- // p is first node
- newNode.lazySetNext(p); // CAS piggyback.
-
- if (p.casPrev(null, newNode)) {
- // Successful CAS is the linearization point
- // for e to become an element of this deque,
- // and for newNode to become "live".
- if (p != h) // hop two nodes at a time
- casHead(h, newNode); // Failure is OK.
-
- return newNode;
- }
- // Lost CAS race to another thread; re-read prev
- }
- }
- }
- }
-
- /**
- * Links e as last element.
- *
- * @param e Element to link.
- */
- private void linkLast(E e) {
- checkNotNull(e);
-
- size.increment();
-
- final Node<E> newNode = new Node<E>(e);
-
- restartFromTail:
- for (;;) {
- for (Node<E> t = tail, p = t, q;;) {
- if ((q = p.next) != null && (q = (p = q).next) != null)
- // Check for tail updates every other hop.
- // If p == q, we are sure to follow tail instead.
- p = (t != (t = tail)) ? t : q;
- else if (p.prev == p) // NEXT_TERMINATOR
- continue restartFromTail;
- else {
- // p is last node
- newNode.lazySetPrev(p); // CAS piggyback.
-
- if (p.casNext(null, newNode)) {
- // Successful CAS is the linearization point
- // for e to become an element of this deque,
- // and for newNode to become "live".
- if (p != t) // hop two nodes at a time
- casTail(t, newNode); // Failure is OK.
-
- return;
- }
- // Lost CAS race to another thread; re-read next
- }
- }
- }
- }
-
- /**
- * Links n as last node.
- *
- * @param n Node to link.
- */
- private void linkLast(Node<E> n) {
- checkNotNull(n);
-
- size.increment();
-
- restartFromTail:
- for (;;) {
- for (Node<E> t = tail, p = t, q;;) {
- if ((q = p.next) != null && (q = (p = q).next) != null)
- // Check for tail updates every other hop.
- // If p == q, we are sure to follow tail instead.
- p = (t != (t = tail)) ? t : q;
- else if (p.prev == p) // NEXT_TERMINATOR
- continue restartFromTail;
- else {
- // p is last node
- n.lazySetPrev(p); // CAS piggyback.
-
- if (p.casNext(null, n)) {
- // Successful CAS is the linearization point
- // for e to become an element of this deque,
- // and for newNode to become "live".
- if (p != t) // hop two nodes at a time
- casTail(t, n); // Failure is OK.
-
- return;
- }
- // Lost CAS race to another thread; re-read next
- }
- }
- }
- }
-
- /**
- * Same as {@link #linkLast(Object)}, but returns {@link Node}.
- *
- * @param e Element to link.
- * @return New node.
- */
- private Node<E> linkLastx(E e) {
- checkNotNull(e);
-
- size.increment();
-
- final Node<E> newNode = new Node<E>(e);
-
- restartFromTail:
- for (;;) {
- for (Node<E> t = tail, p = t, q;;) {
- if ((q = p.next) != null && (q = (p = q).next) != null)
- // Check for tail updates every other hop.
- // If p == q, we are sure to follow tail instead.
- p = (t != (t = tail)) ? t : q;
- else if (p.prev == p) // NEXT_TERMINATOR
- continue restartFromTail;
- else {
- // p is last node
- newNode.lazySetPrev(p); // CAS piggyback.
-
- if (p.casNext(null, newNode)) {
- // Successful CAS is the linearization point
- // for e to become an element of this deque,
- // and for newNode to become "live".
- if (p != t) // hop two nodes at a time
- casTail(t, newNode); // Failure is OK.
-
- return newNode;
- }
- // Lost CAS race to another thread; re-read next
- }
- }
- }
- }
-
- /** Number of HOPs before unlinking head or tail. */
- private static final int HOPS = 2;
-
- /**
- * Unlinks non-null node x, that has not yet been unlinked.
- *
- * @param x Node.
- * @return {@code True} if node was unlinked by this call.
- */
- public boolean unlinkx(Node<E> x) {
- assert x != null;
-
- E item = x.item;
-
- if (item != null && x.casItem(item, null)) {
- unlink(x);
-
- return true;
- }
-
- return false;
- }
-
- /**
- * Unlinks non-null node x.
- */
- private void unlink(Node<E> x) {
- // assert x != null;
- // assert x.item == null;
- // assert x != PREV_TERMINATOR;
- // assert x != NEXT_TERMINATOR;
-
- final Node<E> prev = x.prev;
- final Node<E> next = x.next;
-
- // Unlink should not be called twice for the same node.
- size.decrement();
-
- if (prev == null)
- unlinkFirst(x, next);
- else if (next == null)
- unlinkLast(x, prev);
- else {
- // Unlink interior node.
- //
- // This is the common case, since a series of polls at the
- // same end will be "interior" removes, except perhaps for
- // the first one, since end nodes cannot be unlinked.
- //
- // At any time, all active nodes are mutually reachable by
- // following a sequence of either next or prev pointers.
- //
- // Our strategy is to find the unique active predecessor
- // and successor of x. Try to fix up their links so that
- // they point to each other, leaving x unreachable from
- // active nodes. If successful, and if x has no live
- // predecessor/successor, we additionally try to gc-unlink,
- // leaving active nodes unreachable from x, by rechecking
- // that the status of predecessor and successor are
- // unchanged and ensuring that x is not reachable from
- // tail/head, before setting x's prev/next links to their
- // logical approximate replacements, self/TERMINATOR.
- Node<E> activePred, activeSucc;
-
- boolean isFirst, isLast;
-
- int hops = 1;
-
- // Find active predecessor
- for (Node<E> p = prev; ; ++hops) {
- if (p.item != null) {
- activePred = p;
-
- isFirst = false;
-
- break;
- }
-
- Node<E> q = p.prev;
-
- if (q == null) {
- if (p.next == p)
- return;
-
- activePred = p;
-
- isFirst = true;
-
- break;
- }
- else if (p == q)
- return;
- else
- p = q;
- }
-
- // Find active successor
- for (Node<E> p = next; ; ++hops) {
- if (p.item != null) {
- activeSucc = p;
-
- isLast = false;
-
- break;
- }
-
- Node<E> q = p.next;
-
- if (q == null) {
- if (p.prev == p)
- return;
-
- activeSucc = p;
-
- isLast = true;
-
- break;
- }
- else if (p == q)
- return;
- else
- p = q;
- }
-
- // TODO: better HOP heuristics
- // Always squeeze out interior deleted nodes.
- if (hops < HOPS && (isFirst | isLast))
- return;
-
- // Squeeze out deleted nodes between activePred and
- // activeSucc, including x.
- skipDeletedSuccessors(activePred);
- skipDeletedPredecessors(activeSucc);
-
- // Try to gc-unlink, if possible
- if ((isFirst | isLast) &&
- // Recheck expected state of predecessor and successor
- (activePred.next == activeSucc) &&
- (activeSucc.prev == activePred) &&
- (isFirst ? activePred.prev == null : activePred.item != null)
&&
- (isLast ? activeSucc.next == null : activeSucc.item != null))
{
-
- updateHead(); // Ensure x is not reachable from head
- updateTail(); // Ensure x is not reachable from tail
-
- // Finally, actually gc-unlink
- x.lazySetPrev(isFirst ? prevTerminator() : x);
- x.lazySetNext(isLast ? nextTerminator() : x);
- }
- }
- }
-
- /**
- * Unlinks non-null first node.
- */
- private void unlinkFirst(Node<E> first, Node<E> next) {
- // assert first != null;
- // assert next != null;
- // assert first.item == null;
- for (Node<E> o = null, p = next, q;;) {
- if (p.item != null || (q = p.next) == null) {
- if (o != null && p.prev != p && first.casNext(next, p)) {
- skipDeletedPredecessors(p);
- if (first.prev == null &&
- (p.next == null || p.item != null) &&
- p.prev == first) {
-
- updateHead(); // Ensure o is not reachable from head
- updateTail(); // Ensure o is not reachable from tail
-
- // Finally, actually gc-unlink
- o.lazySetNext(o);
- o.lazySetPrev(prevTerminator());
- }
- }
- return;
- }
- else if (p == q)
- return;
- else {
- o = p;
- p = q;
- }
- }
- }
-
- /**
- * Unlinks non-null last node.
- */
- private void unlinkLast(Node<E> last, Node<E> prev) {
- // assert last != null;
- // assert prev != null;
- // assert last.item == null;
- for (Node<E> o = null, p = prev, q;;) {
- if (p.item != null || (q = p.prev) == null) {
- if (o != null && p.next != p && last.casPrev(prev, p)) {
- skipDeletedSuccessors(p);
- if (last.next == null &&
- (p.prev == null || p.item != null) &&
- p.next == last) {
-
- updateHead(); // Ensure o is not reachable from head
- updateTail(); // Ensure o is not reachable from tail
-
- // Finally, actually gc-unlink
- o.lazySetPrev(o);
- o.lazySetNext(nextTerminator());
- }
- }
- return;
- }
- else if (p == q)
- return;
- else {
- o = p;
- p = q;
- }
- }
- }
-
- /**
- * Guarantees that any node which was unlinked before a call to
- * this method will be unreachable from head after it returns.
- * Does not guarantee to eliminate slack, only that head will
- * point to a node that was active while this method was running.
- */
- private final void updateHead() {
- // Either head already points to an active node, or we keep
- // trying to cas it to the first node until it does.
- Node<E> h, p, q;
-
- restartFromHead:
- while ((h = head).item == null && (p = h.prev) != null) {
- for (;;) {
- if ((q = p.prev) == null || (q = (p = q).prev) == null) {
- // It is possible that p is PREV_TERMINATOR,
- // but if so, the CAS is guaranteed to fail.
- if (casHead(h, p))
- return;
- else
- continue restartFromHead;
- }
- else if (h != head)
- continue restartFromHead;
- else
- p = q;
- }
- }
- }
-
- /**
- * Guarantees that any node which was unlinked before a call to
- * this method will be unreachable from tail after it returns.
- * Does not guarantee to eliminate slack, only that tail will
- * point to a node that was active while this method was running.
- */
- private final void updateTail() {
- // Either tail already points to an active node, or we keep
- // trying to cas it to the last node until it does.
- Node<E> t, p, q;
-
- restartFromTail:
- while ((t = tail).item == null && (p = t.next) != null) {
- for (;;) {
- if ((q = p.next) == null || (q = (p = q).next) == null) {
- // It is possible that p is NEXT_TERMINATOR,
- // but if so, the CAS is guaranteed to fail.
- if (casTail(t, p))
- return;
- else
- continue restartFromTail;
- }
- else if (t != tail)
- continue restartFromTail;
- else
- p = q;
- }
- }
- }
-
- /**
- * @param x Node to start from.
- */
- private void skipDeletedPredecessors(Node<E> x) {
- whileActive:
- do {
- Node<E> prev = x.prev;
- // assert prev != null;
- // assert x != NEXT_TERMINATOR;
- // assert x != PREV_TERMINATOR;
- Node<E> p = prev;
-
- findActive:
- for (;;) {
- if (p.item != null)
- break findActive;
-
- Node<E> q = p.prev;
-
- if (q == null) {
- if (p.next == p)
- continue whileActive;
-
- break findActive;
- }
- else if (p == q)
- continue whileActive;
- else
- p = q;
- }
-
- // found active CAS target
- if (prev == p || x.casPrev(prev, p))
- return;
-
- } while (x.item != null || x.next == null);
- }
-
- /**
- * @param x Node to start from.
- */
- private void skipDeletedSuccessors(Node<E> x) {
- whileActive:
- do {
- Node<E> next = x.next;
- // assert next != null;
- // assert x != NEXT_TERMINATOR;
- // assert x != PREV_TERMINATOR;
- Node<E> p = next;
-
- findActive:
-
- for (;;) {
- if (p.item != null)
- break findActive;
-
- Node<E> q = p.next;
-
- if (q == null) {
- if (p.prev == p)
- continue whileActive;
-
- break findActive;
- }
- else if (p == q)
- continue whileActive;
- else
- p = q;
- }
-
- // found active CAS target
- if (next == p || x.casNext(next, p))
- return;
-
- }
- while (x.item != null || x.prev == null);
- }
-
- /**
- * Returns the successor of p, or the first node if p.next has been
- * linked to self, which will only be true if traversing with a
- * stale pointer that is now off the list.
- *
- * @param p Node to find successor for.
- * @return Successor node.
- */
- final Node<E> successor(Node<E> p) {
- // TODO: should we skip deleted nodes here?
- Node<E> q = p.next;
-
- return (p == q) ? first() : q;
- }
-
- /**
- * Returns the predecessor of p, or the last node if p.prev has been
- * linked to self, which will only be true if traversing with a
- * stale pointer that is now off the list.
- *
- * @param p Node to find predecessor for.
- * @return Predecessor node.
- */
- final Node<E> predecessor(Node<E> p) {
- Node<E> q = p.prev;
- return (p == q) ? last() : q;
- }
-
- /**
- * Returns the first node, the unique node p for which:
- * p.prev == null && p.next != p
- * The returned node may or may not be logically deleted.
- * Guarantees that head is set to the returned node.
- *
- * @return First node.
- */
- @SuppressWarnings( {"TooBroadScope"})
- Node<E> first() {
- restartFromHead:
- for (;;)
- for (Node<E> h = head, p = h, q;;) {
- if ((q = p.prev) != null &&
- (q = (p = q).prev) != null)
- // Check for head updates every other hop.
- // If p == q, we are sure to follow head instead.
- p = (h != (h = head)) ? h : q;
- else if (p == h
- // It is possible that p is PREV_TERMINATOR,
- // but if so, the CAS is guaranteed to fail.
- || casHead(h, p))
- return p;
- else
- continue restartFromHead;
- }
- }
-
- /**
- * Returns the last node, the unique node p for which:
- * p.next == null && p.prev != p
- * The returned node may or may not be logically deleted.
- * Guarantees that tail is set to the returned node.
- *
- * @return Last node.
- */
- @SuppressWarnings( {"TooBroadScope"})
- Node<E> last() {
- restartFromTail:
- for (;;)
- for (Node<E> t = tail, p = t, q;;) {
- if ((q = p.next) != null &&
- (q = (p = q).next) != null)
- // Check for tail updates every other hop.
- // If p == q, we are sure to follow tail instead.
- p = (t != (t = tail)) ? t : q;
- else if (p == t
- // It is possible that p is NEXT_TERMINATOR,
- // but if so, the CAS is guaranteed to fail.
- || casTail(t, p))
- return p;
- else
- continue restartFromTail;
- }
- }
-
- /**
- * Throws NullPointerException if argument is null.
- *
- * @param v the element
- */
- private static void checkNotNull(Object v) {
- if (v == null)
- throw new NullPointerException();
- }
-
- /**
- * Returns element unless it is null, in which case throws
- * NoSuchElementException.
- *
- * @param v the element
- * @return the element
- */
- private E screenNullResult(E v) {
- if (v == null)
- throw new NoSuchElementException();
-
- return v;
- }
-
- /**
- * Creates an array list and fills it with elements of this list.
- * Used by toArray.
- *
- * @return the arrayList
- */
- private ArrayList<E> toArrayList() {
- ArrayList<E> list = new ArrayList<E>();
-
- for (Node<E> p = first(); p != null; p = successor(p)) {
- E item = p.item;
-
- if (item != null)
- list.add(item);
- }
-
- return list;
- }
-
- /**
- * Constructs an empty deque.
- */
- public ConcurrentLinkedDeque8() {
- head = tail = new Node<E>();
- }
-
- /**
- * Constructs a deque initially containing the elements of
- * the given collection, added in traversal order of the
- * collection's iterator.
- *
- * @param c the collection of elements to initially contain
- * @throws NullPointerException if the specified collection or any
- * of its elements are null
- */
- public ConcurrentLinkedDeque8(Iterable<? extends E> c) {
- // Copy c into a private chain of Nodes
- Node<E> h = null, t = null;
-
- for (E e : c) {
- checkNotNull(e);
-
- Node<E> newNode = new Node<E>(e);
-
- if (h == null)
- h = t = newNode;
- else {
- t.lazySetNext(newNode);
- newNode.lazySetPrev(t);
- t = newNode;
- }
- }
-
- initHeadTail(h, t);
- }
-
- /**
- * Initializes head and tail, ensuring invariants hold.
- *
- * @param h Head.
- * @param t Tail.
- */
- private void initHeadTail(Node<E> h, Node<E> t) {
- if (h == t) {
- if (h == null)
- h = t = new Node<E>(null);
- else {
- // Avoid edge case of a single Node with non-null item.
- Node<E> newNode = new Node<E>(null);
-
- t.lazySetNext(newNode);
-
- newNode.lazySetPrev(t);
-
- t = newNode;
- }
- }
-
- head = h;
- tail = t;
- }
-
- /**
- * Inserts the specified element at the front of this deque.
- * As the deque is unbounded, this method will never throw
- * {@link IllegalStateException}.
- *
- * @throws NullPointerException if the specified element is null
- */
- @Override public void addFirst(E e) {
- linkFirst(e);
- }
-
- /**
- * Same as {@link #addFirst(Object)}, but returns new node.
- *
- * @param e Element to add.
- * @return New node.
- */
- public Node<E> addFirstx(E e) {
- return linkFirstx(e);
- }
-
- /**
- * Inserts the specified element at the end of this deque.
- * As the deque is unbounded, this method will never throw
- * {@link IllegalStateException}.
- *
- * <p>This method is equivalent to {@link #add}.
- *
- * @throws NullPointerException if the specified element is null
- */
- @Override public void addLast(E e) {
- linkLast(e);
- }
-
- /**
- * Same as {@link #addLast(Object)}, but returns new node.
- *
- * @param e Element to add.
- * @return New node.
- */
- public Node<E> addLastx(E e) {
- return linkLastx(e);
- }
-
- /**
- * Inserts the specified element at the front of this deque.
- * As the deque is unbounded, this method will never return {@code false}.
- *
- * @return {@code true} (as specified by {@link Deque#offerFirst})
- * @throws NullPointerException if the specified element is null
- */
- @Override public boolean offerFirst(E e) {
- linkFirst(e);
-
- return true;
- }
-
- /**
- * Same as {@link #offerFirst(Object)}, but returns new {@link Node}.
- *
- * @param e Element to add.
- * @return New node.
- */
- public Node<E> offerFirstx(E e) {
- return linkFirstx(e);
- }
-
- /**
- * Inserts the specified element at the end of this deque.
- * As the deque is unbounded, this method will never return {@code false}.
- *
- * <p>This method is equivalent to {@link #add}.
- *
- * @return {@code true} (as specified by {@link Deque#offerLast})
- * @throws NullPointerException if the specified element is null
- */
- @Override public boolean offerLast(E e) {
- linkLast(e);
-
- return true;
- }
-
- /**
- * Same as {@link #offerLast(Object)}, but returns new {@link Node}.
- *
- * @param e Element to add.
- * @return New node.
- */
- public Node<E> offerLastx(E e) {
- return linkLastx(e);
- }
-
- /** {@inheritDoc} */
- @Override public E peekFirst() {
- for (Node<E> p = first(); p != null; p = successor(p)) {
- E item = p.item;
-
- if (item != null)
- return item;
- }
-
- return null;
- }
-
- /**
- * Retrieves, but does not remove, the first node of this deque,
- * or returns {@code null} if this deque is empty.
- *
- * @return The header node of this deque, or <tt>null</tt> if this deque
is empty
- */
- public Node<E> peekFirstx() {
- for (Node<E> p = first(); p != null; p = successor(p)) {
- E item = p.item;
-
- if (item != null)
- return p;
- }
-
- return null;
- }
-
- /** {@inheritDoc} */
- @Override public E peekLast() {
- for (Node<E> p = last(); p != null; p = predecessor(p)) {
- E item = p.item;
-
- if (item != null)
- return item;
- }
-
- return null;
- }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- @Override public E getFirst() {
- return screenNullResult(peekFirst());
- }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- @Override public E getLast() {
- return screenNullResult(peekLast());
- }
-
- /** {@inheritDoc} */
- @Override public E pollFirst() {
- for (Node<E> p = first(); p != null; p = successor(p)) {
- E item = p.item;
-
- if (item != null && p.casItem(item, null)) {
- unlink(p);
-
- return item;
- }
- }
-
- return null;
- }
-
- /** {@inheritDoc} */
- @Override public E pollLast() {
- for (Node<E> p = last(); p != null; p = predecessor(p)) {
- E item = p.item;
-
- if (item != null && p.casItem(item, null)) {
- unlink(p);
-
- return item;
- }
- }
-
- return null;
- }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- @Override public E removeFirst() {
- return screenNullResult(pollFirst());
- }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- @Override public E removeLast() {
- return screenNullResult(pollLast());
- }
-
- /**
- * Inserts the specified element at the tail of this deque.
- * As the deque is unbounded, this method will never return {@code false}.
- *
- * @return {@code true} (as specified by {@link Queue#offer})
- * @throws NullPointerException if the specified element is null
- */
- @Override public boolean offer(E e) {
- return offerLast(e);
- }
-
- /**
- * Same as {@link #offer(Object)}, but returns new {@link Node}.
- *
- * @param e Element to add.
- * @return New node.
- */
- public Node<E> offerx(E e) {
- return offerLastx(e);
- }
-
- /**
- * Inserts the specified element at the tail of this deque.
- * As the deque is unbounded, this method will never throw
- * {@link IllegalStateException} or return {@code false}.
- *
- * @return {@code true} (as specified by {@link Collection#add})
- * @throws NullPointerException if the specified element is null
- */
- @Override public boolean add(E e) {
- return offerLast(e);
- }
-
- /**
- * Same as {@link #add(Object)}, but returns new node.
- *
- * @param e Element to add.
- * @return New node.
- */
- public Node<E> addx(E e) {
- return offerLastx(e);
- }
-
- /** {@inheritDoc} */
- @Override public E poll() {
- return pollFirst();
- }
-
- /** {@inheritDoc} */
- @Override public E remove() {
- return removeFirst();
- }
-
- /** {@inheritDoc} */
- @Override public E peek() {
- return peekFirst();
- }
-
- /**
- * Retrieves, but does not remove, the header node of the queue
represented by
- * this deque (in other words, the first node of this deque), or
- * returns {@code null} if this deque is empty.
- * <p>
- * This method is equivalent to {@link #peekFirst()}.
- *
- * @return The header node of the queue represented by this deque, or
- * {@code null} if this deque is empty
- */
- public Node<E> peekx() {
- return peekFirstx();
- }
-
- /** {@inheritDoc} */
- @Override public E element() {
- return getFirst();
- }
-
- /** {@inheritDoc} */
- @Override public void push(E e) {
- addFirst(e);
- }
-
- /** {@inheritDoc} */
- @Override public E pop() {
- return removeFirst();
- }
-
- /**
- * Removes the first element {@code e} such that
- * {@code o.equals(e)}, if such an element exists in this deque.
- * If the deque does not contain the element, it is unchanged.
- *
- * @param o element to be removed from this deque, if present
- * @return {@code true} if the deque contained the specified element
- * @throws NullPointerException if the specified element is null
- */
- @Override public boolean removeFirstOccurrence(Object o) {
- checkNotNull(o);
-
- for (Node<E> p = first(); p != null; p = successor(p)) {
- E item = p.item;
-
- if (item != null && o.equals(item) && p.casItem(item, null)) {
- unlink(p);
-
- return true;
- }
- }
-
- return false;
- }
-
- /**
- * Removes the last element {@code e} such that
- * {@code o.equals(e)}, if such an element exists in this deque.
- * If the deque does not contain the element, it is unchanged.
- *
- * @param o element to be removed from this deque, if present
- * @return {@code true} if the deque contained the specified element
- * @throws NullPointerException if the specified element is null
- */
- @Override public boolean removeLastOccurrence(Object o) {
- checkNotNull(o);
-
- for (Node<E> p = last(); p != null; p = predecessor(p)) {
- E item = p.item;
-
- if (item != null && o.equals(item) && p.casItem(item, null)) {
- unlink(p);
-
- return true;
- }
- }
-
- return false;
- }
-
- /**
- * Returns {@code true} if this deque contains at least one
- * element {@code e} such that {@code o.equals(e)}.
- *
- * @param o element whose presence in this deque is to be tested
- * @return {@code true} if this deque contains the specified element
- */
- @Override public boolean contains(Object o) {
- if (o == null)
- return false;
-
- for (Node<E> p = first(); p != null; p = successor(p)) {
- E item = p.item;
-
- if (item != null && o.equals(item))
- return true;
- }
-
- return false;
- }
-
- /**
- * Returns {@code true} if this collection contains no elements.
- *
- * @return {@code true} if this collection contains no elements
- */
- @Override public boolean isEmpty() {
- return peekFirst() == null;
- }
-
- /**
- * Returns {@code true} if this collection contains no elements.
- * <p>
- * The difference from {@link #isEmpty()} method is that this method
- * relies on {@link #sizex()} method.
- *
- * @return {@code True} if this collection contains no elements
- */
- public boolean isEmptyx() {
- return sizex() == 0;
- }
-
- /**
- * Returns the number of elements in this deque. If this deque
- * contains more than {@code Integer.MAX_VALUE} elements, it
- * returns {@code Integer.MAX_VALUE}.
- *
- * <p>Beware that, unlike in most collections, this method is
- * <em>NOT</em> a constant-time operation. Because of the
- * asynchronous nature of these deques, determining the current
- * number of elements requires traversing them all to count them.
- * Additionally, it is possible for the size to change during
- * execution of this method, in which case the returned result
- * will be inaccurate. Thus, this method is typically not very
- * useful in concurrent applications.
- *
- * @return the number of elements in this deque
- */
- @Override public int size() {
- int cnt = 0;
-
- for (Node<E> p = first(); p != null; p = successor(p))
- if (p.item != null)
- // Collection.size() spec says to max out
- if (++cnt == Integer.MAX_VALUE)
- break;
-
- return cnt;
- }
-
- /**
- * @return Size based on performed operations.
- */
- public int sizex() {
- return size.intValue();
- }
-
- /**
- * Removes the first element {@code e} such that
- * {@code o.equals(e)}, if such an element exists in this deque.
- * If the deque does not contain the element, it is unchanged.
- *
- * @param o element to be removed from this deque, if present
- * @return {@code true} if the deque contained the specified element
- * @throws NullPointerException if the specified element is null
- */
- @Override public boolean remove(Object o) {
- return removeFirstOccurrence(o);
- }
-
- /**
- * Appends all of the elements in the specified collection to the end of
- * this deque, in the order that they are returned by the specified
- * collection's iterator. Attempts to {@code addAll} of a deque to
- * itself result in {@code IllegalArgumentException}.
- *
- * @param c the elements to be inserted into this deque
- * @return {@code true} if this deque changed as a result of the call
- * @throws NullPointerException if the specified collection or any
- * of its elements are null
- * @throws IllegalArgumentException if the collection is this deque
- */
- @SuppressWarnings( {"TooBroadScope"})
- @Override public boolean addAll(Collection<? extends E> c) {
- if (c == this)
- // As historically specified in AbstractQueue#addAll
- throw new IllegalArgumentException();
-
- // Copy c into a private chain of Nodes
- Node<E> beginningOfTheEnd = null, last = null;
-
- int s = 0;
-
- for (E e : c) {
- checkNotNull(e);
-
- Node<E> newNode = new Node<E>(e);
-
- if (beginningOfTheEnd == null) {
- beginningOfTheEnd = last = newNode;
-
- s++;
- }
- else {
- last.lazySetNext(newNode);
-
- newNode.lazySetPrev(last);
-
- last = newNode;
-
- s++;
- }
- }
-
- if (beginningOfTheEnd == null)
- return false;
-
- size.add(s);
-
- // Atomically append the chain at the tail of this collection
- restartFromTail:
- for (;;) {
- for (Node<E> t = tail, p = t, q;;) {
- if ((q = p.next) != null && (q = (p = q).next) != null)
- // Check for tail updates every other hop.
- // If p == q, we are sure to follow tail instead.
- p = (t != (t = tail)) ? t : q;
- else if (p.prev == p) // NEXT_TERMINATOR
- continue restartFromTail;
- else {
- // p is last node
- beginningOfTheEnd.lazySetPrev(p); // CAS piggyback
-
- if (p.casNext(null, beginningOfTheEnd)) {
- // Successful CAS is the linearization point
- // for all elements to be added to this deque.
- if (!casTail(t, last)) {
- // Try a little harder to update tail,
- // since we may be adding many elements.
- t = tail;
-
- if (last.next == null)
- casTail(t, last);
- }
-
- return true;
- }
- // Lost CAS race to another thread; re-read next
- }
- }
- }
- }
-
- /**
- * Removes all of the elements from this deque.
- */
- @Override public void clear() {
- while (pollFirst() != null) {
- // No-op.
- }
- }
-
- /**
- * Returns an array containing all of the elements in this deque, in
- * proper sequence (from first to last element).
- *
- * <p>The returned array will be "safe" in that no references to it are
- * maintained by this deque. (In other words, this method must allocate
- * a new array). The caller is thus free to modify the returned array.
- *
- * <p>This method acts as bridge between array-based and collection-based
- * APIs.
- *
- * @return an array containing all of the elements in this deque
- */
- @Override public Object[] toArray() {
- return toArrayList().toArray();
- }
-
- /**
- * Returns an array containing all of the elements in this deque,
- * in proper sequence (from first to last element); the runtime
- * type of the returned array is that of the specified array. If
- * the deque fits in the specified array, it is returned therein.
- * Otherwise, a new array is allocated with the runtime type of
- * the specified array and the size of this deque.
- *
- * <p>If this deque fits in the specified array with room to spare
- * (i.e., the array has more elements than this deque), the element in
- * the array immediately following the end of the deque is set to
- * {@code null}.
- *
- * <p>Like the {@link #toArray()} method, this method acts as
- * bridge between array-based and collection-based APIs. Further,
- * this method allows precise control over the runtime type of the
- * output array, and may, under certain circumstances, be used to
- * save allocation costs.
- *
- * <p>Suppose {@code x} is a deque known to contain only strings.
- * The following code can be used to dump the deque into a newly
- * allocated array of {@code String}:
- *
- * <pre>
- * String[] y = x.toArray(new String[0]);</pre>
- *
- * Note that {@code toArray(new Object[0])} is identical in function to
- * {@code toArray()}.
- *
- * @param a the array into which the elements of the deque are to
- * be stored, if it is big enough; otherwise, a new array of the
- * same runtime type is allocated for this purpose
- * @return an array containing all of the elements in this deque
- * @throws ArrayStoreException if the runtime type of the specified array
- * is not a supertype of the runtime type of every element in
- * this deque
- * @throws NullPointerException if the specified array is null
- */
- @SuppressWarnings( {"SuspiciousToArrayCall"})
- @Override public <T> T[] toArray(T[] a) {
- return toArrayList().toArray(a);
- }
-
- /**
- * Returns an iterator over the elements in this deque in proper sequence.
- * The elements will be returned in order from first (head) to last (tail).
- *
- * <p>The returned iterator is a "weakly consistent" iterator that
- * will never throw {@link java.util.ConcurrentModificationException
- * ConcurrentModificationException}, and guarantees to traverse
- * elements as they existed upon construction of the iterator, and
- * may (but is not guaranteed to) reflect any modifications
- * subsequent to construction.
- *
- * @return an iterator over the elements in this deque in proper sequence
- */
- @Override public Iterator<E> iterator() {
- return new Iter();
- }
-
- /**
- * Returns an iterator over the elements in this deque in reverse
- * sequential order. The elements will be returned in order from
- * last (tail) to first (head).
- *
- * <p>The returned iterator is a "weakly consistent" iterator that
- * will never throw {@link java.util.ConcurrentModificationException
- * ConcurrentModificationException}, and guarantees to traverse
- * elements as they existed upon construction of the iterator, and
- * may (but is not guaranteed to) reflect any modifications
- * subsequent to construction.
- *
- * @return an iterator over the elements in this deque in reverse order
- */
- @Override public Iterator<E> descendingIterator() {
- return new DescendingIter();
- }
-
- /**
- * Extended iterator interface.
- */
- public interface IteratorEx<E> extends Iterator<E> {
- /**
- * Same semantics as iterator's remove, but will return {@code false}
if remove did not happen.
- *
- * @return {@code True} if element was removed by this call, {@code
false} otherwise.
- */
- public boolean removex();
- }
-
- /**
- * Abstract iterator.
- */
- private abstract class AbstractIter implements IteratorEx<E> {
- /**
- * Next node to return item for.
- */
- private Node<E> nextNode;
-
- /**
- * nextItem holds on to item fields because once we claim
- * that an element exists in hasNext(), we must return it in
- * the following next() call even if it was in the process of
- * being removed when hasNext() was called.
- */
- private E nextItem;
-
- /**
- * Node returned by most recent call to next. Needed by remove.
- * Reset to null if this element is deleted by a call to remove.
- */
- private Node<E> lastRet;
-
- /**
- * @return Starting node.
- */
- abstract Node<E> startNode();
-
- /**
- * @param p Node.
- * @return Next node.
- */
- abstract Node<E> nextNode(Node<E> p);
-
- /**
- * Advances to first element.
- */
- AbstractIter() {
- advance();
- }
-
- /**
- * Sets nextNode and nextItem to next valid node, or to null
- * if no such.
- */
- private void advance() {
- lastRet = nextNode;
-
- Node<E> p = (nextNode == null) ? startNode() : nextNode(nextNode);
-
- for (;; p = nextNode(p)) {
- if (p == null) {
- // p might be active end or TERMINATOR node; both are OK
- nextNode = null;
- nextItem = null;
-
- break;
- }
-
- E item = p.item;
-
- if (item != null) {
- nextNode = p;
- nextItem = item;
-
- break;
- }
- }
- }
-
- /** {@inheritDoc} */
- @Override public boolean hasNext() {
- return nextItem != null;
- }
-
- /** {@inheritDoc} */
- @Override public E next() {
- E item = nextItem;
-
- if (item == null)
- throw new NoSuchElementException();
-
- advance();
-
- return item;
- }
-
- /** {@inheritDoc} */
- @Override public void remove() {
- Node<E> l = lastRet;
-
- if (l == null)
- throw new IllegalStateException();
-
- unlinkx(l);
-
- lastRet = null;
- }
-
- /** {@inheritDoc} */
- @Override public boolean removex() {
- Node<E> l = lastRet;
-
- if (l == null)
- throw new IllegalStateException();
-
- boolean res = unlinkx(l);
-
- lastRet = null;
-
- return res;
- }
- }
-
- /**
- * Forward iterator
- */
- private class Iter extends AbstractIter {
- /** {@inheritDoc} */
- @Override Node<E> startNode() {
- return first();
- }
-
- /** {@inheritDoc} */
- @Override Node<E> nextNode(Node<E> p) {
- return successor(p);
- }
- }
-
- /**
- * Descending iterator.
- */
- private class DescendingIter extends AbstractIter {
- /** {@inheritDoc} */
- @Override Node<E> startNode() {
- return last();
- }
-
- /** {@inheritDoc} */
- @Override Node<E> nextNode(Node<E> p) {
- return predecessor(p);
- }
- }
-
- /**
- * CAS for head.
- *
- * @param cmp Compare value.
- * @param val New value.
- * @return {@code True} if set.
- */
- private boolean casHead(Node<E> cmp, Node<E> val) {
- return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val);
- }
-
- /**
- * CAS for tail.
- *
- * @param cmp Compare value.
- * @param val New value.
- * @return {@code True} if set.
- */
- private boolean casTail(Node<E> cmp, Node<E> val) {
- return UNSAFE.compareAndSwapObject(this, tailOffset, cmp, val);
- }
-
- /** Unsafe. */
- private static final Unsafe UNSAFE;
-
- /** Head offset. */
- private static final long headOffset;
-
- /** Tail offset. */
- private static final long tailOffset;
-
- /**
- * Initialize terminators using unsafe semantics.
- */
- static {
- PREV_TERMINATOR = new Node<Object>();
- PREV_TERMINATOR.next = PREV_TERMINATOR;
- NEXT_TERMINATOR = new Node<Object>();
- NEXT_TERMINATOR.prev = NEXT_TERMINATOR;
-
- try {
- UNSAFE = unsafe();
-
- Class cls = ConcurrentLinkedDeque8.class;
-
- headOffset =
UNSAFE.objectFieldOffset(cls.getDeclaredField("head"));
- tailOffset =
UNSAFE.objectFieldOffset(cls.getDeclaredField("tail"));
- }
- catch (Exception e) {
- throw new Error(e);
- }
- }
-
- /**
- * @return Instance of Unsafe class.
- */
- static Unsafe unsafe() {
- try {
- return Unsafe.getUnsafe();
- }
- catch (SecurityException ignored) {
- try {
- return AccessController.doPrivileged
- (new PrivilegedExceptionAction<Unsafe>() {
- @Override
- public Unsafe run() throws Exception {
- Field f =
Unsafe.class.getDeclaredField("theUnsafe");
-
- f.setAccessible(true);
-
- return (Unsafe) f.get(null);
- }
- });
- }
- catch (PrivilegedActionException e) {
- throw new RuntimeException("Could not initialize intrinsics.",
e.getCause());
- }
- }
- }
-}
