| /* |
| * 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 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/ |
| */ |
| |
| package java.util.concurrent; |
| |
| import java.lang.invoke.MethodHandles; |
| import java.lang.invoke.VarHandle; |
| import java.util.AbstractCollection; |
| import java.util.Arrays; |
| import java.util.Collection; |
| import java.util.Deque; |
| import java.util.Iterator; |
| import java.util.NoSuchElementException; |
| import java.util.Objects; |
| import java.util.Queue; |
| import java.util.Spliterator; |
| import java.util.Spliterators; |
| import java.util.function.Consumer; |
| import java.util.function.Predicate; |
| |
| /** |
| * 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 and spliterators are |
| * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
| * |
| * <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. |
| * |
| * <p>Bulk operations that add, remove, or examine multiple elements, |
| * such as {@link #addAll}, {@link #removeIf} or {@link #forEach}, |
| * are <em>not</em> guaranteed to be performed atomically. |
| * For example, a {@code forEach} traversal concurrent with an {@code |
| * addAll} operation might observe 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>This class is a member of the |
| * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework"> |
| * Java Collections Framework</a>. |
| * |
| * @since 1.7 |
| * @author Doug Lea |
| * @author Martin Buchholz |
| * @param <E> the type of elements held in this deque |
| */ |
| public class ConcurrentLinkedDeque<E> |
| extends AbstractCollection<E> |
| implements Deque<E>, java.io.Serializable { |
| |
| /* |
| * 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. |
| */ |
| |
| private static final long serialVersionUID = 876323262645176354L; |
| |
| /** |
| * 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 transient 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 transient volatile Node<E> tail; |
| |
| 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; |
| } |
| |
| static final class Node<E> { |
| volatile Node<E> prev; |
| volatile E item; |
| volatile Node<E> next; |
| } |
| |
| /** |
| * Returns a new node holding item. Uses relaxed write because item |
| * can only be seen after piggy-backing publication via CAS. |
| */ |
| static <E> Node<E> newNode(E item) { |
| Node<E> node = new Node<E>(); |
| ITEM.set(node, item); |
| return node; |
| } |
| |
| /** |
| * Links e as first element. |
| */ |
| private void linkFirst(E e) { |
| final Node<E> newNode = newNode(Objects.requireNonNull(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 |
| NEXT.set(newNode, p); // CAS piggyback |
| if (PREV.compareAndSet(p, 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; failure is OK |
| HEAD.weakCompareAndSet(this, h, newNode); |
| return; |
| } |
| // Lost CAS race to another thread; re-read prev |
| } |
| } |
| } |
| |
| /** |
| * Links e as last element. |
| */ |
| private void linkLast(E e) { |
| final Node<E> newNode = newNode(Objects.requireNonNull(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 |
| PREV.set(newNode, p); // CAS piggyback |
| if (NEXT.compareAndSet(p, 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; failure is OK |
| TAIL.weakCompareAndSet(this, t, newNode); |
| return; |
| } |
| // Lost CAS race to another thread; re-read next |
| } |
| } |
| } |
| |
| private static final int HOPS = 2; |
| |
| /** |
| * Unlinks non-null node x. |
| */ |
| 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; |
| 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 |
| if (hops < HOPS |
| // always squeeze out interior deleted nodes |
| && (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 |
| PREV.setRelease(x, isFirst ? prevTerminator() : x); |
| NEXT.setRelease(x, 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 && |
| NEXT.compareAndSet(first, 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 |
| NEXT.setRelease(o, o); |
| PREV.setRelease(o, 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 && |
| PREV.compareAndSet(last, 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 |
| PREV.setRelease(o, o); |
| NEXT.setRelease(o, 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 (HEAD.compareAndSet(this, 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 (TAIL.compareAndSet(this, t, p)) |
| return; |
| else |
| continue restartFromTail; |
| } |
| else if (t != tail) |
| continue restartFromTail; |
| else |
| p = q; |
| } |
| } |
| } |
| |
| 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 || PREV.compareAndSet(x, prev, p)) |
| return; |
| |
| } while (x.item != null || x.next == null); |
| } |
| |
| 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 || NEXT.compareAndSet(x, 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. |
| */ |
| final Node<E> succ(Node<E> p) { |
| // TODO: should we skip deleted nodes here? |
| if (p == (p = p.next)) |
| p = first(); |
| return p; |
| } |
| |
| /** |
| * 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. |
| */ |
| final Node<E> pred(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. |
| */ |
| 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. |
| || HEAD.compareAndSet(this, 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. |
| */ |
| 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. |
| || TAIL.compareAndSet(this, t, p)) |
| return p; |
| else |
| continue restartFromTail; |
| } |
| } |
| |
| // Minor convenience utilities |
| |
| /** |
| * 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; |
| } |
| |
| /** |
| * Constructs an empty deque. |
| */ |
| public ConcurrentLinkedDeque() { |
| 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 ConcurrentLinkedDeque(Collection<? extends E> c) { |
| // Copy c into a private chain of Nodes |
| Node<E> h = null, t = null; |
| for (E e : c) { |
| Node<E> newNode = newNode(Objects.requireNonNull(e)); |
| if (h == null) |
| h = t = newNode; |
| else { |
| NEXT.set(t, newNode); |
| PREV.set(newNode, t); |
| t = newNode; |
| } |
| } |
| initHeadTail(h, t); |
| } |
| |
| /** |
| * Initializes head and tail, ensuring invariants hold. |
| */ |
| private void initHeadTail(Node<E> h, Node<E> t) { |
| if (h == t) { |
| if (h == null) |
| h = t = new Node<E>(); |
| else { |
| // Avoid edge case of a single Node with non-null item. |
| Node<E> newNode = new Node<E>(); |
| NEXT.set(t, newNode); |
| PREV.set(newNode, 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 |
| */ |
| public void addFirst(E e) { |
| linkFirst(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 |
| */ |
| public void addLast(E e) { |
| linkLast(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 |
| */ |
| public boolean offerFirst(E e) { |
| linkFirst(e); |
| return true; |
| } |
| |
| /** |
| * 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 |
| */ |
| public boolean offerLast(E e) { |
| linkLast(e); |
| return true; |
| } |
| |
| public E peekFirst() { |
| for (Node<E> p = first(); p != null; p = succ(p)) { |
| final E item; |
| if ((item = p.item) != null) |
| return item; |
| } |
| return null; |
| } |
| |
| public E peekLast() { |
| for (Node<E> p = last(); p != null; p = pred(p)) { |
| final E item; |
| if ((item = p.item) != null) |
| return item; |
| } |
| return null; |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E getFirst() { |
| return screenNullResult(peekFirst()); |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E getLast() { |
| return screenNullResult(peekLast()); |
| } |
| |
| public E pollFirst() { |
| for (Node<E> p = first(); p != null; p = succ(p)) { |
| final E item; |
| if ((item = p.item) != null |
| && ITEM.compareAndSet(p, item, null)) { |
| unlink(p); |
| return item; |
| } |
| } |
| return null; |
| } |
| |
| public E pollLast() { |
| for (Node<E> p = last(); p != null; p = pred(p)) { |
| final E item; |
| if ((item = p.item) != null |
| && ITEM.compareAndSet(p, item, null)) { |
| unlink(p); |
| return item; |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E removeFirst() { |
| return screenNullResult(pollFirst()); |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E removeLast() { |
| return screenNullResult(pollLast()); |
| } |
| |
| // *** Queue and stack methods *** |
| |
| /** |
| * 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 |
| */ |
| public boolean offer(E e) { |
| return offerLast(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 |
| */ |
| public boolean add(E e) { |
| return offerLast(e); |
| } |
| |
| public E poll() { return pollFirst(); } |
| public E peek() { return peekFirst(); } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E remove() { return removeFirst(); } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E pop() { return removeFirst(); } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E element() { return getFirst(); } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public void push(E e) { addFirst(e); } |
| |
| /** |
| * Removes the first occurrence of the specified element from this deque. |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the first element {@code e} such that |
| * {@code o.equals(e)} (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * @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 |
| */ |
| public boolean removeFirstOccurrence(Object o) { |
| Objects.requireNonNull(o); |
| for (Node<E> p = first(); p != null; p = succ(p)) { |
| final E item; |
| if ((item = p.item) != null |
| && o.equals(item) |
| && ITEM.compareAndSet(p, item, null)) { |
| unlink(p); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Removes the last occurrence of the specified element from this deque. |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the last element {@code e} such that |
| * {@code o.equals(e)} (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * @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 |
| */ |
| public boolean removeLastOccurrence(Object o) { |
| Objects.requireNonNull(o); |
| for (Node<E> p = last(); p != null; p = pred(p)) { |
| final E item; |
| if ((item = p.item) != null |
| && o.equals(item) |
| && ITEM.compareAndSet(p, item, null)) { |
| unlink(p); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| /** |
| * Returns {@code true} if this deque contains the specified element. |
| * More formally, returns {@code true} if and only 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 |
| */ |
| public boolean contains(Object o) { |
| if (o != null) { |
| for (Node<E> p = first(); p != null; p = succ(p)) { |
| final E item; |
| if ((item = p.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 |
| */ |
| public boolean isEmpty() { |
| return peekFirst() == null; |
| } |
| |
| /** |
| * 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 |
| */ |
| public int size() { |
| restartFromHead: for (;;) { |
| int count = 0; |
| for (Node<E> p = first(); p != null;) { |
| if (p.item != null) |
| if (++count == Integer.MAX_VALUE) |
| break; // @see Collection.size() |
| if (p == (p = p.next)) |
| continue restartFromHead; |
| } |
| return count; |
| } |
| } |
| |
| /** |
| * Removes the first occurrence of the specified element from this deque. |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the first element {@code e} such that |
| * {@code o.equals(e)} (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. |
| * |
| * @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 |
| */ |
| 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 |
| */ |
| 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; |
| for (E e : c) { |
| Node<E> newNode = newNode(Objects.requireNonNull(e)); |
| if (beginningOfTheEnd == null) |
| beginningOfTheEnd = last = newNode; |
| else { |
| NEXT.set(last, newNode); |
| PREV.set(newNode, last); |
| last = newNode; |
| } |
| } |
| if (beginningOfTheEnd == null) |
| return false; |
| |
| // 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 |
| PREV.set(beginningOfTheEnd, p); // CAS piggyback |
| if (NEXT.compareAndSet(p, null, beginningOfTheEnd)) { |
| // Successful CAS is the linearization point |
| // for all elements to be added to this deque. |
| if (!TAIL.weakCompareAndSet(this, t, last)) { |
| // Try a little harder to update tail, |
| // since we may be adding many elements. |
| t = tail; |
| if (last.next == null) |
| TAIL.weakCompareAndSet(this, t, last); |
| } |
| return true; |
| } |
| // Lost CAS race to another thread; re-read next |
| } |
| } |
| } |
| |
| /** |
| * Removes all of the elements from this deque. |
| */ |
| public void clear() { |
| while (pollFirst() != null) |
| ; |
| } |
| |
| public String toString() { |
| String[] a = null; |
| restartFromHead: for (;;) { |
| int charLength = 0; |
| int size = 0; |
| for (Node<E> p = first(); p != null;) { |
| final E item; |
| if ((item = p.item) != null) { |
| if (a == null) |
| a = new String[4]; |
| else if (size == a.length) |
| a = Arrays.copyOf(a, 2 * size); |
| String s = item.toString(); |
| a[size++] = s; |
| charLength += s.length(); |
| } |
| if (p == (p = p.next)) |
| continue restartFromHead; |
| } |
| |
| if (size == 0) |
| return "[]"; |
| |
| return Helpers.toString(a, size, charLength); |
| } |
| } |
| |
| private Object[] toArrayInternal(Object[] a) { |
| Object[] x = a; |
| restartFromHead: for (;;) { |
| int size = 0; |
| for (Node<E> p = first(); p != null;) { |
| final E item; |
| if ((item = p.item) != null) { |
| if (x == null) |
| x = new Object[4]; |
| else if (size == x.length) |
| x = Arrays.copyOf(x, 2 * (size + 4)); |
| x[size++] = item; |
| } |
| if (p == (p = p.next)) |
| continue restartFromHead; |
| } |
| if (x == null) |
| return new Object[0]; |
| else if (a != null && size <= a.length) { |
| if (a != x) |
| System.arraycopy(x, 0, a, 0, size); |
| if (size < a.length) |
| a[size] = null; |
| return a; |
| } |
| return (size == x.length) ? x : Arrays.copyOf(x, size); |
| } |
| } |
| |
| /** |
| * 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 |
| */ |
| public Object[] toArray() { |
| return toArrayInternal(null); |
| } |
| |
| /** |
| * 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> {@code 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("unchecked") |
| public <T> T[] toArray(T[] a) { |
| if (a == null) throw new NullPointerException(); |
| return (T[]) toArrayInternal(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 href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
| * |
| * @return an iterator over the elements in this deque in proper sequence |
| */ |
| public Iterator<E> iterator() { |
| return new Itr(); |
| } |
| |
| /** |
| * 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 href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
| * |
| * @return an iterator over the elements in this deque in reverse order |
| */ |
| public Iterator<E> descendingIterator() { |
| return new DescendingItr(); |
| } |
| |
| private abstract class AbstractItr implements Iterator<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; |
| |
| abstract Node<E> startNode(); |
| abstract Node<E> nextNode(Node<E> p); |
| |
| AbstractItr() { |
| 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) { |
| // might be at active end or TERMINATOR node; both are OK |
| nextNode = null; |
| nextItem = null; |
| break; |
| } |
| final E item; |
| if ((item = p.item) != null) { |
| nextNode = p; |
| nextItem = item; |
| break; |
| } |
| } |
| } |
| |
| public boolean hasNext() { |
| return nextItem != null; |
| } |
| |
| public E next() { |
| E item = nextItem; |
| if (item == null) throw new NoSuchElementException(); |
| advance(); |
| return item; |
| } |
| |
| public void remove() { |
| Node<E> l = lastRet; |
| if (l == null) throw new IllegalStateException(); |
| l.item = null; |
| unlink(l); |
| lastRet = null; |
| } |
| } |
| |
| /** Forward iterator */ |
| private class Itr extends AbstractItr { |
| Itr() {} // prevent access constructor creation |
| Node<E> startNode() { return first(); } |
| Node<E> nextNode(Node<E> p) { return succ(p); } |
| } |
| |
| /** Descending iterator */ |
| private class DescendingItr extends AbstractItr { |
| DescendingItr() {} // prevent access constructor creation |
| Node<E> startNode() { return last(); } |
| Node<E> nextNode(Node<E> p) { return pred(p); } |
| } |
| |
| /** A customized variant of Spliterators.IteratorSpliterator */ |
| final class CLDSpliterator implements Spliterator<E> { |
| static final int MAX_BATCH = 1 << 25; // max batch array size; |
| Node<E> current; // current node; null until initialized |
| int batch; // batch size for splits |
| boolean exhausted; // true when no more nodes |
| |
| public Spliterator<E> trySplit() { |
| Node<E> p, q; |
| if ((p = current()) == null || (q = p.next) == null) |
| return null; |
| int i = 0, n = batch = Math.min(batch + 1, MAX_BATCH); |
| Object[] a = null; |
| do { |
| final E e; |
| if ((e = p.item) != null) { |
| if (a == null) |
| a = new Object[n]; |
| a[i++] = e; |
| } |
| if (p == (p = q)) |
| p = first(); |
| } while (p != null && (q = p.next) != null && i < n); |
| setCurrent(p); |
| return (i == 0) ? null : |
| Spliterators.spliterator(a, 0, i, (Spliterator.ORDERED | |
| Spliterator.NONNULL | |
| Spliterator.CONCURRENT)); |
| } |
| |
| public void forEachRemaining(Consumer<? super E> action) { |
| Objects.requireNonNull(action); |
| Node<E> p; |
| if ((p = current()) != null) { |
| current = null; |
| exhausted = true; |
| do { |
| final E e; |
| if ((e = p.item) != null) |
| action.accept(e); |
| if (p == (p = p.next)) |
| p = first(); |
| } while (p != null); |
| } |
| } |
| |
| public boolean tryAdvance(Consumer<? super E> action) { |
| Objects.requireNonNull(action); |
| Node<E> p; |
| if ((p = current()) != null) { |
| E e; |
| do { |
| e = p.item; |
| if (p == (p = p.next)) |
| p = first(); |
| } while (e == null && p != null); |
| setCurrent(p); |
| if (e != null) { |
| action.accept(e); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| private void setCurrent(Node<E> p) { |
| if ((current = p) == null) |
| exhausted = true; |
| } |
| |
| private Node<E> current() { |
| Node<E> p; |
| if ((p = current) == null && !exhausted) |
| setCurrent(p = first()); |
| return p; |
| } |
| |
| public long estimateSize() { return Long.MAX_VALUE; } |
| |
| public int characteristics() { |
| return (Spliterator.ORDERED | |
| Spliterator.NONNULL | |
| Spliterator.CONCURRENT); |
| } |
| } |
| |
| /** |
| * Returns a {@link Spliterator} over the elements in this deque. |
| * |
| * <p>The returned spliterator is |
| * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
| * |
| * <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, |
| * {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. |
| * |
| * @implNote |
| * The {@code Spliterator} implements {@code trySplit} to permit limited |
| * parallelism. |
| * |
| * @return a {@code Spliterator} over the elements in this deque |
| * @since 1.8 |
| */ |
| public Spliterator<E> spliterator() { |
| return new CLDSpliterator(); |
| } |
| |
| /** |
| * Saves this deque to a stream (that is, serializes it). |
| * |
| * @param s the stream |
| * @throws java.io.IOException if an I/O error occurs |
| * @serialData All of the elements (each an {@code E}) in |
| * the proper order, followed by a null |
| */ |
| private void writeObject(java.io.ObjectOutputStream s) |
| throws java.io.IOException { |
| |
| // Write out any hidden stuff |
| s.defaultWriteObject(); |
| |
| // Write out all elements in the proper order. |
| for (Node<E> p = first(); p != null; p = succ(p)) { |
| final E item; |
| if ((item = p.item) != null) |
| s.writeObject(item); |
| } |
| |
| // Use trailing null as sentinel |
| s.writeObject(null); |
| } |
| |
| /** |
| * Reconstitutes this deque from a stream (that is, deserializes it). |
| * @param s the stream |
| * @throws ClassNotFoundException if the class of a serialized object |
| * could not be found |
| * @throws java.io.IOException if an I/O error occurs |
| */ |
| private void readObject(java.io.ObjectInputStream s) |
| throws java.io.IOException, ClassNotFoundException { |
| s.defaultReadObject(); |
| |
| // Read in elements until trailing null sentinel found |
| Node<E> h = null, t = null; |
| for (Object item; (item = s.readObject()) != null; ) { |
| @SuppressWarnings("unchecked") |
| Node<E> newNode = newNode((E) item); |
| if (h == null) |
| h = t = newNode; |
| else { |
| NEXT.set(t, newNode); |
| PREV.set(newNode, t); |
| t = newNode; |
| } |
| } |
| initHeadTail(h, t); |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public boolean removeIf(Predicate<? super E> filter) { |
| Objects.requireNonNull(filter); |
| return bulkRemove(filter); |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public boolean removeAll(Collection<?> c) { |
| Objects.requireNonNull(c); |
| return bulkRemove(e -> c.contains(e)); |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public boolean retainAll(Collection<?> c) { |
| Objects.requireNonNull(c); |
| return bulkRemove(e -> !c.contains(e)); |
| } |
| |
| /** Implementation of bulk remove methods. */ |
| private boolean bulkRemove(Predicate<? super E> filter) { |
| boolean removed = false; |
| for (Node<E> p = first(), succ; p != null; p = succ) { |
| succ = succ(p); |
| final E item; |
| if ((item = p.item) != null |
| && filter.test(item) |
| && ITEM.compareAndSet(p, item, null)) { |
| unlink(p); |
| removed = true; |
| } |
| } |
| return removed; |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public void forEach(Consumer<? super E> action) { |
| Objects.requireNonNull(action); |
| E item; |
| for (Node<E> p = first(); p != null; p = succ(p)) |
| if ((item = p.item) != null) |
| action.accept(item); |
| } |
| |
| // VarHandle mechanics |
| private static final VarHandle HEAD; |
| private static final VarHandle TAIL; |
| private static final VarHandle PREV; |
| private static final VarHandle NEXT; |
| private static final VarHandle ITEM; |
| static { |
| PREV_TERMINATOR = new Node<Object>(); |
| PREV_TERMINATOR.next = PREV_TERMINATOR; |
| NEXT_TERMINATOR = new Node<Object>(); |
| NEXT_TERMINATOR.prev = NEXT_TERMINATOR; |
| try { |
| MethodHandles.Lookup l = MethodHandles.lookup(); |
| HEAD = l.findVarHandle(ConcurrentLinkedDeque.class, "head", |
| Node.class); |
| TAIL = l.findVarHandle(ConcurrentLinkedDeque.class, "tail", |
| Node.class); |
| PREV = l.findVarHandle(Node.class, "prev", Node.class); |
| NEXT = l.findVarHandle(Node.class, "next", Node.class); |
| ITEM = l.findVarHandle(Node.class, "item", Object.class); |
| } catch (ReflectiveOperationException e) { |
| throw new Error(e); |
| } |
| } |
| } |
