jaroslav@1890: /*
jaroslav@1890:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@1890:  *
jaroslav@1890:  * This code is free software; you can redistribute it and/or modify it
jaroslav@1890:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@1890:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@1890:  * particular file as subject to the "Classpath" exception as provided
jaroslav@1890:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@1890:  *
jaroslav@1890:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@1890:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@1890:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@1890:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@1890:  * accompanied this code).
jaroslav@1890:  *
jaroslav@1890:  * You should have received a copy of the GNU General Public License version
jaroslav@1890:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@1890:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@1890:  *
jaroslav@1890:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@1890:  * or visit www.oracle.com if you need additional information or have any
jaroslav@1890:  * questions.
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: /*
jaroslav@1890:  * This file is available under and governed by the GNU General Public
jaroslav@1890:  * License version 2 only, as published by the Free Software Foundation.
jaroslav@1890:  * However, the following notice accompanied the original version of this
jaroslav@1890:  * file:
jaroslav@1890:  *
jaroslav@1890:  * Written by Doug Lea with assistance from members of JCP JSR-166
jaroslav@1890:  * Expert Group and released to the public domain, as explained at
jaroslav@1890:  * http://creativecommons.org/publicdomain/zero/1.0/
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: package java.util.concurrent;
jaroslav@1890: 
jaroslav@1890: import java.util.AbstractQueue;
jaroslav@1890: import java.util.Collection;
jaroslav@1890: import java.util.Iterator;
jaroslav@1890: import java.util.NoSuchElementException;
jaroslav@1890: import java.util.concurrent.locks.Condition;
jaroslav@1890: import java.util.concurrent.locks.ReentrantLock;
jaroslav@1890: 
jaroslav@1890: /**
jaroslav@1890:  * An optionally-bounded {@linkplain BlockingDeque blocking deque} based on
jaroslav@1890:  * linked nodes.
jaroslav@1890:  *
jaroslav@1890:  * <p> The optional capacity bound constructor argument serves as a
jaroslav@1890:  * way to prevent excessive expansion. The capacity, if unspecified,
jaroslav@1890:  * is equal to {@link Integer#MAX_VALUE}.  Linked nodes are
jaroslav@1890:  * dynamically created upon each insertion unless this would bring the
jaroslav@1890:  * deque above capacity.
jaroslav@1890:  *
jaroslav@1890:  * <p>Most operations run in constant time (ignoring time spent
jaroslav@1890:  * blocking).  Exceptions include {@link #remove(Object) remove},
jaroslav@1890:  * {@link #removeFirstOccurrence removeFirstOccurrence}, {@link
jaroslav@1890:  * #removeLastOccurrence removeLastOccurrence}, {@link #contains
jaroslav@1890:  * contains}, {@link #iterator iterator.remove()}, and the bulk
jaroslav@1890:  * operations, all of which run in linear time.
jaroslav@1890:  *
jaroslav@1890:  * <p>This class and its iterator implement all of the
jaroslav@1890:  * <em>optional</em> methods of the {@link Collection} and {@link
jaroslav@1890:  * Iterator} interfaces.
jaroslav@1890:  *
jaroslav@1890:  * <p>This class is a member of the
jaroslav@1890:  * <a href="{@docRoot}/../technotes/guides/collections/index.html">
jaroslav@1890:  * Java Collections Framework</a>.
jaroslav@1890:  *
jaroslav@1890:  * @since 1.6
jaroslav@1890:  * @author  Doug Lea
jaroslav@1890:  * @param <E> the type of elements held in this collection
jaroslav@1890:  */
jaroslav@1890: public class LinkedBlockingDeque<E>
jaroslav@1890:     extends AbstractQueue<E>
jaroslav@1890:     implements BlockingDeque<E>,  java.io.Serializable {
jaroslav@1890: 
jaroslav@1890:     /*
jaroslav@1890:      * Implemented as a simple doubly-linked list protected by a
jaroslav@1890:      * single lock and using conditions to manage blocking.
jaroslav@1890:      *
jaroslav@1890:      * To implement weakly consistent iterators, it appears we need to
jaroslav@1890:      * keep all Nodes GC-reachable from a predecessor dequeued Node.
jaroslav@1890:      * That would cause two problems:
jaroslav@1890:      * - allow a rogue Iterator to cause unbounded memory retention
jaroslav@1890:      * - cause cross-generational linking of old Nodes to new Nodes if
jaroslav@1890:      *   a Node was tenured while live, which generational GCs have a
jaroslav@1890:      *   hard time dealing with, causing repeated major collections.
jaroslav@1890:      * However, only non-deleted Nodes need to be reachable from
jaroslav@1890:      * dequeued Nodes, and reachability does not necessarily have to
jaroslav@1890:      * be of the kind understood by the GC.  We use the trick of
jaroslav@1890:      * linking a Node that has just been dequeued to itself.  Such a
jaroslav@1890:      * self-link implicitly means to jump to "first" (for next links)
jaroslav@1890:      * or "last" (for prev links).
jaroslav@1890:      */
jaroslav@1890: 
jaroslav@1890:     /*
jaroslav@1890:      * We have "diamond" multiple interface/abstract class inheritance
jaroslav@1890:      * here, and that introduces ambiguities. Often we want the
jaroslav@1890:      * BlockingDeque javadoc combined with the AbstractQueue
jaroslav@1890:      * implementation, so a lot of method specs are duplicated here.
jaroslav@1890:      */
jaroslav@1890: 
jaroslav@1890:     private static final long serialVersionUID = -387911632671998426L;
jaroslav@1890: 
jaroslav@1890:     /** Doubly-linked list node class */
jaroslav@1890:     static final class Node<E> {
jaroslav@1890:         /**
jaroslav@1890:          * The item, or null if this node has been removed.
jaroslav@1890:          */
jaroslav@1890:         E item;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * One of:
jaroslav@1890:          * - the real predecessor Node
jaroslav@1890:          * - this Node, meaning the predecessor is tail
jaroslav@1890:          * - null, meaning there is no predecessor
jaroslav@1890:          */
jaroslav@1890:         Node<E> prev;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * One of:
jaroslav@1890:          * - the real successor Node
jaroslav@1890:          * - this Node, meaning the successor is head
jaroslav@1890:          * - null, meaning there is no successor
jaroslav@1890:          */
jaroslav@1890:         Node<E> next;
jaroslav@1890: 
jaroslav@1890:         Node(E x) {
jaroslav@1890:             item = x;
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Pointer to first node.
jaroslav@1890:      * Invariant: (first == null && last == null) ||
jaroslav@1890:      *            (first.prev == null && first.item != null)
jaroslav@1890:      */
jaroslav@1890:     transient Node<E> first;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Pointer to last node.
jaroslav@1890:      * Invariant: (first == null && last == null) ||
jaroslav@1890:      *            (last.next == null && last.item != null)
jaroslav@1890:      */
jaroslav@1890:     transient Node<E> last;
jaroslav@1890: 
jaroslav@1890:     /** Number of items in the deque */
jaroslav@1890:     private transient int count;
jaroslav@1890: 
jaroslav@1890:     /** Maximum number of items in the deque */
jaroslav@1890:     private final int capacity;
jaroslav@1890: 
jaroslav@1890:     /** Main lock guarding all access */
jaroslav@1890:     final ReentrantLock lock = new ReentrantLock();
jaroslav@1890: 
jaroslav@1890:     /** Condition for waiting takes */
jaroslav@1890:     private final Condition notEmpty = lock.newCondition();
jaroslav@1890: 
jaroslav@1890:     /** Condition for waiting puts */
jaroslav@1890:     private final Condition notFull = lock.newCondition();
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a {@code LinkedBlockingDeque} with a capacity of
jaroslav@1890:      * {@link Integer#MAX_VALUE}.
jaroslav@1890:      */
jaroslav@1890:     public LinkedBlockingDeque() {
jaroslav@1890:         this(Integer.MAX_VALUE);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a {@code LinkedBlockingDeque} with the given (fixed) capacity.
jaroslav@1890:      *
jaroslav@1890:      * @param capacity the capacity of this deque
jaroslav@1890:      * @throws IllegalArgumentException if {@code capacity} is less than 1
jaroslav@1890:      */
jaroslav@1890:     public LinkedBlockingDeque(int capacity) {
jaroslav@1890:         if (capacity <= 0) throw new IllegalArgumentException();
jaroslav@1890:         this.capacity = capacity;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a {@code LinkedBlockingDeque} with a capacity of
jaroslav@1890:      * {@link Integer#MAX_VALUE}, initially containing the elements of
jaroslav@1890:      * the given collection, added in traversal order of the
jaroslav@1890:      * collection's iterator.
jaroslav@1890:      *
jaroslav@1890:      * @param c the collection of elements to initially contain
jaroslav@1890:      * @throws NullPointerException if the specified collection or any
jaroslav@1890:      *         of its elements are null
jaroslav@1890:      */
jaroslav@1890:     public LinkedBlockingDeque(Collection<? extends E> c) {
jaroslav@1890:         this(Integer.MAX_VALUE);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock(); // Never contended, but necessary for visibility
jaroslav@1890:         try {
jaroslav@1890:             for (E e : c) {
jaroslav@1890:                 if (e == null)
jaroslav@1890:                     throw new NullPointerException();
jaroslav@1890:                 if (!linkLast(new Node<E>(e)))
jaroslav@1890:                     throw new IllegalStateException("Deque full");
jaroslav@1890:             }
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     // Basic linking and unlinking operations, called only while holding lock
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Links node as first element, or returns false if full.
jaroslav@1890:      */
jaroslav@1890:     private boolean linkFirst(Node<E> node) {
jaroslav@1890:         // assert lock.isHeldByCurrentThread();
jaroslav@1890:         if (count >= capacity)
jaroslav@1890:             return false;
jaroslav@1890:         Node<E> f = first;
jaroslav@1890:         node.next = f;
jaroslav@1890:         first = node;
jaroslav@1890:         if (last == null)
jaroslav@1890:             last = node;
jaroslav@1890:         else
jaroslav@1890:             f.prev = node;
jaroslav@1890:         ++count;
jaroslav@1890:         notEmpty.signal();
jaroslav@1890:         return true;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Links node as last element, or returns false if full.
jaroslav@1890:      */
jaroslav@1890:     private boolean linkLast(Node<E> node) {
jaroslav@1890:         // assert lock.isHeldByCurrentThread();
jaroslav@1890:         if (count >= capacity)
jaroslav@1890:             return false;
jaroslav@1890:         Node<E> l = last;
jaroslav@1890:         node.prev = l;
jaroslav@1890:         last = node;
jaroslav@1890:         if (first == null)
jaroslav@1890:             first = node;
jaroslav@1890:         else
jaroslav@1890:             l.next = node;
jaroslav@1890:         ++count;
jaroslav@1890:         notEmpty.signal();
jaroslav@1890:         return true;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes and returns first element, or null if empty.
jaroslav@1890:      */
jaroslav@1890:     private E unlinkFirst() {
jaroslav@1890:         // assert lock.isHeldByCurrentThread();
jaroslav@1890:         Node<E> f = first;
jaroslav@1890:         if (f == null)
jaroslav@1890:             return null;
jaroslav@1890:         Node<E> n = f.next;
jaroslav@1890:         E item = f.item;
jaroslav@1890:         f.item = null;
jaroslav@1890:         f.next = f; // help GC
jaroslav@1890:         first = n;
jaroslav@1890:         if (n == null)
jaroslav@1890:             last = null;
jaroslav@1890:         else
jaroslav@1890:             n.prev = null;
jaroslav@1890:         --count;
jaroslav@1890:         notFull.signal();
jaroslav@1890:         return item;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes and returns last element, or null if empty.
jaroslav@1890:      */
jaroslav@1890:     private E unlinkLast() {
jaroslav@1890:         // assert lock.isHeldByCurrentThread();
jaroslav@1890:         Node<E> l = last;
jaroslav@1890:         if (l == null)
jaroslav@1890:             return null;
jaroslav@1890:         Node<E> p = l.prev;
jaroslav@1890:         E item = l.item;
jaroslav@1890:         l.item = null;
jaroslav@1890:         l.prev = l; // help GC
jaroslav@1890:         last = p;
jaroslav@1890:         if (p == null)
jaroslav@1890:             first = null;
jaroslav@1890:         else
jaroslav@1890:             p.next = null;
jaroslav@1890:         --count;
jaroslav@1890:         notFull.signal();
jaroslav@1890:         return item;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Unlinks x.
jaroslav@1890:      */
jaroslav@1890:     void unlink(Node<E> x) {
jaroslav@1890:         // assert lock.isHeldByCurrentThread();
jaroslav@1890:         Node<E> p = x.prev;
jaroslav@1890:         Node<E> n = x.next;
jaroslav@1890:         if (p == null) {
jaroslav@1890:             unlinkFirst();
jaroslav@1890:         } else if (n == null) {
jaroslav@1890:             unlinkLast();
jaroslav@1890:         } else {
jaroslav@1890:             p.next = n;
jaroslav@1890:             n.prev = p;
jaroslav@1890:             x.item = null;
jaroslav@1890:             // Don't mess with x's links.  They may still be in use by
jaroslav@1890:             // an iterator.
jaroslav@1890:             --count;
jaroslav@1890:             notFull.signal();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // BlockingDeque methods
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws IllegalStateException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException  {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public void addFirst(E e) {
jaroslav@1890:         if (!offerFirst(e))
jaroslav@1890:             throw new IllegalStateException("Deque full");
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws IllegalStateException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException  {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public void addLast(E e) {
jaroslav@1890:         if (!offerLast(e))
jaroslav@1890:             throw new IllegalStateException("Deque full");
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public boolean offerFirst(E e) {
jaroslav@1890:         if (e == null) throw new NullPointerException();
jaroslav@1890:         Node<E> node = new Node<E>(e);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return linkFirst(node);
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public boolean offerLast(E e) {
jaroslav@1890:         if (e == null) throw new NullPointerException();
jaroslav@1890:         Node<E> node = new Node<E>(e);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return linkLast(node);
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException {@inheritDoc}
jaroslav@1890:      * @throws InterruptedException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public void putFirst(E e) throws InterruptedException {
jaroslav@1890:         if (e == null) throw new NullPointerException();
jaroslav@1890:         Node<E> node = new Node<E>(e);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             while (!linkFirst(node))
jaroslav@1890:                 notFull.await();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException {@inheritDoc}
jaroslav@1890:      * @throws InterruptedException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public void putLast(E e) throws InterruptedException {
jaroslav@1890:         if (e == null) throw new NullPointerException();
jaroslav@1890:         Node<E> node = new Node<E>(e);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             while (!linkLast(node))
jaroslav@1890:                 notFull.await();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException {@inheritDoc}
jaroslav@1890:      * @throws InterruptedException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public boolean offerFirst(E e, long timeout, TimeUnit unit)
jaroslav@1890:         throws InterruptedException {
jaroslav@1890:         if (e == null) throw new NullPointerException();
jaroslav@1890:         Node<E> node = new Node<E>(e);
jaroslav@1890:         long nanos = unit.toNanos(timeout);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lockInterruptibly();
jaroslav@1890:         try {
jaroslav@1890:             while (!linkFirst(node)) {
jaroslav@1890:                 if (nanos <= 0)
jaroslav@1890:                     return false;
jaroslav@1890:                 nanos = notFull.awaitNanos(nanos);
jaroslav@1890:             }
jaroslav@1890:             return true;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException {@inheritDoc}
jaroslav@1890:      * @throws InterruptedException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public boolean offerLast(E e, long timeout, TimeUnit unit)
jaroslav@1890:         throws InterruptedException {
jaroslav@1890:         if (e == null) throw new NullPointerException();
jaroslav@1890:         Node<E> node = new Node<E>(e);
jaroslav@1890:         long nanos = unit.toNanos(timeout);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lockInterruptibly();
jaroslav@1890:         try {
jaroslav@1890:             while (!linkLast(node)) {
jaroslav@1890:                 if (nanos <= 0)
jaroslav@1890:                     return false;
jaroslav@1890:                 nanos = notFull.awaitNanos(nanos);
jaroslav@1890:             }
jaroslav@1890:             return true;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public E removeFirst() {
jaroslav@1890:         E x = pollFirst();
jaroslav@1890:         if (x == null) throw new NoSuchElementException();
jaroslav@1890:         return x;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public E removeLast() {
jaroslav@1890:         E x = pollLast();
jaroslav@1890:         if (x == null) throw new NoSuchElementException();
jaroslav@1890:         return x;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E pollFirst() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return unlinkFirst();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E pollLast() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return unlinkLast();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E takeFirst() throws InterruptedException {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             E x;
jaroslav@1890:             while ( (x = unlinkFirst()) == null)
jaroslav@1890:                 notEmpty.await();
jaroslav@1890:             return x;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E takeLast() throws InterruptedException {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             E x;
jaroslav@1890:             while ( (x = unlinkLast()) == null)
jaroslav@1890:                 notEmpty.await();
jaroslav@1890:             return x;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E pollFirst(long timeout, TimeUnit unit)
jaroslav@1890:         throws InterruptedException {
jaroslav@1890:         long nanos = unit.toNanos(timeout);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lockInterruptibly();
jaroslav@1890:         try {
jaroslav@1890:             E x;
jaroslav@1890:             while ( (x = unlinkFirst()) == null) {
jaroslav@1890:                 if (nanos <= 0)
jaroslav@1890:                     return null;
jaroslav@1890:                 nanos = notEmpty.awaitNanos(nanos);
jaroslav@1890:             }
jaroslav@1890:             return x;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E pollLast(long timeout, TimeUnit unit)
jaroslav@1890:         throws InterruptedException {
jaroslav@1890:         long nanos = unit.toNanos(timeout);
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lockInterruptibly();
jaroslav@1890:         try {
jaroslav@1890:             E x;
jaroslav@1890:             while ( (x = unlinkLast()) == null) {
jaroslav@1890:                 if (nanos <= 0)
jaroslav@1890:                     return null;
jaroslav@1890:                 nanos = notEmpty.awaitNanos(nanos);
jaroslav@1890:             }
jaroslav@1890:             return x;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public E getFirst() {
jaroslav@1890:         E x = peekFirst();
jaroslav@1890:         if (x == null) throw new NoSuchElementException();
jaroslav@1890:         return x;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public E getLast() {
jaroslav@1890:         E x = peekLast();
jaroslav@1890:         if (x == null) throw new NoSuchElementException();
jaroslav@1890:         return x;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E peekFirst() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return (first == null) ? null : first.item;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E peekLast() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return (last == null) ? null : last.item;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public boolean removeFirstOccurrence(Object o) {
jaroslav@1890:         if (o == null) return false;
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             for (Node<E> p = first; p != null; p = p.next) {
jaroslav@1890:                 if (o.equals(p.item)) {
jaroslav@1890:                     unlink(p);
jaroslav@1890:                     return true;
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:             return false;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public boolean removeLastOccurrence(Object o) {
jaroslav@1890:         if (o == null) return false;
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             for (Node<E> p = last; p != null; p = p.prev) {
jaroslav@1890:                 if (o.equals(p.item)) {
jaroslav@1890:                     unlink(p);
jaroslav@1890:                     return true;
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:             return false;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // BlockingQueue methods
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Inserts the specified element at the end of this deque unless it would
jaroslav@1890:      * violate capacity restrictions.  When using a capacity-restricted deque,
jaroslav@1890:      * it is generally preferable to use method {@link #offer(Object) offer}.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method is equivalent to {@link #addLast}.
jaroslav@1890:      *
jaroslav@1890:      * @throws IllegalStateException if the element cannot be added at this
jaroslav@1890:      *         time due to capacity restrictions
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public boolean add(E e) {
jaroslav@1890:         addLast(e);
jaroslav@1890:         return true;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException if the specified element is null
jaroslav@1890:      */
jaroslav@1890:     public boolean offer(E e) {
jaroslav@1890:         return offerLast(e);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException {@inheritDoc}
jaroslav@1890:      * @throws InterruptedException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public void put(E e) throws InterruptedException {
jaroslav@1890:         putLast(e);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NullPointerException {@inheritDoc}
jaroslav@1890:      * @throws InterruptedException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public boolean offer(E e, long timeout, TimeUnit unit)
jaroslav@1890:         throws InterruptedException {
jaroslav@1890:         return offerLast(e, timeout, unit);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Retrieves and removes the head of the queue represented by this deque.
jaroslav@1890:      * This method differs from {@link #poll poll} only in that it throws an
jaroslav@1890:      * exception if this deque is empty.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method is equivalent to {@link #removeFirst() removeFirst}.
jaroslav@1890:      *
jaroslav@1890:      * @return the head of the queue represented by this deque
jaroslav@1890:      * @throws NoSuchElementException if this deque is empty
jaroslav@1890:      */
jaroslav@1890:     public E remove() {
jaroslav@1890:         return removeFirst();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E poll() {
jaroslav@1890:         return pollFirst();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E take() throws InterruptedException {
jaroslav@1890:         return takeFirst();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E poll(long timeout, TimeUnit unit) throws InterruptedException {
jaroslav@1890:         return pollFirst(timeout, unit);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Retrieves, but does not remove, the head of the queue represented by
jaroslav@1890:      * this deque.  This method differs from {@link #peek peek} only in that
jaroslav@1890:      * it throws an exception if this deque is empty.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method is equivalent to {@link #getFirst() getFirst}.
jaroslav@1890:      *
jaroslav@1890:      * @return the head of the queue represented by this deque
jaroslav@1890:      * @throws NoSuchElementException if this deque is empty
jaroslav@1890:      */
jaroslav@1890:     public E element() {
jaroslav@1890:         return getFirst();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public E peek() {
jaroslav@1890:         return peekFirst();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the number of additional elements that this deque can ideally
jaroslav@1890:      * (in the absence of memory or resource constraints) accept without
jaroslav@1890:      * blocking. This is always equal to the initial capacity of this deque
jaroslav@1890:      * less the current {@code size} of this deque.
jaroslav@1890:      *
jaroslav@1890:      * <p>Note that you <em>cannot</em> always tell if an attempt to insert
jaroslav@1890:      * an element will succeed by inspecting {@code remainingCapacity}
jaroslav@1890:      * because it may be the case that another thread is about to
jaroslav@1890:      * insert or remove an element.
jaroslav@1890:      */
jaroslav@1890:     public int remainingCapacity() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return capacity - count;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws UnsupportedOperationException {@inheritDoc}
jaroslav@1890:      * @throws ClassCastException            {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException          {@inheritDoc}
jaroslav@1890:      * @throws IllegalArgumentException      {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public int drainTo(Collection<? super E> c) {
jaroslav@1890:         return drainTo(c, Integer.MAX_VALUE);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws UnsupportedOperationException {@inheritDoc}
jaroslav@1890:      * @throws ClassCastException            {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException          {@inheritDoc}
jaroslav@1890:      * @throws IllegalArgumentException      {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public int drainTo(Collection<? super E> c, int maxElements) {
jaroslav@1890:         if (c == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (c == this)
jaroslav@1890:             throw new IllegalArgumentException();
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             int n = Math.min(maxElements, count);
jaroslav@1890:             for (int i = 0; i < n; i++) {
jaroslav@1890:                 c.add(first.item);   // In this order, in case add() throws.
jaroslav@1890:                 unlinkFirst();
jaroslav@1890:             }
jaroslav@1890:             return n;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Stack methods
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws IllegalStateException {@inheritDoc}
jaroslav@1890:      * @throws NullPointerException  {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public void push(E e) {
jaroslav@1890:         addFirst(e);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * @throws NoSuchElementException {@inheritDoc}
jaroslav@1890:      */
jaroslav@1890:     public E pop() {
jaroslav@1890:         return removeFirst();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Collection methods
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Removes the first occurrence of the specified element from this deque.
jaroslav@1890:      * If the deque does not contain the element, it is unchanged.
jaroslav@1890:      * More formally, removes the first element {@code e} such that
jaroslav@1890:      * {@code o.equals(e)} (if such an element exists).
jaroslav@1890:      * Returns {@code true} if this deque contained the specified element
jaroslav@1890:      * (or equivalently, if this deque changed as a result of the call).
jaroslav@1890:      *
jaroslav@1890:      * <p>This method is equivalent to
jaroslav@1890:      * {@link #removeFirstOccurrence(Object) removeFirstOccurrence}.
jaroslav@1890:      *
jaroslav@1890:      * @param o element to be removed from this deque, if present
jaroslav@1890:      * @return {@code true} if this deque changed as a result of the call
jaroslav@1890:      */
jaroslav@1890:     public boolean remove(Object o) {
jaroslav@1890:         return removeFirstOccurrence(o);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the number of elements in this deque.
jaroslav@1890:      *
jaroslav@1890:      * @return the number of elements in this deque
jaroslav@1890:      */
jaroslav@1890:     public int size() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             return count;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns {@code true} if this deque contains the specified element.
jaroslav@1890:      * More formally, returns {@code true} if and only if this deque contains
jaroslav@1890:      * at least one element {@code e} such that {@code o.equals(e)}.
jaroslav@1890:      *
jaroslav@1890:      * @param o object to be checked for containment in this deque
jaroslav@1890:      * @return {@code true} if this deque contains the specified element
jaroslav@1890:      */
jaroslav@1890:     public boolean contains(Object o) {
jaroslav@1890:         if (o == null) return false;
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             for (Node<E> p = first; p != null; p = p.next)
jaroslav@1890:                 if (o.equals(p.item))
jaroslav@1890:                     return true;
jaroslav@1890:             return false;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /*
jaroslav@1890:      * TODO: Add support for more efficient bulk operations.
jaroslav@1890:      *
jaroslav@1890:      * We don't want to acquire the lock for every iteration, but we
jaroslav@1890:      * also want other threads a chance to interact with the
jaroslav@1890:      * collection, especially when count is close to capacity.
jaroslav@1890:      */
jaroslav@1890: 
jaroslav@1890: //     /**
jaroslav@1890: //      * Adds all of the elements in the specified collection to this
jaroslav@1890: //      * queue.  Attempts to addAll of a queue to itself result in
jaroslav@1890: //      * {@code IllegalArgumentException}. Further, the behavior of
jaroslav@1890: //      * this operation is undefined if the specified collection is
jaroslav@1890: //      * modified while the operation is in progress.
jaroslav@1890: //      *
jaroslav@1890: //      * @param c collection containing elements to be added to this queue
jaroslav@1890: //      * @return {@code true} if this queue changed as a result of the call
jaroslav@1890: //      * @throws ClassCastException            {@inheritDoc}
jaroslav@1890: //      * @throws NullPointerException          {@inheritDoc}
jaroslav@1890: //      * @throws IllegalArgumentException      {@inheritDoc}
jaroslav@1890: //      * @throws IllegalStateException         {@inheritDoc}
jaroslav@1890: //      * @see #add(Object)
jaroslav@1890: //      */
jaroslav@1890: //     public boolean addAll(Collection<? extends E> c) {
jaroslav@1890: //         if (c == null)
jaroslav@1890: //             throw new NullPointerException();
jaroslav@1890: //         if (c == this)
jaroslav@1890: //             throw new IllegalArgumentException();
jaroslav@1890: //         final ReentrantLock lock = this.lock;
jaroslav@1890: //         lock.lock();
jaroslav@1890: //         try {
jaroslav@1890: //             boolean modified = false;
jaroslav@1890: //             for (E e : c)
jaroslav@1890: //                 if (linkLast(e))
jaroslav@1890: //                     modified = true;
jaroslav@1890: //             return modified;
jaroslav@1890: //         } finally {
jaroslav@1890: //             lock.unlock();
jaroslav@1890: //         }
jaroslav@1890: //     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an array containing all of the elements in this deque, in
jaroslav@1890:      * proper sequence (from first to last element).
jaroslav@1890:      *
jaroslav@1890:      * <p>The returned array will be "safe" in that no references to it are
jaroslav@1890:      * maintained by this deque.  (In other words, this method must allocate
jaroslav@1890:      * a new array).  The caller is thus free to modify the returned array.
jaroslav@1890:      *
jaroslav@1890:      * <p>This method acts as bridge between array-based and collection-based
jaroslav@1890:      * APIs.
jaroslav@1890:      *
jaroslav@1890:      * @return an array containing all of the elements in this deque
jaroslav@1890:      */
jaroslav@1890:     @SuppressWarnings("unchecked")
jaroslav@1890:     public Object[] toArray() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             Object[] a = new Object[count];
jaroslav@1890:             int k = 0;
jaroslav@1890:             for (Node<E> p = first; p != null; p = p.next)
jaroslav@1890:                 a[k++] = p.item;
jaroslav@1890:             return a;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an array containing all of the elements in this deque, in
jaroslav@1890:      * proper sequence; the runtime type of the returned array is that of
jaroslav@1890:      * the specified array.  If the deque fits in the specified array, it
jaroslav@1890:      * is returned therein.  Otherwise, a new array is allocated with the
jaroslav@1890:      * runtime type of the specified array and the size of this deque.
jaroslav@1890:      *
jaroslav@1890:      * <p>If this deque fits in the specified array with room to spare
jaroslav@1890:      * (i.e., the array has more elements than this deque), the element in
jaroslav@1890:      * the array immediately following the end of the deque is set to
jaroslav@1890:      * {@code null}.
jaroslav@1890:      *
jaroslav@1890:      * <p>Like the {@link #toArray()} method, this method acts as bridge between
jaroslav@1890:      * array-based and collection-based APIs.  Further, this method allows
jaroslav@1890:      * precise control over the runtime type of the output array, and may,
jaroslav@1890:      * under certain circumstances, be used to save allocation costs.
jaroslav@1890:      *
jaroslav@1890:      * <p>Suppose {@code x} is a deque known to contain only strings.
jaroslav@1890:      * The following code can be used to dump the deque into a newly
jaroslav@1890:      * allocated array of {@code String}:
jaroslav@1890:      *
jaroslav@1890:      * <pre>
jaroslav@1890:      *     String[] y = x.toArray(new String[0]);</pre>
jaroslav@1890:      *
jaroslav@1890:      * Note that {@code toArray(new Object[0])} is identical in function to
jaroslav@1890:      * {@code toArray()}.
jaroslav@1890:      *
jaroslav@1890:      * @param a the array into which the elements of the deque are to
jaroslav@1890:      *          be stored, if it is big enough; otherwise, a new array of the
jaroslav@1890:      *          same runtime type is allocated for this purpose
jaroslav@1890:      * @return an array containing all of the elements in this deque
jaroslav@1890:      * @throws ArrayStoreException if the runtime type of the specified array
jaroslav@1890:      *         is not a supertype of the runtime type of every element in
jaroslav@1890:      *         this deque
jaroslav@1890:      * @throws NullPointerException if the specified array is null
jaroslav@1890:      */
jaroslav@1890:     @SuppressWarnings("unchecked")
jaroslav@1890:     public <T> T[] toArray(T[] a) {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             if (a.length < count)
jaroslav@1890:                 a = (T[])java.lang.reflect.Array.newInstance
jaroslav@1890:                     (a.getClass().getComponentType(), count);
jaroslav@1890: 
jaroslav@1890:             int k = 0;
jaroslav@1890:             for (Node<E> p = first; p != null; p = p.next)
jaroslav@1890:                 a[k++] = (T)p.item;
jaroslav@1890:             if (a.length > k)
jaroslav@1890:                 a[k] = null;
jaroslav@1890:             return a;
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public String toString() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             Node<E> p = first;
jaroslav@1890:             if (p == null)
jaroslav@1890:                 return "[]";
jaroslav@1890: 
jaroslav@1890:             StringBuilder sb = new StringBuilder();
jaroslav@1890:             sb.append('[');
jaroslav@1890:             for (;;) {
jaroslav@1890:                 E e = p.item;
jaroslav@1890:                 sb.append(e == this ? "(this Collection)" : e);
jaroslav@1890:                 p = p.next;
jaroslav@1890:                 if (p == null)
jaroslav@1890:                     return sb.append(']').toString();
jaroslav@1890:                 sb.append(',').append(' ');
jaroslav@1890:             }
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Atomically removes all of the elements from this deque.
jaroslav@1890:      * The deque will be empty after this call returns.
jaroslav@1890:      */
jaroslav@1890:     public void clear() {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             for (Node<E> f = first; f != null; ) {
jaroslav@1890:                 f.item = null;
jaroslav@1890:                 Node<E> n = f.next;
jaroslav@1890:                 f.prev = null;
jaroslav@1890:                 f.next = null;
jaroslav@1890:                 f = n;
jaroslav@1890:             }
jaroslav@1890:             first = last = null;
jaroslav@1890:             count = 0;
jaroslav@1890:             notFull.signalAll();
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an iterator over the elements in this deque in proper sequence.
jaroslav@1890:      * The elements will be returned in order from first (head) to last (tail).
jaroslav@1890:      *
jaroslav@1890:      * <p>The returned iterator is a "weakly consistent" iterator that
jaroslav@1890:      * will never throw {@link java.util.ConcurrentModificationException
jaroslav@1890:      * ConcurrentModificationException}, and guarantees to traverse
jaroslav@1890:      * elements as they existed upon construction of the iterator, and
jaroslav@1890:      * may (but is not guaranteed to) reflect any modifications
jaroslav@1890:      * subsequent to construction.
jaroslav@1890:      *
jaroslav@1890:      * @return an iterator over the elements in this deque in proper sequence
jaroslav@1890:      */
jaroslav@1890:     public Iterator<E> iterator() {
jaroslav@1890:         return new Itr();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an iterator over the elements in this deque in reverse
jaroslav@1890:      * sequential order.  The elements will be returned in order from
jaroslav@1890:      * last (tail) to first (head).
jaroslav@1890:      *
jaroslav@1890:      * <p>The returned iterator is a "weakly consistent" iterator that
jaroslav@1890:      * will never throw {@link java.util.ConcurrentModificationException
jaroslav@1890:      * ConcurrentModificationException}, and guarantees to traverse
jaroslav@1890:      * elements as they existed upon construction of the iterator, and
jaroslav@1890:      * may (but is not guaranteed to) reflect any modifications
jaroslav@1890:      * subsequent to construction.
jaroslav@1890:      *
jaroslav@1890:      * @return an iterator over the elements in this deque in reverse order
jaroslav@1890:      */
jaroslav@1890:     public Iterator<E> descendingIterator() {
jaroslav@1890:         return new DescendingItr();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Base class for Iterators for LinkedBlockingDeque
jaroslav@1890:      */
jaroslav@1890:     private abstract class AbstractItr implements Iterator<E> {
jaroslav@1890:         /**
jaroslav@1890:          * The next node to return in next()
jaroslav@1890:          */
jaroslav@1890:          Node<E> next;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * nextItem holds on to item fields because once we claim that
jaroslav@1890:          * an element exists in hasNext(), we must return item read
jaroslav@1890:          * under lock (in advance()) even if it was in the process of
jaroslav@1890:          * being removed when hasNext() was called.
jaroslav@1890:          */
jaroslav@1890:         E nextItem;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Node returned by most recent call to next. Needed by remove.
jaroslav@1890:          * Reset to null if this element is deleted by a call to remove.
jaroslav@1890:          */
jaroslav@1890:         private Node<E> lastRet;
jaroslav@1890: 
jaroslav@1890:         abstract Node<E> firstNode();
jaroslav@1890:         abstract Node<E> nextNode(Node<E> n);
jaroslav@1890: 
jaroslav@1890:         AbstractItr() {
jaroslav@1890:             // set to initial position
jaroslav@1890:             final ReentrantLock lock = LinkedBlockingDeque.this.lock;
jaroslav@1890:             lock.lock();
jaroslav@1890:             try {
jaroslav@1890:                 next = firstNode();
jaroslav@1890:                 nextItem = (next == null) ? null : next.item;
jaroslav@1890:             } finally {
jaroslav@1890:                 lock.unlock();
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Returns the successor node of the given non-null, but
jaroslav@1890:          * possibly previously deleted, node.
jaroslav@1890:          */
jaroslav@1890:         private Node<E> succ(Node<E> n) {
jaroslav@1890:             // Chains of deleted nodes ending in null or self-links
jaroslav@1890:             // are possible if multiple interior nodes are removed.
jaroslav@1890:             for (;;) {
jaroslav@1890:                 Node<E> s = nextNode(n);
jaroslav@1890:                 if (s == null)
jaroslav@1890:                     return null;
jaroslav@1890:                 else if (s.item != null)
jaroslav@1890:                     return s;
jaroslav@1890:                 else if (s == n)
jaroslav@1890:                     return firstNode();
jaroslav@1890:                 else
jaroslav@1890:                     n = s;
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Advances next.
jaroslav@1890:          */
jaroslav@1890:         void advance() {
jaroslav@1890:             final ReentrantLock lock = LinkedBlockingDeque.this.lock;
jaroslav@1890:             lock.lock();
jaroslav@1890:             try {
jaroslav@1890:                 // assert next != null;
jaroslav@1890:                 next = succ(next);
jaroslav@1890:                 nextItem = (next == null) ? null : next.item;
jaroslav@1890:             } finally {
jaroslav@1890:                 lock.unlock();
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         public boolean hasNext() {
jaroslav@1890:             return next != null;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         public E next() {
jaroslav@1890:             if (next == null)
jaroslav@1890:                 throw new NoSuchElementException();
jaroslav@1890:             lastRet = next;
jaroslav@1890:             E x = nextItem;
jaroslav@1890:             advance();
jaroslav@1890:             return x;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         public void remove() {
jaroslav@1890:             Node<E> n = lastRet;
jaroslav@1890:             if (n == null)
jaroslav@1890:                 throw new IllegalStateException();
jaroslav@1890:             lastRet = null;
jaroslav@1890:             final ReentrantLock lock = LinkedBlockingDeque.this.lock;
jaroslav@1890:             lock.lock();
jaroslav@1890:             try {
jaroslav@1890:                 if (n.item != null)
jaroslav@1890:                     unlink(n);
jaroslav@1890:             } finally {
jaroslav@1890:                 lock.unlock();
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /** Forward iterator */
jaroslav@1890:     private class Itr extends AbstractItr {
jaroslav@1890:         Node<E> firstNode() { return first; }
jaroslav@1890:         Node<E> nextNode(Node<E> n) { return n.next; }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /** Descending iterator */
jaroslav@1890:     private class DescendingItr extends AbstractItr {
jaroslav@1890:         Node<E> firstNode() { return last; }
jaroslav@1890:         Node<E> nextNode(Node<E> n) { return n.prev; }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Save the state of this deque to a stream (that is, serialize it).
jaroslav@1890:      *
jaroslav@1890:      * @serialData The capacity (int), followed by elements (each an
jaroslav@1890:      * {@code Object}) in the proper order, followed by a null
jaroslav@1890:      * @param s the stream
jaroslav@1890:      */
jaroslav@1890:     private void writeObject(java.io.ObjectOutputStream s)
jaroslav@1890:         throws java.io.IOException {
jaroslav@1890:         final ReentrantLock lock = this.lock;
jaroslav@1890:         lock.lock();
jaroslav@1890:         try {
jaroslav@1890:             // Write out capacity and any hidden stuff
jaroslav@1890:             s.defaultWriteObject();
jaroslav@1890:             // Write out all elements in the proper order.
jaroslav@1890:             for (Node<E> p = first; p != null; p = p.next)
jaroslav@1890:                 s.writeObject(p.item);
jaroslav@1890:             // Use trailing null as sentinel
jaroslav@1890:             s.writeObject(null);
jaroslav@1890:         } finally {
jaroslav@1890:             lock.unlock();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Reconstitute this deque from a stream (that is,
jaroslav@1890:      * deserialize it).
jaroslav@1890:      * @param s the stream
jaroslav@1890:      */
jaroslav@1890:     private void readObject(java.io.ObjectInputStream s)
jaroslav@1890:         throws java.io.IOException, ClassNotFoundException {
jaroslav@1890:         s.defaultReadObject();
jaroslav@1890:         count = 0;
jaroslav@1890:         first = null;
jaroslav@1890:         last = null;
jaroslav@1890:         // Read in all elements and place in queue
jaroslav@1890:         for (;;) {
jaroslav@1890:             @SuppressWarnings("unchecked")
jaroslav@1890:             E item = (E)s.readObject();
jaroslav@1890:             if (item == null)
jaroslav@1890:                 break;
jaroslav@1890:             add(item);
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: }