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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package jsr166x; |
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|
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import java.util.*; |
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import java.util.concurrent.*; |
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import java.util.concurrent.locks.*; |
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|
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/** |
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* An optionally-bounded {@linkplain BlockingDeque blocking deque} based on |
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* linked nodes. |
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* |
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* <p>The optional capacity bound constructor argument serves as a |
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* way to prevent excessive expansion. The capacity, if unspecified, |
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* is equal to {@link Integer#MAX_VALUE}. Linked nodes are |
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* dynamically created upon each insertion unless this would bring the |
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* deque above capacity. |
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* |
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* <p>Most operations run in constant time (ignoring time spent |
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* blocking). Exceptions include {@link #remove(Object) remove}, |
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* {@link #removeFirstOccurrence removeFirstOccurrence}, {@link |
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* #removeLastOccurrence removeLastOccurrence}, {@link #contains |
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* contains }, {@link #iterator iterator.remove()}, and the bulk |
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* operations, all of which run in linear time. |
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* |
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* <p>This class and its iterator implement all of the |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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* Iterator} interfaces. This class is a member of the <a |
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* href="{@docRoot}/../guide/collections/index.html"> Java Collections |
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* Framework</a>. |
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* |
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* @since 1.6 |
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* @author Doug Lea |
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* @param <E> the type of elements held in this collection |
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*/ |
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public class LinkedBlockingDeque<E> |
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extends AbstractQueue<E> |
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implements BlockingDeque<E>, java.io.Serializable { |
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|
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/* |
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* Implemented as a simple doubly-linked list protected by a |
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* single lock and using conditions to manage blocking. |
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*/ |
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|
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private static final long serialVersionUID = -387911632671998426L; |
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|
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/** Doubly-linked list node class */ |
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static final class Node<E> { |
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E item; |
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Node<E> prev; |
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Node<E> next; |
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Node(E x, Node<E> p, Node<E> n) { |
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item = x; |
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prev = p; |
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next = n; |
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} |
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} |
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|
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/** Pointer to first node */ |
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private transient Node<E> first; |
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/** Pointer to last node */ |
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private transient Node<E> last; |
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/** Number of items in the deque */ |
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private transient int count; |
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/** Maximum number of items in the deque */ |
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private final int capacity; |
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/** Main lock guarding all access */ |
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private final ReentrantLock lock = new ReentrantLock(); |
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/** Condition for waiting takes */ |
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private final Condition notEmpty = lock.newCondition(); |
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/** Condition for waiting puts */ |
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private final Condition notFull = lock.newCondition(); |
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|
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/** |
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* Creates a {@code LinkedBlockingDeque} with a capacity of |
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* {@link Integer#MAX_VALUE}. |
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*/ |
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public LinkedBlockingDeque() { |
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this(Integer.MAX_VALUE); |
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} |
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|
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/** |
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* Creates a {@code LinkedBlockingDeque} with the given (fixed) |
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* capacity. |
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* @param capacity the capacity of this deque |
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* @throws IllegalArgumentException if {@code capacity} is less than 1 |
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*/ |
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public LinkedBlockingDeque(int capacity) { |
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if (capacity <= 0) throw new IllegalArgumentException(); |
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this.capacity = capacity; |
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} |
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|
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/** |
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* Creates a {@code LinkedBlockingDeque} with a capacity of |
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* {@link Integer#MAX_VALUE}, initially containing the elements of the |
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* given collection, |
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* added in traversal order of the collection's iterator. |
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* @param c the collection of elements to initially contain |
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* @throws NullPointerException if {@code c} or any element within it |
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* is {@code null} |
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*/ |
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public LinkedBlockingDeque(Collection<? extends E> c) { |
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this(Integer.MAX_VALUE); |
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for (E e : c) |
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add(e); |
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} |
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|
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|
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// Basic linking and unlinking operations, called only while holding lock |
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|
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/** |
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* Links e as first element, or returns false if full. |
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*/ |
118 |
private boolean linkFirst(E e) { |
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if (count >= capacity) |
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return false; |
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++count; |
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Node<E> f = first; |
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Node<E> x = new Node<E>(e, null, f); |
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first = x; |
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if (last == null) |
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last = x; |
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else |
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f.prev = x; |
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notEmpty.signal(); |
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return true; |
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} |
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|
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/** |
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* Links e as last element, or returns false if full. |
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*/ |
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private boolean linkLast(E e) { |
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if (count >= capacity) |
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return false; |
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++count; |
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Node<E> l = last; |
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Node<E> x = new Node<E>(e, l, null); |
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last = x; |
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if (first == null) |
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first = x; |
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else |
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l.next = x; |
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notEmpty.signal(); |
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return true; |
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} |
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|
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/** |
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* Removes and returns first element, or null if empty. |
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*/ |
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private E unlinkFirst() { |
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Node<E> f = first; |
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if (f == null) |
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return null; |
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Node<E> n = f.next; |
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first = n; |
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if (n == null) |
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last = null; |
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else |
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n.prev = null; |
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--count; |
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notFull.signal(); |
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return f.item; |
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} |
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|
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/** |
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* Removes and returns last element, or null if empty. |
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*/ |
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private E unlinkLast() { |
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Node<E> l = last; |
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if (l == null) |
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return null; |
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Node<E> p = l.prev; |
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last = p; |
178 |
if (p == null) |
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first = null; |
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else |
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p.next = null; |
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--count; |
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notFull.signal(); |
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return l.item; |
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} |
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|
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/** |
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* Unlink e |
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*/ |
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private void unlink(Node<E> x) { |
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Node<E> p = x.prev; |
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Node<E> n = x.next; |
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if (p == null) { |
194 |
if (n == null) |
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first = last = null; |
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else { |
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n.prev = null; |
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first = n; |
199 |
} |
200 |
} else if (n == null) { |
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p.next = null; |
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last = p; |
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} else { |
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p.next = n; |
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n.prev = p; |
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} |
207 |
--count; |
208 |
notFull.signalAll(); |
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} |
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|
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// Deque methods |
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|
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public boolean offerFirst(E o) { |
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if (o == null) throw new NullPointerException(); |
215 |
lock.lock(); |
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try { |
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return linkFirst(o); |
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} finally { |
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lock.unlock(); |
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} |
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} |
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|
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public boolean offerLast(E o) { |
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if (o == null) throw new NullPointerException(); |
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lock.lock(); |
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try { |
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return linkLast(o); |
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} finally { |
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lock.unlock(); |
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} |
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} |
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|
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public void addFirst(E e) { |
234 |
if (!offerFirst(e)) |
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throw new IllegalStateException("Deque full"); |
236 |
} |
237 |
|
238 |
public void addLast(E e) { |
239 |
if (!offerLast(e)) |
240 |
throw new IllegalStateException("Deque full"); |
241 |
} |
242 |
|
243 |
public E pollFirst() { |
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lock.lock(); |
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try { |
246 |
return unlinkFirst(); |
247 |
} finally { |
248 |
lock.unlock(); |
249 |
} |
250 |
} |
251 |
|
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public E pollLast() { |
253 |
lock.lock(); |
254 |
try { |
255 |
return unlinkLast(); |
256 |
} finally { |
257 |
lock.unlock(); |
258 |
} |
259 |
} |
260 |
|
261 |
public E removeFirst() { |
262 |
E x = pollFirst(); |
263 |
if (x == null) throw new NoSuchElementException(); |
264 |
return x; |
265 |
} |
266 |
|
267 |
public E removeLast() { |
268 |
E x = pollLast(); |
269 |
if (x == null) throw new NoSuchElementException(); |
270 |
return x; |
271 |
} |
272 |
|
273 |
public E peekFirst() { |
274 |
lock.lock(); |
275 |
try { |
276 |
return (first == null) ? null : first.item; |
277 |
} finally { |
278 |
lock.unlock(); |
279 |
} |
280 |
} |
281 |
|
282 |
public E peekLast() { |
283 |
lock.lock(); |
284 |
try { |
285 |
return (last == null) ? null : last.item; |
286 |
} finally { |
287 |
lock.unlock(); |
288 |
} |
289 |
} |
290 |
|
291 |
public E getFirst() { |
292 |
E x = peekFirst(); |
293 |
if (x == null) throw new NoSuchElementException(); |
294 |
return x; |
295 |
} |
296 |
|
297 |
public E getLast() { |
298 |
E x = peekLast(); |
299 |
if (x == null) throw new NoSuchElementException(); |
300 |
return x; |
301 |
} |
302 |
|
303 |
// BlockingDeque methods |
304 |
|
305 |
public void putFirst(E o) throws InterruptedException { |
306 |
if (o == null) throw new NullPointerException(); |
307 |
lock.lock(); |
308 |
try { |
309 |
while (!linkFirst(o)) |
310 |
notFull.await(); |
311 |
} finally { |
312 |
lock.unlock(); |
313 |
} |
314 |
} |
315 |
|
316 |
public void putLast(E o) throws InterruptedException { |
317 |
if (o == null) throw new NullPointerException(); |
318 |
lock.lock(); |
319 |
try { |
320 |
while (!linkLast(o)) |
321 |
notFull.await(); |
322 |
} finally { |
323 |
lock.unlock(); |
324 |
} |
325 |
} |
326 |
|
327 |
public E takeFirst() throws InterruptedException { |
328 |
lock.lock(); |
329 |
try { |
330 |
E x; |
331 |
while ( (x = unlinkFirst()) == null) |
332 |
notEmpty.await(); |
333 |
return x; |
334 |
} finally { |
335 |
lock.unlock(); |
336 |
} |
337 |
} |
338 |
|
339 |
public E takeLast() throws InterruptedException { |
340 |
lock.lock(); |
341 |
try { |
342 |
E x; |
343 |
while ( (x = unlinkLast()) == null) |
344 |
notEmpty.await(); |
345 |
return x; |
346 |
} finally { |
347 |
lock.unlock(); |
348 |
} |
349 |
} |
350 |
|
351 |
public boolean offerFirst(E o, long timeout, TimeUnit unit) |
352 |
throws InterruptedException { |
353 |
if (o == null) throw new NullPointerException(); |
354 |
lock.lockInterruptibly(); |
355 |
try { |
356 |
long nanos = unit.toNanos(timeout); |
357 |
for (;;) { |
358 |
if (linkFirst(o)) |
359 |
return true; |
360 |
if (nanos <= 0) |
361 |
return false; |
362 |
nanos = notFull.awaitNanos(nanos); |
363 |
} |
364 |
} finally { |
365 |
lock.unlock(); |
366 |
} |
367 |
} |
368 |
|
369 |
public boolean offerLast(E o, long timeout, TimeUnit unit) |
370 |
throws InterruptedException { |
371 |
if (o == null) throw new NullPointerException(); |
372 |
lock.lockInterruptibly(); |
373 |
try { |
374 |
long nanos = unit.toNanos(timeout); |
375 |
for (;;) { |
376 |
if (linkLast(o)) |
377 |
return true; |
378 |
if (nanos <= 0) |
379 |
return false; |
380 |
nanos = notFull.awaitNanos(nanos); |
381 |
} |
382 |
} finally { |
383 |
lock.unlock(); |
384 |
} |
385 |
} |
386 |
|
387 |
public E pollFirst(long timeout, TimeUnit unit) |
388 |
throws InterruptedException { |
389 |
lock.lockInterruptibly(); |
390 |
try { |
391 |
long nanos = unit.toNanos(timeout); |
392 |
for (;;) { |
393 |
E x = unlinkFirst(); |
394 |
if (x != null) |
395 |
return x; |
396 |
if (nanos <= 0) |
397 |
return null; |
398 |
nanos = notEmpty.awaitNanos(nanos); |
399 |
} |
400 |
} finally { |
401 |
lock.unlock(); |
402 |
} |
403 |
} |
404 |
|
405 |
public E pollLast(long timeout, TimeUnit unit) |
406 |
throws InterruptedException { |
407 |
lock.lockInterruptibly(); |
408 |
try { |
409 |
long nanos = unit.toNanos(timeout); |
410 |
for (;;) { |
411 |
E x = unlinkLast(); |
412 |
if (x != null) |
413 |
return x; |
414 |
if (nanos <= 0) |
415 |
return null; |
416 |
nanos = notEmpty.awaitNanos(nanos); |
417 |
} |
418 |
} finally { |
419 |
lock.unlock(); |
420 |
} |
421 |
} |
422 |
|
423 |
// Queue and stack methods |
424 |
|
425 |
public boolean offer(E e) { return offerLast(e); } |
426 |
public boolean add(E e) { addLast(e); return true; } |
427 |
public void push(E e) { addFirst(e); } |
428 |
public E poll() { return pollFirst(); } |
429 |
public E remove() { return removeFirst(); } |
430 |
public E pop() { return removeFirst(); } |
431 |
public E peek() { return peekFirst(); } |
432 |
public E element() { return getFirst(); } |
433 |
public boolean remove(Object o) { return removeFirstOccurrence(o); } |
434 |
|
435 |
// BlockingQueue methods |
436 |
|
437 |
public void put(E o) throws InterruptedException { putLast(o); } |
438 |
public E take() throws InterruptedException { return takeFirst(); } |
439 |
public boolean offer(E o, long timeout, TimeUnit unit) |
440 |
throws InterruptedException { return offerLast(o, timeout, unit); } |
441 |
public E poll(long timeout, TimeUnit unit) |
442 |
throws InterruptedException { return pollFirst(timeout, unit); } |
443 |
|
444 |
/** |
445 |
* Returns the number of elements in this deque. |
446 |
* |
447 |
* @return the number of elements in this deque |
448 |
*/ |
449 |
public int size() { |
450 |
lock.lock(); |
451 |
try { |
452 |
return count; |
453 |
} finally { |
454 |
lock.unlock(); |
455 |
} |
456 |
} |
457 |
|
458 |
/** |
459 |
* Returns the number of elements that this deque can ideally (in |
460 |
* the absence of memory or resource constraints) accept without |
461 |
* blocking. This is always equal to the initial capacity of this deque |
462 |
* less the current {@code size} of this deque. |
463 |
* <p>Note that you <em>cannot</em> always tell if |
464 |
* an attempt to {@code add} an element will succeed by |
465 |
* inspecting {@code remainingCapacity} because it may be the |
466 |
* case that a waiting consumer is ready to {@code take} an |
467 |
* element out of an otherwise full deque. |
468 |
*/ |
469 |
public int remainingCapacity() { |
470 |
lock.lock(); |
471 |
try { |
472 |
return capacity - count; |
473 |
} finally { |
474 |
lock.unlock(); |
475 |
} |
476 |
} |
477 |
|
478 |
public boolean contains(Object o) { |
479 |
if (o == null) return false; |
480 |
lock.lock(); |
481 |
try { |
482 |
for (Node<E> p = first; p != null; p = p.next) |
483 |
if (o.equals(p.item)) |
484 |
return true; |
485 |
return false; |
486 |
} finally { |
487 |
lock.unlock(); |
488 |
} |
489 |
} |
490 |
|
491 |
public boolean removeFirstOccurrence(Object e) { |
492 |
if (e == null) throw new NullPointerException(); |
493 |
lock.lock(); |
494 |
try { |
495 |
for (Node<E> p = first; p != null; p = p.next) { |
496 |
if (e.equals(p.item)) { |
497 |
unlink(p); |
498 |
return true; |
499 |
} |
500 |
} |
501 |
return false; |
502 |
} finally { |
503 |
lock.unlock(); |
504 |
} |
505 |
} |
506 |
|
507 |
public boolean removeLastOccurrence(Object e) { |
508 |
if (e == null) throw new NullPointerException(); |
509 |
lock.lock(); |
510 |
try { |
511 |
for (Node<E> p = last; p != null; p = p.prev) { |
512 |
if (e.equals(p.item)) { |
513 |
unlink(p); |
514 |
return true; |
515 |
} |
516 |
} |
517 |
return false; |
518 |
} finally { |
519 |
lock.unlock(); |
520 |
} |
521 |
} |
522 |
|
523 |
/** |
524 |
* Variant of removeFirstOccurrence needed by iterator.remove. |
525 |
* Searches for the node, not its contents. |
526 |
*/ |
527 |
boolean removeNode(Node<E> e) { |
528 |
lock.lock(); |
529 |
try { |
530 |
for (Node<E> p = first; p != null; p = p.next) { |
531 |
if (p == e) { |
532 |
unlink(p); |
533 |
return true; |
534 |
} |
535 |
} |
536 |
return false; |
537 |
} finally { |
538 |
lock.unlock(); |
539 |
} |
540 |
} |
541 |
|
542 |
public Object[] toArray() { |
543 |
lock.lock(); |
544 |
try { |
545 |
Object[] a = new Object[count]; |
546 |
int k = 0; |
547 |
for (Node<E> p = first; p != null; p = p.next) |
548 |
a[k++] = p.item; |
549 |
return a; |
550 |
} finally { |
551 |
lock.unlock(); |
552 |
} |
553 |
} |
554 |
|
555 |
public <T> T[] toArray(T[] a) { |
556 |
lock.lock(); |
557 |
try { |
558 |
if (a.length < count) |
559 |
a = (T[])java.lang.reflect.Array.newInstance( |
560 |
a.getClass().getComponentType(), |
561 |
count |
562 |
); |
563 |
|
564 |
int k = 0; |
565 |
for (Node<E> p = first; p != null; p = p.next) |
566 |
a[k++] = (T)p.item; |
567 |
if (a.length > k) |
568 |
a[k] = null; |
569 |
return a; |
570 |
} finally { |
571 |
lock.unlock(); |
572 |
} |
573 |
} |
574 |
|
575 |
public String toString() { |
576 |
lock.lock(); |
577 |
try { |
578 |
return super.toString(); |
579 |
} finally { |
580 |
lock.unlock(); |
581 |
} |
582 |
} |
583 |
|
584 |
/** |
585 |
* Atomically removes all of the elements from this deque. |
586 |
* The deque will be empty after this call returns. |
587 |
*/ |
588 |
public void clear() { |
589 |
lock.lock(); |
590 |
try { |
591 |
first = last = null; |
592 |
count = 0; |
593 |
notFull.signalAll(); |
594 |
} finally { |
595 |
lock.unlock(); |
596 |
} |
597 |
} |
598 |
|
599 |
public int drainTo(Collection<? super E> c) { |
600 |
if (c == null) |
601 |
throw new NullPointerException(); |
602 |
if (c == this) |
603 |
throw new IllegalArgumentException(); |
604 |
lock.lock(); |
605 |
try { |
606 |
for (Node<E> p = first; p != null; p = p.next) |
607 |
c.add(p.item); |
608 |
int n = count; |
609 |
count = 0; |
610 |
first = last = null; |
611 |
notFull.signalAll(); |
612 |
return n; |
613 |
} finally { |
614 |
lock.unlock(); |
615 |
} |
616 |
} |
617 |
|
618 |
public int drainTo(Collection<? super E> c, int maxElements) { |
619 |
if (c == null) |
620 |
throw new NullPointerException(); |
621 |
if (c == this) |
622 |
throw new IllegalArgumentException(); |
623 |
lock.lock(); |
624 |
try { |
625 |
int n = 0; |
626 |
while (n < maxElements && first != null) { |
627 |
c.add(first.item); |
628 |
first.prev = null; |
629 |
first = first.next; |
630 |
--count; |
631 |
++n; |
632 |
} |
633 |
if (first == null) |
634 |
last = null; |
635 |
notFull.signalAll(); |
636 |
return n; |
637 |
} finally { |
638 |
lock.unlock(); |
639 |
} |
640 |
} |
641 |
|
642 |
/** |
643 |
* Returns an iterator over the elements in this deque in proper sequence. |
644 |
* The returned {@code Iterator} is a "weakly consistent" iterator that |
645 |
* will never throw {@link java.util.ConcurrentModificationException}, |
646 |
* and guarantees to traverse elements as they existed upon |
647 |
* construction of the iterator, and may (but is not guaranteed to) |
648 |
* reflect any modifications subsequent to construction. |
649 |
* |
650 |
* @return an iterator over the elements in this deque in proper sequence |
651 |
*/ |
652 |
public Iterator<E> iterator() { |
653 |
return new Itr(); |
654 |
} |
655 |
|
656 |
/** |
657 |
* Iterator for LinkedBlockingDeque |
658 |
*/ |
659 |
private class Itr implements Iterator<E> { |
660 |
private Node<E> next; |
661 |
|
662 |
/** |
663 |
* nextItem holds on to item fields because once we claim that |
664 |
* an element exists in hasNext(), we must return item read |
665 |
* under lock (in advance()) even if it was in the process of |
666 |
* being removed when hasNext() was called. |
667 |
*/ |
668 |
private E nextItem; |
669 |
|
670 |
/** |
671 |
* Node returned by most recent call to next. Needed by remove. |
672 |
* Reset to null if this element is deleted by a call to remove. |
673 |
*/ |
674 |
private Node<E> last; |
675 |
|
676 |
Itr() { |
677 |
advance(); |
678 |
} |
679 |
|
680 |
/** |
681 |
* Advance next, or if not yet initialized, set to first node. |
682 |
*/ |
683 |
private void advance() { |
684 |
final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
685 |
lock.lock(); |
686 |
try { |
687 |
next = (next == null) ? first : next.next; |
688 |
nextItem = (next == null) ? null : next.item; |
689 |
} finally { |
690 |
lock.unlock(); |
691 |
} |
692 |
} |
693 |
|
694 |
public boolean hasNext() { |
695 |
return next != null; |
696 |
} |
697 |
|
698 |
public E next() { |
699 |
if (next == null) |
700 |
throw new NoSuchElementException(); |
701 |
last = next; |
702 |
E x = nextItem; |
703 |
advance(); |
704 |
return x; |
705 |
} |
706 |
|
707 |
public void remove() { |
708 |
Node<E> n = last; |
709 |
if (n == null) |
710 |
throw new IllegalStateException(); |
711 |
last = null; |
712 |
// Note: removeNode rescans looking for this node to make |
713 |
// sure it was not already removed. Otherwwise, trying to |
714 |
// re-remove could corrupt list. |
715 |
removeNode(n); |
716 |
} |
717 |
} |
718 |
|
719 |
/** |
720 |
* Saves the state to a stream (that is, serializes it). |
721 |
* |
722 |
* @serialData The capacity (int), followed by elements (each an |
723 |
* {@code Object}) in the proper order, followed by a null |
724 |
* @param s the stream |
725 |
*/ |
726 |
private void writeObject(java.io.ObjectOutputStream s) |
727 |
throws java.io.IOException { |
728 |
lock.lock(); |
729 |
try { |
730 |
// Write out capacity and any hidden stuff |
731 |
s.defaultWriteObject(); |
732 |
// Write out all elements in the proper order. |
733 |
for (Node<E> p = first; p != null; p = p.next) |
734 |
s.writeObject(p.item); |
735 |
// Use trailing null as sentinel |
736 |
s.writeObject(null); |
737 |
} finally { |
738 |
lock.unlock(); |
739 |
} |
740 |
} |
741 |
|
742 |
/** |
743 |
* Reconstitutes this deque instance from a stream (that is, |
744 |
* deserializes it). |
745 |
* @param s the stream |
746 |
*/ |
747 |
private void readObject(java.io.ObjectInputStream s) |
748 |
throws java.io.IOException, ClassNotFoundException { |
749 |
s.defaultReadObject(); |
750 |
count = 0; |
751 |
first = null; |
752 |
last = null; |
753 |
// Read in all elements and place in queue |
754 |
for (;;) { |
755 |
E item = (E)s.readObject(); |
756 |
if (item == null) |
757 |
break; |
758 |
add(item); |
759 |
} |
760 |
} |
761 |
|
762 |
} |