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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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|
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package java.util.concurrent; |
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import java.util.*; |
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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 <tt>LinkedBlockingDeque</tt> with a capacity of |
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* {@link Integer#MAX_VALUE}. |
79 |
*/ |
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public LinkedBlockingDeque() { |
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this(Integer.MAX_VALUE); |
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} |
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|
84 |
/** |
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* Creates a <tt>LinkedBlockingDeque</tt> 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 <tt>capacity</tt> 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 <tt>LinkedBlockingDeque</tt> 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 <tt>c</tt> or any element within it |
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* is <tt>null</tt>. |
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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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*/ |
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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; |
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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) { |
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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; |
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} |
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} 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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} |
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--count; |
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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(); |
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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) { |
232 |
if (!offerFirst(e)) |
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throw new IllegalStateException("Deque full"); |
234 |
} |
235 |
|
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public void addLast(E e) { |
237 |
if (!offerLast(e)) |
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throw new IllegalStateException("Deque full"); |
239 |
} |
240 |
|
241 |
public E pollFirst() { |
242 |
lock.lock(); |
243 |
try { |
244 |
return unlinkFirst(); |
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} finally { |
246 |
lock.unlock(); |
247 |
} |
248 |
} |
249 |
|
250 |
public E pollLast() { |
251 |
lock.lock(); |
252 |
try { |
253 |
return unlinkLast(); |
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} finally { |
255 |
lock.unlock(); |
256 |
} |
257 |
} |
258 |
|
259 |
public E removeFirst() { |
260 |
E x = pollFirst(); |
261 |
if (x == null) throw new NoSuchElementException(); |
262 |
return x; |
263 |
} |
264 |
|
265 |
public E removeLast() { |
266 |
E x = pollLast(); |
267 |
if (x == null) throw new NoSuchElementException(); |
268 |
return x; |
269 |
} |
270 |
|
271 |
public E peekFirst() { |
272 |
lock.lock(); |
273 |
try { |
274 |
return (first == null) ? null : first.item; |
275 |
} finally { |
276 |
lock.unlock(); |
277 |
} |
278 |
} |
279 |
|
280 |
public E peekLast() { |
281 |
lock.lock(); |
282 |
try { |
283 |
return (last == null) ? null : last.item; |
284 |
} finally { |
285 |
lock.unlock(); |
286 |
} |
287 |
} |
288 |
|
289 |
public E getFirst() { |
290 |
E x = peekFirst(); |
291 |
if (x == null) throw new NoSuchElementException(); |
292 |
return x; |
293 |
} |
294 |
|
295 |
public E getLast() { |
296 |
E x = peekLast(); |
297 |
if (x == null) throw new NoSuchElementException(); |
298 |
return x; |
299 |
} |
300 |
|
301 |
// BlockingDeque methods |
302 |
|
303 |
public void putFirst(E o) throws InterruptedException { |
304 |
if (o == null) throw new NullPointerException(); |
305 |
lock.lock(); |
306 |
try { |
307 |
while (!linkFirst(o)) |
308 |
notFull.await(); |
309 |
} finally { |
310 |
lock.unlock(); |
311 |
} |
312 |
} |
313 |
|
314 |
public void putLast(E o) throws InterruptedException { |
315 |
if (o == null) throw new NullPointerException(); |
316 |
lock.lock(); |
317 |
try { |
318 |
while (!linkLast(o)) |
319 |
notFull.await(); |
320 |
} finally { |
321 |
lock.unlock(); |
322 |
} |
323 |
} |
324 |
|
325 |
public E takeFirst() throws InterruptedException { |
326 |
lock.lock(); |
327 |
try { |
328 |
E x; |
329 |
while ( (x = unlinkFirst()) == null) |
330 |
notEmpty.await(); |
331 |
return x; |
332 |
} finally { |
333 |
lock.unlock(); |
334 |
} |
335 |
} |
336 |
|
337 |
public E takeLast() throws InterruptedException { |
338 |
lock.lock(); |
339 |
try { |
340 |
E x; |
341 |
while ( (x = unlinkLast()) == null) |
342 |
notEmpty.await(); |
343 |
return x; |
344 |
} finally { |
345 |
lock.unlock(); |
346 |
} |
347 |
} |
348 |
|
349 |
public boolean offerFirst(E o, long timeout, TimeUnit unit) |
350 |
throws InterruptedException { |
351 |
if (o == null) throw new NullPointerException(); |
352 |
lock.lockInterruptibly(); |
353 |
try { |
354 |
long nanos = unit.toNanos(timeout); |
355 |
for (;;) { |
356 |
if (linkFirst(o)) |
357 |
return true; |
358 |
if (nanos <= 0) |
359 |
return false; |
360 |
nanos = notFull.awaitNanos(nanos); |
361 |
} |
362 |
} finally { |
363 |
lock.unlock(); |
364 |
} |
365 |
} |
366 |
|
367 |
public boolean offerLast(E o, long timeout, TimeUnit unit) |
368 |
throws InterruptedException { |
369 |
if (o == null) throw new NullPointerException(); |
370 |
lock.lockInterruptibly(); |
371 |
try { |
372 |
long nanos = unit.toNanos(timeout); |
373 |
for (;;) { |
374 |
if (linkLast(o)) |
375 |
return true; |
376 |
if (nanos <= 0) |
377 |
return false; |
378 |
nanos = notFull.awaitNanos(nanos); |
379 |
} |
380 |
} finally { |
381 |
lock.unlock(); |
382 |
} |
383 |
} |
384 |
|
385 |
public E pollFirst(long timeout, TimeUnit unit) |
386 |
throws InterruptedException { |
387 |
lock.lockInterruptibly(); |
388 |
try { |
389 |
long nanos = unit.toNanos(timeout); |
390 |
for (;;) { |
391 |
E x = unlinkFirst(); |
392 |
if (x != null) |
393 |
return x; |
394 |
if (nanos <= 0) |
395 |
return null; |
396 |
nanos = notEmpty.awaitNanos(nanos); |
397 |
} |
398 |
} finally { |
399 |
lock.unlock(); |
400 |
} |
401 |
} |
402 |
|
403 |
public E pollLast(long timeout, TimeUnit unit) |
404 |
throws InterruptedException { |
405 |
lock.lockInterruptibly(); |
406 |
try { |
407 |
long nanos = unit.toNanos(timeout); |
408 |
for (;;) { |
409 |
E x = unlinkLast(); |
410 |
if (x != null) |
411 |
return x; |
412 |
if (nanos <= 0) |
413 |
return null; |
414 |
nanos = notEmpty.awaitNanos(nanos); |
415 |
} |
416 |
} finally { |
417 |
lock.unlock(); |
418 |
} |
419 |
} |
420 |
|
421 |
// Queue and stack methods |
422 |
|
423 |
public boolean offer(E e) { return offerLast(e); } |
424 |
public boolean add(E e) { addLast(e); return true; } |
425 |
public void push(E e) { addFirst(e); } |
426 |
public E poll() { return pollFirst(); } |
427 |
public E remove() { return removeFirst(); } |
428 |
public E pop() { return removeFirst(); } |
429 |
public E peek() { return peekFirst(); } |
430 |
public E element() { return getFirst(); } |
431 |
public boolean remove(Object o) { return removeFirstOccurrence(o); } |
432 |
|
433 |
// BlockingQueue methods |
434 |
|
435 |
public void put(E o) throws InterruptedException { putLast(o); } |
436 |
public E take() throws InterruptedException { return takeFirst(); } |
437 |
public boolean offer(E o, long timeout, TimeUnit unit) |
438 |
throws InterruptedException { return offerLast(o, timeout, unit); } |
439 |
public E poll(long timeout, TimeUnit unit) |
440 |
throws InterruptedException { return pollFirst(timeout, unit); } |
441 |
|
442 |
/** |
443 |
* Returns the number of elements in this deque. |
444 |
* |
445 |
* @return the number of elements in this deque. |
446 |
*/ |
447 |
public int size() { |
448 |
lock.lock(); |
449 |
try { |
450 |
return count; |
451 |
} finally { |
452 |
lock.unlock(); |
453 |
} |
454 |
} |
455 |
|
456 |
/** |
457 |
* Returns the number of additional elements that this deque can ideally |
458 |
* (in the absence of memory or resource constraints) accept without |
459 |
* blocking. This is always equal to the initial capacity of this deque |
460 |
* less the current <tt>size</tt> of this deque. |
461 |
* |
462 |
* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
463 |
* an element will succeed by inspecting <tt>remainingCapacity</tt> |
464 |
* because it may be the case that another thread is about to |
465 |
* <tt>put</tt> or <tt>take</tt> an element. |
466 |
*/ |
467 |
public int remainingCapacity() { |
468 |
lock.lock(); |
469 |
try { |
470 |
return capacity - count; |
471 |
} finally { |
472 |
lock.unlock(); |
473 |
} |
474 |
} |
475 |
|
476 |
public boolean contains(Object o) { |
477 |
if (o == null) return false; |
478 |
lock.lock(); |
479 |
try { |
480 |
for (Node<E> p = first; p != null; p = p.next) |
481 |
if (o.equals(p.item)) |
482 |
return true; |
483 |
return false; |
484 |
} finally { |
485 |
lock.unlock(); |
486 |
} |
487 |
} |
488 |
|
489 |
public boolean removeFirstOccurrence(Object e) { |
490 |
if (e == null) throw new NullPointerException(); |
491 |
lock.lock(); |
492 |
try { |
493 |
for (Node<E> p = first; p != null; p = p.next) { |
494 |
if (e.equals(p.item)) { |
495 |
unlink(p); |
496 |
return true; |
497 |
} |
498 |
} |
499 |
return false; |
500 |
} finally { |
501 |
lock.unlock(); |
502 |
} |
503 |
} |
504 |
|
505 |
public boolean removeLastOccurrence(Object e) { |
506 |
if (e == null) throw new NullPointerException(); |
507 |
lock.lock(); |
508 |
try { |
509 |
for (Node<E> p = last; p != null; p = p.prev) { |
510 |
if (e.equals(p.item)) { |
511 |
unlink(p); |
512 |
return true; |
513 |
} |
514 |
} |
515 |
return false; |
516 |
} finally { |
517 |
lock.unlock(); |
518 |
} |
519 |
} |
520 |
|
521 |
/** |
522 |
* Variant of removeFirstOccurrence needed by iterator.remove. |
523 |
* Searches for the node, not its contents. |
524 |
*/ |
525 |
boolean removeNode(Node<E> e) { |
526 |
lock.lock(); |
527 |
try { |
528 |
for (Node<E> p = first; p != null; p = p.next) { |
529 |
if (p == e) { |
530 |
unlink(p); |
531 |
return true; |
532 |
} |
533 |
} |
534 |
return false; |
535 |
} finally { |
536 |
lock.unlock(); |
537 |
} |
538 |
} |
539 |
|
540 |
public Object[] toArray() { |
541 |
lock.lock(); |
542 |
try { |
543 |
Object[] a = new Object[count]; |
544 |
int k = 0; |
545 |
for (Node<E> p = first; p != null; p = p.next) |
546 |
a[k++] = p.item; |
547 |
return a; |
548 |
} finally { |
549 |
lock.unlock(); |
550 |
} |
551 |
} |
552 |
|
553 |
public <T> T[] toArray(T[] a) { |
554 |
lock.lock(); |
555 |
try { |
556 |
if (a.length < count) |
557 |
a = (T[])java.lang.reflect.Array.newInstance( |
558 |
a.getClass().getComponentType(), |
559 |
count |
560 |
); |
561 |
|
562 |
int k = 0; |
563 |
for (Node<E> p = first; p != null; p = p.next) |
564 |
a[k++] = (T)p.item; |
565 |
if (a.length > k) |
566 |
a[k] = null; |
567 |
return a; |
568 |
} finally { |
569 |
lock.unlock(); |
570 |
} |
571 |
} |
572 |
|
573 |
public String toString() { |
574 |
lock.lock(); |
575 |
try { |
576 |
return super.toString(); |
577 |
} finally { |
578 |
lock.unlock(); |
579 |
} |
580 |
} |
581 |
|
582 |
/** |
583 |
* Atomically removes all of the elements from this deque. |
584 |
* The deque will be empty after this call returns. |
585 |
*/ |
586 |
public void clear() { |
587 |
lock.lock(); |
588 |
try { |
589 |
first = last = null; |
590 |
count = 0; |
591 |
notFull.signalAll(); |
592 |
} finally { |
593 |
lock.unlock(); |
594 |
} |
595 |
} |
596 |
|
597 |
public int drainTo(Collection<? super E> c) { |
598 |
if (c == null) |
599 |
throw new NullPointerException(); |
600 |
if (c == this) |
601 |
throw new IllegalArgumentException(); |
602 |
lock.lock(); |
603 |
try { |
604 |
for (Node<E> p = first; p != null; p = p.next) |
605 |
c.add(p.item); |
606 |
int n = count; |
607 |
count = 0; |
608 |
first = last = null; |
609 |
notFull.signalAll(); |
610 |
return n; |
611 |
} finally { |
612 |
lock.unlock(); |
613 |
} |
614 |
} |
615 |
|
616 |
public int drainTo(Collection<? super E> c, int maxElements) { |
617 |
if (c == null) |
618 |
throw new NullPointerException(); |
619 |
if (c == this) |
620 |
throw new IllegalArgumentException(); |
621 |
lock.lock(); |
622 |
try { |
623 |
int n = 0; |
624 |
while (n < maxElements && first != null) { |
625 |
c.add(first.item); |
626 |
first.prev = null; |
627 |
first = first.next; |
628 |
--count; |
629 |
++n; |
630 |
} |
631 |
if (first == null) |
632 |
last = null; |
633 |
notFull.signalAll(); |
634 |
return n; |
635 |
} finally { |
636 |
lock.unlock(); |
637 |
} |
638 |
} |
639 |
|
640 |
/** |
641 |
* Returns an iterator over the elements in this deque in proper sequence. |
642 |
* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that |
643 |
* will never throw {@link ConcurrentModificationException}, |
644 |
* and guarantees to traverse elements as they existed upon |
645 |
* construction of the iterator, and may (but is not guaranteed to) |
646 |
* reflect any modifications subsequent to construction. |
647 |
* |
648 |
* @return an iterator over the elements in this deque in proper sequence. |
649 |
*/ |
650 |
public Iterator<E> iterator() { |
651 |
return new Itr(); |
652 |
} |
653 |
|
654 |
/** |
655 |
* Iterator for LinkedBlockingDeque |
656 |
*/ |
657 |
private class Itr implements Iterator<E> { |
658 |
private Node<E> next; |
659 |
|
660 |
/** |
661 |
* nextItem holds on to item fields because once we claim that |
662 |
* an element exists in hasNext(), we must return item read |
663 |
* under lock (in advance()) even if it was in the process of |
664 |
* being removed when hasNext() was called. |
665 |
*/ |
666 |
private E nextItem; |
667 |
|
668 |
/** |
669 |
* Node returned by most recent call to next. Needed by remove. |
670 |
* Reset to null if this element is deleted by a call to remove. |
671 |
*/ |
672 |
private Node<E> last; |
673 |
|
674 |
Itr() { |
675 |
advance(); |
676 |
} |
677 |
|
678 |
/** |
679 |
* Advance next, or if not yet initialized, set to first node. |
680 |
*/ |
681 |
private void advance() { |
682 |
final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
683 |
lock.lock(); |
684 |
try { |
685 |
next = (next == null)? first : next.next; |
686 |
nextItem = (next == null)? null : next.item; |
687 |
} finally { |
688 |
lock.unlock(); |
689 |
} |
690 |
} |
691 |
|
692 |
public boolean hasNext() { |
693 |
return next != null; |
694 |
} |
695 |
|
696 |
public E next() { |
697 |
if (next == null) |
698 |
throw new NoSuchElementException(); |
699 |
last = next; |
700 |
E x = nextItem; |
701 |
advance(); |
702 |
return x; |
703 |
} |
704 |
|
705 |
public void remove() { |
706 |
Node<E> n = last; |
707 |
if (n == null) |
708 |
throw new IllegalStateException(); |
709 |
last = null; |
710 |
// Note: removeNode rescans looking for this node to make |
711 |
// sure it was not already removed. Otherwise, trying to |
712 |
// re-remove could corrupt list. |
713 |
removeNode(n); |
714 |
} |
715 |
} |
716 |
|
717 |
/** |
718 |
* Save the state of this deque to a stream (that is, serialize it). |
719 |
* |
720 |
* @serialData The capacity (int), followed by elements (each an |
721 |
* <tt>Object</tt>) in the proper order, followed by a null |
722 |
* @param s the stream |
723 |
*/ |
724 |
private void writeObject(java.io.ObjectOutputStream s) |
725 |
throws java.io.IOException { |
726 |
lock.lock(); |
727 |
try { |
728 |
// Write out capacity and any hidden stuff |
729 |
s.defaultWriteObject(); |
730 |
// Write out all elements in the proper order. |
731 |
for (Node<E> p = first; p != null; p = p.next) |
732 |
s.writeObject(p.item); |
733 |
// Use trailing null as sentinel |
734 |
s.writeObject(null); |
735 |
} finally { |
736 |
lock.unlock(); |
737 |
} |
738 |
} |
739 |
|
740 |
/** |
741 |
* Reconstitute this deque from a stream (that is, |
742 |
* deserialize it). |
743 |
* @param s the stream |
744 |
*/ |
745 |
private void readObject(java.io.ObjectInputStream s) |
746 |
throws java.io.IOException, ClassNotFoundException { |
747 |
s.defaultReadObject(); |
748 |
count = 0; |
749 |
first = null; |
750 |
last = null; |
751 |
// Read in all elements and place in queue |
752 |
for (;;) { |
753 |
E item = (E)s.readObject(); |
754 |
if (item == null) |
755 |
break; |
756 |
add(item); |
757 |
} |
758 |
} |
759 |
|
760 |
} |