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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.concurrent.atomic.*; |
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import java.util.concurrent.locks.*; |
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import java.util.*; |
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|
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/** |
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* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on |
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* linked nodes. |
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* This queue orders elements FIFO (first-in-first-out). |
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* The <em>head</em> of the queue is that element that has been on the |
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* queue the longest time. |
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* The <em>tail</em> of the queue is that element that has been on the |
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* queue the shortest time. New elements |
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* are inserted at the tail of the queue, and the queue retrieval |
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* operations obtain elements at the head of the queue. |
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* Linked queues typically have higher throughput than array-based queues but |
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* less predictable performance in most concurrent applications. |
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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 queue 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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* queue above capacity. |
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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. |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @since 1.5 |
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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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*/ |
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public class LinkedBlockingQueue<E> extends AbstractQueue<E> |
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implements BlockingQueue<E>, java.io.Serializable { |
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private static final long serialVersionUID = -6903933977591709194L; |
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|
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/* |
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* A variant of the "two lock queue" algorithm. The putLock gates |
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* entry to put (and offer), and has an associated condition for |
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* waiting puts. Similarly for the takeLock. The "count" field |
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* that they both rely on is maintained as an atomic to avoid |
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* needing to get both locks in most cases. Also, to minimize need |
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* for puts to get takeLock and vice-versa, cascading notifies are |
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* used. When a put notices that it has enabled at least one take, |
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* it signals taker. That taker in turn signals others if more |
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* items have been entered since the signal. And symmetrically for |
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* takes signalling puts. Operations such as remove(Object) and |
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* iterators acquire both locks. |
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*/ |
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|
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/** |
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* Linked list node class |
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*/ |
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static class Node<E> { |
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/** The item, volatile to ensure barrier separating write and read */ |
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volatile E item; |
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Node<E> next; |
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Node(E x) { item = x; } |
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} |
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|
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/** The capacity bound, or Integer.MAX_VALUE if none */ |
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private final int capacity; |
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|
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/** Current number of elements */ |
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private final AtomicInteger count = new AtomicInteger(0); |
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|
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/** Head of linked list */ |
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private transient Node<E> head; |
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|
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/** Tail of linked list */ |
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private transient Node<E> last; |
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|
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/** Lock held by take, poll, etc */ |
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private final ReentrantLock takeLock = new ReentrantLock(); |
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|
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/** Wait queue for waiting takes */ |
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private final Condition notEmpty = takeLock.newCondition(); |
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|
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/** Lock held by put, offer, etc */ |
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private final ReentrantLock putLock = new ReentrantLock(); |
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|
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/** Wait queue for waiting puts */ |
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private final Condition notFull = putLock.newCondition(); |
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|
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/** |
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* Signals a waiting take. Called only from put/offer (which do not |
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* otherwise ordinarily lock takeLock.) |
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*/ |
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private void signalNotEmpty() { |
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final ReentrantLock takeLock = this.takeLock; |
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takeLock.lock(); |
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try { |
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notEmpty.signal(); |
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} finally { |
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takeLock.unlock(); |
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} |
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} |
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|
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/** |
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* Signals a waiting put. Called only from take/poll. |
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*/ |
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private void signalNotFull() { |
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final ReentrantLock putLock = this.putLock; |
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putLock.lock(); |
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try { |
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notFull.signal(); |
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} finally { |
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putLock.unlock(); |
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} |
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} |
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|
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/** |
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* Creates a node and links it at end of queue. |
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* @param x the item |
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*/ |
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private void insert(E x) { |
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last = last.next = new Node<E>(x); |
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} |
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|
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/** |
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* Removes a node from head of queue, |
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* @return the node |
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*/ |
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private E extract() { |
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Node<E> h = head; |
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Node<E> first = h.next; |
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h.next = null; // help GC |
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head = first; |
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E x = first.item; |
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first.item = null; |
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return x; |
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} |
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|
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/** |
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* Lock to prevent both puts and takes. |
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*/ |
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private void fullyLock() { |
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putLock.lock(); |
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takeLock.lock(); |
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} |
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|
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/** |
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* Unlock to allow both puts and takes. |
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*/ |
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private void fullyUnlock() { |
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takeLock.unlock(); |
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putLock.unlock(); |
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} |
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|
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|
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/** |
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* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of |
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* {@link Integer#MAX_VALUE}. |
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*/ |
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public LinkedBlockingQueue() { |
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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 <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity. |
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* |
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* @param capacity the capacity of this queue |
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* @throws IllegalArgumentException if <tt>capacity</tt> is not greater |
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* than zero |
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*/ |
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public LinkedBlockingQueue(int capacity) { |
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if (capacity <= 0) throw new IllegalArgumentException(); |
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this.capacity = capacity; |
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last = head = new Node<E>(null); |
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} |
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|
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/** |
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* Creates a <tt>LinkedBlockingQueue</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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* |
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* @param c the collection of elements to initially contain |
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* @throws NullPointerException if the specified collection or any |
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* of its elements are null |
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*/ |
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public LinkedBlockingQueue(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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// this doc comment is overridden to remove the reference to collections |
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// greater in size than Integer.MAX_VALUE |
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/** |
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* Returns the number of elements in this queue. |
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* |
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* @return the number of elements in this queue |
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*/ |
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public int size() { |
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return count.get(); |
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} |
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|
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// this doc comment is a modified copy of the inherited doc comment, |
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// without the reference to unlimited queues. |
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/** |
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* Returns the number of additional elements that this queue can ideally |
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* (in the absence of memory or resource constraints) accept without |
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* blocking. This is always equal to the initial capacity of this queue |
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* less the current <tt>size</tt> of this queue. |
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* |
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* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
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* an element will succeed by inspecting <tt>remainingCapacity</tt> |
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* because it may be the case that another thread is about to |
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* insert or remove an element. |
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*/ |
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public int remainingCapacity() { |
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return capacity - count.get(); |
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} |
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|
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/** |
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* Inserts the specified element at the tail of this queue, waiting if |
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* necessary for space to become available. |
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* |
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* @throws InterruptedException {@inheritDoc} |
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* @throws NullPointerException {@inheritDoc} |
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*/ |
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public void put(E e) throws InterruptedException { |
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if (e == null) throw new NullPointerException(); |
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// Note: convention in all put/take/etc is to preset |
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// local var holding count negative to indicate failure unless set. |
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int c = -1; |
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final ReentrantLock putLock = this.putLock; |
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final AtomicInteger count = this.count; |
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putLock.lockInterruptibly(); |
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try { |
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/* |
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* Note that count is used in wait guard even though it is |
246 |
* not protected by lock. This works because count can |
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* only decrease at this point (all other puts are shut |
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* out by lock), and we (or some other waiting put) are |
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* signalled if it ever changes from |
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* capacity. Similarly for all other uses of count in |
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* other wait guards. |
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*/ |
253 |
try { |
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while (count.get() == capacity) |
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notFull.await(); |
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} catch (InterruptedException ie) { |
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notFull.signal(); // propagate to a non-interrupted thread |
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throw ie; |
259 |
} |
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insert(e); |
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c = count.getAndIncrement(); |
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if (c + 1 < capacity) |
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notFull.signal(); |
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} finally { |
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putLock.unlock(); |
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} |
267 |
if (c == 0) |
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signalNotEmpty(); |
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} |
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|
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/** |
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* Inserts the specified element at the tail of this queue, waiting if |
273 |
* necessary up to the specified wait time for space to become available. |
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* |
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* @return <tt>true</tt> if successful, or <tt>false</tt> if |
276 |
* the specified waiting time elapses before space is available. |
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* @throws InterruptedException {@inheritDoc} |
278 |
* @throws NullPointerException {@inheritDoc} |
279 |
*/ |
280 |
public boolean offer(E e, long timeout, TimeUnit unit) |
281 |
throws InterruptedException { |
282 |
|
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if (e == null) throw new NullPointerException(); |
284 |
long nanos = unit.toNanos(timeout); |
285 |
int c = -1; |
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final ReentrantLock putLock = this.putLock; |
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final AtomicInteger count = this.count; |
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putLock.lockInterruptibly(); |
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try { |
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for (;;) { |
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if (count.get() < capacity) { |
292 |
insert(e); |
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c = count.getAndIncrement(); |
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if (c + 1 < capacity) |
295 |
notFull.signal(); |
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break; |
297 |
} |
298 |
if (nanos <= 0) |
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return false; |
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try { |
301 |
nanos = notFull.awaitNanos(nanos); |
302 |
} catch (InterruptedException ie) { |
303 |
notFull.signal(); // propagate to a non-interrupted thread |
304 |
throw ie; |
305 |
} |
306 |
} |
307 |
} finally { |
308 |
putLock.unlock(); |
309 |
} |
310 |
if (c == 0) |
311 |
signalNotEmpty(); |
312 |
return true; |
313 |
} |
314 |
|
315 |
/** |
316 |
* Inserts the specified element at the tail of this queue if it is |
317 |
* possible to do so immediately without exceeding the queue's capacity, |
318 |
* returning <tt>true</tt> upon success and <tt>false</tt> if this queue |
319 |
* is full. |
320 |
* When using a capacity-restricted queue, this method is generally |
321 |
* preferable to method {@link BlockingQueue#add add}, which can fail to |
322 |
* insert an element only by throwing an exception. |
323 |
* |
324 |
* @throws NullPointerException if the specified element is null |
325 |
*/ |
326 |
public boolean offer(E e) { |
327 |
if (e == null) throw new NullPointerException(); |
328 |
final AtomicInteger count = this.count; |
329 |
if (count.get() == capacity) |
330 |
return false; |
331 |
int c = -1; |
332 |
final ReentrantLock putLock = this.putLock; |
333 |
putLock.lock(); |
334 |
try { |
335 |
if (count.get() < capacity) { |
336 |
insert(e); |
337 |
c = count.getAndIncrement(); |
338 |
if (c + 1 < capacity) |
339 |
notFull.signal(); |
340 |
} |
341 |
} finally { |
342 |
putLock.unlock(); |
343 |
} |
344 |
if (c == 0) |
345 |
signalNotEmpty(); |
346 |
return c >= 0; |
347 |
} |
348 |
|
349 |
|
350 |
public E take() throws InterruptedException { |
351 |
E x; |
352 |
int c = -1; |
353 |
final AtomicInteger count = this.count; |
354 |
final ReentrantLock takeLock = this.takeLock; |
355 |
takeLock.lockInterruptibly(); |
356 |
try { |
357 |
try { |
358 |
while (count.get() == 0) |
359 |
notEmpty.await(); |
360 |
} catch (InterruptedException ie) { |
361 |
notEmpty.signal(); // propagate to a non-interrupted thread |
362 |
throw ie; |
363 |
} |
364 |
|
365 |
x = extract(); |
366 |
c = count.getAndDecrement(); |
367 |
if (c > 1) |
368 |
notEmpty.signal(); |
369 |
} finally { |
370 |
takeLock.unlock(); |
371 |
} |
372 |
if (c == capacity) |
373 |
signalNotFull(); |
374 |
return x; |
375 |
} |
376 |
|
377 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
378 |
E x = null; |
379 |
int c = -1; |
380 |
long nanos = unit.toNanos(timeout); |
381 |
final AtomicInteger count = this.count; |
382 |
final ReentrantLock takeLock = this.takeLock; |
383 |
takeLock.lockInterruptibly(); |
384 |
try { |
385 |
for (;;) { |
386 |
if (count.get() > 0) { |
387 |
x = extract(); |
388 |
c = count.getAndDecrement(); |
389 |
if (c > 1) |
390 |
notEmpty.signal(); |
391 |
break; |
392 |
} |
393 |
if (nanos <= 0) |
394 |
return null; |
395 |
try { |
396 |
nanos = notEmpty.awaitNanos(nanos); |
397 |
} catch (InterruptedException ie) { |
398 |
notEmpty.signal(); // propagate to a non-interrupted thread |
399 |
throw ie; |
400 |
} |
401 |
} |
402 |
} finally { |
403 |
takeLock.unlock(); |
404 |
} |
405 |
if (c == capacity) |
406 |
signalNotFull(); |
407 |
return x; |
408 |
} |
409 |
|
410 |
public E poll() { |
411 |
final AtomicInteger count = this.count; |
412 |
if (count.get() == 0) |
413 |
return null; |
414 |
E x = null; |
415 |
int c = -1; |
416 |
final ReentrantLock takeLock = this.takeLock; |
417 |
takeLock.lock(); |
418 |
try { |
419 |
if (count.get() > 0) { |
420 |
x = extract(); |
421 |
c = count.getAndDecrement(); |
422 |
if (c > 1) |
423 |
notEmpty.signal(); |
424 |
} |
425 |
} finally { |
426 |
takeLock.unlock(); |
427 |
} |
428 |
if (c == capacity) |
429 |
signalNotFull(); |
430 |
return x; |
431 |
} |
432 |
|
433 |
|
434 |
public E peek() { |
435 |
if (count.get() == 0) |
436 |
return null; |
437 |
final ReentrantLock takeLock = this.takeLock; |
438 |
takeLock.lock(); |
439 |
try { |
440 |
Node<E> first = head.next; |
441 |
if (first == null) |
442 |
return null; |
443 |
else |
444 |
return first.item; |
445 |
} finally { |
446 |
takeLock.unlock(); |
447 |
} |
448 |
} |
449 |
|
450 |
/** |
451 |
* Removes a single instance of the specified element from this queue, |
452 |
* if it is present. More formally, removes an element <tt>e</tt> such |
453 |
* that <tt>o.equals(e)</tt>, if this queue contains one or more such |
454 |
* elements. |
455 |
* Returns <tt>true</tt> if this queue contained the specified element |
456 |
* (or equivalently, if this queue changed as a result of the call). |
457 |
* |
458 |
* @param o element to be removed from this queue, if present |
459 |
* @return <tt>true</tt> if this queue changed as a result of the call |
460 |
*/ |
461 |
public boolean remove(Object o) { |
462 |
if (o == null) return false; |
463 |
boolean removed = false; |
464 |
fullyLock(); |
465 |
try { |
466 |
Node<E> trail = head; |
467 |
Node<E> p = head.next; |
468 |
while (p != null) { |
469 |
if (o.equals(p.item)) { |
470 |
removed = true; |
471 |
break; |
472 |
} |
473 |
trail = p; |
474 |
p = p.next; |
475 |
} |
476 |
if (removed) { |
477 |
p.item = null; |
478 |
trail.next = p.next; |
479 |
if (last == p) |
480 |
last = trail; |
481 |
if (count.getAndDecrement() == capacity) |
482 |
notFull.signalAll(); |
483 |
} |
484 |
} finally { |
485 |
fullyUnlock(); |
486 |
} |
487 |
return removed; |
488 |
} |
489 |
|
490 |
/** |
491 |
* Returns an array containing all of the elements in this queue, in |
492 |
* proper sequence. |
493 |
* |
494 |
* <p>The returned array will be "safe" in that no references to it are |
495 |
* maintained by this queue. (In other words, this method must allocate |
496 |
* a new array). The caller is thus free to modify the returned array. |
497 |
* |
498 |
* <p>This method acts as bridge between array-based and collection-based |
499 |
* APIs. |
500 |
* |
501 |
* @return an array containing all of the elements in this queue |
502 |
*/ |
503 |
public Object[] toArray() { |
504 |
fullyLock(); |
505 |
try { |
506 |
int size = count.get(); |
507 |
Object[] a = new Object[size]; |
508 |
int k = 0; |
509 |
for (Node<E> p = head.next; p != null; p = p.next) |
510 |
a[k++] = p.item; |
511 |
return a; |
512 |
} finally { |
513 |
fullyUnlock(); |
514 |
} |
515 |
} |
516 |
|
517 |
/** |
518 |
* Returns an array containing all of the elements in this queue, in |
519 |
* proper sequence; the runtime type of the returned array is that of |
520 |
* the specified array. If the queue fits in the specified array, it |
521 |
* is returned therein. Otherwise, a new array is allocated with the |
522 |
* runtime type of the specified array and the size of this queue. |
523 |
* |
524 |
* <p>If this queue fits in the specified array with room to spare |
525 |
* (i.e., the array has more elements than this queue), the element in |
526 |
* the array immediately following the end of the queue is set to |
527 |
* <tt>null</tt>. |
528 |
* |
529 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
530 |
* array-based and collection-based APIs. Further, this method allows |
531 |
* precise control over the runtime type of the output array, and may, |
532 |
* under certain circumstances, be used to save allocation costs. |
533 |
* |
534 |
* <p>Suppose <tt>x</tt> is a queue known to contain only strings. |
535 |
* The following code can be used to dump the queue into a newly |
536 |
* allocated array of <tt>String</tt>: |
537 |
* |
538 |
* <pre> |
539 |
* String[] y = x.toArray(new String[0]);</pre> |
540 |
* |
541 |
* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
542 |
* <tt>toArray()</tt>. |
543 |
* |
544 |
* @param a the array into which the elements of the queue are to |
545 |
* be stored, if it is big enough; otherwise, a new array of the |
546 |
* same runtime type is allocated for this purpose |
547 |
* @return an array containing all of the elements in this queue |
548 |
* @throws ArrayStoreException if the runtime type of the specified array |
549 |
* is not a supertype of the runtime type of every element in |
550 |
* this queue |
551 |
* @throws NullPointerException if the specified array is null |
552 |
*/ |
553 |
public <T> T[] toArray(T[] a) { |
554 |
fullyLock(); |
555 |
try { |
556 |
int size = count.get(); |
557 |
if (a.length < size) |
558 |
a = (T[])java.lang.reflect.Array.newInstance |
559 |
(a.getClass().getComponentType(), size); |
560 |
|
561 |
int k = 0; |
562 |
for (Node p = head.next; p != null; p = p.next) |
563 |
a[k++] = (T)p.item; |
564 |
if (a.length > k) |
565 |
a[k] = null; |
566 |
return a; |
567 |
} finally { |
568 |
fullyUnlock(); |
569 |
} |
570 |
} |
571 |
|
572 |
public String toString() { |
573 |
fullyLock(); |
574 |
try { |
575 |
return super.toString(); |
576 |
} finally { |
577 |
fullyUnlock(); |
578 |
} |
579 |
} |
580 |
|
581 |
/** |
582 |
* Atomically removes all of the elements from this queue. |
583 |
* The queue will be empty after this call returns. |
584 |
*/ |
585 |
public void clear() { |
586 |
fullyLock(); |
587 |
try { |
588 |
head.next = null; |
589 |
assert head.item == null; |
590 |
last = head; |
591 |
if (count.getAndSet(0) == capacity) |
592 |
notFull.signalAll(); |
593 |
} finally { |
594 |
fullyUnlock(); |
595 |
} |
596 |
} |
597 |
|
598 |
/** |
599 |
* @throws UnsupportedOperationException {@inheritDoc} |
600 |
* @throws ClassCastException {@inheritDoc} |
601 |
* @throws NullPointerException {@inheritDoc} |
602 |
* @throws IllegalArgumentException {@inheritDoc} |
603 |
*/ |
604 |
public int drainTo(Collection<? super E> c) { |
605 |
if (c == null) |
606 |
throw new NullPointerException(); |
607 |
if (c == this) |
608 |
throw new IllegalArgumentException(); |
609 |
Node<E> first; |
610 |
fullyLock(); |
611 |
try { |
612 |
first = head.next; |
613 |
head.next = null; |
614 |
assert head.item == null; |
615 |
last = head; |
616 |
if (count.getAndSet(0) == capacity) |
617 |
notFull.signalAll(); |
618 |
} finally { |
619 |
fullyUnlock(); |
620 |
} |
621 |
// Transfer the elements outside of locks |
622 |
int n = 0; |
623 |
for (Node<E> p = first; p != null; p = p.next) { |
624 |
c.add(p.item); |
625 |
p.item = null; |
626 |
++n; |
627 |
} |
628 |
return n; |
629 |
} |
630 |
|
631 |
/** |
632 |
* @throws UnsupportedOperationException {@inheritDoc} |
633 |
* @throws ClassCastException {@inheritDoc} |
634 |
* @throws NullPointerException {@inheritDoc} |
635 |
* @throws IllegalArgumentException {@inheritDoc} |
636 |
*/ |
637 |
public int drainTo(Collection<? super E> c, int maxElements) { |
638 |
if (c == null) |
639 |
throw new NullPointerException(); |
640 |
if (c == this) |
641 |
throw new IllegalArgumentException(); |
642 |
fullyLock(); |
643 |
try { |
644 |
int n = 0; |
645 |
Node<E> p = head.next; |
646 |
while (p != null && n < maxElements) { |
647 |
c.add(p.item); |
648 |
p.item = null; |
649 |
p = p.next; |
650 |
++n; |
651 |
} |
652 |
if (n != 0) { |
653 |
head.next = p; |
654 |
assert head.item == null; |
655 |
if (p == null) |
656 |
last = head; |
657 |
if (count.getAndAdd(-n) == capacity) |
658 |
notFull.signalAll(); |
659 |
} |
660 |
return n; |
661 |
} finally { |
662 |
fullyUnlock(); |
663 |
} |
664 |
} |
665 |
|
666 |
/** |
667 |
* Returns an iterator over the elements in this queue in proper sequence. |
668 |
* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that |
669 |
* will never throw {@link ConcurrentModificationException}, |
670 |
* and guarantees to traverse elements as they existed upon |
671 |
* construction of the iterator, and may (but is not guaranteed to) |
672 |
* reflect any modifications subsequent to construction. |
673 |
* |
674 |
* @return an iterator over the elements in this queue in proper sequence |
675 |
*/ |
676 |
public Iterator<E> iterator() { |
677 |
return new Itr(); |
678 |
} |
679 |
|
680 |
private class Itr implements Iterator<E> { |
681 |
/* |
682 |
* Basic weak-consistent iterator. At all times hold the next |
683 |
* item to hand out so that if hasNext() reports true, we will |
684 |
* still have it to return even if lost race with a take etc. |
685 |
*/ |
686 |
private Node<E> current; |
687 |
private Node<E> lastRet; |
688 |
private E currentElement; |
689 |
|
690 |
Itr() { |
691 |
final ReentrantLock putLock = LinkedBlockingQueue.this.putLock; |
692 |
final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock; |
693 |
putLock.lock(); |
694 |
takeLock.lock(); |
695 |
try { |
696 |
current = head.next; |
697 |
if (current != null) |
698 |
currentElement = current.item; |
699 |
} finally { |
700 |
takeLock.unlock(); |
701 |
putLock.unlock(); |
702 |
} |
703 |
} |
704 |
|
705 |
public boolean hasNext() { |
706 |
return current != null; |
707 |
} |
708 |
|
709 |
public E next() { |
710 |
final ReentrantLock putLock = LinkedBlockingQueue.this.putLock; |
711 |
final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock; |
712 |
putLock.lock(); |
713 |
takeLock.lock(); |
714 |
try { |
715 |
if (current == null) |
716 |
throw new NoSuchElementException(); |
717 |
E x = currentElement; |
718 |
lastRet = current; |
719 |
current = current.next; |
720 |
if (current != null) |
721 |
currentElement = current.item; |
722 |
return x; |
723 |
} finally { |
724 |
takeLock.unlock(); |
725 |
putLock.unlock(); |
726 |
} |
727 |
} |
728 |
|
729 |
public void remove() { |
730 |
if (lastRet == null) |
731 |
throw new IllegalStateException(); |
732 |
final ReentrantLock putLock = LinkedBlockingQueue.this.putLock; |
733 |
final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock; |
734 |
putLock.lock(); |
735 |
takeLock.lock(); |
736 |
try { |
737 |
Node<E> node = lastRet; |
738 |
lastRet = null; |
739 |
Node<E> trail = head; |
740 |
Node<E> p = head.next; |
741 |
while (p != null && p != node) { |
742 |
trail = p; |
743 |
p = p.next; |
744 |
} |
745 |
if (p == node) { |
746 |
p.item = null; |
747 |
trail.next = p.next; |
748 |
if (last == p) |
749 |
last = trail; |
750 |
int c = count.getAndDecrement(); |
751 |
if (c == capacity) |
752 |
notFull.signalAll(); |
753 |
} |
754 |
} finally { |
755 |
takeLock.unlock(); |
756 |
putLock.unlock(); |
757 |
} |
758 |
} |
759 |
} |
760 |
|
761 |
/** |
762 |
* Save the state to a stream (that is, serialize it). |
763 |
* |
764 |
* @serialData The capacity is emitted (int), followed by all of |
765 |
* its elements (each an <tt>Object</tt>) in the proper order, |
766 |
* followed by a null |
767 |
* @param s the stream |
768 |
*/ |
769 |
private void writeObject(java.io.ObjectOutputStream s) |
770 |
throws java.io.IOException { |
771 |
|
772 |
fullyLock(); |
773 |
try { |
774 |
// Write out any hidden stuff, plus capacity |
775 |
s.defaultWriteObject(); |
776 |
|
777 |
// Write out all elements in the proper order. |
778 |
for (Node<E> p = head.next; p != null; p = p.next) |
779 |
s.writeObject(p.item); |
780 |
|
781 |
// Use trailing null as sentinel |
782 |
s.writeObject(null); |
783 |
} finally { |
784 |
fullyUnlock(); |
785 |
} |
786 |
} |
787 |
|
788 |
/** |
789 |
* Reconstitute this queue instance from a stream (that is, |
790 |
* deserialize it). |
791 |
* @param s the stream |
792 |
*/ |
793 |
private void readObject(java.io.ObjectInputStream s) |
794 |
throws java.io.IOException, ClassNotFoundException { |
795 |
// Read in capacity, and any hidden stuff |
796 |
s.defaultReadObject(); |
797 |
|
798 |
count.set(0); |
799 |
last = head = new Node<E>(null); |
800 |
|
801 |
// Read in all elements and place in queue |
802 |
for (;;) { |
803 |
E item = (E)s.readObject(); |
804 |
if (item == null) |
805 |
break; |
806 |
add(item); |
807 |
} |
808 |
} |
809 |
} |