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jsr166 |
1.1 |
/* |
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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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package java.util.concurrent; |
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import java.util.AbstractQueue; |
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import java.util.Collection; |
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import java.util.Iterator; |
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import java.util.NoSuchElementException; |
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jsr166 |
1.2 |
import java.util.Objects; |
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jsr166 |
1.1 |
import java.util.Spliterator; |
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import java.util.Spliterators; |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.util.concurrent.locks.Condition; |
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import java.util.concurrent.locks.ReentrantLock; |
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import java.util.function.Consumer; |
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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 queue |
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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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* 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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* Visibility between writers and readers is provided as follows: |
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* |
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* Whenever an element is enqueued, the putLock is acquired and |
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* count updated. A subsequent reader guarantees visibility to the |
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* enqueued Node by either acquiring the putLock (via fullyLock) |
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* or by acquiring the takeLock, and then reading n = count.get(); |
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* this gives visibility to the first n items. |
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* |
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* To implement weakly consistent iterators, it appears we need to |
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* keep all Nodes GC-reachable from a predecessor dequeued Node. |
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* That would cause two problems: |
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* - allow a rogue Iterator to cause unbounded memory retention |
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* - cause cross-generational linking of old Nodes to new Nodes if |
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* a Node was tenured while live, which generational GCs have a |
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* hard time dealing with, causing repeated major collections. |
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* However, only non-deleted Nodes need to be reachable from |
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* dequeued Nodes, and reachability does not necessarily have to |
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* be of the kind understood by the GC. We use the trick of |
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* linking a Node that has just been dequeued to itself. Such a |
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* self-link implicitly means to advance to head.next. |
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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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E item; |
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/** |
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* One of: |
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* - the real successor Node |
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* - this Node, meaning the successor is head.next |
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* - null, meaning there is no successor (this is the last node) |
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*/ |
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Node<E> next; |
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Node(E x) { item = x; } |
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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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/** Current number of elements */ |
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private final AtomicInteger count = new AtomicInteger(); |
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/** |
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* Head of linked list. |
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* Invariant: head.item == null |
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*/ |
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transient Node<E> head; |
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/** |
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* Tail of linked list. |
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* Invariant: last.next == null |
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*/ |
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private transient Node<E> last; |
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/** Lock held by take, poll, etc */ |
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private final ReentrantLock takeLock = new ReentrantLock(); |
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/** Wait queue for waiting takes */ |
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private final Condition notEmpty = takeLock.newCondition(); |
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/** Lock held by put, offer, etc */ |
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private final ReentrantLock putLock = new ReentrantLock(); |
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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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* 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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* 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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* Links node at end of queue. |
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* |
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* @param node the node |
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*/ |
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private void enqueue(Node<E> node) { |
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// assert putLock.isHeldByCurrentThread(); |
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// assert last.next == null; |
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last = last.next = node; |
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} |
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/** |
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* Removes a node from head of queue. |
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* |
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* @return the node |
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*/ |
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private E dequeue() { |
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// assert takeLock.isHeldByCurrentThread(); |
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// assert head.item == null; |
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Node<E> h = head; |
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Node<E> first = h.next; |
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h.next = h; // 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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* Locks to prevent both puts and takes. |
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*/ |
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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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* Unlocks to allow both puts and takes. |
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*/ |
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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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* Creates a {@code LinkedBlockingQueue} 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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* Creates a {@code LinkedBlockingQueue} 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 {@code capacity} 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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* Creates a {@code LinkedBlockingQueue} 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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final ReentrantLock putLock = this.putLock; |
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putLock.lock(); // Never contended, but necessary for visibility |
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try { |
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int n = 0; |
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for (E e : c) { |
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if (e == null) |
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throw new NullPointerException(); |
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if (n == capacity) |
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throw new IllegalStateException("Queue full"); |
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enqueue(new Node<E>(e)); |
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++n; |
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} |
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count.set(n); |
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} finally { |
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putLock.unlock(); |
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} |
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} |
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260 |
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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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// 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 {@code size} 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 {@code remainingCapacity} |
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* because it may be the case that another thread is about to |
282 |
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* insert or remove an element. |
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*/ |
284 |
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public int remainingCapacity() { |
285 |
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return capacity - count.get(); |
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} |
287 |
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288 |
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/** |
289 |
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* Inserts the specified element at the tail of this queue, waiting if |
290 |
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* necessary for space to become available. |
291 |
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* |
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* @throws InterruptedException {@inheritDoc} |
293 |
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* @throws NullPointerException {@inheritDoc} |
294 |
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*/ |
295 |
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public void put(E e) throws InterruptedException { |
296 |
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if (e == null) throw new NullPointerException(); |
297 |
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// Note: convention in all put/take/etc is to preset local var |
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// holding count negative to indicate failure unless set. |
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int c = -1; |
300 |
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Node<E> node = new Node<E>(e); |
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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 |
307 |
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* not protected by lock. This works because count can |
308 |
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* only decrease at this point (all other puts are shut |
309 |
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* out by lock), and we (or some other waiting put) are |
310 |
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* signalled if it ever changes from capacity. Similarly |
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* for all other uses of count in other wait guards. |
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*/ |
313 |
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while (count.get() == capacity) { |
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notFull.await(); |
315 |
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} |
316 |
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enqueue(node); |
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c = count.getAndIncrement(); |
318 |
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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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} |
323 |
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if (c == 0) |
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signalNotEmpty(); |
325 |
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} |
326 |
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327 |
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/** |
328 |
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* Inserts the specified element at the tail of this queue, waiting if |
329 |
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* necessary up to the specified wait time for space to become available. |
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* |
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* @return {@code true} if successful, or {@code false} if |
332 |
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* the specified waiting time elapses before space is available |
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* @throws InterruptedException {@inheritDoc} |
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* @throws NullPointerException {@inheritDoc} |
335 |
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*/ |
336 |
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public boolean offer(E e, long timeout, TimeUnit unit) |
337 |
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throws InterruptedException { |
338 |
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339 |
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if (e == null) throw new NullPointerException(); |
340 |
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long nanos = unit.toNanos(timeout); |
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int c = -1; |
342 |
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final ReentrantLock putLock = this.putLock; |
343 |
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final AtomicInteger count = this.count; |
344 |
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putLock.lockInterruptibly(); |
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try { |
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while (count.get() == capacity) { |
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if (nanos <= 0L) |
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return false; |
349 |
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nanos = notFull.awaitNanos(nanos); |
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} |
351 |
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enqueue(new Node<E>(e)); |
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c = count.getAndIncrement(); |
353 |
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if (c + 1 < capacity) |
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notFull.signal(); |
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} finally { |
356 |
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putLock.unlock(); |
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} |
358 |
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if (c == 0) |
359 |
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signalNotEmpty(); |
360 |
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return true; |
361 |
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} |
362 |
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|
363 |
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/** |
364 |
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* Inserts the specified element at the tail of this queue if it is |
365 |
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* possible to do so immediately without exceeding the queue's capacity, |
366 |
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* returning {@code true} upon success and {@code false} if this queue |
367 |
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* is full. |
368 |
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* When using a capacity-restricted queue, this method is generally |
369 |
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* preferable to method {@link BlockingQueue#add add}, which can fail to |
370 |
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* insert an element only by throwing an exception. |
371 |
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* |
372 |
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* @throws NullPointerException if the specified element is null |
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*/ |
374 |
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public boolean offer(E e) { |
375 |
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if (e == null) throw new NullPointerException(); |
376 |
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final AtomicInteger count = this.count; |
377 |
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if (count.get() == capacity) |
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return false; |
379 |
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int c = -1; |
380 |
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Node<E> node = new Node<E>(e); |
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final ReentrantLock putLock = this.putLock; |
382 |
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putLock.lock(); |
383 |
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try { |
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if (count.get() < capacity) { |
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enqueue(node); |
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c = count.getAndIncrement(); |
387 |
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if (c + 1 < capacity) |
388 |
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notFull.signal(); |
389 |
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} |
390 |
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} finally { |
391 |
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putLock.unlock(); |
392 |
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} |
393 |
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if (c == 0) |
394 |
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signalNotEmpty(); |
395 |
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return c >= 0; |
396 |
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} |
397 |
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|
398 |
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public E take() throws InterruptedException { |
399 |
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E x; |
400 |
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int c = -1; |
401 |
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final AtomicInteger count = this.count; |
402 |
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final ReentrantLock takeLock = this.takeLock; |
403 |
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takeLock.lockInterruptibly(); |
404 |
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try { |
405 |
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while (count.get() == 0) { |
406 |
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notEmpty.await(); |
407 |
|
|
} |
408 |
|
|
x = dequeue(); |
409 |
|
|
c = count.getAndDecrement(); |
410 |
|
|
if (c > 1) |
411 |
|
|
notEmpty.signal(); |
412 |
|
|
} finally { |
413 |
|
|
takeLock.unlock(); |
414 |
|
|
} |
415 |
|
|
if (c == capacity) |
416 |
|
|
signalNotFull(); |
417 |
|
|
return x; |
418 |
|
|
} |
419 |
|
|
|
420 |
|
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
421 |
|
|
E x = null; |
422 |
|
|
int c = -1; |
423 |
|
|
long nanos = unit.toNanos(timeout); |
424 |
|
|
final AtomicInteger count = this.count; |
425 |
|
|
final ReentrantLock takeLock = this.takeLock; |
426 |
|
|
takeLock.lockInterruptibly(); |
427 |
|
|
try { |
428 |
|
|
while (count.get() == 0) { |
429 |
|
|
if (nanos <= 0L) |
430 |
|
|
return null; |
431 |
|
|
nanos = notEmpty.awaitNanos(nanos); |
432 |
|
|
} |
433 |
|
|
x = dequeue(); |
434 |
|
|
c = count.getAndDecrement(); |
435 |
|
|
if (c > 1) |
436 |
|
|
notEmpty.signal(); |
437 |
|
|
} finally { |
438 |
|
|
takeLock.unlock(); |
439 |
|
|
} |
440 |
|
|
if (c == capacity) |
441 |
|
|
signalNotFull(); |
442 |
|
|
return x; |
443 |
|
|
} |
444 |
|
|
|
445 |
|
|
public E poll() { |
446 |
|
|
final AtomicInteger count = this.count; |
447 |
|
|
if (count.get() == 0) |
448 |
|
|
return null; |
449 |
|
|
E x = null; |
450 |
|
|
int c = -1; |
451 |
|
|
final ReentrantLock takeLock = this.takeLock; |
452 |
|
|
takeLock.lock(); |
453 |
|
|
try { |
454 |
|
|
if (count.get() > 0) { |
455 |
|
|
x = dequeue(); |
456 |
|
|
c = count.getAndDecrement(); |
457 |
|
|
if (c > 1) |
458 |
|
|
notEmpty.signal(); |
459 |
|
|
} |
460 |
|
|
} finally { |
461 |
|
|
takeLock.unlock(); |
462 |
|
|
} |
463 |
|
|
if (c == capacity) |
464 |
|
|
signalNotFull(); |
465 |
|
|
return x; |
466 |
|
|
} |
467 |
|
|
|
468 |
|
|
public E peek() { |
469 |
|
|
if (count.get() == 0) |
470 |
|
|
return null; |
471 |
|
|
final ReentrantLock takeLock = this.takeLock; |
472 |
|
|
takeLock.lock(); |
473 |
|
|
try { |
474 |
|
|
return (count.get() > 0) ? head.next.item : null; |
475 |
|
|
} finally { |
476 |
|
|
takeLock.unlock(); |
477 |
|
|
} |
478 |
|
|
} |
479 |
|
|
|
480 |
|
|
/** |
481 |
|
|
* Unlinks interior Node p with predecessor trail. |
482 |
|
|
*/ |
483 |
|
|
void unlink(Node<E> p, Node<E> trail) { |
484 |
jsr166 |
1.2 |
// assert putLock.isHeldByCurrentThread(); |
485 |
|
|
// assert takeLock.isHeldByCurrentThread(); |
486 |
jsr166 |
1.1 |
// p.next is not changed, to allow iterators that are |
487 |
|
|
// traversing p to maintain their weak-consistency guarantee. |
488 |
|
|
p.item = null; |
489 |
|
|
trail.next = p.next; |
490 |
|
|
if (last == p) |
491 |
|
|
last = trail; |
492 |
|
|
if (count.getAndDecrement() == capacity) |
493 |
|
|
notFull.signal(); |
494 |
|
|
} |
495 |
|
|
|
496 |
|
|
/** |
497 |
|
|
* Removes a single instance of the specified element from this queue, |
498 |
|
|
* if it is present. More formally, removes an element {@code e} such |
499 |
|
|
* that {@code o.equals(e)}, if this queue contains one or more such |
500 |
|
|
* elements. |
501 |
|
|
* Returns {@code true} if this queue contained the specified element |
502 |
|
|
* (or equivalently, if this queue changed as a result of the call). |
503 |
|
|
* |
504 |
|
|
* @param o element to be removed from this queue, if present |
505 |
|
|
* @return {@code true} if this queue changed as a result of the call |
506 |
|
|
*/ |
507 |
|
|
public boolean remove(Object o) { |
508 |
|
|
if (o == null) return false; |
509 |
|
|
fullyLock(); |
510 |
|
|
try { |
511 |
|
|
for (Node<E> trail = head, p = trail.next; |
512 |
|
|
p != null; |
513 |
|
|
trail = p, p = p.next) { |
514 |
|
|
if (o.equals(p.item)) { |
515 |
|
|
unlink(p, trail); |
516 |
|
|
return true; |
517 |
|
|
} |
518 |
|
|
} |
519 |
|
|
return false; |
520 |
|
|
} finally { |
521 |
|
|
fullyUnlock(); |
522 |
|
|
} |
523 |
|
|
} |
524 |
|
|
|
525 |
|
|
/** |
526 |
|
|
* Returns {@code true} if this queue contains the specified element. |
527 |
|
|
* More formally, returns {@code true} if and only if this queue contains |
528 |
|
|
* at least one element {@code e} such that {@code o.equals(e)}. |
529 |
|
|
* |
530 |
|
|
* @param o object to be checked for containment in this queue |
531 |
|
|
* @return {@code true} if this queue contains the specified element |
532 |
|
|
*/ |
533 |
|
|
public boolean contains(Object o) { |
534 |
|
|
if (o == null) return false; |
535 |
|
|
fullyLock(); |
536 |
|
|
try { |
537 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
538 |
|
|
if (o.equals(p.item)) |
539 |
|
|
return true; |
540 |
|
|
return false; |
541 |
|
|
} finally { |
542 |
|
|
fullyUnlock(); |
543 |
|
|
} |
544 |
|
|
} |
545 |
|
|
|
546 |
|
|
/** |
547 |
|
|
* Returns an array containing all of the elements in this queue, in |
548 |
|
|
* proper sequence. |
549 |
|
|
* |
550 |
|
|
* <p>The returned array will be "safe" in that no references to it are |
551 |
|
|
* maintained by this queue. (In other words, this method must allocate |
552 |
|
|
* a new array). The caller is thus free to modify the returned array. |
553 |
|
|
* |
554 |
|
|
* <p>This method acts as bridge between array-based and collection-based |
555 |
|
|
* APIs. |
556 |
|
|
* |
557 |
|
|
* @return an array containing all of the elements in this queue |
558 |
|
|
*/ |
559 |
|
|
public Object[] toArray() { |
560 |
|
|
fullyLock(); |
561 |
|
|
try { |
562 |
|
|
int size = count.get(); |
563 |
|
|
Object[] a = new Object[size]; |
564 |
|
|
int k = 0; |
565 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
566 |
|
|
a[k++] = p.item; |
567 |
|
|
return a; |
568 |
|
|
} finally { |
569 |
|
|
fullyUnlock(); |
570 |
|
|
} |
571 |
|
|
} |
572 |
|
|
|
573 |
|
|
/** |
574 |
|
|
* Returns an array containing all of the elements in this queue, in |
575 |
|
|
* proper sequence; the runtime type of the returned array is that of |
576 |
|
|
* the specified array. If the queue fits in the specified array, it |
577 |
|
|
* is returned therein. Otherwise, a new array is allocated with the |
578 |
|
|
* runtime type of the specified array and the size of this queue. |
579 |
|
|
* |
580 |
|
|
* <p>If this queue fits in the specified array with room to spare |
581 |
|
|
* (i.e., the array has more elements than this queue), the element in |
582 |
|
|
* the array immediately following the end of the queue is set to |
583 |
|
|
* {@code null}. |
584 |
|
|
* |
585 |
|
|
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
586 |
|
|
* array-based and collection-based APIs. Further, this method allows |
587 |
|
|
* precise control over the runtime type of the output array, and may, |
588 |
|
|
* under certain circumstances, be used to save allocation costs. |
589 |
|
|
* |
590 |
|
|
* <p>Suppose {@code x} is a queue known to contain only strings. |
591 |
|
|
* The following code can be used to dump the queue into a newly |
592 |
|
|
* allocated array of {@code String}: |
593 |
|
|
* |
594 |
|
|
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
595 |
|
|
* |
596 |
|
|
* Note that {@code toArray(new Object[0])} is identical in function to |
597 |
|
|
* {@code toArray()}. |
598 |
|
|
* |
599 |
|
|
* @param a the array into which the elements of the queue are to |
600 |
|
|
* be stored, if it is big enough; otherwise, a new array of the |
601 |
|
|
* same runtime type is allocated for this purpose |
602 |
|
|
* @return an array containing all of the elements in this queue |
603 |
|
|
* @throws ArrayStoreException if the runtime type of the specified array |
604 |
|
|
* is not a supertype of the runtime type of every element in |
605 |
|
|
* this queue |
606 |
|
|
* @throws NullPointerException if the specified array is null |
607 |
|
|
*/ |
608 |
|
|
@SuppressWarnings("unchecked") |
609 |
|
|
public <T> T[] toArray(T[] a) { |
610 |
|
|
fullyLock(); |
611 |
|
|
try { |
612 |
|
|
int size = count.get(); |
613 |
|
|
if (a.length < size) |
614 |
|
|
a = (T[])java.lang.reflect.Array.newInstance |
615 |
|
|
(a.getClass().getComponentType(), size); |
616 |
|
|
|
617 |
|
|
int k = 0; |
618 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
619 |
|
|
a[k++] = (T)p.item; |
620 |
|
|
if (a.length > k) |
621 |
|
|
a[k] = null; |
622 |
|
|
return a; |
623 |
|
|
} finally { |
624 |
|
|
fullyUnlock(); |
625 |
|
|
} |
626 |
|
|
} |
627 |
|
|
|
628 |
|
|
public String toString() { |
629 |
|
|
return Helpers.collectionToString(this); |
630 |
|
|
} |
631 |
|
|
|
632 |
|
|
/** |
633 |
|
|
* Atomically removes all of the elements from this queue. |
634 |
|
|
* The queue will be empty after this call returns. |
635 |
|
|
*/ |
636 |
|
|
public void clear() { |
637 |
|
|
fullyLock(); |
638 |
|
|
try { |
639 |
|
|
for (Node<E> p, h = head; (p = h.next) != null; h = p) { |
640 |
|
|
h.next = h; |
641 |
|
|
p.item = null; |
642 |
|
|
} |
643 |
|
|
head = last; |
644 |
|
|
// assert head.item == null && head.next == null; |
645 |
|
|
if (count.getAndSet(0) == capacity) |
646 |
|
|
notFull.signal(); |
647 |
|
|
} finally { |
648 |
|
|
fullyUnlock(); |
649 |
|
|
} |
650 |
|
|
} |
651 |
|
|
|
652 |
|
|
/** |
653 |
|
|
* @throws UnsupportedOperationException {@inheritDoc} |
654 |
|
|
* @throws ClassCastException {@inheritDoc} |
655 |
|
|
* @throws NullPointerException {@inheritDoc} |
656 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
657 |
|
|
*/ |
658 |
|
|
public int drainTo(Collection<? super E> c) { |
659 |
|
|
return drainTo(c, Integer.MAX_VALUE); |
660 |
|
|
} |
661 |
|
|
|
662 |
|
|
/** |
663 |
|
|
* @throws UnsupportedOperationException {@inheritDoc} |
664 |
|
|
* @throws ClassCastException {@inheritDoc} |
665 |
|
|
* @throws NullPointerException {@inheritDoc} |
666 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
667 |
|
|
*/ |
668 |
|
|
public int drainTo(Collection<? super E> c, int maxElements) { |
669 |
jsr166 |
1.2 |
Objects.requireNonNull(c); |
670 |
jsr166 |
1.1 |
if (c == this) |
671 |
|
|
throw new IllegalArgumentException(); |
672 |
|
|
if (maxElements <= 0) |
673 |
|
|
return 0; |
674 |
|
|
boolean signalNotFull = false; |
675 |
|
|
final ReentrantLock takeLock = this.takeLock; |
676 |
|
|
takeLock.lock(); |
677 |
|
|
try { |
678 |
|
|
int n = Math.min(maxElements, count.get()); |
679 |
|
|
// count.get provides visibility to first n Nodes |
680 |
|
|
Node<E> h = head; |
681 |
|
|
int i = 0; |
682 |
|
|
try { |
683 |
|
|
while (i < n) { |
684 |
|
|
Node<E> p = h.next; |
685 |
|
|
c.add(p.item); |
686 |
|
|
p.item = null; |
687 |
|
|
h.next = h; |
688 |
|
|
h = p; |
689 |
|
|
++i; |
690 |
|
|
} |
691 |
|
|
return n; |
692 |
|
|
} finally { |
693 |
|
|
// Restore invariants even if c.add() threw |
694 |
|
|
if (i > 0) { |
695 |
|
|
// assert h.item == null; |
696 |
|
|
head = h; |
697 |
|
|
signalNotFull = (count.getAndAdd(-i) == capacity); |
698 |
|
|
} |
699 |
|
|
} |
700 |
|
|
} finally { |
701 |
|
|
takeLock.unlock(); |
702 |
|
|
if (signalNotFull) |
703 |
|
|
signalNotFull(); |
704 |
|
|
} |
705 |
|
|
} |
706 |
|
|
|
707 |
|
|
/** |
708 |
jsr166 |
1.2 |
* Used for any element traversal that is not entirely under lock. |
709 |
|
|
* Such traversals must handle both: |
710 |
|
|
* - dequeued nodes (p.next == p) |
711 |
|
|
* - (possibly multiple) interior removed nodes (p.item == null) |
712 |
|
|
*/ |
713 |
|
|
Node<E> succ(Node<E> p) { |
714 |
|
|
return (p == (p = p.next)) ? head.next : p; |
715 |
|
|
} |
716 |
|
|
|
717 |
|
|
/** |
718 |
jsr166 |
1.1 |
* Returns an iterator over the elements in this queue in proper sequence. |
719 |
|
|
* The elements will be returned in order from first (head) to last (tail). |
720 |
|
|
* |
721 |
|
|
* <p>The returned iterator is |
722 |
|
|
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
723 |
|
|
* |
724 |
|
|
* @return an iterator over the elements in this queue in proper sequence |
725 |
|
|
*/ |
726 |
|
|
public Iterator<E> iterator() { |
727 |
|
|
return new Itr(); |
728 |
|
|
} |
729 |
|
|
|
730 |
|
|
private class Itr implements Iterator<E> { |
731 |
|
|
/* |
732 |
|
|
* Basic weakly-consistent iterator. At all times hold the next |
733 |
|
|
* item to hand out so that if hasNext() reports true, we will |
734 |
|
|
* still have it to return even if lost race with a take etc. |
735 |
|
|
*/ |
736 |
|
|
|
737 |
|
|
private Node<E> current; |
738 |
|
|
private Node<E> lastRet; |
739 |
|
|
private E currentElement; |
740 |
|
|
|
741 |
|
|
Itr() { |
742 |
|
|
fullyLock(); |
743 |
|
|
try { |
744 |
jsr166 |
1.2 |
if ((current = head.next) != null) |
745 |
jsr166 |
1.1 |
currentElement = current.item; |
746 |
|
|
} finally { |
747 |
|
|
fullyUnlock(); |
748 |
|
|
} |
749 |
|
|
} |
750 |
|
|
|
751 |
|
|
public boolean hasNext() { |
752 |
|
|
return current != null; |
753 |
|
|
} |
754 |
|
|
|
755 |
|
|
public E next() { |
756 |
jsr166 |
1.2 |
Node<E> p; |
757 |
|
|
if ((p = current) == null) |
758 |
|
|
throw new NoSuchElementException(); |
759 |
|
|
E ret = currentElement, e = null; |
760 |
|
|
lastRet = p; |
761 |
jsr166 |
1.1 |
fullyLock(); |
762 |
|
|
try { |
763 |
jsr166 |
1.2 |
for (p = p.next; p != null; p = succ(p)) |
764 |
|
|
if ((e = p.item) != null) |
765 |
|
|
break; |
766 |
jsr166 |
1.1 |
} finally { |
767 |
|
|
fullyUnlock(); |
768 |
|
|
} |
769 |
jsr166 |
1.2 |
current = p; |
770 |
|
|
currentElement = e; |
771 |
|
|
return ret; |
772 |
|
|
} |
773 |
|
|
|
774 |
|
|
public void forEachRemaining(Consumer<? super E> action) { |
775 |
|
|
// A variant of forEachFrom |
776 |
|
|
Objects.requireNonNull(action); |
777 |
|
|
Node<E> p; |
778 |
|
|
if ((p = current) == null) return; |
779 |
|
|
lastRet = current; |
780 |
|
|
current = null; |
781 |
|
|
final int batchSize = 32; |
782 |
|
|
Object[] es = null; |
783 |
|
|
int n, len = 1; |
784 |
|
|
do { |
785 |
|
|
fullyLock(); |
786 |
|
|
try { |
787 |
|
|
if (es == null) { |
788 |
|
|
p = p.next; |
789 |
|
|
for (Node<E> q = p; q != null; q = succ(q)) |
790 |
|
|
if (q.item != null && ++len == batchSize) |
791 |
|
|
break; |
792 |
|
|
es = new Object[len]; |
793 |
|
|
es[0] = currentElement; |
794 |
|
|
currentElement = null; |
795 |
|
|
n = 1; |
796 |
|
|
} else |
797 |
|
|
n = 0; |
798 |
|
|
for (; p != null && n < len; p = succ(p)) |
799 |
|
|
if ((es[n] = p.item) != null) { |
800 |
|
|
lastRet = p; |
801 |
|
|
n++; |
802 |
|
|
} |
803 |
|
|
} finally { |
804 |
|
|
fullyUnlock(); |
805 |
|
|
} |
806 |
|
|
for (int i = 0; i < n; i++) { |
807 |
|
|
@SuppressWarnings("unchecked") E e = (E) es[i]; |
808 |
|
|
action.accept(e); |
809 |
|
|
} |
810 |
|
|
} while (n > 0 && p != null); |
811 |
jsr166 |
1.1 |
} |
812 |
|
|
|
813 |
|
|
public void remove() { |
814 |
|
|
if (lastRet == null) |
815 |
|
|
throw new IllegalStateException(); |
816 |
|
|
fullyLock(); |
817 |
|
|
try { |
818 |
|
|
Node<E> node = lastRet; |
819 |
|
|
lastRet = null; |
820 |
|
|
for (Node<E> trail = head, p = trail.next; |
821 |
|
|
p != null; |
822 |
|
|
trail = p, p = p.next) { |
823 |
|
|
if (p == node) { |
824 |
|
|
unlink(p, trail); |
825 |
|
|
break; |
826 |
|
|
} |
827 |
|
|
} |
828 |
|
|
} finally { |
829 |
|
|
fullyUnlock(); |
830 |
|
|
} |
831 |
|
|
} |
832 |
|
|
} |
833 |
|
|
|
834 |
jsr166 |
1.2 |
/** |
835 |
|
|
* A customized variant of Spliterators.IteratorSpliterator. |
836 |
|
|
* Keep this class in sync with (very similar) LBDSpliterator. |
837 |
|
|
*/ |
838 |
|
|
private final class LBQSpliterator implements Spliterator<E> { |
839 |
jsr166 |
1.1 |
static final int MAX_BATCH = 1 << 25; // max batch array size; |
840 |
|
|
Node<E> current; // current node; null until initialized |
841 |
|
|
int batch; // batch size for splits |
842 |
|
|
boolean exhausted; // true when no more nodes |
843 |
jsr166 |
1.2 |
long est = size(); // size estimate |
844 |
|
|
|
845 |
|
|
LBQSpliterator() {} |
846 |
jsr166 |
1.1 |
|
847 |
|
|
public long estimateSize() { return est; } |
848 |
|
|
|
849 |
|
|
public Spliterator<E> trySplit() { |
850 |
|
|
Node<E> h; |
851 |
|
|
int b = batch; |
852 |
|
|
int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1; |
853 |
|
|
if (!exhausted && |
854 |
jsr166 |
1.2 |
((h = current) != null || (h = head.next) != null) |
855 |
|
|
&& h.next != null) { |
856 |
jsr166 |
1.1 |
Object[] a = new Object[n]; |
857 |
|
|
int i = 0; |
858 |
|
|
Node<E> p = current; |
859 |
jsr166 |
1.2 |
fullyLock(); |
860 |
jsr166 |
1.1 |
try { |
861 |
jsr166 |
1.2 |
if (p != null || (p = head.next) != null) |
862 |
|
|
for (; p != null && i < n; p = succ(p)) |
863 |
jsr166 |
1.1 |
if ((a[i] = p.item) != null) |
864 |
jsr166 |
1.2 |
i++; |
865 |
jsr166 |
1.1 |
} finally { |
866 |
jsr166 |
1.2 |
fullyUnlock(); |
867 |
jsr166 |
1.1 |
} |
868 |
|
|
if ((current = p) == null) { |
869 |
|
|
est = 0L; |
870 |
|
|
exhausted = true; |
871 |
|
|
} |
872 |
|
|
else if ((est -= i) < 0L) |
873 |
|
|
est = 0L; |
874 |
|
|
if (i > 0) { |
875 |
|
|
batch = i; |
876 |
|
|
return Spliterators.spliterator |
877 |
|
|
(a, 0, i, (Spliterator.ORDERED | |
878 |
|
|
Spliterator.NONNULL | |
879 |
|
|
Spliterator.CONCURRENT)); |
880 |
|
|
} |
881 |
|
|
} |
882 |
|
|
return null; |
883 |
|
|
} |
884 |
|
|
|
885 |
jsr166 |
1.2 |
public boolean tryAdvance(Consumer<? super E> action) { |
886 |
|
|
Objects.requireNonNull(action); |
887 |
jsr166 |
1.1 |
if (!exhausted) { |
888 |
|
|
Node<E> p = current; |
889 |
|
|
E e = null; |
890 |
jsr166 |
1.2 |
fullyLock(); |
891 |
jsr166 |
1.1 |
try { |
892 |
jsr166 |
1.2 |
if (p != null || (p = head.next) != null) |
893 |
|
|
do { |
894 |
|
|
e = p.item; |
895 |
|
|
p = succ(p); |
896 |
|
|
} while (e == null && p != null); |
897 |
jsr166 |
1.1 |
} finally { |
898 |
jsr166 |
1.2 |
fullyUnlock(); |
899 |
jsr166 |
1.1 |
} |
900 |
jsr166 |
1.2 |
exhausted = ((current = p) == null); |
901 |
jsr166 |
1.1 |
if (e != null) { |
902 |
|
|
action.accept(e); |
903 |
|
|
return true; |
904 |
|
|
} |
905 |
|
|
} |
906 |
|
|
return false; |
907 |
|
|
} |
908 |
|
|
|
909 |
jsr166 |
1.2 |
public void forEachRemaining(Consumer<? super E> action) { |
910 |
|
|
Objects.requireNonNull(action); |
911 |
|
|
if (!exhausted) { |
912 |
|
|
exhausted = true; |
913 |
|
|
Node<E> p = current; |
914 |
|
|
current = null; |
915 |
|
|
forEachFrom(action, p); |
916 |
|
|
} |
917 |
|
|
} |
918 |
|
|
|
919 |
jsr166 |
1.1 |
public int characteristics() { |
920 |
jsr166 |
1.2 |
return (Spliterator.ORDERED | |
921 |
|
|
Spliterator.NONNULL | |
922 |
|
|
Spliterator.CONCURRENT); |
923 |
jsr166 |
1.1 |
} |
924 |
|
|
} |
925 |
|
|
|
926 |
|
|
/** |
927 |
|
|
* Returns a {@link Spliterator} over the elements in this queue. |
928 |
|
|
* |
929 |
|
|
* <p>The returned spliterator is |
930 |
|
|
* <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
931 |
|
|
* |
932 |
|
|
* <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, |
933 |
|
|
* {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. |
934 |
|
|
* |
935 |
|
|
* @implNote |
936 |
|
|
* The {@code Spliterator} implements {@code trySplit} to permit limited |
937 |
|
|
* parallelism. |
938 |
|
|
* |
939 |
|
|
* @return a {@code Spliterator} over the elements in this queue |
940 |
|
|
* @since 1.8 |
941 |
|
|
*/ |
942 |
|
|
public Spliterator<E> spliterator() { |
943 |
jsr166 |
1.2 |
return new LBQSpliterator(); |
944 |
|
|
} |
945 |
|
|
|
946 |
|
|
/** |
947 |
|
|
* @throws NullPointerException {@inheritDoc} |
948 |
|
|
*/ |
949 |
|
|
public void forEach(Consumer<? super E> action) { |
950 |
|
|
Objects.requireNonNull(action); |
951 |
|
|
forEachFrom(action, null); |
952 |
|
|
} |
953 |
|
|
|
954 |
|
|
/** |
955 |
|
|
* Runs action on each element found during a traversal starting at p. |
956 |
|
|
* If p is null, traversal starts at head. |
957 |
|
|
*/ |
958 |
|
|
void forEachFrom(Consumer<? super E> action, Node<E> p) { |
959 |
|
|
// Extract batches of elements while holding the lock; then |
960 |
|
|
// run the action on the elements while not |
961 |
|
|
final int batchSize = 32; // max number of elements per batch |
962 |
|
|
Object[] es = null; // container for batch of elements |
963 |
|
|
int n, len = 0; |
964 |
|
|
do { |
965 |
|
|
fullyLock(); |
966 |
|
|
try { |
967 |
|
|
if (es == null) { |
968 |
|
|
if (p == null) p = head.next; |
969 |
|
|
for (Node<E> q = p; q != null; q = succ(q)) |
970 |
|
|
if (q.item != null && ++len == batchSize) |
971 |
|
|
break; |
972 |
|
|
es = new Object[len]; |
973 |
|
|
} |
974 |
|
|
for (n = 0; p != null && n < len; p = succ(p)) |
975 |
|
|
if ((es[n] = p.item) != null) |
976 |
|
|
n++; |
977 |
|
|
} finally { |
978 |
|
|
fullyUnlock(); |
979 |
|
|
} |
980 |
|
|
for (int i = 0; i < n; i++) { |
981 |
|
|
@SuppressWarnings("unchecked") E e = (E) es[i]; |
982 |
|
|
action.accept(e); |
983 |
|
|
} |
984 |
|
|
} while (n > 0 && p != null); |
985 |
jsr166 |
1.1 |
} |
986 |
|
|
|
987 |
|
|
/** |
988 |
|
|
* Saves this queue to a stream (that is, serializes it). |
989 |
|
|
* |
990 |
|
|
* @param s the stream |
991 |
|
|
* @throws java.io.IOException if an I/O error occurs |
992 |
|
|
* @serialData The capacity is emitted (int), followed by all of |
993 |
|
|
* its elements (each an {@code Object}) in the proper order, |
994 |
|
|
* followed by a null |
995 |
|
|
*/ |
996 |
|
|
private void writeObject(java.io.ObjectOutputStream s) |
997 |
|
|
throws java.io.IOException { |
998 |
|
|
|
999 |
|
|
fullyLock(); |
1000 |
|
|
try { |
1001 |
|
|
// Write out any hidden stuff, plus capacity |
1002 |
|
|
s.defaultWriteObject(); |
1003 |
|
|
|
1004 |
|
|
// Write out all elements in the proper order. |
1005 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
1006 |
|
|
s.writeObject(p.item); |
1007 |
|
|
|
1008 |
|
|
// Use trailing null as sentinel |
1009 |
|
|
s.writeObject(null); |
1010 |
|
|
} finally { |
1011 |
|
|
fullyUnlock(); |
1012 |
|
|
} |
1013 |
|
|
} |
1014 |
|
|
|
1015 |
|
|
/** |
1016 |
|
|
* Reconstitutes this queue from a stream (that is, deserializes it). |
1017 |
|
|
* @param s the stream |
1018 |
|
|
* @throws ClassNotFoundException if the class of a serialized object |
1019 |
|
|
* could not be found |
1020 |
|
|
* @throws java.io.IOException if an I/O error occurs |
1021 |
|
|
*/ |
1022 |
|
|
private void readObject(java.io.ObjectInputStream s) |
1023 |
|
|
throws java.io.IOException, ClassNotFoundException { |
1024 |
|
|
// Read in capacity, and any hidden stuff |
1025 |
|
|
s.defaultReadObject(); |
1026 |
|
|
|
1027 |
|
|
count.set(0); |
1028 |
|
|
last = head = new Node<E>(null); |
1029 |
|
|
|
1030 |
|
|
// Read in all elements and place in queue |
1031 |
|
|
for (;;) { |
1032 |
|
|
@SuppressWarnings("unchecked") |
1033 |
|
|
E item = (E)s.readObject(); |
1034 |
|
|
if (item == null) |
1035 |
|
|
break; |
1036 |
|
|
add(item); |
1037 |
|
|
} |
1038 |
|
|
} |
1039 |
|
|
} |