| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent; |
| |
| import java.util.AbstractQueue; |
| import java.util.Collection; |
| import java.util.Iterator; |
| import java.util.NoSuchElementException; |
| import java.util.Spliterator; |
| import java.util.Spliterators; |
| import java.util.concurrent.atomic.AtomicInteger; |
| import java.util.concurrent.locks.Condition; |
| import java.util.concurrent.locks.ReentrantLock; |
| import java.util.function.Consumer; |
| |
| // BEGIN android-note |
| // removed link to collections framework docs |
| // END android-note |
| |
| /** |
| * An optionally-bounded {@linkplain BlockingQueue blocking queue} based on |
| * linked nodes. |
| * This queue orders elements FIFO (first-in-first-out). |
| * The <em>head</em> of the queue is that element that has been on the |
| * queue the longest time. |
| * The <em>tail</em> of the queue is that element that has been on the |
| * queue the shortest time. New elements |
| * are inserted at the tail of the queue, and the queue retrieval |
| * operations obtain elements at the head of the queue. |
| * Linked queues typically have higher throughput than array-based queues but |
| * less predictable performance in most concurrent applications. |
| * |
| * <p>The optional capacity bound constructor argument serves as a |
| * way to prevent excessive queue expansion. The capacity, if unspecified, |
| * is equal to {@link Integer#MAX_VALUE}. Linked nodes are |
| * dynamically created upon each insertion unless this would bring the |
| * queue above capacity. |
| * |
| * <p>This class and its iterator implement all of the |
| * <em>optional</em> methods of the {@link Collection} and {@link |
| * Iterator} interfaces. |
| * |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <E> the type of elements held in this queue |
| */ |
| public class LinkedBlockingQueue<E> extends AbstractQueue<E> |
| implements BlockingQueue<E>, java.io.Serializable { |
| private static final long serialVersionUID = -6903933977591709194L; |
| |
| /* |
| * A variant of the "two lock queue" algorithm. The putLock gates |
| * entry to put (and offer), and has an associated condition for |
| * waiting puts. Similarly for the takeLock. The "count" field |
| * that they both rely on is maintained as an atomic to avoid |
| * needing to get both locks in most cases. Also, to minimize need |
| * for puts to get takeLock and vice-versa, cascading notifies are |
| * used. When a put notices that it has enabled at least one take, |
| * it signals taker. That taker in turn signals others if more |
| * items have been entered since the signal. And symmetrically for |
| * takes signalling puts. Operations such as remove(Object) and |
| * iterators acquire both locks. |
| * |
| * Visibility between writers and readers is provided as follows: |
| * |
| * Whenever an element is enqueued, the putLock is acquired and |
| * count updated. A subsequent reader guarantees visibility to the |
| * enqueued Node by either acquiring the putLock (via fullyLock) |
| * or by acquiring the takeLock, and then reading n = count.get(); |
| * this gives visibility to the first n items. |
| * |
| * To implement weakly consistent iterators, it appears we need to |
| * keep all Nodes GC-reachable from a predecessor dequeued Node. |
| * That would cause two problems: |
| * - allow a rogue Iterator to cause unbounded memory retention |
| * - cause cross-generational linking of old Nodes to new Nodes if |
| * a Node was tenured while live, which generational GCs have a |
| * hard time dealing with, causing repeated major collections. |
| * However, only non-deleted Nodes need to be reachable from |
| * dequeued Nodes, and reachability does not necessarily have to |
| * be of the kind understood by the GC. We use the trick of |
| * linking a Node that has just been dequeued to itself. Such a |
| * self-link implicitly means to advance to head.next. |
| */ |
| |
| /** |
| * Linked list node class. |
| */ |
| static class Node<E> { |
| E item; |
| |
| /** |
| * One of: |
| * - the real successor Node |
| * - this Node, meaning the successor is head.next |
| * - null, meaning there is no successor (this is the last node) |
| */ |
| Node<E> next; |
| |
| Node(E x) { item = x; } |
| } |
| |
| /** The capacity bound, or Integer.MAX_VALUE if none */ |
| private final int capacity; |
| |
| /** Current number of elements */ |
| private final AtomicInteger count = new AtomicInteger(); |
| |
| /** |
| * Head of linked list. |
| * Invariant: head.item == null |
| */ |
| transient Node<E> head; |
| |
| /** |
| * Tail of linked list. |
| * Invariant: last.next == null |
| */ |
| private transient Node<E> last; |
| |
| /** Lock held by take, poll, etc */ |
| private final ReentrantLock takeLock = new ReentrantLock(); |
| |
| /** Wait queue for waiting takes */ |
| private final Condition notEmpty = takeLock.newCondition(); |
| |
| /** Lock held by put, offer, etc */ |
| private final ReentrantLock putLock = new ReentrantLock(); |
| |
| /** Wait queue for waiting puts */ |
| private final Condition notFull = putLock.newCondition(); |
| |
| /** |
| * Signals a waiting take. Called only from put/offer (which do not |
| * otherwise ordinarily lock takeLock.) |
| */ |
| private void signalNotEmpty() { |
| final ReentrantLock takeLock = this.takeLock; |
| takeLock.lock(); |
| try { |
| notEmpty.signal(); |
| } finally { |
| takeLock.unlock(); |
| } |
| } |
| |
| /** |
| * Signals a waiting put. Called only from take/poll. |
| */ |
| private void signalNotFull() { |
| final ReentrantLock putLock = this.putLock; |
| putLock.lock(); |
| try { |
| notFull.signal(); |
| } finally { |
| putLock.unlock(); |
| } |
| } |
| |
| /** |
| * Links node at end of queue. |
| * |
| * @param node the node |
| */ |
| private void enqueue(Node<E> node) { |
| // assert putLock.isHeldByCurrentThread(); |
| // assert last.next == null; |
| last = last.next = node; |
| } |
| |
| /** |
| * Removes a node from head of queue. |
| * |
| * @return the node |
| */ |
| private E dequeue() { |
| // assert takeLock.isHeldByCurrentThread(); |
| // assert head.item == null; |
| Node<E> h = head; |
| Node<E> first = h.next; |
| h.next = h; // help GC |
| head = first; |
| E x = first.item; |
| first.item = null; |
| return x; |
| } |
| |
| /** |
| * Locks to prevent both puts and takes. |
| */ |
| void fullyLock() { |
| putLock.lock(); |
| takeLock.lock(); |
| } |
| |
| /** |
| * Unlocks to allow both puts and takes. |
| */ |
| void fullyUnlock() { |
| takeLock.unlock(); |
| putLock.unlock(); |
| } |
| |
| // /** |
| // * Tells whether both locks are held by current thread. |
| // */ |
| // boolean isFullyLocked() { |
| // return (putLock.isHeldByCurrentThread() && |
| // takeLock.isHeldByCurrentThread()); |
| // } |
| |
| /** |
| * Creates a {@code LinkedBlockingQueue} with a capacity of |
| * {@link Integer#MAX_VALUE}. |
| */ |
| public LinkedBlockingQueue() { |
| this(Integer.MAX_VALUE); |
| } |
| |
| /** |
| * Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity. |
| * |
| * @param capacity the capacity of this queue |
| * @throws IllegalArgumentException if {@code capacity} is not greater |
| * than zero |
| */ |
| public LinkedBlockingQueue(int capacity) { |
| if (capacity <= 0) throw new IllegalArgumentException(); |
| this.capacity = capacity; |
| last = head = new Node<E>(null); |
| } |
| |
| /** |
| * Creates a {@code LinkedBlockingQueue} with a capacity of |
| * {@link Integer#MAX_VALUE}, initially containing the elements of the |
| * given collection, |
| * added in traversal order of the collection's iterator. |
| * |
| * @param c the collection of elements to initially contain |
| * @throws NullPointerException if the specified collection or any |
| * of its elements are null |
| */ |
| public LinkedBlockingQueue(Collection<? extends E> c) { |
| this(Integer.MAX_VALUE); |
| final ReentrantLock putLock = this.putLock; |
| putLock.lock(); // Never contended, but necessary for visibility |
| try { |
| int n = 0; |
| for (E e : c) { |
| if (e == null) |
| throw new NullPointerException(); |
| if (n == capacity) |
| throw new IllegalStateException("Queue full"); |
| enqueue(new Node<E>(e)); |
| ++n; |
| } |
| count.set(n); |
| } finally { |
| putLock.unlock(); |
| } |
| } |
| |
| // this doc comment is overridden to remove the reference to collections |
| // greater in size than Integer.MAX_VALUE |
| /** |
| * Returns the number of elements in this queue. |
| * |
| * @return the number of elements in this queue |
| */ |
| public int size() { |
| return count.get(); |
| } |
| |
| // this doc comment is a modified copy of the inherited doc comment, |
| // without the reference to unlimited queues. |
| /** |
| * Returns the number of additional elements that this queue can ideally |
| * (in the absence of memory or resource constraints) accept without |
| * blocking. This is always equal to the initial capacity of this queue |
| * less the current {@code size} of this queue. |
| * |
| * <p>Note that you <em>cannot</em> always tell if an attempt to insert |
| * an element will succeed by inspecting {@code remainingCapacity} |
| * because it may be the case that another thread is about to |
| * insert or remove an element. |
| */ |
| public int remainingCapacity() { |
| return capacity - count.get(); |
| } |
| |
| /** |
| * Inserts the specified element at the tail of this queue, waiting if |
| * necessary for space to become available. |
| * |
| * @throws InterruptedException {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public void put(E e) throws InterruptedException { |
| if (e == null) throw new NullPointerException(); |
| // Note: convention in all put/take/etc is to preset local var |
| // holding count negative to indicate failure unless set. |
| int c = -1; |
| Node<E> node = new Node<E>(e); |
| final ReentrantLock putLock = this.putLock; |
| final AtomicInteger count = this.count; |
| putLock.lockInterruptibly(); |
| try { |
| /* |
| * Note that count is used in wait guard even though it is |
| * not protected by lock. This works because count can |
| * only decrease at this point (all other puts are shut |
| * out by lock), and we (or some other waiting put) are |
| * signalled if it ever changes from capacity. Similarly |
| * for all other uses of count in other wait guards. |
| */ |
| while (count.get() == capacity) { |
| notFull.await(); |
| } |
| enqueue(node); |
| c = count.getAndIncrement(); |
| if (c + 1 < capacity) |
| notFull.signal(); |
| } finally { |
| putLock.unlock(); |
| } |
| if (c == 0) |
| signalNotEmpty(); |
| } |
| |
| /** |
| * Inserts the specified element at the tail of this queue, waiting if |
| * necessary up to the specified wait time for space to become available. |
| * |
| * @return {@code true} if successful, or {@code false} if |
| * the specified waiting time elapses before space is available |
| * @throws InterruptedException {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public boolean offer(E e, long timeout, TimeUnit unit) |
| throws InterruptedException { |
| |
| if (e == null) throw new NullPointerException(); |
| long nanos = unit.toNanos(timeout); |
| int c = -1; |
| final ReentrantLock putLock = this.putLock; |
| final AtomicInteger count = this.count; |
| putLock.lockInterruptibly(); |
| try { |
| while (count.get() == capacity) { |
| if (nanos <= 0L) |
| return false; |
| nanos = notFull.awaitNanos(nanos); |
| } |
| enqueue(new Node<E>(e)); |
| c = count.getAndIncrement(); |
| if (c + 1 < capacity) |
| notFull.signal(); |
| } finally { |
| putLock.unlock(); |
| } |
| if (c == 0) |
| signalNotEmpty(); |
| return true; |
| } |
| |
| /** |
| * Inserts the specified element at the tail of this queue if it is |
| * possible to do so immediately without exceeding the queue's capacity, |
| * returning {@code true} upon success and {@code false} if this queue |
| * is full. |
| * When using a capacity-restricted queue, this method is generally |
| * preferable to method {@link BlockingQueue#add add}, which can fail to |
| * insert an element only by throwing an exception. |
| * |
| * @throws NullPointerException if the specified element is null |
| */ |
| public boolean offer(E e) { |
| if (e == null) throw new NullPointerException(); |
| final AtomicInteger count = this.count; |
| if (count.get() == capacity) |
| return false; |
| int c = -1; |
| Node<E> node = new Node<E>(e); |
| final ReentrantLock putLock = this.putLock; |
| putLock.lock(); |
| try { |
| if (count.get() < capacity) { |
| enqueue(node); |
| c = count.getAndIncrement(); |
| if (c + 1 < capacity) |
| notFull.signal(); |
| } |
| } finally { |
| putLock.unlock(); |
| } |
| if (c == 0) |
| signalNotEmpty(); |
| return c >= 0; |
| } |
| |
| public E take() throws InterruptedException { |
| E x; |
| int c = -1; |
| final AtomicInteger count = this.count; |
| final ReentrantLock takeLock = this.takeLock; |
| takeLock.lockInterruptibly(); |
| try { |
| while (count.get() == 0) { |
| notEmpty.await(); |
| } |
| x = dequeue(); |
| c = count.getAndDecrement(); |
| if (c > 1) |
| notEmpty.signal(); |
| } finally { |
| takeLock.unlock(); |
| } |
| if (c == capacity) |
| signalNotFull(); |
| return x; |
| } |
| |
| public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
| E x = null; |
| int c = -1; |
| long nanos = unit.toNanos(timeout); |
| final AtomicInteger count = this.count; |
| final ReentrantLock takeLock = this.takeLock; |
| takeLock.lockInterruptibly(); |
| try { |
| while (count.get() == 0) { |
| if (nanos <= 0L) |
| return null; |
| nanos = notEmpty.awaitNanos(nanos); |
| } |
| x = dequeue(); |
| c = count.getAndDecrement(); |
| if (c > 1) |
| notEmpty.signal(); |
| } finally { |
| takeLock.unlock(); |
| } |
| if (c == capacity) |
| signalNotFull(); |
| return x; |
| } |
| |
| public E poll() { |
| final AtomicInteger count = this.count; |
| if (count.get() == 0) |
| return null; |
| E x = null; |
| int c = -1; |
| final ReentrantLock takeLock = this.takeLock; |
| takeLock.lock(); |
| try { |
| if (count.get() > 0) { |
| x = dequeue(); |
| c = count.getAndDecrement(); |
| if (c > 1) |
| notEmpty.signal(); |
| } |
| } finally { |
| takeLock.unlock(); |
| } |
| if (c == capacity) |
| signalNotFull(); |
| return x; |
| } |
| |
| public E peek() { |
| if (count.get() == 0) |
| return null; |
| final ReentrantLock takeLock = this.takeLock; |
| takeLock.lock(); |
| try { |
| return (count.get() > 0) ? head.next.item : null; |
| } finally { |
| takeLock.unlock(); |
| } |
| } |
| |
| /** |
| * Unlinks interior Node p with predecessor trail. |
| */ |
| void unlink(Node<E> p, Node<E> trail) { |
| // assert isFullyLocked(); |
| // p.next is not changed, to allow iterators that are |
| // traversing p to maintain their weak-consistency guarantee. |
| p.item = null; |
| trail.next = p.next; |
| if (last == p) |
| last = trail; |
| if (count.getAndDecrement() == capacity) |
| notFull.signal(); |
| } |
| |
| /** |
| * Removes a single instance of the specified element from this queue, |
| * if it is present. More formally, removes an element {@code e} such |
| * that {@code o.equals(e)}, if this queue contains one or more such |
| * elements. |
| * Returns {@code true} if this queue contained the specified element |
| * (or equivalently, if this queue changed as a result of the call). |
| * |
| * @param o element to be removed from this queue, if present |
| * @return {@code true} if this queue changed as a result of the call |
| */ |
| public boolean remove(Object o) { |
| if (o == null) return false; |
| fullyLock(); |
| try { |
| for (Node<E> trail = head, p = trail.next; |
| p != null; |
| trail = p, p = p.next) { |
| if (o.equals(p.item)) { |
| unlink(p, trail); |
| return true; |
| } |
| } |
| return false; |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| |
| /** |
| * Returns {@code true} if this queue contains the specified element. |
| * More formally, returns {@code true} if and only if this queue contains |
| * at least one element {@code e} such that {@code o.equals(e)}. |
| * |
| * @param o object to be checked for containment in this queue |
| * @return {@code true} if this queue contains the specified element |
| */ |
| public boolean contains(Object o) { |
| if (o == null) return false; |
| fullyLock(); |
| try { |
| for (Node<E> p = head.next; p != null; p = p.next) |
| if (o.equals(p.item)) |
| return true; |
| return false; |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| |
| /** |
| * Returns an array containing all of the elements in this queue, in |
| * proper sequence. |
| * |
| * <p>The returned array will be "safe" in that no references to it are |
| * maintained by this queue. (In other words, this method must allocate |
| * a new array). The caller is thus free to modify the returned array. |
| * |
| * <p>This method acts as bridge between array-based and collection-based |
| * APIs. |
| * |
| * @return an array containing all of the elements in this queue |
| */ |
| public Object[] toArray() { |
| fullyLock(); |
| try { |
| int size = count.get(); |
| Object[] a = new Object[size]; |
| int k = 0; |
| for (Node<E> p = head.next; p != null; p = p.next) |
| a[k++] = p.item; |
| return a; |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| |
| /** |
| * Returns an array containing all of the elements in this queue, in |
| * proper sequence; the runtime type of the returned array is that of |
| * the specified array. If the queue fits in the specified array, it |
| * is returned therein. Otherwise, a new array is allocated with the |
| * runtime type of the specified array and the size of this queue. |
| * |
| * <p>If this queue fits in the specified array with room to spare |
| * (i.e., the array has more elements than this queue), the element in |
| * the array immediately following the end of the queue is set to |
| * {@code null}. |
| * |
| * <p>Like the {@link #toArray()} method, this method acts as bridge between |
| * array-based and collection-based APIs. Further, this method allows |
| * precise control over the runtime type of the output array, and may, |
| * under certain circumstances, be used to save allocation costs. |
| * |
| * <p>Suppose {@code x} is a queue known to contain only strings. |
| * The following code can be used to dump the queue into a newly |
| * allocated array of {@code String}: |
| * |
| * <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
| * |
| * Note that {@code toArray(new Object[0])} is identical in function to |
| * {@code toArray()}. |
| * |
| * @param a the array into which the elements of the queue are to |
| * be stored, if it is big enough; otherwise, a new array of the |
| * same runtime type is allocated for this purpose |
| * @return an array containing all of the elements in this queue |
| * @throws ArrayStoreException if the runtime type of the specified array |
| * is not a supertype of the runtime type of every element in |
| * this queue |
| * @throws NullPointerException if the specified array is null |
| */ |
| @SuppressWarnings("unchecked") |
| public <T> T[] toArray(T[] a) { |
| fullyLock(); |
| try { |
| int size = count.get(); |
| if (a.length < size) |
| a = (T[])java.lang.reflect.Array.newInstance |
| (a.getClass().getComponentType(), size); |
| |
| int k = 0; |
| for (Node<E> p = head.next; p != null; p = p.next) |
| a[k++] = (T)p.item; |
| if (a.length > k) |
| a[k] = null; |
| return a; |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| |
| public String toString() { |
| return Helpers.collectionToString(this); |
| } |
| |
| /** |
| * Atomically removes all of the elements from this queue. |
| * The queue will be empty after this call returns. |
| */ |
| public void clear() { |
| fullyLock(); |
| try { |
| for (Node<E> p, h = head; (p = h.next) != null; h = p) { |
| h.next = h; |
| p.item = null; |
| } |
| head = last; |
| // assert head.item == null && head.next == null; |
| if (count.getAndSet(0) == capacity) |
| notFull.signal(); |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| |
| /** |
| * @throws UnsupportedOperationException {@inheritDoc} |
| * @throws ClassCastException {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| */ |
| public int drainTo(Collection<? super E> c) { |
| return drainTo(c, Integer.MAX_VALUE); |
| } |
| |
| /** |
| * @throws UnsupportedOperationException {@inheritDoc} |
| * @throws ClassCastException {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| */ |
| public int drainTo(Collection<? super E> c, int maxElements) { |
| if (c == null) |
| throw new NullPointerException(); |
| if (c == this) |
| throw new IllegalArgumentException(); |
| if (maxElements <= 0) |
| return 0; |
| boolean signalNotFull = false; |
| final ReentrantLock takeLock = this.takeLock; |
| takeLock.lock(); |
| try { |
| int n = Math.min(maxElements, count.get()); |
| // count.get provides visibility to first n Nodes |
| Node<E> h = head; |
| int i = 0; |
| try { |
| while (i < n) { |
| Node<E> p = h.next; |
| c.add(p.item); |
| p.item = null; |
| h.next = h; |
| h = p; |
| ++i; |
| } |
| return n; |
| } finally { |
| // Restore invariants even if c.add() threw |
| if (i > 0) { |
| // assert h.item == null; |
| head = h; |
| signalNotFull = (count.getAndAdd(-i) == capacity); |
| } |
| } |
| } finally { |
| takeLock.unlock(); |
| if (signalNotFull) |
| signalNotFull(); |
| } |
| } |
| |
| /** |
| * Returns an iterator over the elements in this queue in proper sequence. |
| * The elements will be returned in order from first (head) to last (tail). |
| * |
| * <p>The returned iterator is |
| * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
| * |
| * @return an iterator over the elements in this queue in proper sequence |
| */ |
| public Iterator<E> iterator() { |
| return new Itr(); |
| } |
| |
| private class Itr implements Iterator<E> { |
| /* |
| * Basic weakly-consistent iterator. At all times hold the next |
| * item to hand out so that if hasNext() reports true, we will |
| * still have it to return even if lost race with a take etc. |
| */ |
| |
| private Node<E> current; |
| private Node<E> lastRet; |
| private E currentElement; |
| |
| Itr() { |
| fullyLock(); |
| try { |
| current = head.next; |
| if (current != null) |
| currentElement = current.item; |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| |
| public boolean hasNext() { |
| return current != null; |
| } |
| |
| public E next() { |
| fullyLock(); |
| try { |
| if (current == null) |
| throw new NoSuchElementException(); |
| lastRet = current; |
| E item = null; |
| // Unlike other traversal methods, iterators must handle both: |
| // - dequeued nodes (p.next == p) |
| // - (possibly multiple) interior removed nodes (p.item == null) |
| for (Node<E> p = current, q;; p = q) { |
| if ((q = p.next) == p) |
| q = head.next; |
| if (q == null || (item = q.item) != null) { |
| current = q; |
| E x = currentElement; |
| currentElement = item; |
| return x; |
| } |
| } |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| |
| public void remove() { |
| if (lastRet == null) |
| throw new IllegalStateException(); |
| fullyLock(); |
| try { |
| Node<E> node = lastRet; |
| lastRet = null; |
| for (Node<E> trail = head, p = trail.next; |
| p != null; |
| trail = p, p = p.next) { |
| if (p == node) { |
| unlink(p, trail); |
| break; |
| } |
| } |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| } |
| |
| /** A customized variant of Spliterators.IteratorSpliterator */ |
| static final class LBQSpliterator<E> implements Spliterator<E> { |
| static final int MAX_BATCH = 1 << 25; // max batch array size; |
| final LinkedBlockingQueue<E> queue; |
| Node<E> current; // current node; null until initialized |
| int batch; // batch size for splits |
| boolean exhausted; // true when no more nodes |
| long est; // size estimate |
| LBQSpliterator(LinkedBlockingQueue<E> queue) { |
| this.queue = queue; |
| this.est = queue.size(); |
| } |
| |
| public long estimateSize() { return est; } |
| |
| public Spliterator<E> trySplit() { |
| Node<E> h; |
| final LinkedBlockingQueue<E> q = this.queue; |
| int b = batch; |
| int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1; |
| if (!exhausted && |
| ((h = current) != null || (h = q.head.next) != null) && |
| h.next != null) { |
| Object[] a = new Object[n]; |
| int i = 0; |
| Node<E> p = current; |
| q.fullyLock(); |
| try { |
| if (p != null || (p = q.head.next) != null) { |
| do { |
| if ((a[i] = p.item) != null) |
| ++i; |
| } while ((p = p.next) != null && i < n); |
| } |
| } finally { |
| q.fullyUnlock(); |
| } |
| if ((current = p) == null) { |
| est = 0L; |
| exhausted = true; |
| } |
| else if ((est -= i) < 0L) |
| est = 0L; |
| if (i > 0) { |
| batch = i; |
| return Spliterators.spliterator |
| (a, 0, i, (Spliterator.ORDERED | |
| Spliterator.NONNULL | |
| Spliterator.CONCURRENT)); |
| } |
| } |
| return null; |
| } |
| |
| public void forEachRemaining(Consumer<? super E> action) { |
| if (action == null) throw new NullPointerException(); |
| final LinkedBlockingQueue<E> q = this.queue; |
| if (!exhausted) { |
| exhausted = true; |
| Node<E> p = current; |
| do { |
| E e = null; |
| q.fullyLock(); |
| try { |
| if (p == null) |
| p = q.head.next; |
| while (p != null) { |
| e = p.item; |
| p = p.next; |
| if (e != null) |
| break; |
| } |
| } finally { |
| q.fullyUnlock(); |
| } |
| if (e != null) |
| action.accept(e); |
| } while (p != null); |
| } |
| } |
| |
| public boolean tryAdvance(Consumer<? super E> action) { |
| if (action == null) throw new NullPointerException(); |
| final LinkedBlockingQueue<E> q = this.queue; |
| if (!exhausted) { |
| E e = null; |
| q.fullyLock(); |
| try { |
| if (current == null) |
| current = q.head.next; |
| while (current != null) { |
| e = current.item; |
| current = current.next; |
| if (e != null) |
| break; |
| } |
| } finally { |
| q.fullyUnlock(); |
| } |
| if (current == null) |
| exhausted = true; |
| if (e != null) { |
| action.accept(e); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| public int characteristics() { |
| return Spliterator.ORDERED | Spliterator.NONNULL | |
| Spliterator.CONCURRENT; |
| } |
| } |
| |
| /** |
| * Returns a {@link Spliterator} over the elements in this queue. |
| * |
| * <p>The returned spliterator is |
| * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>. |
| * |
| * <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT}, |
| * {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}. |
| * |
| * @implNote |
| * The {@code Spliterator} implements {@code trySplit} to permit limited |
| * parallelism. |
| * |
| * @return a {@code Spliterator} over the elements in this queue |
| * @since 1.8 |
| */ |
| public Spliterator<E> spliterator() { |
| return new LBQSpliterator<E>(this); |
| } |
| |
| /** |
| * Saves this queue to a stream (that is, serializes it). |
| * |
| * @param s the stream |
| * @throws java.io.IOException if an I/O error occurs |
| * @serialData The capacity is emitted (int), followed by all of |
| * its elements (each an {@code Object}) in the proper order, |
| * followed by a null |
| */ |
| private void writeObject(java.io.ObjectOutputStream s) |
| throws java.io.IOException { |
| |
| fullyLock(); |
| try { |
| // Write out any hidden stuff, plus capacity |
| s.defaultWriteObject(); |
| |
| // Write out all elements in the proper order. |
| for (Node<E> p = head.next; p != null; p = p.next) |
| s.writeObject(p.item); |
| |
| // Use trailing null as sentinel |
| s.writeObject(null); |
| } finally { |
| fullyUnlock(); |
| } |
| } |
| |
| /** |
| * Reconstitutes this queue from a stream (that is, deserializes it). |
| * @param s the stream |
| * @throws ClassNotFoundException if the class of a serialized object |
| * could not be found |
| * @throws java.io.IOException if an I/O error occurs |
| */ |
| private void readObject(java.io.ObjectInputStream s) |
| throws java.io.IOException, ClassNotFoundException { |
| // Read in capacity, and any hidden stuff |
| s.defaultReadObject(); |
| |
| count.set(0); |
| last = head = new Node<E>(null); |
| |
| // Read in all elements and place in queue |
| for (;;) { |
| @SuppressWarnings("unchecked") |
| E item = (E)s.readObject(); |
| if (item == null) |
| break; |
| add(item); |
| } |
| } |
| } |
