| /* |
| * 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/licenses/publicdomain |
| */ |
| |
| package java.util.concurrent; |
| import java.util.*; |
| import java.util.concurrent.locks.*; |
| |
| /** |
| * An optionally-bounded {@linkplain BlockingDeque blocking deque} based on |
| * linked nodes. |
| * |
| * <p> The optional capacity bound constructor argument serves as a |
| * way to prevent excessive 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 |
| * deque above capacity. |
| * |
| * <p>Most operations run in constant time (ignoring time spent |
| * blocking). Exceptions include {@link #remove(Object) remove}, |
| * {@link #removeFirstOccurrence removeFirstOccurrence}, {@link |
| * #removeLastOccurrence removeLastOccurrence}, {@link #contains |
| * contains}, {@link #iterator iterator.remove()}, and the bulk |
| * operations, all of which run in linear time. |
| * |
| * <p>This class and its iterator implement all of the |
| * <em>optional</em> methods of the {@link Collection} and {@link |
| * Iterator} interfaces. |
| * |
| * <p>This class is a member of the |
| * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| * Java Collections Framework</a>. |
| * |
| * @since 1.6 |
| * @author Doug Lea |
| * @param <E> the type of elements held in this collection |
| */ |
| public class LinkedBlockingDeque<E> |
| extends AbstractQueue<E> |
| implements BlockingDeque<E>, java.io.Serializable { |
| |
| /* |
| * Implemented as a simple doubly-linked list protected by a |
| * single lock and using conditions to manage blocking. |
| */ |
| |
| /* |
| * We have "diamond" multiple interface/abstract class inheritance |
| * here, and that introduces ambiguities. Often we want the |
| * BlockingDeque javadoc combined with the AbstractQueue |
| * implementation, so a lot of method specs are duplicated here. |
| */ |
| |
| private static final long serialVersionUID = -387911632671998426L; |
| |
| /** Doubly-linked list node class */ |
| static final class Node<E> { |
| E item; |
| Node<E> prev; |
| Node<E> next; |
| Node(E x, Node<E> p, Node<E> n) { |
| item = x; |
| prev = p; |
| next = n; |
| } |
| } |
| |
| /** Pointer to first node */ |
| private transient Node<E> first; |
| /** Pointer to last node */ |
| private transient Node<E> last; |
| /** Number of items in the deque */ |
| private transient int count; |
| /** Maximum number of items in the deque */ |
| private final int capacity; |
| /** Main lock guarding all access */ |
| private final ReentrantLock lock = new ReentrantLock(); |
| /** Condition for waiting takes */ |
| private final Condition notEmpty = lock.newCondition(); |
| /** Condition for waiting puts */ |
| private final Condition notFull = lock.newCondition(); |
| |
| /** |
| * Creates a <tt>LinkedBlockingDeque</tt> with a capacity of |
| * {@link Integer#MAX_VALUE}. |
| */ |
| public LinkedBlockingDeque() { |
| this(Integer.MAX_VALUE); |
| } |
| |
| /** |
| * Creates a <tt>LinkedBlockingDeque</tt> with the given (fixed) capacity. |
| * |
| * @param capacity the capacity of this deque |
| * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1 |
| */ |
| public LinkedBlockingDeque(int capacity) { |
| if (capacity <= 0) throw new IllegalArgumentException(); |
| this.capacity = capacity; |
| } |
| |
| /** |
| * Creates a <tt>LinkedBlockingDeque</tt> 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 LinkedBlockingDeque(Collection<? extends E> c) { |
| this(Integer.MAX_VALUE); |
| for (E e : c) |
| add(e); |
| } |
| |
| |
| // Basic linking and unlinking operations, called only while holding lock |
| |
| /** |
| * Links e as first element, or returns false if full. |
| */ |
| private boolean linkFirst(E e) { |
| if (count >= capacity) |
| return false; |
| ++count; |
| Node<E> f = first; |
| Node<E> x = new Node<E>(e, null, f); |
| first = x; |
| if (last == null) |
| last = x; |
| else |
| f.prev = x; |
| notEmpty.signal(); |
| return true; |
| } |
| |
| /** |
| * Links e as last element, or returns false if full. |
| */ |
| private boolean linkLast(E e) { |
| if (count >= capacity) |
| return false; |
| ++count; |
| Node<E> l = last; |
| Node<E> x = new Node<E>(e, l, null); |
| last = x; |
| if (first == null) |
| first = x; |
| else |
| l.next = x; |
| notEmpty.signal(); |
| return true; |
| } |
| |
| /** |
| * Removes and returns first element, or null if empty. |
| */ |
| private E unlinkFirst() { |
| Node<E> f = first; |
| if (f == null) |
| return null; |
| Node<E> n = f.next; |
| first = n; |
| if (n == null) |
| last = null; |
| else |
| n.prev = null; |
| --count; |
| notFull.signal(); |
| return f.item; |
| } |
| |
| /** |
| * Removes and returns last element, or null if empty. |
| */ |
| private E unlinkLast() { |
| Node<E> l = last; |
| if (l == null) |
| return null; |
| Node<E> p = l.prev; |
| last = p; |
| if (p == null) |
| first = null; |
| else |
| p.next = null; |
| --count; |
| notFull.signal(); |
| return l.item; |
| } |
| |
| /** |
| * Unlink e |
| */ |
| private void unlink(Node<E> x) { |
| Node<E> p = x.prev; |
| Node<E> n = x.next; |
| if (p == null) { |
| if (n == null) |
| first = last = null; |
| else { |
| n.prev = null; |
| first = n; |
| } |
| } else if (n == null) { |
| p.next = null; |
| last = p; |
| } else { |
| p.next = n; |
| n.prev = p; |
| } |
| --count; |
| notFull.signalAll(); |
| } |
| |
| // BlockingDeque methods |
| |
| /** |
| * @throws IllegalStateException {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public void addFirst(E e) { |
| if (!offerFirst(e)) |
| throw new IllegalStateException("Deque full"); |
| } |
| |
| /** |
| * @throws IllegalStateException {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public void addLast(E e) { |
| if (!offerLast(e)) |
| throw new IllegalStateException("Deque full"); |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public boolean offerFirst(E e) { |
| if (e == null) throw new NullPointerException(); |
| lock.lock(); |
| try { |
| return linkFirst(e); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public boolean offerLast(E e) { |
| if (e == null) throw new NullPointerException(); |
| lock.lock(); |
| try { |
| return linkLast(e); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| * @throws InterruptedException {@inheritDoc} |
| */ |
| public void putFirst(E e) throws InterruptedException { |
| if (e == null) throw new NullPointerException(); |
| lock.lock(); |
| try { |
| while (!linkFirst(e)) |
| notFull.await(); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| * @throws InterruptedException {@inheritDoc} |
| */ |
| public void putLast(E e) throws InterruptedException { |
| if (e == null) throw new NullPointerException(); |
| lock.lock(); |
| try { |
| while (!linkLast(e)) |
| notFull.await(); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| * @throws InterruptedException {@inheritDoc} |
| */ |
| public boolean offerFirst(E e, long timeout, TimeUnit unit) |
| throws InterruptedException { |
| if (e == null) throw new NullPointerException(); |
| long nanos = unit.toNanos(timeout); |
| lock.lockInterruptibly(); |
| try { |
| for (;;) { |
| if (linkFirst(e)) |
| return true; |
| if (nanos <= 0) |
| return false; |
| nanos = notFull.awaitNanos(nanos); |
| } |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| * @throws InterruptedException {@inheritDoc} |
| */ |
| public boolean offerLast(E e, long timeout, TimeUnit unit) |
| throws InterruptedException { |
| if (e == null) throw new NullPointerException(); |
| long nanos = unit.toNanos(timeout); |
| lock.lockInterruptibly(); |
| try { |
| for (;;) { |
| if (linkLast(e)) |
| return true; |
| if (nanos <= 0) |
| return false; |
| nanos = notFull.awaitNanos(nanos); |
| } |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E removeFirst() { |
| E x = pollFirst(); |
| if (x == null) throw new NoSuchElementException(); |
| return x; |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E removeLast() { |
| E x = pollLast(); |
| if (x == null) throw new NoSuchElementException(); |
| return x; |
| } |
| |
| public E pollFirst() { |
| lock.lock(); |
| try { |
| return unlinkFirst(); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public E pollLast() { |
| lock.lock(); |
| try { |
| return unlinkLast(); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public E takeFirst() throws InterruptedException { |
| lock.lock(); |
| try { |
| E x; |
| while ( (x = unlinkFirst()) == null) |
| notEmpty.await(); |
| return x; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public E takeLast() throws InterruptedException { |
| lock.lock(); |
| try { |
| E x; |
| while ( (x = unlinkLast()) == null) |
| notEmpty.await(); |
| return x; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public E pollFirst(long timeout, TimeUnit unit) |
| throws InterruptedException { |
| long nanos = unit.toNanos(timeout); |
| lock.lockInterruptibly(); |
| try { |
| for (;;) { |
| E x = unlinkFirst(); |
| if (x != null) |
| return x; |
| if (nanos <= 0) |
| return null; |
| nanos = notEmpty.awaitNanos(nanos); |
| } |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public E pollLast(long timeout, TimeUnit unit) |
| throws InterruptedException { |
| long nanos = unit.toNanos(timeout); |
| lock.lockInterruptibly(); |
| try { |
| for (;;) { |
| E x = unlinkLast(); |
| if (x != null) |
| return x; |
| if (nanos <= 0) |
| return null; |
| nanos = notEmpty.awaitNanos(nanos); |
| } |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E getFirst() { |
| E x = peekFirst(); |
| if (x == null) throw new NoSuchElementException(); |
| return x; |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E getLast() { |
| E x = peekLast(); |
| if (x == null) throw new NoSuchElementException(); |
| return x; |
| } |
| |
| public E peekFirst() { |
| lock.lock(); |
| try { |
| return (first == null) ? null : first.item; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public E peekLast() { |
| lock.lock(); |
| try { |
| return (last == null) ? null : last.item; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public boolean removeFirstOccurrence(Object o) { |
| if (o == null) return false; |
| lock.lock(); |
| try { |
| for (Node<E> p = first; p != null; p = p.next) { |
| if (o.equals(p.item)) { |
| unlink(p); |
| return true; |
| } |
| } |
| return false; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public boolean removeLastOccurrence(Object o) { |
| if (o == null) return false; |
| lock.lock(); |
| try { |
| for (Node<E> p = last; p != null; p = p.prev) { |
| if (o.equals(p.item)) { |
| unlink(p); |
| return true; |
| } |
| } |
| return false; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| // BlockingQueue methods |
| |
| /** |
| * Inserts the specified element at the end of this deque unless it would |
| * violate capacity restrictions. When using a capacity-restricted deque, |
| * it is generally preferable to use method {@link #offer(Object) offer}. |
| * |
| * <p>This method is equivalent to {@link #addLast}. |
| * |
| * @throws IllegalStateException if the element cannot be added at this |
| * time due to capacity restrictions |
| * @throws NullPointerException if the specified element is null |
| */ |
| public boolean add(E e) { |
| addLast(e); |
| return true; |
| } |
| |
| /** |
| * @throws NullPointerException if the specified element is null |
| */ |
| public boolean offer(E e) { |
| return offerLast(e); |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| * @throws InterruptedException {@inheritDoc} |
| */ |
| public void put(E e) throws InterruptedException { |
| putLast(e); |
| } |
| |
| /** |
| * @throws NullPointerException {@inheritDoc} |
| * @throws InterruptedException {@inheritDoc} |
| */ |
| public boolean offer(E e, long timeout, TimeUnit unit) |
| throws InterruptedException { |
| return offerLast(e, timeout, unit); |
| } |
| |
| /** |
| * Retrieves and removes the head of the queue represented by this deque. |
| * This method differs from {@link #poll poll} only in that it throws an |
| * exception if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #removeFirst() removeFirst}. |
| * |
| * @return the head of the queue represented by this deque |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| public E remove() { |
| return removeFirst(); |
| } |
| |
| public E poll() { |
| return pollFirst(); |
| } |
| |
| public E take() throws InterruptedException { |
| return takeFirst(); |
| } |
| |
| public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
| return pollFirst(timeout, unit); |
| } |
| |
| /** |
| * Retrieves, but does not remove, the head of the queue represented by |
| * this deque. This method differs from {@link #peek peek} only in that |
| * it throws an exception if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #getFirst() getFirst}. |
| * |
| * @return the head of the queue represented by this deque |
| * @throws NoSuchElementException if this deque is empty |
| */ |
| public E element() { |
| return getFirst(); |
| } |
| |
| public E peek() { |
| return peekFirst(); |
| } |
| |
| /** |
| * Returns the number of additional elements that this deque can ideally |
| * (in the absence of memory or resource constraints) accept without |
| * blocking. This is always equal to the initial capacity of this deque |
| * less the current <tt>size</tt> of this deque. |
| * |
| * <p>Note that you <em>cannot</em> always tell if an attempt to insert |
| * an element will succeed by inspecting <tt>remainingCapacity</tt> |
| * because it may be the case that another thread is about to |
| * insert or remove an element. |
| */ |
| public int remainingCapacity() { |
| lock.lock(); |
| try { |
| return capacity - count; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @throws UnsupportedOperationException {@inheritDoc} |
| * @throws ClassCastException {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| */ |
| public int drainTo(Collection<? super E> c) { |
| if (c == null) |
| throw new NullPointerException(); |
| if (c == this) |
| throw new IllegalArgumentException(); |
| lock.lock(); |
| try { |
| for (Node<E> p = first; p != null; p = p.next) |
| c.add(p.item); |
| int n = count; |
| count = 0; |
| first = last = null; |
| notFull.signalAll(); |
| return n; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * @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(); |
| lock.lock(); |
| try { |
| int n = 0; |
| while (n < maxElements && first != null) { |
| c.add(first.item); |
| first.prev = null; |
| first = first.next; |
| --count; |
| ++n; |
| } |
| if (first == null) |
| last = null; |
| notFull.signalAll(); |
| return n; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| // Stack methods |
| |
| /** |
| * @throws IllegalStateException {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| */ |
| public void push(E e) { |
| addFirst(e); |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E pop() { |
| return removeFirst(); |
| } |
| |
| // Collection methods |
| |
| /** |
| * Removes the first occurrence of the specified element from this deque. |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the first element <tt>e</tt> such that |
| * <tt>o.equals(e)</tt> (if such an element exists). |
| * Returns <tt>true</tt> if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * <p>This method is equivalent to |
| * {@link #removeFirstOccurrence(Object) removeFirstOccurrence}. |
| * |
| * @param o element to be removed from this deque, if present |
| * @return <tt>true</tt> if this deque changed as a result of the call |
| */ |
| public boolean remove(Object o) { |
| return removeFirstOccurrence(o); |
| } |
| |
| /** |
| * Returns the number of elements in this deque. |
| * |
| * @return the number of elements in this deque |
| */ |
| public int size() { |
| lock.lock(); |
| try { |
| return count; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * Returns <tt>true</tt> if this deque contains the specified element. |
| * More formally, returns <tt>true</tt> if and only if this deque contains |
| * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
| * |
| * @param o object to be checked for containment in this deque |
| * @return <tt>true</tt> if this deque contains the specified element |
| */ |
| public boolean contains(Object o) { |
| if (o == null) return false; |
| lock.lock(); |
| try { |
| for (Node<E> p = first; p != null; p = p.next) |
| if (o.equals(p.item)) |
| return true; |
| return false; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * Variant of removeFirstOccurrence needed by iterator.remove. |
| * Searches for the node, not its contents. |
| */ |
| boolean removeNode(Node<E> e) { |
| lock.lock(); |
| try { |
| for (Node<E> p = first; p != null; p = p.next) { |
| if (p == e) { |
| unlink(p); |
| return true; |
| } |
| } |
| return false; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * Returns an array containing all of the elements in this deque, in |
| * proper sequence (from first to last element). |
| * |
| * <p>The returned array will be "safe" in that no references to it are |
| * maintained by this deque. (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 deque |
| */ |
| public Object[] toArray() { |
| lock.lock(); |
| try { |
| Object[] a = new Object[count]; |
| int k = 0; |
| for (Node<E> p = first; p != null; p = p.next) |
| a[k++] = p.item; |
| return a; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * Returns an array containing all of the elements in this deque, in |
| * proper sequence; the runtime type of the returned array is that of |
| * the specified array. If the deque 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 deque. |
| * |
| * <p>If this deque fits in the specified array with room to spare |
| * (i.e., the array has more elements than this deque), the element in |
| * the array immediately following the end of the deque is set to |
| * <tt>null</tt>. |
| * |
| * <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 <tt>x</tt> is a deque known to contain only strings. |
| * The following code can be used to dump the deque into a newly |
| * allocated array of <tt>String</tt>: |
| * |
| * <pre> |
| * String[] y = x.toArray(new String[0]);</pre> |
| * |
| * Note that <tt>toArray(new Object[0])</tt> is identical in function to |
| * <tt>toArray()</tt>. |
| * |
| * @param a the array into which the elements of the deque 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 deque |
| * @throws ArrayStoreException if the runtime type of the specified array |
| * is not a supertype of the runtime type of every element in |
| * this deque |
| * @throws NullPointerException if the specified array is null |
| */ |
| public <T> T[] toArray(T[] a) { |
| lock.lock(); |
| try { |
| if (a.length < count) |
| a = (T[])java.lang.reflect.Array.newInstance( |
| a.getClass().getComponentType(), |
| count |
| ); |
| |
| int k = 0; |
| for (Node<E> p = first; p != null; p = p.next) |
| a[k++] = (T)p.item; |
| if (a.length > k) |
| a[k] = null; |
| return a; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| public String toString() { |
| lock.lock(); |
| try { |
| return super.toString(); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * Atomically removes all of the elements from this deque. |
| * The deque will be empty after this call returns. |
| */ |
| public void clear() { |
| lock.lock(); |
| try { |
| first = last = null; |
| count = 0; |
| notFull.signalAll(); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * Returns an iterator over the elements in this deque in proper sequence. |
| * The elements will be returned in order from first (head) to last (tail). |
| * The returned <tt>Iterator</tt> is a "weakly consistent" iterator that |
| * will never throw {@link ConcurrentModificationException}, |
| * and guarantees to traverse elements as they existed upon |
| * construction of the iterator, and may (but is not guaranteed to) |
| * reflect any modifications subsequent to construction. |
| * |
| * @return an iterator over the elements in this deque in proper sequence |
| */ |
| public Iterator<E> iterator() { |
| return new Itr(); |
| } |
| |
| /** |
| * Returns an iterator over the elements in this deque in reverse |
| * sequential order. The elements will be returned in order from |
| * last (tail) to first (head). |
| * The returned <tt>Iterator</tt> is a "weakly consistent" iterator that |
| * will never throw {@link ConcurrentModificationException}, |
| * and guarantees to traverse elements as they existed upon |
| * construction of the iterator, and may (but is not guaranteed to) |
| * reflect any modifications subsequent to construction. |
| */ |
| public Iterator<E> descendingIterator() { |
| return new DescendingItr(); |
| } |
| |
| /** |
| * Base class for Iterators for LinkedBlockingDeque |
| */ |
| private abstract class AbstractItr implements Iterator<E> { |
| /** |
| * The next node to return in next |
| */ |
| Node<E> next; |
| |
| /** |
| * nextItem holds on to item fields because once we claim that |
| * an element exists in hasNext(), we must return item read |
| * under lock (in advance()) even if it was in the process of |
| * being removed when hasNext() was called. |
| */ |
| E nextItem; |
| |
| /** |
| * Node returned by most recent call to next. Needed by remove. |
| * Reset to null if this element is deleted by a call to remove. |
| */ |
| private Node<E> lastRet; |
| |
| AbstractItr() { |
| advance(); // set to initial position |
| } |
| |
| /** |
| * Advances next, or if not yet initialized, sets to first node. |
| * Implemented to move forward vs backward in the two subclasses. |
| */ |
| abstract void advance(); |
| |
| public boolean hasNext() { |
| return next != null; |
| } |
| |
| public E next() { |
| if (next == null) |
| throw new NoSuchElementException(); |
| lastRet = next; |
| E x = nextItem; |
| advance(); |
| return x; |
| } |
| |
| public void remove() { |
| Node<E> n = lastRet; |
| if (n == null) |
| throw new IllegalStateException(); |
| lastRet = null; |
| // Note: removeNode rescans looking for this node to make |
| // sure it was not already removed. Otherwise, trying to |
| // re-remove could corrupt list. |
| removeNode(n); |
| } |
| } |
| |
| /** Forward iterator */ |
| private class Itr extends AbstractItr { |
| void advance() { |
| final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
| lock.lock(); |
| try { |
| next = (next == null)? first : next.next; |
| nextItem = (next == null)? null : next.item; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| } |
| |
| /** |
| * Descending iterator for LinkedBlockingDeque |
| */ |
| private class DescendingItr extends AbstractItr { |
| void advance() { |
| final ReentrantLock lock = LinkedBlockingDeque.this.lock; |
| lock.lock(); |
| try { |
| next = (next == null)? last : next.prev; |
| nextItem = (next == null)? null : next.item; |
| } finally { |
| lock.unlock(); |
| } |
| } |
| } |
| |
| /** |
| * Save the state of this deque to a stream (that is, serialize it). |
| * |
| * @serialData The capacity (int), followed by elements (each an |
| * <tt>Object</tt>) in the proper order, followed by a null |
| * @param s the stream |
| */ |
| private void writeObject(java.io.ObjectOutputStream s) |
| throws java.io.IOException { |
| lock.lock(); |
| try { |
| // Write out capacity and any hidden stuff |
| s.defaultWriteObject(); |
| // Write out all elements in the proper order. |
| for (Node<E> p = first; p != null; p = p.next) |
| s.writeObject(p.item); |
| // Use trailing null as sentinel |
| s.writeObject(null); |
| } finally { |
| lock.unlock(); |
| } |
| } |
| |
| /** |
| * Reconstitute this deque from a stream (that is, |
| * deserialize it). |
| * @param s the stream |
| */ |
| private void readObject(java.io.ObjectInputStream s) |
| throws java.io.IOException, ClassNotFoundException { |
| s.defaultReadObject(); |
| count = 0; |
| first = null; |
| last = null; |
| // Read in all elements and place in queue |
| for (;;) { |
| E item = (E)s.readObject(); |
| if (item == null) |
| break; |
| add(item); |
| } |
| } |
| |
| } |