/*
* 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 com.smartandroid.sa.zUImageLoader.core.assist.deque;
import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
/**
* 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.
*
* 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 jump to "first" (for next links) or "last" (for prev
* links).
*/
/*
* 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> {
/**
* The item, or null if this node has been removed.
*/
E item;
/**
* One of: - the real predecessor Node - this Node, meaning the
* predecessor is tail - null, meaning there is no predecessor
*/
Node<E> prev;
/**
* One of: - the real successor Node - this Node, meaning the successor
* is head - null, meaning there is no successor
*/
Node<E> next;
Node(E x) {
item = x;
}
}
/**
* Pointer to first node. Invariant: (first == null && last == null) ||
* (first.prev == null && first.item != null)
*/
transient Node<E> first;
/**
* Pointer to last node. Invariant: (first == null && last == null) ||
* (last.next == null && last.item != null)
*/
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 */
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 {@code LinkedBlockingDeque} with a capacity of
* {@link Integer#MAX_VALUE}.
*/
public LinkedBlockingDeque() {
this(Integer.MAX_VALUE);
}
/**
* Creates a {@code LinkedBlockingDeque} with the given (fixed) capacity.
*
* @param capacity
* the capacity of this deque
* @throws IllegalArgumentException
* if {@code capacity} is less than 1
*/
public LinkedBlockingDeque(int capacity) {
if (capacity <= 0)
throw new IllegalArgumentException();
this.capacity = capacity;
}
/**
* Creates a {@code LinkedBlockingDeque} 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);
final ReentrantLock lock = this.lock;
lock.lock(); // Never contended, but necessary for visibility
try {
for (E e : c) {
if (e == null)
throw new NullPointerException();
if (!linkLast(new Node<E>(e)))
throw new IllegalStateException("Deque full");
}
} finally {
lock.unlock();
}
}
// Basic linking and unlinking operations, called only while holding lock
/**
* Links node as first element, or returns false if full.
*/
private boolean linkFirst(Node<E> node) {
// assert lock.isHeldByCurrentThread();
if (count >= capacity)
return false;
Node<E> f = first;
node.next = f;
first = node;
if (last == null)
last = node;
else
f.prev = node;
++count;
notEmpty.signal();
return true;
}
/**
* Links node as last element, or returns false if full.
*/
private boolean linkLast(Node<E> node) {
// assert lock.isHeldByCurrentThread();
if (count >= capacity)
return false;
Node<E> l = last;
node.prev = l;
last = node;
if (first == null)
first = node;
else
l.next = node;
++count;
notEmpty.signal();
return true;
}
/**
* Removes and returns first element, or null if empty.
*/
private E unlinkFirst() {
// assert lock.isHeldByCurrentThread();
Node<E> f = first;
if (f == null)
return null;
Node<E> n = f.next;
E item = f.item;
f.item = null;
f.next = f; // help GC
first = n;
if (n == null)
last = null;
else
n.prev = null;
--count;
notFull.signal();
return item;
}
/**
* Removes and returns last element, or null if empty.
*/
private E unlinkLast() {
// assert lock.isHeldByCurrentThread();
Node<E> l = last;
if (l == null)
return null;
Node<E> p = l.prev;
E item = l.item;
l.item = null;
l.prev = l; // help GC
last = p;
if (p == null)
first = null;
else
p.next = null;
--count;
notFull.signal();
return item;
}
/**
* Unlinks x.
*/
void unlink(Node<E> x) {
// assert lock.isHeldByCurrentThread();
Node<E> p = x.prev;
Node<E> n = x.next;
if (p == null) {
unlinkFirst();
} else if (n == null) {
unlinkLast();
} else {
p.next = n;
n.prev = p;
x.item = null;
// Don't mess with x's links. They may still be in use by
// an iterator.
--count;
notFull.signal();
}
}
// 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();
Node<E> node = new Node<E>(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
return linkFirst(node);
} finally {
lock.unlock();
}
}
/**
* @throws NullPointerException
* {@inheritDoc}
*/
public boolean offerLast(E e) {
if (e == null)
throw new NullPointerException();
Node<E> node = new Node<E>(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
return linkLast(node);
} finally {
lock.unlock();
}
}
/**
* @throws NullPointerException
* {@inheritDoc}
* @throws InterruptedException
* {@inheritDoc}
*/
public void putFirst(E e) throws InterruptedException {
if (e == null)
throw new NullPointerException();
Node<E> node = new Node<E>(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
while (!linkFirst(node))
notFull.await();
} finally {
lock.unlock();
}
}
/**
* @throws NullPointerException
* {@inheritDoc}
* @throws InterruptedException
* {@inheritDoc}
*/
public void putLast(E e) throws InterruptedException {
if (e == null)
throw new NullPointerException();
Node<E> node = new Node<E>(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
while (!linkLast(node))
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();
Node<E> node = new Node<E>(e);
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (!linkFirst(node)) {
if (nanos <= 0)
return false;
nanos = notFull.awaitNanos(nanos);
}
return true;
} 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();
Node<E> node = new Node<E>(e);
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (!linkLast(node)) {
if (nanos <= 0)
return false;
nanos = notFull.awaitNanos(nanos);
}
return true;
} 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() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return unlinkFirst();
} finally {
lock.unlock();
}
}
public E pollLast() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return unlinkLast();
} finally {
lock.unlock();
}
}
public E takeFirst() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lock();
try {
E x;
while ((x = unlinkFirst()) == null)
notEmpty.await();
return x;
} finally {
lock.unlock();
}
}
public E takeLast() throws InterruptedException {
final ReentrantLock lock = this.lock;
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);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
E x;
while ((x = unlinkFirst()) == null) {
if (nanos <= 0)
return null;
nanos = notEmpty.awaitNanos(nanos);
}
return x;
} finally {
lock.unlock();
}
}
public E pollLast(long timeout, TimeUnit unit) throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
E x;
while ((x = unlinkLast()) == null) {
if (nanos <= 0)
return null;
nanos = notEmpty.awaitNanos(nanos);
}
return x;
} 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() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (first == null) ? null : first.item;
} finally {
lock.unlock();
}
}
public E peekLast() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return (last == null) ? null : last.item;
} finally {
lock.unlock();
}
}
public boolean removeFirstOccurrence(Object o) {
if (o == null)
return false;
final ReentrantLock lock = this.lock;
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;
final ReentrantLock lock = this.lock;
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 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 {@code size} of this deque.
*
* <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() {
final ReentrantLock lock = this.lock;
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) {
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();
final ReentrantLock lock = this.lock;
lock.lock();
try {
int n = Math.min(maxElements, count);
for (int i = 0; i < n; i++) {
c.add(first.item); // In this order, in case add() throws.
unlinkFirst();
}
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 {@code e} such that {@code o.equals(e)} (if
* such an element exists). Returns {@code true} 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 {@code true} 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() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return count;
} finally {
lock.unlock();
}
}
/**
* Returns {@code true} if this deque contains the specified element. More
* formally, returns {@code true} if and only if this deque contains at
* least one element {@code e} such that {@code o.equals(e)}.
*
* @param o
* object to be checked for containment in this deque
* @return {@code true} if this deque contains the specified element
*/
public boolean contains(Object o) {
if (o == null)
return false;
final ReentrantLock lock = this.lock;
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();
}
}
/*
* TODO: Add support for more efficient bulk operations.
*
* We don't want to acquire the lock for every iteration, but we also want
* other threads a chance to interact with the collection, especially when
* count is close to capacity.
*/
// /**
// * Adds all of the elements in the specified collection to this
// * queue. Attempts to addAll of a queue to itself result in
// * {@code IllegalArgumentException}. Further, the behavior of
// * this operation is undefined if the specified collection is
// * modified while the operation is in progress.
// *
// * @param c collection containing elements to be added to this queue
// * @return {@code true} if this queue changed as a result of the call
// * @throws ClassCastException {@inheritDoc}
// * @throws NullPointerException {@inheritDoc}
// * @throws IllegalArgumentException {@inheritDoc}
// * @throws IllegalStateException {@inheritDoc}
// * @see #add(Object)
// */
// public boolean addAll(Collection<? extends E> c) {
// if (c == null)
// throw new NullPointerException();
// if (c == this)
// throw new IllegalArgumentException();
// final ReentrantLock lock = this.lock;
// lock.lock();
// try {
// boolean modified = false;
// for (E e : c)
// if (linkLast(e))
// modified = true;
// return modified;
// } 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() {
final ReentrantLock lock = this.lock;
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 {@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 deque known to contain only strings. The following
* code can be used to dump the deque into a newly allocated array of
* {@code String}:
*
* <pre>
* 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 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
*/
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
final ReentrantLock lock = this.lock;
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() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Node<E> p = first;
if (p == null)
return "[]";
StringBuilder sb = new StringBuilder();
sb.append('[');
for (;;) {
E e = p.item;
sb.append(e == this ? "(this Collection)" : e);
p = p.next;
if (p == null)
return sb.append(']').toString();
sb.append(',').append(' ');
}
} finally {
lock.unlock();
}
}
/**
* Atomically removes all of the elements from this deque. The deque will be
* empty after this call returns.
*/
public void clear() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
for (Node<E> f = first; f != null;) {
f.item = null;
Node<E> n = f.next;
f.prev = null;
f.next = null;
f = n;
}
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).
*
* <p>
* The returned iterator is a "weakly consistent" iterator that will never
* throw {@link java.util.ConcurrentModificationException
* 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).
*
* <p>
* The returned iterator is a "weakly consistent" iterator that will never
* throw {@link java.util.ConcurrentModificationException
* 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 reverse order
*/
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;
abstract Node<E> firstNode();
abstract Node<E> nextNode(Node<E> n);
AbstractItr() {
// set to initial position
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
lock.lock();
try {
next = firstNode();
nextItem = (next == null) ? null : next.item;
} finally {
lock.unlock();
}
}
/**
* Returns the successor node of the given non-null, but possibly
* previously deleted, node.
*/
private Node<E> succ(Node<E> n) {
// Chains of deleted nodes ending in null or self-links
// are possible if multiple interior nodes are removed.
for (;;) {
Node<E> s = nextNode(n);
if (s == null)
return null;
else if (s.item != null)
return s;
else if (s == n)
return firstNode();
else
n = s;
}
}
/**
* Advances next.
*/
void advance() {
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
lock.lock();
try {
// assert next != null;
next = succ(next);
nextItem = (next == null) ? null : next.item;
} finally {
lock.unlock();
}
}
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;
final ReentrantLock lock = LinkedBlockingDeque.this.lock;
lock.lock();
try {
if (n.item != null)
unlink(n);
} finally {
lock.unlock();
}
}
}
/** Forward iterator */
private class Itr extends AbstractItr {
Node<E> firstNode() {
return first;
}
Node<E> nextNode(Node<E> n) {
return n.next;
}
}
/** Descending iterator */
private class DescendingItr extends AbstractItr {
Node<E> firstNode() {
return last;
}
Node<E> nextNode(Node<E> n) {
return n.prev;
}
}
/**
* Save the state of this deque to a stream (that is, serialize it).
*
* @serialData The capacity (int), followed by elements (each an
* {@code Object}) in the proper order, followed by a null
* @param s
* the stream
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
final ReentrantLock lock = this.lock;
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 (;;) {
@SuppressWarnings("unchecked")
E item = (E) s.readObject();
if (item == null)
break;
add(item);
}
}
}