/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
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/*
*
*
*
*
*
* 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.concurrent.locks.
Condition;
import java.util.concurrent.locks.
ReentrantLock;
import java.util.
Spliterator;
import java.util.
Spliterators;
import java.util.function.
Consumer;
/**
* 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 if this deque is full
* @throws NullPointerException {@inheritDoc}
*/
public void
addFirst(E
e) {
if (!
offerFirst(
e))
throw new
IllegalStateException("Deque full");
}
/**
* @throws IllegalStateException if this deque is full
* @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(Object) offer}.
*
* <p>This method is equivalent to {@link #addLast}.
*
* @throws IllegalStateException if this deque is full
* @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();
if (
maxElements <= 0)
return 0;
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 if this deque is full
* @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 if this deque is full
// * @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
*/
@
SuppressWarnings("unchecked")
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> {@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 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 href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* @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 href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
*
* @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; }
}
/** A customized variant of Spliterators.IteratorSpliterator */
static final class
LBDSpliterator<E> implements
Spliterator<E> {
static final int
MAX_BATCH = 1 << 25; // max batch array size;
final
LinkedBlockingDeque<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
LBDSpliterator(
LinkedBlockingDeque<E>
queue) {
this.
queue =
queue;
this.
est =
queue.
size();
}
public long
estimateSize() { return
est; }
public
Spliterator<E>
trySplit() {
Node<E>
h;
final
LinkedBlockingDeque<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.
first) != null) &&
h.
next != null) {
Object[]
a = new
Object[
n];
final
ReentrantLock lock =
q.
lock;
int
i = 0;
Node<E>
p =
current;
lock.
lock();
try {
if (
p != null || (
p =
q.
first) != null) {
do {
if ((
a[
i] =
p.
item) != null)
++
i;
} while ((
p =
p.
next) != null &&
i <
n);
}
} finally {
lock.
unlock();
}
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
LinkedBlockingDeque<E>
q = this.
queue;
final
ReentrantLock lock =
q.
lock;
if (!
exhausted) {
exhausted = true;
Node<E>
p =
current;
do {
E
e = null;
lock.
lock();
try {
if (
p == null)
p =
q.
first;
while (
p != null) {
e =
p.
item;
p =
p.
next;
if (
e != null)
break;
}
} finally {
lock.
unlock();
}
if (
e != null)
action.
accept(
e);
} while (
p != null);
}
}
public boolean
tryAdvance(
Consumer<? super E>
action) {
if (
action == null) throw new
NullPointerException();
final
LinkedBlockingDeque<E>
q = this.
queue;
final
ReentrantLock lock =
q.
lock;
if (!
exhausted) {
E
e = null;
lock.
lock();
try {
if (
current == null)
current =
q.
first;
while (
current != null) {
e =
current.
item;
current =
current.
next;
if (
e != null)
break;
}
} finally {
lock.
unlock();
}
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 deque.
*
* <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 deque
* @since 1.8
*/
public
Spliterator<E>
spliterator() {
return new
LBDSpliterator<E>(this);
}
/**
* Saves this deque to a stream (that is, serializes it).
*
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @serialData The capacity (int), followed by elements (each an
* {@code Object}) in the proper order, followed by a null
*/
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();
}
}
/**
* Reconstitutes this deque 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 {
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);
}
}
}