/*
* @(#)LinkedBlockingDeque.java 1.4 06/04/21
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
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);
}
}
}
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