util/concurrent/LinkedBlockingQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;
import java.util.*;

/**
 * An optionally-bounded {@linkplain BlockingQueue blocking queue} based on
 * linked nodes.
 * This queue orders elements FIFO (first-in-first-out).
 * The <em>head</em> of the queue is that element that has been on the
 * queue the longest time.
 * The <em>tail</em> of the queue is that element that has been on the
 * queue the shortest time.
 * Linked queues typically have higher throughput than array-based queues but
 * less predictable performance in most concurrent applications.
 *
 * <p> The optional capacity bound constructor argument serves as a
 * way to prevent excessive queue expansion. The capacity, if unspecified,
 * is equal to {@link Integer#MAX_VALUE}.  Linked nodes are
 * dynamically created upon each insertion unless this would bring the
 * queue above capacity.
 *
 * @since 1.5
 * @author Doug Lea
 *
 **/
public class LinkedBlockingQueue<E> extends AbstractQueue<E>
        implements BlockingQueue<E>, java.io.Serializable {

    /*
     * A variant of the "two lock queue" algorithm.  The putLock gates
     * entry to put (and offer), and has an associated condition for
     * waiting puts.  Similarly for the takeLock.  The "count" field
     * that they both rely on is maintained as an atomic to avoid
     * needing to get both locks in most cases. Also, to minimize need
     * for puts to get takeLock and vice-versa, cascading notifies are
     * used. When a put notices that it has enabled at least one take,
     * it signals taker. That taker in turn signals others if more
     * items have been entered since the signal. And symmetrically for
     * takes signalling puts. Operations such as remove(Object) and
     * iterators acquire both locks.
    */

    /**
     * Linked list node class
     */
    static class Node<E> {
        /** The item, volatile to ensure barrier separating write and read */
        volatile E item;
        Node<E> next;
        Node(E x) { item = x; }
    }

    /** The capacity bound, or Integer.MAX_VALUE if none */
    private final int capacity;

    /** Current number of elements */
    private transient final AtomicInteger count = new AtomicInteger(0);

    /** Head of linked list */
    private transient Node<E> head;

    /** Tail of linked list */
    private transient Node<E> last;

    /** Lock held by take, poll, etc */
    private final ReentrantLock takeLock = new ReentrantLock();

    /** Wait queue for waiting takes */
    private final Condition notEmpty = takeLock.newCondition();

    /** Lock held by put, offer, etc */
    private final ReentrantLock putLock = new ReentrantLock();

    /** Wait queue for waiting puts */
    private final Condition notFull = putLock.newCondition();

    /**
     * Signal a waiting take. Called only from put/offer (which do not
     * otherwise ordinarily lock takeLock.)
     */
    private void signalNotEmpty() {
        takeLock.lock();
        try {
            notEmpty.signal();
        }
        finally {
            takeLock.unlock();
        }
    }

    /**
     * Signal a waiting put. Called only from take/poll.
     */
    private void signalNotFull() {
        putLock.lock();
        try {
            notFull.signal();
        }
        finally {
            putLock.unlock();
        }
    }

    /**
     * Create a node and link it at end of queue
     * @param x the item
     */
    private void insert(E x) {
        last = last.next = new Node<E>(x);
    }

    /**
     * Remove a node from head of queue,
     * @return the node
     */
    private E extract() {
        Node<E> first = head.next;
        head = first;
        E x = (E)first.item;
        first.item = null;
        return x;
    }

    /**
     * Lock to prevent both puts and takes.
     */
    private void fullyLock() {
        putLock.lock();
        takeLock.lock();
    }

    /**
     * Unlock to allow both puts and takes.
     */
    private void fullyUnlock() {
        takeLock.unlock();
        putLock.unlock();
    }


    /**
     * Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
     * {@link Integer#MAX_VALUE}.
     */
    public LinkedBlockingQueue() {
        this(Integer.MAX_VALUE);
    }

    /**
     * Creates a <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity
     * @param capacity the capacity of this queue.
     * @throws IllegalArgumentException if <tt>capacity</tt> is not greater
     * than zero.
     */
    public LinkedBlockingQueue(int capacity) {
        if (capacity <= 0) throw new IllegalArgumentException();
        this.capacity = capacity;
        last = head = new Node<E>(null);
    }

    /**
     * Creates a <tt>LinkedBlockingQueue</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 <tt>c</tt> or any element within it
     * is <tt>null</tt>
     */
    public LinkedBlockingQueue(Collection<? extends E> c) {
        this(Integer.MAX_VALUE);
        for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
            add(it.next());
    }

    // Have to override just to update the javadoc 

    /**
     * Adds the specified element to the tail of this queue.
     * @return <tt>true</tt> (as per the general contract of
     * <tt>Collection.add</tt>).
     * @throws IllegalStateException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean add(E o) {
        return super.add(o);
    }

    /**
     * Adds all of the elements in the specified collection to this queue.
     * The behavior of this operation is undefined if
     * the specified collection is modified while the operation is in
     * progress.  (This implies that the behavior of this call is undefined if
     * the specified collection is this queue, and this queue is nonempty.)
     * <p>
     * This implementation iterates over the specified collection, and adds
     * each object returned by the iterator to this queue's tail, in turn.
     * @throws IllegalStateException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean addAll(Collection<? extends E> c) {
        return super.addAll(c);
    }

    // this doc comment is overridden to remove the reference to collections
    // greater in size than Integer.MAX_VALUE
    /**
     * Returns the number of elements in this collection.
     */
    public int size() {
        return count.get();
    }

    // this doc comment is a modified copy of the inherited doc comment,
    // without the reference to unlimited queues.
    /**
     * Returns the number of elements that this queue can ideally (in
     * the absence of memory or resource constraints) accept without
     * blocking. This is always equal to the initial capacity of this queue
     * less the current <tt>size</tt> of this queue.
     * <p>Note that you <em>cannot</em> always tell if
     * an attempt to <tt>add</tt> an element will succeed by
     * inspecting <tt>remainingCapacity</tt> because it may be the
     * case that a waiting consumer is ready to <tt>take</tt> an
     * element out of an otherwise full queue.
     */
    public int remainingCapacity() {
        return capacity - count.get();
    }

    /**
     * Adds the specified element to the tail of this queue, waiting if
     * necessary for space to become available.
     * @throws NullPointerException {@inheritDoc}
     */
    public void put(E o) throws InterruptedException {
        if (o == null) throw new NullPointerException();
        // Note: convention in all put/take/etc is to preset
        // local var holding count  negative to indicate failure unless set.
        int c = -1;
        putLock.lockInterruptibly();
        try {
            /*
             * Note that count is used in wait guard even though it is
             * not protected by lock. This works because count can
             * only decrease at this point (all other puts are shut
             * out by lock), and we (or some other waiting put) are
             * signalled if it ever changes from
             * capacity. Similarly for all other uses of count in
             * other wait guards.
             */
            try {
                while (count.get() == capacity)
                    notFull.await();
            }
            catch (InterruptedException ie) {
                notFull.signal(); // propagate to a non-interrupted thread
                throw ie;
            }
            insert(o);
            c = count.getAndIncrement();
            if (c + 1 < capacity)
                notFull.signal();
        }
        finally {
            putLock.unlock();
        }
        if (c == 0)
            signalNotEmpty();
    }

    /**
     * Adds the specified element to the tail of this queue, waiting if
     * necessary up to the specified wait time for space to become available.
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean offer(E o, long timeout, TimeUnit unit)
        throws InterruptedException {

        if (o == null) throw new NullPointerException();
        long nanos = unit.toNanos(timeout);
        int c = -1;
        putLock.lockInterruptibly();
        try {
            for (;;) {
                if (count.get() < capacity) {
                    insert(o);
                    c = count.getAndIncrement();
                    if (c + 1 < capacity)
                        notFull.signal();
                    break;
                }
                if (nanos <= 0)
                    return false;
                try {
                    nanos = notFull.awaitNanos(nanos);
                }
                catch (InterruptedException ie) {
                    notFull.signal(); // propagate to a non-interrupted thread
                    throw ie;
                }
            }
        }
        finally {
            putLock.unlock();
        }
        if (c == 0)
            signalNotEmpty();
        return true;
    }

   /**
    * Adds the specified element to the tail of this queue if possible,
    * returning immediately if this queue is full.
    *
    * @throws NullPointerException {@inheritDoc}
    */
    public boolean offer(E o) {
        if (o == null) throw new NullPointerException();
        if (count.get() == capacity)
            return false;
        int c = -1;
        putLock.lock();
        try {
            if (count.get() < capacity) {
                insert(o);
                c = count.getAndIncrement();
                if (c + 1 < capacity)
                    notFull.signal();
            }
        }
        finally {
            putLock.unlock();
        }
        if (c == 0)
            signalNotEmpty();
        return c >= 0;
    }


    public E take() throws InterruptedException {
        E x;
        int c = -1;
        takeLock.lockInterruptibly();
        try {
            try {
                while (count.get() == 0)
                    notEmpty.await();
            }
            catch (InterruptedException ie) {
                notEmpty.signal(); // propagate to a non-interrupted thread
                throw ie;
            }

            x = extract();
            c = count.getAndDecrement();
            if (c > 1)
                notEmpty.signal();
        }
        finally {
            takeLock.unlock();
        }
        if (c == capacity)
            signalNotFull();
        return x;
    }

    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        E x = null;
        int c = -1;
        long nanos = unit.toNanos(timeout);
        takeLock.lockInterruptibly();
        try {
            for (;;) {
                if (count.get() > 0) {
                    x = extract();
                    c = count.getAndDecrement();
                    if (c > 1)
                        notEmpty.signal();
                    break;
                }
                if (nanos <= 0)
                    return null;
                try {
                    nanos = notEmpty.awaitNanos(nanos);
                }
                catch (InterruptedException ie) {
                    notEmpty.signal(); // propagate to a non-interrupted thread
                    throw ie;
                }
            }
        }
        finally {
            takeLock.unlock();
        }
        if (c == capacity)
            signalNotFull();
        return x;
    }

    public E poll() {
        if (count.get() == 0)
            return null;
        E x = null;
        int c = -1;
        takeLock.tryLock();
        try {
            if (count.get() > 0) {
                x = extract();
                c = count.getAndDecrement();
                if (c > 1)
                    notEmpty.signal();
            }
        }
        finally {
            takeLock.unlock();
        }
        if (c == capacity)
            signalNotFull();
        return x;
    }


    public E peek() {
        if (count.get() == 0)
            return null;
        takeLock.lock();
        try {
            Node<E> first = head.next;
            if (first == null)
                return null;
            else
                return first.item;
        }
        finally {
            takeLock.unlock();
        }
    }

    /**
     * Removes a single instance of the specified element from this
     * queue, if it is present.  More formally,
     * removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
     * o.equals(e))</tt>, if the queue contains one or more such
     * elements.  Returns <tt>true</tt> if the queue contained the
     * specified element (or equivalently, if the queue changed as a
     * result of the call).
     *
     * <p>This implementation iterates over the queue looking for the
     * specified element.  If it finds the element, it removes the element
     * from the queue using the iterator's remove method.<p>
     *
     */
    public boolean remove(Object o) {
        if (o == null) return false;
        boolean removed = false;
        fullyLock();
        try {
            Node<E> trail = head;
            Node<E> p = head.next;
            while (p != null) {
                if (o.equals(p.item)) {
                    removed = true;
                    break;
                }
                trail = p;
                p = p.next;
            }
            if (removed) {
                p.item = null;
                trail.next = p.next;
                if (count.getAndDecrement() == capacity)
                    notFull.signalAll();
            }
        }
        finally {
            fullyUnlock();
        }
        return removed;
    }

    public Object[] toArray() {
        fullyLock();
        try {
            int size = count.get();
            Object[] a = new Object[size];
            int k = 0;
            for (Node<E> p = head.next; p != null; p = p.next)
                a[k++] = p.item;
            return a;
        }
        finally {
            fullyUnlock();
        }
    }

    public <T> T[] toArray(T[] a) {
        fullyLock();
        try {
            int size = count.get();
            if (a.length < size)
                a = (T[])java.lang.reflect.Array.newInstance
                    (a.getClass().getComponentType(), size);

            int k = 0;
            for (Node p = head.next; p != null; p = p.next)
                a[k++] = (T)p.item;
            return a;
        }
        finally {
            fullyUnlock();
        }
    }

    public String toString() {
        fullyLock();
        try {
            return super.toString();
        }
        finally {
            fullyUnlock();
        }
    }

    /**
     * Returns an iterator over the elements in this queue in proper sequence.
     *
     * @return an iterator over the elements in this queue in proper sequence.
     */
    public Iterator<E> iterator() {
      return new Itr();
    }

    private class Itr implements Iterator<E> {
        /*
         * Basic weak-consistent iterator.  At all times hold the next
         * item to hand out so that if hasNext() reports true, we will
         * still have it to return even if lost race with a take etc.
         */
        Node<E> current;
        Node<E> lastRet;
        E currentElement;

        Itr() {
            fullyLock();
            try {
                current = head.next;
                if (current != null)
                    currentElement = current.item;
            }
            finally {
                fullyUnlock();
            }
        }

        public boolean hasNext() {
            return current != null;
        }

        public E next() {
            fullyLock();
            try {
                if (current == null)
                    throw new NoSuchElementException();
                E x = currentElement;
                lastRet = current;
                current = current.next;
                if (current != null)
                    currentElement = current.item;
                return x;
            }
            finally {
                fullyUnlock();
            }

        }

        public void remove() {
            if (lastRet == null)
                throw new IllegalStateException();
            fullyLock();
            try {
                Node<E> node = lastRet;
                lastRet = null;
                Node<E> trail = head;
                Node<E> p = head.next;
                while (p != null && p != node) {
                    trail = p;
                    p = p.next;
                }
                if (p == node) {
                    p.item = null;
                    trail.next = p.next;
                    int c = count.getAndDecrement();
                    if (c == capacity)
                        notFull.signalAll();
                }
            }
            finally {
                fullyUnlock();
            }
        }
    }

    /**
     * Save the state to a stream (that is, serialize it).
     *
     * @serialData The capacity is emitted (int), followed by all of
     * its 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 {

        fullyLock();
        try {
            // Write out any hidden stuff, plus capacity
            s.defaultWriteObject();

            // Write out all elements in the proper order.
            for (Node<E> p = head.next; p != null; p = p.next)
                s.writeObject(p.item);

            // Use trailing null as sentinel
            s.writeObject(null);
        }
        finally {
            fullyUnlock();
        }
    }

    /**
     * Reconstitute this queue instance from a stream (that is,
     * deserialize it).
     * @param s the stream
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in capacity, and any hidden stuff
        s.defaultReadObject();

        // Read in all elements and place in queue
        for (;;) {
            E item = (E)s.readObject();
            if (item == null)
                break;
            add(item);
        }
    }
}


Revision:	1.14
Committed:	Wed Aug 6 01:57:53 2003 UTC (20 years, 10 months ago) by dholmes
Branch:	MAIN
Changes since 1.13:	+42 -14 lines
Log Message:	Final major updates to Collection related classes.
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7	tim	1.1	package java.util.concurrent;
8	dl	1.2	import java.util.concurrent.atomic.*;
9	dl	1.7	import java.util.concurrent.locks.*;
10	tim	1.1	import java.util.*;
11
12			/**
13	dholmes	1.14	* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on
14	dholmes	1.8	* linked nodes.
15			* This queue orders elements FIFO (first-in-first-out).
16	tim	1.12	* The <em>head</em> of the queue is that element that has been on the
17	dholmes	1.8	* queue the longest time.
18			* The <em>tail</em> of the queue is that element that has been on the
19			* queue the shortest time.
20			* Linked queues typically have higher throughput than array-based queues but
21			* less predictable performance in most concurrent applications.
22	tim	1.12	*
23	dl	1.3	* <p> The optional capacity bound constructor argument serves as a
24	dholmes	1.8	* way to prevent excessive queue expansion. The capacity, if unspecified,
25			* is equal to {@link Integer#MAX_VALUE}. Linked nodes are
26	dl	1.3	* dynamically created upon each insertion unless this would bring the
27			* queue above capacity.
28	dholmes	1.8	*
29	dl	1.6	* @since 1.5
30			* @author Doug Lea
31	tim	1.12	*
32	tim	1.1	**/
33	dl	1.2	public class LinkedBlockingQueue<E> extends AbstractQueue<E>
34	tim	1.1	implements BlockingQueue<E>, java.io.Serializable {
35
36	dl	1.2	/*
37			* A variant of the "two lock queue" algorithm. The putLock gates
38			* entry to put (and offer), and has an associated condition for
39			* waiting puts. Similarly for the takeLock. The "count" field
40			* that they both rely on is maintained as an atomic to avoid
41			* needing to get both locks in most cases. Also, to minimize need
42			* for puts to get takeLock and vice-versa, cascading notifies are
43			* used. When a put notices that it has enabled at least one take,
44			* it signals taker. That taker in turn signals others if more
45			* items have been entered since the signal. And symmetrically for
46	tim	1.12	* takes signalling puts. Operations such as remove(Object) and
47	dl	1.2	* iterators acquire both locks.
48			*/
49
50	dl	1.6	/**
51			* Linked list node class
52			*/
53	dl	1.2	static class Node<E> {
54	dl	1.6	/** The item, volatile to ensure barrier separating write and read */
55	dl	1.2	volatile E item;
56			Node<E> next;
57			Node(E x) { item = x; }
58			}
59
60	dl	1.6	/** The capacity bound, or Integer.MAX_VALUE if none */
61	dl	1.2	private final int capacity;
62	dl	1.6
63			/** Current number of elements */
64	dl	1.2	private transient final AtomicInteger count = new AtomicInteger(0);
65
66	dl	1.6	/** Head of linked list */
67			private transient Node<E> head;
68
69	dholmes	1.8	/** Tail of linked list */
70	dl	1.6	private transient Node<E> last;
71	dl	1.2
72	dl	1.6	/** Lock held by take, poll, etc */
73	dl	1.5	private final ReentrantLock takeLock = new ReentrantLock();
74	dl	1.6
75			/** Wait queue for waiting takes */
76	dl	1.5	private final Condition notEmpty = takeLock.newCondition();
77	dl	1.2
78	dl	1.6	/** Lock held by put, offer, etc */
79	dl	1.5	private final ReentrantLock putLock = new ReentrantLock();
80	dl	1.6
81			/** Wait queue for waiting puts */
82	dl	1.5	private final Condition notFull = putLock.newCondition();
83	dl	1.2
84			/**
85			* Signal a waiting take. Called only from put/offer (which do not
86	dl	1.4	* otherwise ordinarily lock takeLock.)
87	dl	1.2	*/
88			private void signalNotEmpty() {
89			takeLock.lock();
90			try {
91			notEmpty.signal();
92			}
93			finally {
94			takeLock.unlock();
95			}
96			}
97
98			/**
99			* Signal a waiting put. Called only from take/poll.
100			*/
101			private void signalNotFull() {
102			putLock.lock();
103			try {
104			notFull.signal();
105			}
106			finally {
107			putLock.unlock();
108			}
109			}
110
111			/**
112	dholmes	1.8	* Create a node and link it at end of queue
113	dl	1.6	* @param x the item
114	dl	1.2	*/
115			private void insert(E x) {
116			last = last.next = new Node<E>(x);
117			}
118
119			/**
120			* Remove a node from head of queue,
121	dl	1.6	* @return the node
122	dl	1.2	*/
123			private E extract() {
124			Node<E> first = head.next;
125			head = first;
126			E x = (E)first.item;
127			first.item = null;
128			return x;
129			}
130
131			/**
132	tim	1.12	* Lock to prevent both puts and takes.
133	dl	1.2	*/
134			private void fullyLock() {
135			putLock.lock();
136			takeLock.lock();
137	tim	1.1	}
138	dl	1.2
139			/**
140	tim	1.12	* Unlock to allow both puts and takes.
141	dl	1.2	*/
142			private void fullyUnlock() {
143			takeLock.unlock();
144			putLock.unlock();
145			}
146
147
148			/**
149	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
150	dholmes	1.8	* {@link Integer#MAX_VALUE}.
151	dl	1.2	*/
152			public LinkedBlockingQueue() {
153			this(Integer.MAX_VALUE);
154			}
155
156			/**
157	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity
158	dholmes	1.8	* @param capacity the capacity of this queue.
159			* @throws IllegalArgumentException if <tt>capacity</tt> is not greater
160			* than zero.
161	dl	1.2	*/
162			public LinkedBlockingQueue(int capacity) {
163	dholmes	1.8	if (capacity <= 0) throw new IllegalArgumentException();
164	dl	1.2	this.capacity = capacity;
165	dl	1.6	last = head = new Node<E>(null);
166	dl	1.2	}
167
168			/**
169	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
170	dholmes	1.14	* {@link Integer#MAX_VALUE}, initially containing the elements of the
171	tim	1.12	* given collection,
172	dholmes	1.8	* added in traversal order of the collection's iterator.
173	dholmes	1.9	* @param c the collection of elements to initially contain
174			* @throws NullPointerException if <tt>c</tt> or any element within it
175			* is <tt>null</tt>
176	dl	1.2	*/
177	dholmes	1.10	public LinkedBlockingQueue(Collection<? extends E> c) {
178	dl	1.2	this(Integer.MAX_VALUE);
179	tim	1.12	for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
180			add(it.next());
181	dl	1.2	}
182
183	dholmes	1.14	// Have to override just to update the javadoc
184	dholmes	1.9
185			/**
186	dholmes	1.14	* Adds the specified element to the tail of this queue.
187			* @return <tt>true</tt> (as per the general contract of
188			* <tt>Collection.add</tt>).
189	dholmes	1.9	* @throws IllegalStateException {@inheritDoc}
190			* @throws NullPointerException {@inheritDoc}
191			*/
192			public boolean add(E o) {
193			return super.add(o);
194			}
195
196			/**
197	dholmes	1.14	* Adds all of the elements in the specified collection to this queue.
198			* The behavior of this operation is undefined if
199			* the specified collection is modified while the operation is in
200			* progress. (This implies that the behavior of this call is undefined if
201			* the specified collection is this queue, and this queue is nonempty.)
202			* <p>
203			* This implementation iterates over the specified collection, and adds
204			* each object returned by the iterator to this queue's tail, in turn.
205	dholmes	1.9	* @throws IllegalStateException {@inheritDoc}
206			* @throws NullPointerException {@inheritDoc}
207			*/
208			public boolean addAll(Collection<? extends E> c) {
209			return super.addAll(c);
210			}
211
212	dholmes	1.8	// this doc comment is overridden to remove the reference to collections
213			// greater in size than Integer.MAX_VALUE
214	tim	1.12	/**
215	dholmes	1.13	* Returns the number of elements in this collection.
216	dholmes	1.8	*/
217	dl	1.2	public int size() {
218			return count.get();
219	tim	1.1	}
220	dl	1.2
221	dholmes	1.8	// this doc comment is a modified copy of the inherited doc comment,
222			// without the reference to unlimited queues.
223	tim	1.12	/**
224	dholmes	1.13	* Returns the number of elements that this queue can ideally (in
225	dholmes	1.8	* the absence of memory or resource constraints) accept without
226			* blocking. This is always equal to the initial capacity of this queue
227			* less the current <tt>size</tt> of this queue.
228			* <p>Note that you <em>cannot</em> always tell if
229			* an attempt to <tt>add</tt> an element will succeed by
230			* inspecting <tt>remainingCapacity</tt> because it may be the
231			* case that a waiting consumer is ready to <tt>take</tt> an
232			* element out of an otherwise full queue.
233			*/
234	dl	1.2	public int remainingCapacity() {
235			return capacity - count.get();
236			}
237
238	dholmes	1.8	/**
239	dholmes	1.13	* Adds the specified element to the tail of this queue, waiting if
240	dholmes	1.8	* necessary for space to become available.
241			* @throws NullPointerException {@inheritDoc}
242			*/
243	dholmes	1.14	public void put(E o) throws InterruptedException {
244			if (o == null) throw new NullPointerException();
245	dl	1.2	// Note: convention in all put/take/etc is to preset
246			// local var holding count negative to indicate failure unless set.
247	tim	1.12	int c = -1;
248	dl	1.2	putLock.lockInterruptibly();
249			try {
250			/*
251			* Note that count is used in wait guard even though it is
252			* not protected by lock. This works because count can
253			* only decrease at this point (all other puts are shut
254			* out by lock), and we (or some other waiting put) are
255			* signalled if it ever changes from
256			* capacity. Similarly for all other uses of count in
257			* other wait guards.
258			*/
259			try {
260	tim	1.12	while (count.get() == capacity)
261	dl	1.2	notFull.await();
262			}
263			catch (InterruptedException ie) {
264			notFull.signal(); // propagate to a non-interrupted thread
265			throw ie;
266			}
267	dholmes	1.14	insert(o);
268	dl	1.2	c = count.getAndIncrement();
269	dl	1.6	if (c + 1 < capacity)
270	dl	1.2	notFull.signal();
271			}
272			finally {
273			putLock.unlock();
274			}
275	tim	1.12	if (c == 0)
276	dl	1.2	signalNotEmpty();
277	tim	1.1	}
278	dl	1.2
279	dholmes	1.8	/**
280	dholmes	1.13	* Adds the specified element to the tail of this queue, waiting if
281	dholmes	1.8	* necessary up to the specified wait time for space to become available.
282			* @throws NullPointerException {@inheritDoc}
283			*/
284	dholmes	1.14	public boolean offer(E o, long timeout, TimeUnit unit)
285	dholmes	1.8	throws InterruptedException {
286	tim	1.12
287	dholmes	1.14	if (o == null) throw new NullPointerException();
288	dl	1.2	long nanos = unit.toNanos(timeout);
289			int c = -1;
290	dholmes	1.8	putLock.lockInterruptibly();
291	dl	1.2	try {
292			for (;;) {
293			if (count.get() < capacity) {
294	dholmes	1.14	insert(o);
295	dl	1.2	c = count.getAndIncrement();
296	dl	1.6	if (c + 1 < capacity)
297	dl	1.2	notFull.signal();
298			break;
299			}
300			if (nanos <= 0)
301			return false;
302			try {
303			nanos = notFull.awaitNanos(nanos);
304			}
305			catch (InterruptedException ie) {
306			notFull.signal(); // propagate to a non-interrupted thread
307			throw ie;
308			}
309			}
310			}
311			finally {
312			putLock.unlock();
313			}
314	tim	1.12	if (c == 0)
315	dl	1.2	signalNotEmpty();
316			return true;
317	tim	1.1	}
318	dl	1.2
319	tim	1.12	/**
320	dholmes	1.13	* Adds the specified element to the tail of this queue if possible,
321	dholmes	1.8	* returning immediately if this queue is full.
322			*
323			* @throws NullPointerException {@inheritDoc}
324			*/
325	dholmes	1.14	public boolean offer(E o) {
326			if (o == null) throw new NullPointerException();
327	dl	1.2	if (count.get() == capacity)
328			return false;
329	tim	1.12	int c = -1;
330	dholmes	1.8	putLock.lock();
331	dl	1.2	try {
332			if (count.get() < capacity) {
333	dholmes	1.14	insert(o);
334	dl	1.2	c = count.getAndIncrement();
335	dl	1.6	if (c + 1 < capacity)
336	dl	1.2	notFull.signal();
337			}
338			}
339			finally {
340			putLock.unlock();
341			}
342	tim	1.12	if (c == 0)
343	dl	1.2	signalNotEmpty();
344			return c >= 0;
345	tim	1.1	}
346	dl	1.2
347
348			public E take() throws InterruptedException {
349			E x;
350			int c = -1;
351			takeLock.lockInterruptibly();
352			try {
353			try {
354	tim	1.12	while (count.get() == 0)
355	dl	1.2	notEmpty.await();
356			}
357			catch (InterruptedException ie) {
358			notEmpty.signal(); // propagate to a non-interrupted thread
359			throw ie;
360			}
361
362			x = extract();
363			c = count.getAndDecrement();
364			if (c > 1)
365			notEmpty.signal();
366			}
367			finally {
368			takeLock.unlock();
369			}
370	tim	1.12	if (c == capacity)
371	dl	1.2	signalNotFull();
372			return x;
373			}
374
375			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
376			E x = null;
377			int c = -1;
378	dholmes	1.8	long nanos = unit.toNanos(timeout);
379	dl	1.2	takeLock.lockInterruptibly();
380			try {
381			for (;;) {
382			if (count.get() > 0) {
383			x = extract();
384			c = count.getAndDecrement();
385			if (c > 1)
386			notEmpty.signal();
387			break;
388			}
389			if (nanos <= 0)
390			return null;
391			try {
392			nanos = notEmpty.awaitNanos(nanos);
393			}
394			catch (InterruptedException ie) {
395			notEmpty.signal(); // propagate to a non-interrupted thread
396			throw ie;
397			}
398			}
399			}
400			finally {
401			takeLock.unlock();
402			}
403	tim	1.12	if (c == capacity)
404	dl	1.2	signalNotFull();
405			return x;
406			}
407
408			public E poll() {
409			if (count.get() == 0)
410			return null;
411			E x = null;
412	tim	1.12	int c = -1;
413	dl	1.2	takeLock.tryLock();
414			try {
415			if (count.get() > 0) {
416			x = extract();
417			c = count.getAndDecrement();
418			if (c > 1)
419			notEmpty.signal();
420			}
421			}
422			finally {
423			takeLock.unlock();
424			}
425	tim	1.12	if (c == capacity)
426	dl	1.2	signalNotFull();
427			return x;
428	tim	1.1	}
429	dl	1.2
430
431			public E peek() {
432			if (count.get() == 0)
433			return null;
434	dholmes	1.8	takeLock.lock();
435	dl	1.2	try {
436			Node<E> first = head.next;
437			if (first == null)
438			return null;
439			else
440			return first.item;
441			}
442			finally {
443			takeLock.unlock();
444			}
445	tim	1.1	}
446
447	dholmes	1.14	/**
448			* Removes a single instance of the specified element from this
449			* queue, if it is present. More formally,
450			* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
451			* o.equals(e))</tt>, if the queue contains one or more such
452			* elements. Returns <tt>true</tt> if the queue contained the
453			* specified element (or equivalently, if the queue changed as a
454			* result of the call).
455			*
456			* <p>This implementation iterates over the queue looking for the
457			* specified element. If it finds the element, it removes the element
458			* from the queue using the iterator's remove method.<p>
459			*
460			*/
461	dholmes	1.9	public boolean remove(Object o) {
462			if (o == null) return false;
463	dl	1.2	boolean removed = false;
464			fullyLock();
465			try {
466			Node<E> trail = head;
467			Node<E> p = head.next;
468			while (p != null) {
469	dholmes	1.9	if (o.equals(p.item)) {
470	dl	1.2	removed = true;
471			break;
472			}
473			trail = p;
474			p = p.next;
475			}
476			if (removed) {
477			p.item = null;
478			trail.next = p.next;
479			if (count.getAndDecrement() == capacity)
480			notFull.signalAll();
481			}
482			}
483			finally {
484			fullyUnlock();
485			}
486			return removed;
487	tim	1.1	}
488	dl	1.2
489			public Object[] toArray() {
490			fullyLock();
491			try {
492			int size = count.get();
493	tim	1.12	Object[] a = new Object[size];
494	dl	1.2	int k = 0;
495	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
496	dl	1.2	a[k++] = p.item;
497			return a;
498			}
499			finally {
500			fullyUnlock();
501			}
502	tim	1.1	}
503	dl	1.2
504			public <T> T[] toArray(T[] a) {
505			fullyLock();
506			try {
507			int size = count.get();
508			if (a.length < size)
509	dl	1.4	a = (T[])java.lang.reflect.Array.newInstance
510			(a.getClass().getComponentType(), size);
511	tim	1.12
512	dl	1.2	int k = 0;
513	tim	1.12	for (Node p = head.next; p != null; p = p.next)
514	dl	1.2	a[k++] = (T)p.item;
515			return a;
516			}
517			finally {
518			fullyUnlock();
519			}
520	tim	1.1	}
521	dl	1.2
522			public String toString() {
523			fullyLock();
524			try {
525			return super.toString();
526			}
527			finally {
528			fullyUnlock();
529			}
530	tim	1.1	}
531	dl	1.2
532	dholmes	1.14	/**
533			* Returns an iterator over the elements in this queue in proper sequence.
534			*
535			* @return an iterator over the elements in this queue in proper sequence.
536			*/
537	dl	1.2	public Iterator<E> iterator() {
538			return new Itr();
539	tim	1.1	}
540	dl	1.2
541			private class Itr implements Iterator<E> {
542	tim	1.12	/*
543	dl	1.4	* Basic weak-consistent iterator. At all times hold the next
544			* item to hand out so that if hasNext() reports true, we will
545			* still have it to return even if lost race with a take etc.
546			*/
547	dl	1.2	Node<E> current;
548			Node<E> lastRet;
549	dl	1.4	E currentElement;
550	tim	1.12
551	dl	1.2	Itr() {
552			fullyLock();
553			try {
554			current = head.next;
555	dl	1.4	if (current != null)
556			currentElement = current.item;
557	dl	1.2	}
558			finally {
559			fullyUnlock();
560			}
561			}
562	tim	1.12
563			public boolean hasNext() {
564	dl	1.2	return current != null;
565			}
566
567	tim	1.12	public E next() {
568	dl	1.2	fullyLock();
569			try {
570			if (current == null)
571			throw new NoSuchElementException();
572	dl	1.4	E x = currentElement;
573	dl	1.2	lastRet = current;
574			current = current.next;
575	dl	1.4	if (current != null)
576			currentElement = current.item;
577	dl	1.2	return x;
578			}
579			finally {
580			fullyUnlock();
581			}
582	tim	1.12
583	dl	1.2	}
584
585	tim	1.12	public void remove() {
586	dl	1.2	if (lastRet == null)
587	tim	1.12	throw new IllegalStateException();
588	dl	1.2	fullyLock();
589			try {
590			Node<E> node = lastRet;
591			lastRet = null;
592			Node<E> trail = head;
593			Node<E> p = head.next;
594			while (p != null && p != node) {
595			trail = p;
596			p = p.next;
597			}
598			if (p == node) {
599			p.item = null;
600			trail.next = p.next;
601			int c = count.getAndDecrement();
602			if (c == capacity)
603			notFull.signalAll();
604			}
605			}
606			finally {
607			fullyUnlock();
608			}
609			}
610	tim	1.1	}
611	dl	1.2
612			/**
613			* Save the state to a stream (that is, serialize it).
614			*
615			* @serialData The capacity is emitted (int), followed by all of
616			* its elements (each an <tt>Object</tt>) in the proper order,
617			* followed by a null
618	dl	1.6	* @param s the stream
619	dl	1.2	*/
620			private void writeObject(java.io.ObjectOutputStream s)
621			throws java.io.IOException {
622
623	tim	1.12	fullyLock();
624	dl	1.2	try {
625			// Write out any hidden stuff, plus capacity
626			s.defaultWriteObject();
627
628			// Write out all elements in the proper order.
629	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
630	dl	1.2	s.writeObject(p.item);
631
632			// Use trailing null as sentinel
633			s.writeObject(null);
634			}
635			finally {
636			fullyUnlock();
637			}
638	tim	1.1	}
639
640	dl	1.2	/**
641	dholmes	1.8	* Reconstitute this queue instance from a stream (that is,
642	dl	1.2	* deserialize it).
643	dl	1.6	* @param s the stream
644	dl	1.2	*/
645			private void readObject(java.io.ObjectInputStream s)
646			throws java.io.IOException, ClassNotFoundException {
647	tim	1.12	// Read in capacity, and any hidden stuff
648			s.defaultReadObject();
649	dl	1.2
650	dl	1.6	// Read in all elements and place in queue
651	dl	1.2	for (;;) {
652			E item = (E)s.readObject();
653			if (item == null)
654			break;
655			add(item);
656			}
657	tim	1.1	}
658			}
659	dholmes	1.8
660
661
662
663	tim	1.1