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. New elements
 * are inserted at the tail of the queue, and the queue retrieval
 * operations obtain elements at the head of the queue.
 * 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.
 *
 * <p>This class implements all of the <em>optional</em> methods
 * of the {@link Collection} and {@link Iterator} interfaces.
 *
 * @since 1.5
 * @author Doug Lea
 *
 **/
public class LinkedBlockingQueue<E> extends AbstractQueue<E>
        implements BlockingQueue<E>, java.io.Serializable {
    private static final long serialVersionUID = -6903933977591709194L;

    /*
     * 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 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());
    }


    // 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 queue.
     *
     * @return  the number of elements in this queue.
     */
    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.
     * @param o the element to add
     * @throws InterruptedException if interrupted while waiting.
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    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();
    }

    /**
     * Inserts the specified element at the tail of this queue, waiting if
     * necessary up to the specified wait time for space to become available.
     * @param o the element to add
     * @param timeout how long to wait before giving up, in units of
     * <tt>unit</tt>
     * @param unit a <tt>TimeUnit</tt> determining how to interpret the
     * <tt>timeout</tt> parameter
     * @return <tt>true</tt> if successful, or <tt>false</tt> if
     * the specified waiting time elapses before space is available.
     * @throws InterruptedException if interrupted while waiting.
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    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;
    }

    /**
     * Inserts the specified element at the tail of this queue if possible,
     * returning immediately if this queue is full.
     *
     * @param o the element to add.
     * @return <tt>true</tt> if it was possible to add the element to
     *         this queue, else <tt>false</tt>
     * @throws NullPointerException if the specified element is <tt>null</tt>
     */
    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();
        }
    }

    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();
        }
    }

    public void clear() {
        fullyLock();
        try {
            head.next = null;
            if (count.getAndSet(0) == capacity)
                notFull.signalAll();
        } finally {
            fullyUnlock();
        }
    }

    public int drainTo(Collection<? super E> c) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        Node first;
        fullyLock();
        try {
            first = head.next;
            head.next = null;
            if (count.getAndSet(0) == capacity)
                notFull.signalAll();
        } finally {
            fullyUnlock();
        }
        // Transfer the elements outside of locks
        int n = 0;
        for (Node p = first; p != null; p = p.next) {
            c.add((E)p.item);
            p.item = null;
            ++n;
        }
        return n;
    }
        
    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;
        fullyLock();
        try {
            int n = 0;
            Node p = head.next;
            while (p != null && n < maxElements) {
                c.add((E)p.item);
                p.item = null;
                p = p.next;
                ++n;
            }
            if (n != 0) {
                head.next = p;
                if (count.getAndAdd(-n) == capacity)
                    notFull.signalAll();
            }
            return n;
        } finally {
            fullyUnlock();
        }
    }
        

    /**
     * Returns an iterator over the elements in this queue in proper sequence.
     * The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
     * will never throw {@link java.util.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 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();

        count.set(0);
        last = head = new Node<E>(null);

        // Read in all elements and place in queue
        for (;;) {
            E item = (E)s.readObject();
            if (item == null)
                break;
            add(item);
        }
    }
}
Revision:	1.24
Committed:	Sun Oct 5 23:00:18 2003 UTC (20 years, 8 months ago) by dl
Branch:	MAIN
Changes since 1.23:	+66 -0 lines
Log Message:	added drainTo; clarified various exception specs
#	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	dl	1.20	* queue the shortest time. New elements
20			* are inserted at the tail of the queue, and the queue retrieval
21			* operations obtain elements at the head of the queue.
22	dholmes	1.8	* Linked queues typically have higher throughput than array-based queues but
23			* less predictable performance in most concurrent applications.
24	tim	1.12	*
25	dl	1.3	* <p> The optional capacity bound constructor argument serves as a
26	dholmes	1.8	* way to prevent excessive queue expansion. The capacity, if unspecified,
27			* is equal to {@link Integer#MAX_VALUE}. Linked nodes are
28	dl	1.3	* dynamically created upon each insertion unless this would bring the
29			* queue above capacity.
30	dholmes	1.8	*
31	dl	1.21	* <p>This class implements all of the <em>optional</em> methods
32			* of the {@link Collection} and {@link Iterator} interfaces.
33			*
34	dl	1.6	* @since 1.5
35			* @author Doug Lea
36	tim	1.12	*
37	tim	1.1	**/
38	dl	1.2	public class LinkedBlockingQueue<E> extends AbstractQueue<E>
39	tim	1.1	implements BlockingQueue<E>, java.io.Serializable {
40	dl	1.18	private static final long serialVersionUID = -6903933977591709194L;
41	tim	1.1
42	dl	1.2	/*
43			* A variant of the "two lock queue" algorithm. The putLock gates
44			* entry to put (and offer), and has an associated condition for
45			* waiting puts. Similarly for the takeLock. The "count" field
46			* that they both rely on is maintained as an atomic to avoid
47			* needing to get both locks in most cases. Also, to minimize need
48			* for puts to get takeLock and vice-versa, cascading notifies are
49			* used. When a put notices that it has enabled at least one take,
50			* it signals taker. That taker in turn signals others if more
51			* items have been entered since the signal. And symmetrically for
52	tim	1.12	* takes signalling puts. Operations such as remove(Object) and
53	dl	1.2	* iterators acquire both locks.
54			*/
55
56	dl	1.6	/**
57			* Linked list node class
58			*/
59	dl	1.2	static class Node<E> {
60	dl	1.6	/** The item, volatile to ensure barrier separating write and read */
61	dl	1.2	volatile E item;
62			Node<E> next;
63			Node(E x) { item = x; }
64			}
65
66	dl	1.6	/** The capacity bound, or Integer.MAX_VALUE if none */
67	dl	1.2	private final int capacity;
68	dl	1.6
69			/** Current number of elements */
70	dl	1.19	private final AtomicInteger count = new AtomicInteger(0);
71	dl	1.2
72	dl	1.6	/** Head of linked list */
73			private transient Node<E> head;
74
75	dholmes	1.8	/** Tail of linked list */
76	dl	1.6	private transient Node<E> last;
77	dl	1.2
78	dl	1.6	/** Lock held by take, poll, etc */
79	dl	1.5	private final ReentrantLock takeLock = new ReentrantLock();
80	dl	1.6
81			/** Wait queue for waiting takes */
82	dl	1.5	private final Condition notEmpty = takeLock.newCondition();
83	dl	1.2
84	dl	1.6	/** Lock held by put, offer, etc */
85	dl	1.5	private final ReentrantLock putLock = new ReentrantLock();
86	dl	1.6
87			/** Wait queue for waiting puts */
88	dl	1.5	private final Condition notFull = putLock.newCondition();
89	dl	1.2
90			/**
91			* Signal a waiting take. Called only from put/offer (which do not
92	dl	1.4	* otherwise ordinarily lock takeLock.)
93	dl	1.2	*/
94			private void signalNotEmpty() {
95			takeLock.lock();
96			try {
97			notEmpty.signal();
98	tim	1.17	} finally {
99	dl	1.2	takeLock.unlock();
100			}
101			}
102
103			/**
104			* Signal a waiting put. Called only from take/poll.
105			*/
106			private void signalNotFull() {
107			putLock.lock();
108			try {
109			notFull.signal();
110	tim	1.17	} finally {
111	dl	1.2	putLock.unlock();
112			}
113			}
114
115			/**
116	dholmes	1.8	* Create a node and link it at end of queue
117	dl	1.6	* @param x the item
118	dl	1.2	*/
119			private void insert(E x) {
120			last = last.next = new Node<E>(x);
121			}
122
123			/**
124			* Remove a node from head of queue,
125	dl	1.6	* @return the node
126	dl	1.2	*/
127			private E extract() {
128			Node<E> first = head.next;
129			head = first;
130			E x = (E)first.item;
131			first.item = null;
132			return x;
133			}
134
135			/**
136	tim	1.12	* Lock to prevent both puts and takes.
137	dl	1.2	*/
138			private void fullyLock() {
139			putLock.lock();
140			takeLock.lock();
141	tim	1.1	}
142	dl	1.2
143			/**
144	tim	1.12	* Unlock to allow both puts and takes.
145	dl	1.2	*/
146			private void fullyUnlock() {
147			takeLock.unlock();
148			putLock.unlock();
149			}
150
151
152			/**
153	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
154	dholmes	1.8	* {@link Integer#MAX_VALUE}.
155	dl	1.2	*/
156			public LinkedBlockingQueue() {
157			this(Integer.MAX_VALUE);
158			}
159
160			/**
161	tim	1.16	* Creates a <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity.
162			*
163	dholmes	1.8	* @param capacity the capacity of this queue.
164			* @throws IllegalArgumentException if <tt>capacity</tt> is not greater
165	tim	1.16	* than zero.
166	dl	1.2	*/
167			public LinkedBlockingQueue(int capacity) {
168	dholmes	1.8	if (capacity <= 0) throw new IllegalArgumentException();
169	dl	1.2	this.capacity = capacity;
170	dl	1.6	last = head = new Node<E>(null);
171	dl	1.2	}
172
173			/**
174	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
175	dholmes	1.14	* {@link Integer#MAX_VALUE}, initially containing the elements of the
176	tim	1.12	* given collection,
177	dholmes	1.8	* added in traversal order of the collection's iterator.
178	dholmes	1.9	* @param c the collection of elements to initially contain
179			* @throws NullPointerException if <tt>c</tt> or any element within it
180			* is <tt>null</tt>
181	dl	1.2	*/
182	dholmes	1.10	public LinkedBlockingQueue(Collection<? extends E> c) {
183	dl	1.2	this(Integer.MAX_VALUE);
184	tim	1.12	for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
185			add(it.next());
186	dl	1.2	}
187
188	dholmes	1.9
189	dholmes	1.8	// this doc comment is overridden to remove the reference to collections
190			// greater in size than Integer.MAX_VALUE
191	tim	1.12	/**
192	dl	1.20	* Returns the number of elements in this queue.
193			*
194			* @return the number of elements in this queue.
195	dholmes	1.8	*/
196	dl	1.2	public int size() {
197			return count.get();
198	tim	1.1	}
199	dl	1.2
200	dholmes	1.8	// this doc comment is a modified copy of the inherited doc comment,
201			// without the reference to unlimited queues.
202	tim	1.12	/**
203	dholmes	1.13	* Returns the number of elements that this queue can ideally (in
204	dholmes	1.8	* the absence of memory or resource constraints) accept without
205			* blocking. This is always equal to the initial capacity of this queue
206			* less the current <tt>size</tt> of this queue.
207			* <p>Note that you <em>cannot</em> always tell if
208			* an attempt to <tt>add</tt> an element will succeed by
209			* inspecting <tt>remainingCapacity</tt> because it may be the
210			* case that a waiting consumer is ready to <tt>take</tt> an
211			* element out of an otherwise full queue.
212			*/
213	dl	1.2	public int remainingCapacity() {
214			return capacity - count.get();
215			}
216
217	dholmes	1.22	/**
218			* Adds the specified element to the tail of this queue, waiting if
219			* necessary for space to become available.
220	dl	1.23	* @param o the element to add
221			* @throws InterruptedException if interrupted while waiting.
222	dholmes	1.22	* @throws NullPointerException if the specified element is <tt>null</tt>.
223			*/
224	dholmes	1.14	public void put(E o) throws InterruptedException {
225			if (o == null) throw new NullPointerException();
226	dl	1.2	// Note: convention in all put/take/etc is to preset
227			// local var holding count negative to indicate failure unless set.
228	tim	1.12	int c = -1;
229	dl	1.2	putLock.lockInterruptibly();
230			try {
231			/*
232			* Note that count is used in wait guard even though it is
233			* not protected by lock. This works because count can
234			* only decrease at this point (all other puts are shut
235			* out by lock), and we (or some other waiting put) are
236			* signalled if it ever changes from
237			* capacity. Similarly for all other uses of count in
238			* other wait guards.
239			*/
240			try {
241	tim	1.12	while (count.get() == capacity)
242	dl	1.2	notFull.await();
243	tim	1.17	} catch (InterruptedException ie) {
244	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
245			throw ie;
246			}
247	dholmes	1.14	insert(o);
248	dl	1.2	c = count.getAndIncrement();
249	dl	1.6	if (c + 1 < capacity)
250	dl	1.2	notFull.signal();
251	tim	1.17	} finally {
252	dl	1.2	putLock.unlock();
253			}
254	tim	1.12	if (c == 0)
255	dl	1.2	signalNotEmpty();
256	tim	1.1	}
257	dl	1.2
258	dholmes	1.22	/**
259			* Inserts the specified element at the tail of this queue, waiting if
260			* necessary up to the specified wait time for space to become available.
261	dl	1.23	* @param o the element to add
262			* @param timeout how long to wait before giving up, in units of
263			* <tt>unit</tt>
264			* @param unit a <tt>TimeUnit</tt> determining how to interpret the
265			* <tt>timeout</tt> parameter
266			* @return <tt>true</tt> if successful, or <tt>false</tt> if
267			* the specified waiting time elapses before space is available.
268			* @throws InterruptedException if interrupted while waiting.
269	dholmes	1.22	* @throws NullPointerException if the specified element is <tt>null</tt>.
270			*/
271	dholmes	1.14	public boolean offer(E o, long timeout, TimeUnit unit)
272	dholmes	1.8	throws InterruptedException {
273	tim	1.12
274	dholmes	1.14	if (o == null) throw new NullPointerException();
275	dl	1.2	long nanos = unit.toNanos(timeout);
276			int c = -1;
277	dholmes	1.8	putLock.lockInterruptibly();
278	dl	1.2	try {
279			for (;;) {
280			if (count.get() < capacity) {
281	dholmes	1.14	insert(o);
282	dl	1.2	c = count.getAndIncrement();
283	dl	1.6	if (c + 1 < capacity)
284	dl	1.2	notFull.signal();
285			break;
286			}
287			if (nanos <= 0)
288			return false;
289			try {
290			nanos = notFull.awaitNanos(nanos);
291	tim	1.17	} catch (InterruptedException ie) {
292	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
293			throw ie;
294			}
295			}
296	tim	1.17	} finally {
297	dl	1.2	putLock.unlock();
298			}
299	tim	1.12	if (c == 0)
300	dl	1.2	signalNotEmpty();
301			return true;
302	tim	1.1	}
303	dl	1.2
304	dl	1.23	/**
305			* Inserts the specified element at the tail of this queue if possible,
306			* returning immediately if this queue is full.
307			*
308			* @param o the element to add.
309			* @return <tt>true</tt> if it was possible to add the element to
310			* this queue, else <tt>false</tt>
311			* @throws NullPointerException if the specified element is <tt>null</tt>
312			*/
313	dholmes	1.14	public boolean offer(E o) {
314			if (o == null) throw new NullPointerException();
315	dl	1.2	if (count.get() == capacity)
316			return false;
317	tim	1.12	int c = -1;
318	dholmes	1.8	putLock.lock();
319	dl	1.2	try {
320			if (count.get() < capacity) {
321	dholmes	1.14	insert(o);
322	dl	1.2	c = count.getAndIncrement();
323	dl	1.6	if (c + 1 < capacity)
324	dl	1.2	notFull.signal();
325			}
326	tim	1.17	} finally {
327	dl	1.2	putLock.unlock();
328			}
329	tim	1.12	if (c == 0)
330	dl	1.2	signalNotEmpty();
331			return c >= 0;
332	tim	1.1	}
333	dl	1.2
334
335			public E take() throws InterruptedException {
336			E x;
337			int c = -1;
338			takeLock.lockInterruptibly();
339			try {
340			try {
341	tim	1.12	while (count.get() == 0)
342	dl	1.2	notEmpty.await();
343	tim	1.17	} catch (InterruptedException ie) {
344	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
345			throw ie;
346			}
347
348			x = extract();
349			c = count.getAndDecrement();
350			if (c > 1)
351			notEmpty.signal();
352	tim	1.17	} finally {
353	dl	1.2	takeLock.unlock();
354			}
355	tim	1.12	if (c == capacity)
356	dl	1.2	signalNotFull();
357			return x;
358			}
359
360			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
361			E x = null;
362			int c = -1;
363	dholmes	1.8	long nanos = unit.toNanos(timeout);
364	dl	1.2	takeLock.lockInterruptibly();
365			try {
366			for (;;) {
367			if (count.get() > 0) {
368			x = extract();
369			c = count.getAndDecrement();
370			if (c > 1)
371			notEmpty.signal();
372			break;
373			}
374			if (nanos <= 0)
375			return null;
376			try {
377			nanos = notEmpty.awaitNanos(nanos);
378	tim	1.17	} catch (InterruptedException ie) {
379	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
380			throw ie;
381			}
382			}
383	tim	1.17	} finally {
384	dl	1.2	takeLock.unlock();
385			}
386	tim	1.12	if (c == capacity)
387	dl	1.2	signalNotFull();
388			return x;
389			}
390
391			public E poll() {
392			if (count.get() == 0)
393			return null;
394			E x = null;
395	tim	1.12	int c = -1;
396	dl	1.2	takeLock.tryLock();
397			try {
398			if (count.get() > 0) {
399			x = extract();
400			c = count.getAndDecrement();
401			if (c > 1)
402			notEmpty.signal();
403			}
404	tim	1.17	} finally {
405	dl	1.2	takeLock.unlock();
406			}
407	tim	1.12	if (c == capacity)
408	dl	1.2	signalNotFull();
409			return x;
410	tim	1.1	}
411	dl	1.2
412
413			public E peek() {
414			if (count.get() == 0)
415			return null;
416	dholmes	1.8	takeLock.lock();
417	dl	1.2	try {
418			Node<E> first = head.next;
419			if (first == null)
420			return null;
421			else
422			return first.item;
423	tim	1.17	} finally {
424	dl	1.2	takeLock.unlock();
425			}
426	tim	1.1	}
427
428	dholmes	1.9	public boolean remove(Object o) {
429			if (o == null) return false;
430	dl	1.2	boolean removed = false;
431			fullyLock();
432			try {
433			Node<E> trail = head;
434			Node<E> p = head.next;
435			while (p != null) {
436	dholmes	1.9	if (o.equals(p.item)) {
437	dl	1.2	removed = true;
438			break;
439			}
440			trail = p;
441			p = p.next;
442			}
443			if (removed) {
444			p.item = null;
445			trail.next = p.next;
446			if (count.getAndDecrement() == capacity)
447			notFull.signalAll();
448			}
449	tim	1.17	} finally {
450	dl	1.2	fullyUnlock();
451			}
452			return removed;
453	tim	1.1	}
454	dl	1.2
455			public Object[] toArray() {
456			fullyLock();
457			try {
458			int size = count.get();
459	tim	1.12	Object[] a = new Object[size];
460	dl	1.2	int k = 0;
461	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
462	dl	1.2	a[k++] = p.item;
463			return a;
464	tim	1.17	} finally {
465	dl	1.2	fullyUnlock();
466			}
467	tim	1.1	}
468	dl	1.2
469			public <T> T[] toArray(T[] a) {
470			fullyLock();
471			try {
472			int size = count.get();
473			if (a.length < size)
474	dl	1.4	a = (T[])java.lang.reflect.Array.newInstance
475			(a.getClass().getComponentType(), size);
476	tim	1.12
477	dl	1.2	int k = 0;
478	tim	1.12	for (Node p = head.next; p != null; p = p.next)
479	dl	1.2	a[k++] = (T)p.item;
480			return a;
481	tim	1.17	} finally {
482	dl	1.2	fullyUnlock();
483			}
484	tim	1.1	}
485	dl	1.2
486			public String toString() {
487			fullyLock();
488			try {
489			return super.toString();
490	tim	1.17	} finally {
491	dl	1.2	fullyUnlock();
492			}
493	tim	1.1	}
494	dl	1.2
495	dl	1.24	public void clear() {
496			fullyLock();
497			try {
498			head.next = null;
499			if (count.getAndSet(0) == capacity)
500			notFull.signalAll();
501			} finally {
502			fullyUnlock();
503			}
504			}
505
506			public int drainTo(Collection<? super E> c) {
507			if (c == null)
508			throw new NullPointerException();
509			if (c == this)
510			throw new IllegalArgumentException();
511			Node first;
512			fullyLock();
513			try {
514			first = head.next;
515			head.next = null;
516			if (count.getAndSet(0) == capacity)
517			notFull.signalAll();
518			} finally {
519			fullyUnlock();
520			}
521			// Transfer the elements outside of locks
522			int n = 0;
523			for (Node p = first; p != null; p = p.next) {
524			c.add((E)p.item);
525			p.item = null;
526			++n;
527			}
528			return n;
529			}
530
531			public int drainTo(Collection<? super E> c, int maxElements) {
532			if (c == null)
533			throw new NullPointerException();
534			if (c == this)
535			throw new IllegalArgumentException();
536			if (maxElements <= 0)
537			return 0;
538			fullyLock();
539			try {
540			int n = 0;
541			Node p = head.next;
542			while (p != null && n < maxElements) {
543			c.add((E)p.item);
544			p.item = null;
545			p = p.next;
546			++n;
547			}
548			if (n != 0) {
549			head.next = p;
550			if (count.getAndAdd(-n) == capacity)
551			notFull.signalAll();
552			}
553			return n;
554			} finally {
555			fullyUnlock();
556			}
557			}
558
559
560
561	dholmes	1.14	/**
562			* Returns an iterator over the elements in this queue in proper sequence.
563	dl	1.15	* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
564			* will never throw {@link java.util.ConcurrentModificationException},
565			* and guarantees to traverse elements as they existed upon
566			* construction of the iterator, and may (but is not guaranteed to)
567			* reflect any modifications subsequent to construction.
568	dholmes	1.14	*
569			* @return an iterator over the elements in this queue in proper sequence.
570			*/
571	dl	1.2	public Iterator<E> iterator() {
572			return new Itr();
573	tim	1.1	}
574	dl	1.2
575			private class Itr implements Iterator<E> {
576	tim	1.12	/*
577	dl	1.4	* Basic weak-consistent iterator. At all times hold the next
578			* item to hand out so that if hasNext() reports true, we will
579			* still have it to return even if lost race with a take etc.
580			*/
581	dl	1.2	Node<E> current;
582			Node<E> lastRet;
583	dl	1.4	E currentElement;
584	tim	1.12
585	dl	1.2	Itr() {
586			fullyLock();
587			try {
588			current = head.next;
589	dl	1.4	if (current != null)
590			currentElement = current.item;
591	tim	1.17	} finally {
592	dl	1.2	fullyUnlock();
593			}
594			}
595	tim	1.12
596			public boolean hasNext() {
597	dl	1.2	return current != null;
598			}
599
600	tim	1.12	public E next() {
601	dl	1.2	fullyLock();
602			try {
603			if (current == null)
604			throw new NoSuchElementException();
605	dl	1.4	E x = currentElement;
606	dl	1.2	lastRet = current;
607			current = current.next;
608	dl	1.4	if (current != null)
609			currentElement = current.item;
610	dl	1.2	return x;
611	tim	1.17	} finally {
612	dl	1.2	fullyUnlock();
613			}
614	tim	1.12
615	dl	1.2	}
616
617	tim	1.12	public void remove() {
618	dl	1.2	if (lastRet == null)
619	tim	1.12	throw new IllegalStateException();
620	dl	1.2	fullyLock();
621			try {
622			Node<E> node = lastRet;
623			lastRet = null;
624			Node<E> trail = head;
625			Node<E> p = head.next;
626			while (p != null && p != node) {
627			trail = p;
628			p = p.next;
629			}
630			if (p == node) {
631			p.item = null;
632			trail.next = p.next;
633			int c = count.getAndDecrement();
634			if (c == capacity)
635			notFull.signalAll();
636			}
637	tim	1.17	} finally {
638	dl	1.2	fullyUnlock();
639			}
640			}
641	tim	1.1	}
642	dl	1.2
643			/**
644			* Save the state to a stream (that is, serialize it).
645			*
646			* @serialData The capacity is emitted (int), followed by all of
647			* its elements (each an <tt>Object</tt>) in the proper order,
648			* followed by a null
649	dl	1.6	* @param s the stream
650	dl	1.2	*/
651			private void writeObject(java.io.ObjectOutputStream s)
652			throws java.io.IOException {
653
654	tim	1.12	fullyLock();
655	dl	1.2	try {
656			// Write out any hidden stuff, plus capacity
657			s.defaultWriteObject();
658
659			// Write out all elements in the proper order.
660	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
661	dl	1.2	s.writeObject(p.item);
662
663			// Use trailing null as sentinel
664			s.writeObject(null);
665	tim	1.17	} finally {
666	dl	1.2	fullyUnlock();
667			}
668	tim	1.1	}
669
670	dl	1.2	/**
671	dholmes	1.8	* Reconstitute this queue instance from a stream (that is,
672	dl	1.2	* deserialize it).
673	dl	1.6	* @param s the stream
674	dl	1.2	*/
675			private void readObject(java.io.ObjectInputStream s)
676			throws java.io.IOException, ClassNotFoundException {
677	tim	1.12	// Read in capacity, and any hidden stuff
678			s.defaultReadObject();
679	dl	1.2
680	dl	1.19	count.set(0);
681			last = head = new Node<E>(null);
682
683	dl	1.6	// Read in all elements and place in queue
684	dl	1.2	for (;;) {
685			E item = (E)s.readObject();
686			if (item == null)
687			break;
688			add(item);
689			}
690	tim	1.1	}
691			}