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();
    }

    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();
    }

    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.
    *
    * @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();
        }
    }

    /**
     * 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:	1.21
Committed:	Sat Sep 13 18:51:11 2003 UTC (20 years, 9 months ago) by dl
Branch:	MAIN
Changes since 1.20:	+3 -0 lines
Log Message:	Proofreading pass -- many minor adjustments
#	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	1.14	public void put(E o) throws InterruptedException {
218			if (o == null) throw new NullPointerException();
219	dl	1.2	// Note: convention in all put/take/etc is to preset
220			// local var holding count negative to indicate failure unless set.
221	tim	1.12	int c = -1;
222	dl	1.2	putLock.lockInterruptibly();
223			try {
224			/*
225			* Note that count is used in wait guard even though it is
226			* not protected by lock. This works because count can
227			* only decrease at this point (all other puts are shut
228			* out by lock), and we (or some other waiting put) are
229			* signalled if it ever changes from
230			* capacity. Similarly for all other uses of count in
231			* other wait guards.
232			*/
233			try {
234	tim	1.12	while (count.get() == capacity)
235	dl	1.2	notFull.await();
236	tim	1.17	} catch (InterruptedException ie) {
237	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
238			throw ie;
239			}
240	dholmes	1.14	insert(o);
241	dl	1.2	c = count.getAndIncrement();
242	dl	1.6	if (c + 1 < capacity)
243	dl	1.2	notFull.signal();
244	tim	1.17	} finally {
245	dl	1.2	putLock.unlock();
246			}
247	tim	1.12	if (c == 0)
248	dl	1.2	signalNotEmpty();
249	tim	1.1	}
250	dl	1.2
251	dholmes	1.14	public boolean offer(E o, long timeout, TimeUnit unit)
252	dholmes	1.8	throws InterruptedException {
253	tim	1.12
254	dholmes	1.14	if (o == null) throw new NullPointerException();
255	dl	1.2	long nanos = unit.toNanos(timeout);
256			int c = -1;
257	dholmes	1.8	putLock.lockInterruptibly();
258	dl	1.2	try {
259			for (;;) {
260			if (count.get() < capacity) {
261	dholmes	1.14	insert(o);
262	dl	1.2	c = count.getAndIncrement();
263	dl	1.6	if (c + 1 < capacity)
264	dl	1.2	notFull.signal();
265			break;
266			}
267			if (nanos <= 0)
268			return false;
269			try {
270			nanos = notFull.awaitNanos(nanos);
271	tim	1.17	} catch (InterruptedException ie) {
272	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
273			throw ie;
274			}
275			}
276	tim	1.17	} finally {
277	dl	1.2	putLock.unlock();
278			}
279	tim	1.12	if (c == 0)
280	dl	1.2	signalNotEmpty();
281			return true;
282	tim	1.1	}
283	dl	1.2
284	tim	1.12	/**
285	dholmes	1.13	* Adds the specified element to the tail of this queue if possible,
286	dholmes	1.8	* returning immediately if this queue is full.
287			*
288	dl	1.20	* @param o the element to add.
289			* @return <tt>true</tt> if it was possible to add the element to
290			* this queue, else <tt>false</tt>
291			* @throws NullPointerException if the specified element is <tt>null</tt>
292	dholmes	1.8	*/
293	dholmes	1.14	public boolean offer(E o) {
294			if (o == null) throw new NullPointerException();
295	dl	1.2	if (count.get() == capacity)
296			return false;
297	tim	1.12	int c = -1;
298	dholmes	1.8	putLock.lock();
299	dl	1.2	try {
300			if (count.get() < capacity) {
301	dholmes	1.14	insert(o);
302	dl	1.2	c = count.getAndIncrement();
303	dl	1.6	if (c + 1 < capacity)
304	dl	1.2	notFull.signal();
305			}
306	tim	1.17	} finally {
307	dl	1.2	putLock.unlock();
308			}
309	tim	1.12	if (c == 0)
310	dl	1.2	signalNotEmpty();
311			return c >= 0;
312	tim	1.1	}
313	dl	1.2
314
315			public E take() throws InterruptedException {
316			E x;
317			int c = -1;
318			takeLock.lockInterruptibly();
319			try {
320			try {
321	tim	1.12	while (count.get() == 0)
322	dl	1.2	notEmpty.await();
323	tim	1.17	} catch (InterruptedException ie) {
324	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
325			throw ie;
326			}
327
328			x = extract();
329			c = count.getAndDecrement();
330			if (c > 1)
331			notEmpty.signal();
332	tim	1.17	} finally {
333	dl	1.2	takeLock.unlock();
334			}
335	tim	1.12	if (c == capacity)
336	dl	1.2	signalNotFull();
337			return x;
338			}
339
340			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
341			E x = null;
342			int c = -1;
343	dholmes	1.8	long nanos = unit.toNanos(timeout);
344	dl	1.2	takeLock.lockInterruptibly();
345			try {
346			for (;;) {
347			if (count.get() > 0) {
348			x = extract();
349			c = count.getAndDecrement();
350			if (c > 1)
351			notEmpty.signal();
352			break;
353			}
354			if (nanos <= 0)
355			return null;
356			try {
357			nanos = notEmpty.awaitNanos(nanos);
358	tim	1.17	} catch (InterruptedException ie) {
359	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
360			throw ie;
361			}
362			}
363	tim	1.17	} finally {
364	dl	1.2	takeLock.unlock();
365			}
366	tim	1.12	if (c == capacity)
367	dl	1.2	signalNotFull();
368			return x;
369			}
370
371			public E poll() {
372			if (count.get() == 0)
373			return null;
374			E x = null;
375	tim	1.12	int c = -1;
376	dl	1.2	takeLock.tryLock();
377			try {
378			if (count.get() > 0) {
379			x = extract();
380			c = count.getAndDecrement();
381			if (c > 1)
382			notEmpty.signal();
383			}
384	tim	1.17	} finally {
385	dl	1.2	takeLock.unlock();
386			}
387	tim	1.12	if (c == capacity)
388	dl	1.2	signalNotFull();
389			return x;
390	tim	1.1	}
391	dl	1.2
392
393			public E peek() {
394			if (count.get() == 0)
395			return null;
396	dholmes	1.8	takeLock.lock();
397	dl	1.2	try {
398			Node<E> first = head.next;
399			if (first == null)
400			return null;
401			else
402			return first.item;
403	tim	1.17	} finally {
404	dl	1.2	takeLock.unlock();
405			}
406	tim	1.1	}
407
408	dholmes	1.9	public boolean remove(Object o) {
409			if (o == null) return false;
410	dl	1.2	boolean removed = false;
411			fullyLock();
412			try {
413			Node<E> trail = head;
414			Node<E> p = head.next;
415			while (p != null) {
416	dholmes	1.9	if (o.equals(p.item)) {
417	dl	1.2	removed = true;
418			break;
419			}
420			trail = p;
421			p = p.next;
422			}
423			if (removed) {
424			p.item = null;
425			trail.next = p.next;
426			if (count.getAndDecrement() == capacity)
427			notFull.signalAll();
428			}
429	tim	1.17	} finally {
430	dl	1.2	fullyUnlock();
431			}
432			return removed;
433	tim	1.1	}
434	dl	1.2
435			public Object[] toArray() {
436			fullyLock();
437			try {
438			int size = count.get();
439	tim	1.12	Object[] a = new Object[size];
440	dl	1.2	int k = 0;
441	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
442	dl	1.2	a[k++] = p.item;
443			return a;
444	tim	1.17	} finally {
445	dl	1.2	fullyUnlock();
446			}
447	tim	1.1	}
448	dl	1.2
449			public <T> T[] toArray(T[] a) {
450			fullyLock();
451			try {
452			int size = count.get();
453			if (a.length < size)
454	dl	1.4	a = (T[])java.lang.reflect.Array.newInstance
455			(a.getClass().getComponentType(), size);
456	tim	1.12
457	dl	1.2	int k = 0;
458	tim	1.12	for (Node p = head.next; p != null; p = p.next)
459	dl	1.2	a[k++] = (T)p.item;
460			return a;
461	tim	1.17	} finally {
462	dl	1.2	fullyUnlock();
463			}
464	tim	1.1	}
465	dl	1.2
466			public String toString() {
467			fullyLock();
468			try {
469			return super.toString();
470	tim	1.17	} finally {
471	dl	1.2	fullyUnlock();
472			}
473	tim	1.1	}
474	dl	1.2
475	dholmes	1.14	/**
476			* Returns an iterator over the elements in this queue in proper sequence.
477	dl	1.15	* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
478			* will never throw {@link java.util.ConcurrentModificationException},
479			* and guarantees to traverse elements as they existed upon
480			* construction of the iterator, and may (but is not guaranteed to)
481			* reflect any modifications subsequent to construction.
482	dholmes	1.14	*
483			* @return an iterator over the elements in this queue in proper sequence.
484			*/
485	dl	1.2	public Iterator<E> iterator() {
486			return new Itr();
487	tim	1.1	}
488	dl	1.2
489			private class Itr implements Iterator<E> {
490	tim	1.12	/*
491	dl	1.4	* Basic weak-consistent iterator. At all times hold the next
492			* item to hand out so that if hasNext() reports true, we will
493			* still have it to return even if lost race with a take etc.
494			*/
495	dl	1.2	Node<E> current;
496			Node<E> lastRet;
497	dl	1.4	E currentElement;
498	tim	1.12
499	dl	1.2	Itr() {
500			fullyLock();
501			try {
502			current = head.next;
503	dl	1.4	if (current != null)
504			currentElement = current.item;
505	tim	1.17	} finally {
506	dl	1.2	fullyUnlock();
507			}
508			}
509	tim	1.12
510			public boolean hasNext() {
511	dl	1.2	return current != null;
512			}
513
514	tim	1.12	public E next() {
515	dl	1.2	fullyLock();
516			try {
517			if (current == null)
518			throw new NoSuchElementException();
519	dl	1.4	E x = currentElement;
520	dl	1.2	lastRet = current;
521			current = current.next;
522	dl	1.4	if (current != null)
523			currentElement = current.item;
524	dl	1.2	return x;
525	tim	1.17	} finally {
526	dl	1.2	fullyUnlock();
527			}
528	tim	1.12
529	dl	1.2	}
530
531	tim	1.12	public void remove() {
532	dl	1.2	if (lastRet == null)
533	tim	1.12	throw new IllegalStateException();
534	dl	1.2	fullyLock();
535			try {
536			Node<E> node = lastRet;
537			lastRet = null;
538			Node<E> trail = head;
539			Node<E> p = head.next;
540			while (p != null && p != node) {
541			trail = p;
542			p = p.next;
543			}
544			if (p == node) {
545			p.item = null;
546			trail.next = p.next;
547			int c = count.getAndDecrement();
548			if (c == capacity)
549			notFull.signalAll();
550			}
551	tim	1.17	} finally {
552	dl	1.2	fullyUnlock();
553			}
554			}
555	tim	1.1	}
556	dl	1.2
557			/**
558			* Save the state to a stream (that is, serialize it).
559			*
560			* @serialData The capacity is emitted (int), followed by all of
561			* its elements (each an <tt>Object</tt>) in the proper order,
562			* followed by a null
563	dl	1.6	* @param s the stream
564	dl	1.2	*/
565			private void writeObject(java.io.ObjectOutputStream s)
566			throws java.io.IOException {
567
568	tim	1.12	fullyLock();
569	dl	1.2	try {
570			// Write out any hidden stuff, plus capacity
571			s.defaultWriteObject();
572
573			// Write out all elements in the proper order.
574	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
575	dl	1.2	s.writeObject(p.item);
576
577			// Use trailing null as sentinel
578			s.writeObject(null);
579	tim	1.17	} finally {
580	dl	1.2	fullyUnlock();
581			}
582	tim	1.1	}
583
584	dl	1.2	/**
585	dholmes	1.8	* Reconstitute this queue instance from a stream (that is,
586	dl	1.2	* deserialize it).
587	dl	1.6	* @param s the stream
588	dl	1.2	*/
589			private void readObject(java.io.ObjectInputStream s)
590			throws java.io.IOException, ClassNotFoundException {
591	tim	1.12	// Read in capacity, and any hidden stuff
592			s.defaultReadObject();
593	dl	1.2
594	dl	1.19	count.set(0);
595			last = head = new Node<E>(null);
596
597	dl	1.6	// Read in all elements and place in queue
598	dl	1.2	for (;;) {
599			E item = (E)s.readObject();
600			if (item == null)
601			break;
602			add(item);
603			}
604	tim	1.1	}
605			}