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.
     * @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.
     * @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.
    *
    * @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:	1.22
Committed:	Mon Sep 15 06:24:21 2003 UTC (20 years, 9 months ago) by dholmes
Branch:	MAIN
Changes since 1.21:	+11 -4 lines
Log Message:	Restored overriding commenst referring to insertion at tail
#	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			* @throws NullPointerException if the specified element is <tt>null</tt>.
221			*/
222	dholmes	1.14	public void put(E o) throws InterruptedException {
223			if (o == null) throw new NullPointerException();
224	dl	1.2	// Note: convention in all put/take/etc is to preset
225			// local var holding count negative to indicate failure unless set.
226	tim	1.12	int c = -1;
227	dl	1.2	putLock.lockInterruptibly();
228			try {
229			/*
230			* Note that count is used in wait guard even though it is
231			* not protected by lock. This works because count can
232			* only decrease at this point (all other puts are shut
233			* out by lock), and we (or some other waiting put) are
234			* signalled if it ever changes from
235			* capacity. Similarly for all other uses of count in
236			* other wait guards.
237			*/
238			try {
239	tim	1.12	while (count.get() == capacity)
240	dl	1.2	notFull.await();
241	tim	1.17	} catch (InterruptedException ie) {
242	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
243			throw ie;
244			}
245	dholmes	1.14	insert(o);
246	dl	1.2	c = count.getAndIncrement();
247	dl	1.6	if (c + 1 < capacity)
248	dl	1.2	notFull.signal();
249	tim	1.17	} finally {
250	dl	1.2	putLock.unlock();
251			}
252	tim	1.12	if (c == 0)
253	dl	1.2	signalNotEmpty();
254	tim	1.1	}
255	dl	1.2
256	dholmes	1.22	/**
257			* Inserts the specified element at the tail of this queue, waiting if
258			* necessary up to the specified wait time for space to become available.
259			* @throws NullPointerException if the specified element is <tt>null</tt>.
260			*/
261	dholmes	1.14	public boolean offer(E o, long timeout, TimeUnit unit)
262	dholmes	1.8	throws InterruptedException {
263	tim	1.12
264	dholmes	1.14	if (o == null) throw new NullPointerException();
265	dl	1.2	long nanos = unit.toNanos(timeout);
266			int c = -1;
267	dholmes	1.8	putLock.lockInterruptibly();
268	dl	1.2	try {
269			for (;;) {
270			if (count.get() < capacity) {
271	dholmes	1.14	insert(o);
272	dl	1.2	c = count.getAndIncrement();
273	dl	1.6	if (c + 1 < capacity)
274	dl	1.2	notFull.signal();
275			break;
276			}
277			if (nanos <= 0)
278			return false;
279			try {
280			nanos = notFull.awaitNanos(nanos);
281	tim	1.17	} catch (InterruptedException ie) {
282	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
283			throw ie;
284			}
285			}
286	tim	1.17	} finally {
287	dl	1.2	putLock.unlock();
288			}
289	tim	1.12	if (c == 0)
290	dl	1.2	signalNotEmpty();
291			return true;
292	tim	1.1	}
293	dl	1.2
294	tim	1.12	/**
295	dholmes	1.22	* Inserts the specified element at the tail of this queue if possible,
296	dholmes	1.8	* returning immediately if this queue is full.
297			*
298	dl	1.20	* @throws NullPointerException if the specified element is <tt>null</tt>
299	dholmes	1.8	*/
300	dholmes	1.14	public boolean offer(E o) {
301			if (o == null) throw new NullPointerException();
302	dl	1.2	if (count.get() == capacity)
303			return false;
304	tim	1.12	int c = -1;
305	dholmes	1.8	putLock.lock();
306	dl	1.2	try {
307			if (count.get() < capacity) {
308	dholmes	1.14	insert(o);
309	dl	1.2	c = count.getAndIncrement();
310	dl	1.6	if (c + 1 < capacity)
311	dl	1.2	notFull.signal();
312			}
313	tim	1.17	} finally {
314	dl	1.2	putLock.unlock();
315			}
316	tim	1.12	if (c == 0)
317	dl	1.2	signalNotEmpty();
318			return c >= 0;
319	tim	1.1	}
320	dl	1.2
321
322			public E take() throws InterruptedException {
323			E x;
324			int c = -1;
325			takeLock.lockInterruptibly();
326			try {
327			try {
328	tim	1.12	while (count.get() == 0)
329	dl	1.2	notEmpty.await();
330	tim	1.17	} catch (InterruptedException ie) {
331	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
332			throw ie;
333			}
334
335			x = extract();
336			c = count.getAndDecrement();
337			if (c > 1)
338			notEmpty.signal();
339	tim	1.17	} finally {
340	dl	1.2	takeLock.unlock();
341			}
342	tim	1.12	if (c == capacity)
343	dl	1.2	signalNotFull();
344			return x;
345			}
346
347			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
348			E x = null;
349			int c = -1;
350	dholmes	1.8	long nanos = unit.toNanos(timeout);
351	dl	1.2	takeLock.lockInterruptibly();
352			try {
353			for (;;) {
354			if (count.get() > 0) {
355			x = extract();
356			c = count.getAndDecrement();
357			if (c > 1)
358			notEmpty.signal();
359			break;
360			}
361			if (nanos <= 0)
362			return null;
363			try {
364			nanos = notEmpty.awaitNanos(nanos);
365	tim	1.17	} catch (InterruptedException ie) {
366	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
367			throw ie;
368			}
369			}
370	tim	1.17	} finally {
371	dl	1.2	takeLock.unlock();
372			}
373	tim	1.12	if (c == capacity)
374	dl	1.2	signalNotFull();
375			return x;
376			}
377
378			public E poll() {
379			if (count.get() == 0)
380			return null;
381			E x = null;
382	tim	1.12	int c = -1;
383	dl	1.2	takeLock.tryLock();
384			try {
385			if (count.get() > 0) {
386			x = extract();
387			c = count.getAndDecrement();
388			if (c > 1)
389			notEmpty.signal();
390			}
391	tim	1.17	} finally {
392	dl	1.2	takeLock.unlock();
393			}
394	tim	1.12	if (c == capacity)
395	dl	1.2	signalNotFull();
396			return x;
397	tim	1.1	}
398	dl	1.2
399
400			public E peek() {
401			if (count.get() == 0)
402			return null;
403	dholmes	1.8	takeLock.lock();
404	dl	1.2	try {
405			Node<E> first = head.next;
406			if (first == null)
407			return null;
408			else
409			return first.item;
410	tim	1.17	} finally {
411	dl	1.2	takeLock.unlock();
412			}
413	tim	1.1	}
414
415	dholmes	1.9	public boolean remove(Object o) {
416			if (o == null) return false;
417	dl	1.2	boolean removed = false;
418			fullyLock();
419			try {
420			Node<E> trail = head;
421			Node<E> p = head.next;
422			while (p != null) {
423	dholmes	1.9	if (o.equals(p.item)) {
424	dl	1.2	removed = true;
425			break;
426			}
427			trail = p;
428			p = p.next;
429			}
430			if (removed) {
431			p.item = null;
432			trail.next = p.next;
433			if (count.getAndDecrement() == capacity)
434			notFull.signalAll();
435			}
436	tim	1.17	} finally {
437	dl	1.2	fullyUnlock();
438			}
439			return removed;
440	tim	1.1	}
441	dl	1.2
442			public Object[] toArray() {
443			fullyLock();
444			try {
445			int size = count.get();
446	tim	1.12	Object[] a = new Object[size];
447	dl	1.2	int k = 0;
448	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
449	dl	1.2	a[k++] = p.item;
450			return a;
451	tim	1.17	} finally {
452	dl	1.2	fullyUnlock();
453			}
454	tim	1.1	}
455	dl	1.2
456			public <T> T[] toArray(T[] a) {
457			fullyLock();
458			try {
459			int size = count.get();
460			if (a.length < size)
461	dl	1.4	a = (T[])java.lang.reflect.Array.newInstance
462			(a.getClass().getComponentType(), size);
463	tim	1.12
464	dl	1.2	int k = 0;
465	tim	1.12	for (Node p = head.next; p != null; p = p.next)
466	dl	1.2	a[k++] = (T)p.item;
467			return a;
468	tim	1.17	} finally {
469	dl	1.2	fullyUnlock();
470			}
471	tim	1.1	}
472	dl	1.2
473			public String toString() {
474			fullyLock();
475			try {
476			return super.toString();
477	tim	1.17	} finally {
478	dl	1.2	fullyUnlock();
479			}
480	tim	1.1	}
481	dl	1.2
482	dholmes	1.14	/**
483			* Returns an iterator over the elements in this queue in proper sequence.
484	dl	1.15	* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
485			* will never throw {@link java.util.ConcurrentModificationException},
486			* and guarantees to traverse elements as they existed upon
487			* construction of the iterator, and may (but is not guaranteed to)
488			* reflect any modifications subsequent to construction.
489	dholmes	1.14	*
490			* @return an iterator over the elements in this queue in proper sequence.
491			*/
492	dl	1.2	public Iterator<E> iterator() {
493			return new Itr();
494	tim	1.1	}
495	dl	1.2
496			private class Itr implements Iterator<E> {
497	tim	1.12	/*
498	dl	1.4	* Basic weak-consistent iterator. At all times hold the next
499			* item to hand out so that if hasNext() reports true, we will
500			* still have it to return even if lost race with a take etc.
501			*/
502	dl	1.2	Node<E> current;
503			Node<E> lastRet;
504	dl	1.4	E currentElement;
505	tim	1.12
506	dl	1.2	Itr() {
507			fullyLock();
508			try {
509			current = head.next;
510	dl	1.4	if (current != null)
511			currentElement = current.item;
512	tim	1.17	} finally {
513	dl	1.2	fullyUnlock();
514			}
515			}
516	tim	1.12
517			public boolean hasNext() {
518	dl	1.2	return current != null;
519			}
520
521	tim	1.12	public E next() {
522	dl	1.2	fullyLock();
523			try {
524			if (current == null)
525			throw new NoSuchElementException();
526	dl	1.4	E x = currentElement;
527	dl	1.2	lastRet = current;
528			current = current.next;
529	dl	1.4	if (current != null)
530			currentElement = current.item;
531	dl	1.2	return x;
532	tim	1.17	} finally {
533	dl	1.2	fullyUnlock();
534			}
535	tim	1.12
536	dl	1.2	}
537
538	tim	1.12	public void remove() {
539	dl	1.2	if (lastRet == null)
540	tim	1.12	throw new IllegalStateException();
541	dl	1.2	fullyLock();
542			try {
543			Node<E> node = lastRet;
544			lastRet = null;
545			Node<E> trail = head;
546			Node<E> p = head.next;
547			while (p != null && p != node) {
548			trail = p;
549			p = p.next;
550			}
551			if (p == node) {
552			p.item = null;
553			trail.next = p.next;
554			int c = count.getAndDecrement();
555			if (c == capacity)
556			notFull.signalAll();
557			}
558	tim	1.17	} finally {
559	dl	1.2	fullyUnlock();
560			}
561			}
562	tim	1.1	}
563	dl	1.2
564			/**
565			* Save the state to a stream (that is, serialize it).
566			*
567			* @serialData The capacity is emitted (int), followed by all of
568			* its elements (each an <tt>Object</tt>) in the proper order,
569			* followed by a null
570	dl	1.6	* @param s the stream
571	dl	1.2	*/
572			private void writeObject(java.io.ObjectOutputStream s)
573			throws java.io.IOException {
574
575	tim	1.12	fullyLock();
576	dl	1.2	try {
577			// Write out any hidden stuff, plus capacity
578			s.defaultWriteObject();
579
580			// Write out all elements in the proper order.
581	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
582	dl	1.2	s.writeObject(p.item);
583
584			// Use trailing null as sentinel
585			s.writeObject(null);
586	tim	1.17	} finally {
587	dl	1.2	fullyUnlock();
588			}
589	tim	1.1	}
590
591	dl	1.2	/**
592	dholmes	1.8	* Reconstitute this queue instance from a stream (that is,
593	dl	1.2	* deserialize it).
594	dl	1.6	* @param s the stream
595	dl	1.2	*/
596			private void readObject(java.io.ObjectInputStream s)
597			throws java.io.IOException, ClassNotFoundException {
598	tim	1.12	// Read in capacity, and any hidden stuff
599			s.defaultReadObject();
600	dl	1.2
601	dl	1.19	count.set(0);
602			last = head = new Node<E>(null);
603
604	dl	1.6	// Read in all elements and place in queue
605	dl	1.2	for (;;) {
606			E item = (E)s.readObject();
607			if (item == null)
608			break;
609			add(item);
610			}
611	tim	1.1	}
612			}