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.
 *
 * @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:	1.20
Committed:	Fri Sep 12 15:40:10 2003 UTC (20 years, 9 months ago) by dl
Branch:	MAIN
Changes since 1.19:	+10 -51 lines
Log Message:	Adapt AbstractQueue changes; Conditionalize CancellableTask.reset; new TimeUnit methods
#	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	1.6	* @since 1.5
32			* @author Doug Lea
33	tim	1.12	*
34	tim	1.1	**/
35	dl	1.2	public class LinkedBlockingQueue<E> extends AbstractQueue<E>
36	tim	1.1	implements BlockingQueue<E>, java.io.Serializable {
37	dl	1.18	private static final long serialVersionUID = -6903933977591709194L;
38	tim	1.1
39	dl	1.2	/*
40			* A variant of the "two lock queue" algorithm. The putLock gates
41			* entry to put (and offer), and has an associated condition for
42			* waiting puts. Similarly for the takeLock. The "count" field
43			* that they both rely on is maintained as an atomic to avoid
44			* needing to get both locks in most cases. Also, to minimize need
45			* for puts to get takeLock and vice-versa, cascading notifies are
46			* used. When a put notices that it has enabled at least one take,
47			* it signals taker. That taker in turn signals others if more
48			* items have been entered since the signal. And symmetrically for
49	tim	1.12	* takes signalling puts. Operations such as remove(Object) and
50	dl	1.2	* iterators acquire both locks.
51			*/
52
53	dl	1.6	/**
54			* Linked list node class
55			*/
56	dl	1.2	static class Node<E> {
57	dl	1.6	/** The item, volatile to ensure barrier separating write and read */
58	dl	1.2	volatile E item;
59			Node<E> next;
60			Node(E x) { item = x; }
61			}
62
63	dl	1.6	/** The capacity bound, or Integer.MAX_VALUE if none */
64	dl	1.2	private final int capacity;
65	dl	1.6
66			/** Current number of elements */
67	dl	1.19	private final AtomicInteger count = new AtomicInteger(0);
68	dl	1.2
69	dl	1.6	/** Head of linked list */
70			private transient Node<E> head;
71
72	dholmes	1.8	/** Tail of linked list */
73	dl	1.6	private transient Node<E> last;
74	dl	1.2
75	dl	1.6	/** Lock held by take, poll, etc */
76	dl	1.5	private final ReentrantLock takeLock = new ReentrantLock();
77	dl	1.6
78			/** Wait queue for waiting takes */
79	dl	1.5	private final Condition notEmpty = takeLock.newCondition();
80	dl	1.2
81	dl	1.6	/** Lock held by put, offer, etc */
82	dl	1.5	private final ReentrantLock putLock = new ReentrantLock();
83	dl	1.6
84			/** Wait queue for waiting puts */
85	dl	1.5	private final Condition notFull = putLock.newCondition();
86	dl	1.2
87			/**
88			* Signal a waiting take. Called only from put/offer (which do not
89	dl	1.4	* otherwise ordinarily lock takeLock.)
90	dl	1.2	*/
91			private void signalNotEmpty() {
92			takeLock.lock();
93			try {
94			notEmpty.signal();
95	tim	1.17	} finally {
96	dl	1.2	takeLock.unlock();
97			}
98			}
99
100			/**
101			* Signal a waiting put. Called only from take/poll.
102			*/
103			private void signalNotFull() {
104			putLock.lock();
105			try {
106			notFull.signal();
107	tim	1.17	} finally {
108	dl	1.2	putLock.unlock();
109			}
110			}
111
112			/**
113	dholmes	1.8	* Create a node and link it at end of queue
114	dl	1.6	* @param x the item
115	dl	1.2	*/
116			private void insert(E x) {
117			last = last.next = new Node<E>(x);
118			}
119
120			/**
121			* Remove a node from head of queue,
122	dl	1.6	* @return the node
123	dl	1.2	*/
124			private E extract() {
125			Node<E> first = head.next;
126			head = first;
127			E x = (E)first.item;
128			first.item = null;
129			return x;
130			}
131
132			/**
133	tim	1.12	* Lock to prevent both puts and takes.
134	dl	1.2	*/
135			private void fullyLock() {
136			putLock.lock();
137			takeLock.lock();
138	tim	1.1	}
139	dl	1.2
140			/**
141	tim	1.12	* Unlock to allow both puts and takes.
142	dl	1.2	*/
143			private void fullyUnlock() {
144			takeLock.unlock();
145			putLock.unlock();
146			}
147
148
149			/**
150	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
151	dholmes	1.8	* {@link Integer#MAX_VALUE}.
152	dl	1.2	*/
153			public LinkedBlockingQueue() {
154			this(Integer.MAX_VALUE);
155			}
156
157			/**
158	tim	1.16	* Creates a <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity.
159			*
160	dholmes	1.8	* @param capacity the capacity of this queue.
161			* @throws IllegalArgumentException if <tt>capacity</tt> is not greater
162	tim	1.16	* than zero.
163	dl	1.2	*/
164			public LinkedBlockingQueue(int capacity) {
165	dholmes	1.8	if (capacity <= 0) throw new IllegalArgumentException();
166	dl	1.2	this.capacity = capacity;
167	dl	1.6	last = head = new Node<E>(null);
168	dl	1.2	}
169
170			/**
171	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
172	dholmes	1.14	* {@link Integer#MAX_VALUE}, initially containing the elements of the
173	tim	1.12	* given collection,
174	dholmes	1.8	* added in traversal order of the collection's iterator.
175	dholmes	1.9	* @param c the collection of elements to initially contain
176			* @throws NullPointerException if <tt>c</tt> or any element within it
177			* is <tt>null</tt>
178	dl	1.2	*/
179	dholmes	1.10	public LinkedBlockingQueue(Collection<? extends E> c) {
180	dl	1.2	this(Integer.MAX_VALUE);
181	tim	1.12	for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
182			add(it.next());
183	dl	1.2	}
184
185	dholmes	1.9
186	dholmes	1.8	// this doc comment is overridden to remove the reference to collections
187			// greater in size than Integer.MAX_VALUE
188	tim	1.12	/**
189	dl	1.20	* Returns the number of elements in this queue.
190			*
191			* @return the number of elements in this queue.
192	dholmes	1.8	*/
193	dl	1.2	public int size() {
194			return count.get();
195	tim	1.1	}
196	dl	1.2
197	dholmes	1.8	// this doc comment is a modified copy of the inherited doc comment,
198			// without the reference to unlimited queues.
199	tim	1.12	/**
200	dholmes	1.13	* Returns the number of elements that this queue can ideally (in
201	dholmes	1.8	* the absence of memory or resource constraints) accept without
202			* blocking. This is always equal to the initial capacity of this queue
203			* less the current <tt>size</tt> of this queue.
204			* <p>Note that you <em>cannot</em> always tell if
205			* an attempt to <tt>add</tt> an element will succeed by
206			* inspecting <tt>remainingCapacity</tt> because it may be the
207			* case that a waiting consumer is ready to <tt>take</tt> an
208			* element out of an otherwise full queue.
209			*/
210	dl	1.2	public int remainingCapacity() {
211			return capacity - count.get();
212			}
213
214	dholmes	1.14	public void put(E o) throws InterruptedException {
215			if (o == null) throw new NullPointerException();
216	dl	1.2	// Note: convention in all put/take/etc is to preset
217			// local var holding count negative to indicate failure unless set.
218	tim	1.12	int c = -1;
219	dl	1.2	putLock.lockInterruptibly();
220			try {
221			/*
222			* Note that count is used in wait guard even though it is
223			* not protected by lock. This works because count can
224			* only decrease at this point (all other puts are shut
225			* out by lock), and we (or some other waiting put) are
226			* signalled if it ever changes from
227			* capacity. Similarly for all other uses of count in
228			* other wait guards.
229			*/
230			try {
231	tim	1.12	while (count.get() == capacity)
232	dl	1.2	notFull.await();
233	tim	1.17	} catch (InterruptedException ie) {
234	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
235			throw ie;
236			}
237	dholmes	1.14	insert(o);
238	dl	1.2	c = count.getAndIncrement();
239	dl	1.6	if (c + 1 < capacity)
240	dl	1.2	notFull.signal();
241	tim	1.17	} finally {
242	dl	1.2	putLock.unlock();
243			}
244	tim	1.12	if (c == 0)
245	dl	1.2	signalNotEmpty();
246	tim	1.1	}
247	dl	1.2
248	dholmes	1.14	public boolean offer(E o, long timeout, TimeUnit unit)
249	dholmes	1.8	throws InterruptedException {
250	tim	1.12
251	dholmes	1.14	if (o == null) throw new NullPointerException();
252	dl	1.2	long nanos = unit.toNanos(timeout);
253			int c = -1;
254	dholmes	1.8	putLock.lockInterruptibly();
255	dl	1.2	try {
256			for (;;) {
257			if (count.get() < capacity) {
258	dholmes	1.14	insert(o);
259	dl	1.2	c = count.getAndIncrement();
260	dl	1.6	if (c + 1 < capacity)
261	dl	1.2	notFull.signal();
262			break;
263			}
264			if (nanos <= 0)
265			return false;
266			try {
267			nanos = notFull.awaitNanos(nanos);
268	tim	1.17	} catch (InterruptedException ie) {
269	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
270			throw ie;
271			}
272			}
273	tim	1.17	} finally {
274	dl	1.2	putLock.unlock();
275			}
276	tim	1.12	if (c == 0)
277	dl	1.2	signalNotEmpty();
278			return true;
279	tim	1.1	}
280	dl	1.2
281	tim	1.12	/**
282	dholmes	1.13	* Adds the specified element to the tail of this queue if possible,
283	dholmes	1.8	* returning immediately if this queue is full.
284			*
285	dl	1.20	* @param o the element to add.
286			* @return <tt>true</tt> if it was possible to add the element to
287			* this queue, else <tt>false</tt>
288			* @throws NullPointerException if the specified element is <tt>null</tt>
289	dholmes	1.8	*/
290	dholmes	1.14	public boolean offer(E o) {
291			if (o == null) throw new NullPointerException();
292	dl	1.2	if (count.get() == capacity)
293			return false;
294	tim	1.12	int c = -1;
295	dholmes	1.8	putLock.lock();
296	dl	1.2	try {
297			if (count.get() < capacity) {
298	dholmes	1.14	insert(o);
299	dl	1.2	c = count.getAndIncrement();
300	dl	1.6	if (c + 1 < capacity)
301	dl	1.2	notFull.signal();
302			}
303	tim	1.17	} finally {
304	dl	1.2	putLock.unlock();
305			}
306	tim	1.12	if (c == 0)
307	dl	1.2	signalNotEmpty();
308			return c >= 0;
309	tim	1.1	}
310	dl	1.2
311
312			public E take() throws InterruptedException {
313			E x;
314			int c = -1;
315			takeLock.lockInterruptibly();
316			try {
317			try {
318	tim	1.12	while (count.get() == 0)
319	dl	1.2	notEmpty.await();
320	tim	1.17	} catch (InterruptedException ie) {
321	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
322			throw ie;
323			}
324
325			x = extract();
326			c = count.getAndDecrement();
327			if (c > 1)
328			notEmpty.signal();
329	tim	1.17	} finally {
330	dl	1.2	takeLock.unlock();
331			}
332	tim	1.12	if (c == capacity)
333	dl	1.2	signalNotFull();
334			return x;
335			}
336
337			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
338			E x = null;
339			int c = -1;
340	dholmes	1.8	long nanos = unit.toNanos(timeout);
341	dl	1.2	takeLock.lockInterruptibly();
342			try {
343			for (;;) {
344			if (count.get() > 0) {
345			x = extract();
346			c = count.getAndDecrement();
347			if (c > 1)
348			notEmpty.signal();
349			break;
350			}
351			if (nanos <= 0)
352			return null;
353			try {
354			nanos = notEmpty.awaitNanos(nanos);
355	tim	1.17	} catch (InterruptedException ie) {
356	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
357			throw ie;
358			}
359			}
360	tim	1.17	} finally {
361	dl	1.2	takeLock.unlock();
362			}
363	tim	1.12	if (c == capacity)
364	dl	1.2	signalNotFull();
365			return x;
366			}
367
368			public E poll() {
369			if (count.get() == 0)
370			return null;
371			E x = null;
372	tim	1.12	int c = -1;
373	dl	1.2	takeLock.tryLock();
374			try {
375			if (count.get() > 0) {
376			x = extract();
377			c = count.getAndDecrement();
378			if (c > 1)
379			notEmpty.signal();
380			}
381	tim	1.17	} finally {
382	dl	1.2	takeLock.unlock();
383			}
384	tim	1.12	if (c == capacity)
385	dl	1.2	signalNotFull();
386			return x;
387	tim	1.1	}
388	dl	1.2
389
390			public E peek() {
391			if (count.get() == 0)
392			return null;
393	dholmes	1.8	takeLock.lock();
394	dl	1.2	try {
395			Node<E> first = head.next;
396			if (first == null)
397			return null;
398			else
399			return first.item;
400	tim	1.17	} finally {
401	dl	1.2	takeLock.unlock();
402			}
403	tim	1.1	}
404
405	dholmes	1.9	public boolean remove(Object o) {
406			if (o == null) return false;
407	dl	1.2	boolean removed = false;
408			fullyLock();
409			try {
410			Node<E> trail = head;
411			Node<E> p = head.next;
412			while (p != null) {
413	dholmes	1.9	if (o.equals(p.item)) {
414	dl	1.2	removed = true;
415			break;
416			}
417			trail = p;
418			p = p.next;
419			}
420			if (removed) {
421			p.item = null;
422			trail.next = p.next;
423			if (count.getAndDecrement() == capacity)
424			notFull.signalAll();
425			}
426	tim	1.17	} finally {
427	dl	1.2	fullyUnlock();
428			}
429			return removed;
430	tim	1.1	}
431	dl	1.2
432			public Object[] toArray() {
433			fullyLock();
434			try {
435			int size = count.get();
436	tim	1.12	Object[] a = new Object[size];
437	dl	1.2	int k = 0;
438	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
439	dl	1.2	a[k++] = p.item;
440			return a;
441	tim	1.17	} finally {
442	dl	1.2	fullyUnlock();
443			}
444	tim	1.1	}
445	dl	1.2
446			public <T> T[] toArray(T[] a) {
447			fullyLock();
448			try {
449			int size = count.get();
450			if (a.length < size)
451	dl	1.4	a = (T[])java.lang.reflect.Array.newInstance
452			(a.getClass().getComponentType(), size);
453	tim	1.12
454	dl	1.2	int k = 0;
455	tim	1.12	for (Node p = head.next; p != null; p = p.next)
456	dl	1.2	a[k++] = (T)p.item;
457			return a;
458	tim	1.17	} finally {
459	dl	1.2	fullyUnlock();
460			}
461	tim	1.1	}
462	dl	1.2
463			public String toString() {
464			fullyLock();
465			try {
466			return super.toString();
467	tim	1.17	} finally {
468	dl	1.2	fullyUnlock();
469			}
470	tim	1.1	}
471	dl	1.2
472	dholmes	1.14	/**
473			* Returns an iterator over the elements in this queue in proper sequence.
474	dl	1.15	* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
475			* will never throw {@link java.util.ConcurrentModificationException},
476			* and guarantees to traverse elements as they existed upon
477			* construction of the iterator, and may (but is not guaranteed to)
478			* reflect any modifications subsequent to construction.
479	dholmes	1.14	*
480			* @return an iterator over the elements in this queue in proper sequence.
481			*/
482	dl	1.2	public Iterator<E> iterator() {
483			return new Itr();
484	tim	1.1	}
485	dl	1.2
486			private class Itr implements Iterator<E> {
487	tim	1.12	/*
488	dl	1.4	* Basic weak-consistent iterator. At all times hold the next
489			* item to hand out so that if hasNext() reports true, we will
490			* still have it to return even if lost race with a take etc.
491			*/
492	dl	1.2	Node<E> current;
493			Node<E> lastRet;
494	dl	1.4	E currentElement;
495	tim	1.12
496	dl	1.2	Itr() {
497			fullyLock();
498			try {
499			current = head.next;
500	dl	1.4	if (current != null)
501			currentElement = current.item;
502	tim	1.17	} finally {
503	dl	1.2	fullyUnlock();
504			}
505			}
506	tim	1.12
507			public boolean hasNext() {
508	dl	1.2	return current != null;
509			}
510
511	tim	1.12	public E next() {
512	dl	1.2	fullyLock();
513			try {
514			if (current == null)
515			throw new NoSuchElementException();
516	dl	1.4	E x = currentElement;
517	dl	1.2	lastRet = current;
518			current = current.next;
519	dl	1.4	if (current != null)
520			currentElement = current.item;
521	dl	1.2	return x;
522	tim	1.17	} finally {
523	dl	1.2	fullyUnlock();
524			}
525	tim	1.12
526	dl	1.2	}
527
528	tim	1.12	public void remove() {
529	dl	1.2	if (lastRet == null)
530	tim	1.12	throw new IllegalStateException();
531	dl	1.2	fullyLock();
532			try {
533			Node<E> node = lastRet;
534			lastRet = null;
535			Node<E> trail = head;
536			Node<E> p = head.next;
537			while (p != null && p != node) {
538			trail = p;
539			p = p.next;
540			}
541			if (p == node) {
542			p.item = null;
543			trail.next = p.next;
544			int c = count.getAndDecrement();
545			if (c == capacity)
546			notFull.signalAll();
547			}
548	tim	1.17	} finally {
549	dl	1.2	fullyUnlock();
550			}
551			}
552	tim	1.1	}
553	dl	1.2
554			/**
555			* Save the state to a stream (that is, serialize it).
556			*
557			* @serialData The capacity is emitted (int), followed by all of
558			* its elements (each an <tt>Object</tt>) in the proper order,
559			* followed by a null
560	dl	1.6	* @param s the stream
561	dl	1.2	*/
562			private void writeObject(java.io.ObjectOutputStream s)
563			throws java.io.IOException {
564
565	tim	1.12	fullyLock();
566	dl	1.2	try {
567			// Write out any hidden stuff, plus capacity
568			s.defaultWriteObject();
569
570			// Write out all elements in the proper order.
571	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
572	dl	1.2	s.writeObject(p.item);
573
574			// Use trailing null as sentinel
575			s.writeObject(null);
576	tim	1.17	} finally {
577	dl	1.2	fullyUnlock();
578			}
579	tim	1.1	}
580
581	dl	1.2	/**
582	dholmes	1.8	* Reconstitute this queue instance from a stream (that is,
583	dl	1.2	* deserialize it).
584	dl	1.6	* @param s the stream
585	dl	1.2	*/
586			private void readObject(java.io.ObjectInputStream s)
587			throws java.io.IOException, ClassNotFoundException {
588	tim	1.12	// Read in capacity, and any hidden stuff
589			s.defaultReadObject();
590	dl	1.2
591	dl	1.19	count.set(0);
592			last = head = new Node<E>(null);
593
594	dl	1.6	// Read in all elements and place in queue
595	dl	1.2	for (;;) {
596			E item = (E)s.readObject();
597			if (item == null)
598			break;
599			add(item);
600			}
601	tim	1.1	}
602			}