util/concurrent/LinkedBlockingQueue.java

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

    /**
     * Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
     * {@link Integer#MAX_VALUE}, initially containing the elements of the
     * given collection,
     * added in traversal order of the collection's iterator.
     * @param c the collection of elements to initially contain
     * @throws NullPointerException if <tt>c</tt> or any element within it
     * is <tt>null</tt>
     */
    public LinkedBlockingQueue(Collection<? extends E> c) {
        this(Integer.MAX_VALUE);
        for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
            add(it.next());
    }

    // Have to override just to update the javadoc 

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

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

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

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

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

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

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

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


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

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

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

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


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

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

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

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

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

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

    /**
     * Returns an iterator over the elements in this queue in proper sequence.
     * 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();

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


Revision:	1.16
Committed:	Wed Aug 6 18:22:09 2003 UTC (20 years, 10 months ago) by tim
Branch:	MAIN
CVS Tags:	JSR166_CR1
Changes since 1.15:	+3 -2 lines
Log Message:	Fixes to minor errors found by DocCheck
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7	tim	1.1	package java.util.concurrent;
8	dl	1.2	import java.util.concurrent.atomic.*;
9	dl	1.7	import java.util.concurrent.locks.*;
10	tim	1.1	import java.util.*;
11
12			/**
13	dholmes	1.14	* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on
14	dholmes	1.8	* linked nodes.
15			* This queue orders elements FIFO (first-in-first-out).
16	tim	1.12	* The <em>head</em> of the queue is that element that has been on the
17	dholmes	1.8	* queue the longest time.
18			* The <em>tail</em> of the queue is that element that has been on the
19			* queue the shortest time.
20			* Linked queues typically have higher throughput than array-based queues but
21			* less predictable performance in most concurrent applications.
22	tim	1.12	*
23	dl	1.3	* <p> The optional capacity bound constructor argument serves as a
24	dholmes	1.8	* way to prevent excessive queue expansion. The capacity, if unspecified,
25			* is equal to {@link Integer#MAX_VALUE}. Linked nodes are
26	dl	1.3	* dynamically created upon each insertion unless this would bring the
27			* queue above capacity.
28	dholmes	1.8	*
29	dl	1.6	* @since 1.5
30			* @author Doug Lea
31	tim	1.12	*
32	tim	1.1	**/
33	dl	1.2	public class LinkedBlockingQueue<E> extends AbstractQueue<E>
34	tim	1.1	implements BlockingQueue<E>, java.io.Serializable {
35
36	dl	1.2	/*
37			* A variant of the "two lock queue" algorithm. The putLock gates
38			* entry to put (and offer), and has an associated condition for
39			* waiting puts. Similarly for the takeLock. The "count" field
40			* that they both rely on is maintained as an atomic to avoid
41			* needing to get both locks in most cases. Also, to minimize need
42			* for puts to get takeLock and vice-versa, cascading notifies are
43			* used. When a put notices that it has enabled at least one take,
44			* it signals taker. That taker in turn signals others if more
45			* items have been entered since the signal. And symmetrically for
46	tim	1.12	* takes signalling puts. Operations such as remove(Object) and
47	dl	1.2	* iterators acquire both locks.
48			*/
49
50	dl	1.6	/**
51			* Linked list node class
52			*/
53	dl	1.2	static class Node<E> {
54	dl	1.6	/** The item, volatile to ensure barrier separating write and read */
55	dl	1.2	volatile E item;
56			Node<E> next;
57			Node(E x) { item = x; }
58			}
59
60	dl	1.6	/** The capacity bound, or Integer.MAX_VALUE if none */
61	dl	1.2	private final int capacity;
62	dl	1.6
63			/** Current number of elements */
64	dl	1.2	private transient final AtomicInteger count = new AtomicInteger(0);
65
66	dl	1.6	/** Head of linked list */
67			private transient Node<E> head;
68
69	dholmes	1.8	/** Tail of linked list */
70	dl	1.6	private transient Node<E> last;
71	dl	1.2
72	dl	1.6	/** Lock held by take, poll, etc */
73	dl	1.5	private final ReentrantLock takeLock = new ReentrantLock();
74	dl	1.6
75			/** Wait queue for waiting takes */
76	dl	1.5	private final Condition notEmpty = takeLock.newCondition();
77	dl	1.2
78	dl	1.6	/** Lock held by put, offer, etc */
79	dl	1.5	private final ReentrantLock putLock = new ReentrantLock();
80	dl	1.6
81			/** Wait queue for waiting puts */
82	dl	1.5	private final Condition notFull = putLock.newCondition();
83	dl	1.2
84			/**
85			* Signal a waiting take. Called only from put/offer (which do not
86	dl	1.4	* otherwise ordinarily lock takeLock.)
87	dl	1.2	*/
88			private void signalNotEmpty() {
89			takeLock.lock();
90			try {
91			notEmpty.signal();
92			}
93			finally {
94			takeLock.unlock();
95			}
96			}
97
98			/**
99			* Signal a waiting put. Called only from take/poll.
100			*/
101			private void signalNotFull() {
102			putLock.lock();
103			try {
104			notFull.signal();
105			}
106			finally {
107			putLock.unlock();
108			}
109			}
110
111			/**
112	dholmes	1.8	* Create a node and link it at end of queue
113	dl	1.6	* @param x the item
114	dl	1.2	*/
115			private void insert(E x) {
116			last = last.next = new Node<E>(x);
117			}
118
119			/**
120			* Remove a node from head of queue,
121	dl	1.6	* @return the node
122	dl	1.2	*/
123			private E extract() {
124			Node<E> first = head.next;
125			head = first;
126			E x = (E)first.item;
127			first.item = null;
128			return x;
129			}
130
131			/**
132	tim	1.12	* Lock to prevent both puts and takes.
133	dl	1.2	*/
134			private void fullyLock() {
135			putLock.lock();
136			takeLock.lock();
137	tim	1.1	}
138	dl	1.2
139			/**
140	tim	1.12	* Unlock to allow both puts and takes.
141	dl	1.2	*/
142			private void fullyUnlock() {
143			takeLock.unlock();
144			putLock.unlock();
145			}
146
147
148			/**
149	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
150	dholmes	1.8	* {@link Integer#MAX_VALUE}.
151	dl	1.2	*/
152			public LinkedBlockingQueue() {
153			this(Integer.MAX_VALUE);
154			}
155
156			/**
157	tim	1.16	* Creates a <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity.
158			*
159	dholmes	1.8	* @param capacity the capacity of this queue.
160			* @throws IllegalArgumentException if <tt>capacity</tt> is not greater
161	tim	1.16	* than zero.
162	dl	1.2	*/
163			public LinkedBlockingQueue(int capacity) {
164	dholmes	1.8	if (capacity <= 0) throw new IllegalArgumentException();
165	dl	1.2	this.capacity = capacity;
166	dl	1.6	last = head = new Node<E>(null);
167	dl	1.2	}
168
169			/**
170	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
171	dholmes	1.14	* {@link Integer#MAX_VALUE}, initially containing the elements of the
172	tim	1.12	* given collection,
173	dholmes	1.8	* added in traversal order of the collection's iterator.
174	dholmes	1.9	* @param c the collection of elements to initially contain
175			* @throws NullPointerException if <tt>c</tt> or any element within it
176			* is <tt>null</tt>
177	dl	1.2	*/
178	dholmes	1.10	public LinkedBlockingQueue(Collection<? extends E> c) {
179	dl	1.2	this(Integer.MAX_VALUE);
180	tim	1.12	for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
181			add(it.next());
182	dl	1.2	}
183
184	dholmes	1.14	// Have to override just to update the javadoc
185	dholmes	1.9
186			/**
187	dholmes	1.14	* Adds the specified element to the tail of this queue.
188			* @return <tt>true</tt> (as per the general contract of
189			* <tt>Collection.add</tt>).
190	dholmes	1.9	* @throws IllegalStateException {@inheritDoc}
191			* @throws NullPointerException {@inheritDoc}
192			*/
193			public boolean add(E o) {
194			return super.add(o);
195			}
196
197			/**
198	dholmes	1.14	* Adds all of the elements in the specified collection to this queue.
199			* The behavior of this operation is undefined if
200			* the specified collection is modified while the operation is in
201			* progress. (This implies that the behavior of this call is undefined if
202			* the specified collection is this queue, and this queue is nonempty.)
203			* <p>
204			* This implementation iterates over the specified collection, and adds
205			* each object returned by the iterator to this queue's tail, in turn.
206	dholmes	1.9	* @throws IllegalStateException {@inheritDoc}
207			* @throws NullPointerException {@inheritDoc}
208			*/
209			public boolean addAll(Collection<? extends E> c) {
210			return super.addAll(c);
211			}
212
213	dholmes	1.8	// this doc comment is overridden to remove the reference to collections
214			// greater in size than Integer.MAX_VALUE
215	tim	1.12	/**
216	dholmes	1.13	* Returns the number of elements in this collection.
217	dholmes	1.8	*/
218	dl	1.2	public int size() {
219			return count.get();
220	tim	1.1	}
221	dl	1.2
222	dholmes	1.8	// this doc comment is a modified copy of the inherited doc comment,
223			// without the reference to unlimited queues.
224	tim	1.12	/**
225	dholmes	1.13	* Returns the number of elements that this queue can ideally (in
226	dholmes	1.8	* the absence of memory or resource constraints) accept without
227			* blocking. This is always equal to the initial capacity of this queue
228			* less the current <tt>size</tt> of this queue.
229			* <p>Note that you <em>cannot</em> always tell if
230			* an attempt to <tt>add</tt> an element will succeed by
231			* inspecting <tt>remainingCapacity</tt> because it may be the
232			* case that a waiting consumer is ready to <tt>take</tt> an
233			* element out of an otherwise full queue.
234			*/
235	dl	1.2	public int remainingCapacity() {
236			return capacity - count.get();
237			}
238
239	dholmes	1.8	/**
240	dholmes	1.13	* Adds the specified element to the tail of this queue, waiting if
241	dholmes	1.8	* necessary for space to become available.
242			* @throws NullPointerException {@inheritDoc}
243			*/
244	dholmes	1.14	public void put(E o) throws InterruptedException {
245			if (o == null) throw new NullPointerException();
246	dl	1.2	// Note: convention in all put/take/etc is to preset
247			// local var holding count negative to indicate failure unless set.
248	tim	1.12	int c = -1;
249	dl	1.2	putLock.lockInterruptibly();
250			try {
251			/*
252			* Note that count is used in wait guard even though it is
253			* not protected by lock. This works because count can
254			* only decrease at this point (all other puts are shut
255			* out by lock), and we (or some other waiting put) are
256			* signalled if it ever changes from
257			* capacity. Similarly for all other uses of count in
258			* other wait guards.
259			*/
260			try {
261	tim	1.12	while (count.get() == capacity)
262	dl	1.2	notFull.await();
263			}
264			catch (InterruptedException ie) {
265			notFull.signal(); // propagate to a non-interrupted thread
266			throw ie;
267			}
268	dholmes	1.14	insert(o);
269	dl	1.2	c = count.getAndIncrement();
270	dl	1.6	if (c + 1 < capacity)
271	dl	1.2	notFull.signal();
272			}
273			finally {
274			putLock.unlock();
275			}
276	tim	1.12	if (c == 0)
277	dl	1.2	signalNotEmpty();
278	tim	1.1	}
279	dl	1.2
280	dholmes	1.8	/**
281	dholmes	1.13	* Adds the specified element to the tail of this queue, waiting if
282	dholmes	1.8	* necessary up to the specified wait time for space to become available.
283			* @throws NullPointerException {@inheritDoc}
284			*/
285	dholmes	1.14	public boolean offer(E o, long timeout, TimeUnit unit)
286	dholmes	1.8	throws InterruptedException {
287	tim	1.12
288	dholmes	1.14	if (o == null) throw new NullPointerException();
289	dl	1.2	long nanos = unit.toNanos(timeout);
290			int c = -1;
291	dholmes	1.8	putLock.lockInterruptibly();
292	dl	1.2	try {
293			for (;;) {
294			if (count.get() < capacity) {
295	dholmes	1.14	insert(o);
296	dl	1.2	c = count.getAndIncrement();
297	dl	1.6	if (c + 1 < capacity)
298	dl	1.2	notFull.signal();
299			break;
300			}
301			if (nanos <= 0)
302			return false;
303			try {
304			nanos = notFull.awaitNanos(nanos);
305			}
306			catch (InterruptedException ie) {
307			notFull.signal(); // propagate to a non-interrupted thread
308			throw ie;
309			}
310			}
311			}
312			finally {
313			putLock.unlock();
314			}
315	tim	1.12	if (c == 0)
316	dl	1.2	signalNotEmpty();
317			return true;
318	tim	1.1	}
319	dl	1.2
320	tim	1.12	/**
321	dholmes	1.13	* Adds the specified element to the tail of this queue if possible,
322	dholmes	1.8	* returning immediately if this queue is full.
323			*
324			* @throws NullPointerException {@inheritDoc}
325			*/
326	dholmes	1.14	public boolean offer(E o) {
327			if (o == null) throw new NullPointerException();
328	dl	1.2	if (count.get() == capacity)
329			return false;
330	tim	1.12	int c = -1;
331	dholmes	1.8	putLock.lock();
332	dl	1.2	try {
333			if (count.get() < capacity) {
334	dholmes	1.14	insert(o);
335	dl	1.2	c = count.getAndIncrement();
336	dl	1.6	if (c + 1 < capacity)
337	dl	1.2	notFull.signal();
338			}
339			}
340			finally {
341			putLock.unlock();
342			}
343	tim	1.12	if (c == 0)
344	dl	1.2	signalNotEmpty();
345			return c >= 0;
346	tim	1.1	}
347	dl	1.2
348
349			public E take() throws InterruptedException {
350			E x;
351			int c = -1;
352			takeLock.lockInterruptibly();
353			try {
354			try {
355	tim	1.12	while (count.get() == 0)
356	dl	1.2	notEmpty.await();
357			}
358			catch (InterruptedException ie) {
359			notEmpty.signal(); // propagate to a non-interrupted thread
360			throw ie;
361			}
362
363			x = extract();
364			c = count.getAndDecrement();
365			if (c > 1)
366			notEmpty.signal();
367			}
368			finally {
369			takeLock.unlock();
370			}
371	tim	1.12	if (c == capacity)
372	dl	1.2	signalNotFull();
373			return x;
374			}
375
376			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
377			E x = null;
378			int c = -1;
379	dholmes	1.8	long nanos = unit.toNanos(timeout);
380	dl	1.2	takeLock.lockInterruptibly();
381			try {
382			for (;;) {
383			if (count.get() > 0) {
384			x = extract();
385			c = count.getAndDecrement();
386			if (c > 1)
387			notEmpty.signal();
388			break;
389			}
390			if (nanos <= 0)
391			return null;
392			try {
393			nanos = notEmpty.awaitNanos(nanos);
394			}
395			catch (InterruptedException ie) {
396			notEmpty.signal(); // propagate to a non-interrupted thread
397			throw ie;
398			}
399			}
400			}
401			finally {
402			takeLock.unlock();
403			}
404	tim	1.12	if (c == capacity)
405	dl	1.2	signalNotFull();
406			return x;
407			}
408
409			public E poll() {
410			if (count.get() == 0)
411			return null;
412			E x = null;
413	tim	1.12	int c = -1;
414	dl	1.2	takeLock.tryLock();
415			try {
416			if (count.get() > 0) {
417			x = extract();
418			c = count.getAndDecrement();
419			if (c > 1)
420			notEmpty.signal();
421			}
422			}
423			finally {
424			takeLock.unlock();
425			}
426	tim	1.12	if (c == capacity)
427	dl	1.2	signalNotFull();
428			return x;
429	tim	1.1	}
430	dl	1.2
431
432			public E peek() {
433			if (count.get() == 0)
434			return null;
435	dholmes	1.8	takeLock.lock();
436	dl	1.2	try {
437			Node<E> first = head.next;
438			if (first == null)
439			return null;
440			else
441			return first.item;
442			}
443			finally {
444			takeLock.unlock();
445			}
446	tim	1.1	}
447
448	dholmes	1.14	/**
449			* Removes a single instance of the specified element from this
450			* queue, if it is present. More formally,
451			* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
452			* o.equals(e))</tt>, if the queue contains one or more such
453			* elements. Returns <tt>true</tt> if the queue contained the
454			* specified element (or equivalently, if the queue changed as a
455			* result of the call).
456			*
457			* <p>This implementation iterates over the queue looking for the
458			* specified element. If it finds the element, it removes the element
459			* from the queue using the iterator's remove method.<p>
460			*
461			*/
462	dholmes	1.9	public boolean remove(Object o) {
463			if (o == null) return false;
464	dl	1.2	boolean removed = false;
465			fullyLock();
466			try {
467			Node<E> trail = head;
468			Node<E> p = head.next;
469			while (p != null) {
470	dholmes	1.9	if (o.equals(p.item)) {
471	dl	1.2	removed = true;
472			break;
473			}
474			trail = p;
475			p = p.next;
476			}
477			if (removed) {
478			p.item = null;
479			trail.next = p.next;
480			if (count.getAndDecrement() == capacity)
481			notFull.signalAll();
482			}
483			}
484			finally {
485			fullyUnlock();
486			}
487			return removed;
488	tim	1.1	}
489	dl	1.2
490			public Object[] toArray() {
491			fullyLock();
492			try {
493			int size = count.get();
494	tim	1.12	Object[] a = new Object[size];
495	dl	1.2	int k = 0;
496	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
497	dl	1.2	a[k++] = p.item;
498			return a;
499			}
500			finally {
501			fullyUnlock();
502			}
503	tim	1.1	}
504	dl	1.2
505			public <T> T[] toArray(T[] a) {
506			fullyLock();
507			try {
508			int size = count.get();
509			if (a.length < size)
510	dl	1.4	a = (T[])java.lang.reflect.Array.newInstance
511			(a.getClass().getComponentType(), size);
512	tim	1.12
513	dl	1.2	int k = 0;
514	tim	1.12	for (Node p = head.next; p != null; p = p.next)
515	dl	1.2	a[k++] = (T)p.item;
516			return a;
517			}
518			finally {
519			fullyUnlock();
520			}
521	tim	1.1	}
522	dl	1.2
523			public String toString() {
524			fullyLock();
525			try {
526			return super.toString();
527			}
528			finally {
529			fullyUnlock();
530			}
531	tim	1.1	}
532	dl	1.2
533	dholmes	1.14	/**
534			* Returns an iterator over the elements in this queue in proper sequence.
535	dl	1.15	* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
536			* will never throw {@link java.util.ConcurrentModificationException},
537			* and guarantees to traverse elements as they existed upon
538			* construction of the iterator, and may (but is not guaranteed to)
539			* reflect any modifications subsequent to construction.
540	dholmes	1.14	*
541			* @return an iterator over the elements in this queue in proper sequence.
542			*/
543	dl	1.2	public Iterator<E> iterator() {
544			return new Itr();
545	tim	1.1	}
546	dl	1.2
547			private class Itr implements Iterator<E> {
548	tim	1.12	/*
549	dl	1.4	* Basic weak-consistent iterator. At all times hold the next
550			* item to hand out so that if hasNext() reports true, we will
551			* still have it to return even if lost race with a take etc.
552			*/
553	dl	1.2	Node<E> current;
554			Node<E> lastRet;
555	dl	1.4	E currentElement;
556	tim	1.12
557	dl	1.2	Itr() {
558			fullyLock();
559			try {
560			current = head.next;
561	dl	1.4	if (current != null)
562			currentElement = current.item;
563	dl	1.2	}
564			finally {
565			fullyUnlock();
566			}
567			}
568	tim	1.12
569			public boolean hasNext() {
570	dl	1.2	return current != null;
571			}
572
573	tim	1.12	public E next() {
574	dl	1.2	fullyLock();
575			try {
576			if (current == null)
577			throw new NoSuchElementException();
578	dl	1.4	E x = currentElement;
579	dl	1.2	lastRet = current;
580			current = current.next;
581	dl	1.4	if (current != null)
582			currentElement = current.item;
583	dl	1.2	return x;
584			}
585			finally {
586			fullyUnlock();
587			}
588	tim	1.12
589	dl	1.2	}
590
591	tim	1.12	public void remove() {
592	dl	1.2	if (lastRet == null)
593	tim	1.12	throw new IllegalStateException();
594	dl	1.2	fullyLock();
595			try {
596			Node<E> node = lastRet;
597			lastRet = null;
598			Node<E> trail = head;
599			Node<E> p = head.next;
600			while (p != null && p != node) {
601			trail = p;
602			p = p.next;
603			}
604			if (p == node) {
605			p.item = null;
606			trail.next = p.next;
607			int c = count.getAndDecrement();
608			if (c == capacity)
609			notFull.signalAll();
610			}
611			}
612			finally {
613			fullyUnlock();
614			}
615			}
616	tim	1.1	}
617	dl	1.2
618			/**
619			* Save the state to a stream (that is, serialize it).
620			*
621			* @serialData The capacity is emitted (int), followed by all of
622			* its elements (each an <tt>Object</tt>) in the proper order,
623			* followed by a null
624	dl	1.6	* @param s the stream
625	dl	1.2	*/
626			private void writeObject(java.io.ObjectOutputStream s)
627			throws java.io.IOException {
628
629	tim	1.12	fullyLock();
630	dl	1.2	try {
631			// Write out any hidden stuff, plus capacity
632			s.defaultWriteObject();
633
634			// Write out all elements in the proper order.
635	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
636	dl	1.2	s.writeObject(p.item);
637
638			// Use trailing null as sentinel
639			s.writeObject(null);
640			}
641			finally {
642			fullyUnlock();
643			}
644	tim	1.1	}
645
646	dl	1.2	/**
647	dholmes	1.8	* Reconstitute this queue instance from a stream (that is,
648	dl	1.2	* deserialize it).
649	dl	1.6	* @param s the stream
650	dl	1.2	*/
651			private void readObject(java.io.ObjectInputStream s)
652			throws java.io.IOException, ClassNotFoundException {
653	tim	1.12	// Read in capacity, and any hidden stuff
654			s.defaultReadObject();
655	dl	1.2
656	dl	1.6	// Read in all elements and place in queue
657	dl	1.2	for (;;) {
658			E item = (E)s.readObject();
659			if (item == null)
660			break;
661			add(item);
662			}
663	tim	1.1	}
664			}
665	dholmes	1.8
666
667
668
669	tim	1.1