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
 * @param <E> the type of elements held in this collection
 *
 **/
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() {
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lock();
        try {
            notEmpty.signal();
        } finally {
            takeLock.unlock();
        }
    }

    /**
     * Signal a waiting put. Called only from take/poll.
     */
    private void signalNotFull() {
        final ReentrantLock putLock = this.putLock;
        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 = first.item;
        first.item = null;
        return x;
    }

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

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


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

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

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


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

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

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

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

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

    /**
     * Inserts the specified element at the tail of this queue if possible,
     * returning immediately if this queue is full.
     *
     * @param o the element to add.
     * @return <tt>true</tt> if it was possible to add the element to
     *         this queue, else <tt>false</tt>
     * @throws NullPointerException if the specified element is <tt>null</tt>
     */
    public boolean offer(E o) {
        if (o == null) throw new NullPointerException();
        final AtomicInteger count = this.count;
        if (count.get() == capacity)
            return false;
        int c = -1;
        final ReentrantLock putLock = this.putLock;
        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;
        final AtomicInteger count = this.count;
        final ReentrantLock takeLock = this.takeLock;
        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);
        final AtomicInteger count = this.count;
        final ReentrantLock takeLock = this.takeLock;
        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() {
        final AtomicInteger count = this.count;
        if (count.get() == 0)
            return null;
        E x = null;
        int c = -1;
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lock();
        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;
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lock();
        try {
            Node<E> first = head.next;
            if (first == null)
                return null;
            else
                return first.item;
        } finally {
            takeLock.unlock();
        }
    }

    public boolean remove(Object o) {
        if (o == null) return false;
        boolean removed = false;
        fullyLock();
        try {
            Node<E> trail = head;
            Node<E> p = head.next;
            while (p != null) {
                if (o.equals(p.item)) {
                    removed = true;
                    break;
                }
                trail = p;
                p = p.next;
            }
            if (removed) {
                p.item = null;
                trail.next = p.next;
                if (count.getAndDecrement() == capacity)
                    notFull.signalAll();
            }
        } finally {
            fullyUnlock();
        }
        return removed;
    }

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

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

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

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

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

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

    /**
     * Returns an iterator over the elements in this queue in proper sequence.
     * The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
     * will never throw {@link java.util.ConcurrentModificationException},
     * and guarantees to traverse elements as they existed upon
     * construction of the iterator, and may (but is not guaranteed to)
     * reflect any modifications subsequent to construction.
     *
     * @return an iterator over the elements in this queue in proper sequence.
     */
    public Iterator<E> iterator() {
      return new Itr();
    }

    private class Itr implements Iterator<E> {
        /*
         * Basic weak-consistent iterator.  At all times hold the next
         * item to hand out so that if hasNext() reports true, we will
         * still have it to return even if lost race with a take etc.
         */
        private Node<E> current;
        private Node<E> lastRet;
        private E currentElement;

        Itr() {
            final ReentrantLock putLock = LinkedBlockingQueue.this.putLock;
            final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock;
            putLock.lock();
            takeLock.lock();
            try {
                current = head.next;
                if (current != null)
                    currentElement = current.item;
            } finally {
                takeLock.unlock();
                putLock.unlock();
            }
        }

        public boolean hasNext() {
            return current != null;
        }

        public E next() {
            final ReentrantLock putLock = LinkedBlockingQueue.this.putLock;
            final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock;
            putLock.lock();
            takeLock.lock();
            try {
                if (current == null)
                    throw new NoSuchElementException();
                E x = currentElement;
                lastRet = current;
                current = current.next;
                if (current != null)
                    currentElement = current.item;
                return x;
            } finally {
                takeLock.unlock();
                putLock.unlock();
            }
        }

        public void remove() {
            if (lastRet == null)
                throw new IllegalStateException();
            final ReentrantLock putLock = LinkedBlockingQueue.this.putLock;
            final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock;
            putLock.lock();
            takeLock.lock();
            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 {
                takeLock.unlock();
                putLock.unlock();
            }
        }
    }

    /**
     * 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:	1.32
Committed:	Sat Dec 27 17:19:03 2003 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.31:	+2 -2 lines
Log Message:	Adapt to AbstractQueuedSynchronizer
#	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	dl	1.27	* @param <E> the type of elements held in this collection
37	tim	1.12	*
38	tim	1.1	**/
39	dl	1.2	public class LinkedBlockingQueue<E> extends AbstractQueue<E>
40	tim	1.1	implements BlockingQueue<E>, java.io.Serializable {
41	dl	1.18	private static final long serialVersionUID = -6903933977591709194L;
42	tim	1.1
43	dl	1.2	/*
44			* A variant of the "two lock queue" algorithm. The putLock gates
45			* entry to put (and offer), and has an associated condition for
46			* waiting puts. Similarly for the takeLock. The "count" field
47			* that they both rely on is maintained as an atomic to avoid
48			* needing to get both locks in most cases. Also, to minimize need
49			* for puts to get takeLock and vice-versa, cascading notifies are
50			* used. When a put notices that it has enabled at least one take,
51			* it signals taker. That taker in turn signals others if more
52			* items have been entered since the signal. And symmetrically for
53	tim	1.12	* takes signalling puts. Operations such as remove(Object) and
54	dl	1.2	* iterators acquire both locks.
55			*/
56
57	dl	1.6	/**
58			* Linked list node class
59			*/
60	dl	1.2	static class Node<E> {
61	dl	1.6	/** The item, volatile to ensure barrier separating write and read */
62	dl	1.2	volatile E item;
63			Node<E> next;
64			Node(E x) { item = x; }
65			}
66
67	dl	1.6	/** The capacity bound, or Integer.MAX_VALUE if none */
68	dl	1.2	private final int capacity;
69	dl	1.6
70			/** Current number of elements */
71	dl	1.19	private final AtomicInteger count = new AtomicInteger(0);
72	dl	1.2
73	dl	1.6	/** Head of linked list */
74			private transient Node<E> head;
75
76	dholmes	1.8	/** Tail of linked list */
77	dl	1.6	private transient Node<E> last;
78	dl	1.2
79	dl	1.6	/** Lock held by take, poll, etc */
80	dl	1.5	private final ReentrantLock takeLock = new ReentrantLock();
81	dl	1.6
82			/** Wait queue for waiting takes */
83	dl	1.32	private final Condition notEmpty = takeLock.newCondition();
84	dl	1.2
85	dl	1.6	/** Lock held by put, offer, etc */
86	dl	1.5	private final ReentrantLock putLock = new ReentrantLock();
87	dl	1.6
88			/** Wait queue for waiting puts */
89	dl	1.32	private final Condition notFull = putLock.newCondition();
90	dl	1.2
91			/**
92			* Signal a waiting take. Called only from put/offer (which do not
93	dl	1.4	* otherwise ordinarily lock takeLock.)
94	dl	1.2	*/
95			private void signalNotEmpty() {
96	dl	1.31	final ReentrantLock takeLock = this.takeLock;
97	dl	1.2	takeLock.lock();
98			try {
99			notEmpty.signal();
100	tim	1.17	} finally {
101	dl	1.2	takeLock.unlock();
102			}
103			}
104
105			/**
106			* Signal a waiting put. Called only from take/poll.
107			*/
108			private void signalNotFull() {
109	dl	1.31	final ReentrantLock putLock = this.putLock;
110	dl	1.2	putLock.lock();
111			try {
112			notFull.signal();
113	tim	1.17	} finally {
114	dl	1.2	putLock.unlock();
115			}
116			}
117
118			/**
119	dholmes	1.8	* Create a node and link it at end of queue
120	dl	1.6	* @param x the item
121	dl	1.2	*/
122			private void insert(E x) {
123			last = last.next = new Node<E>(x);
124			}
125
126			/**
127			* Remove a node from head of queue,
128	dl	1.6	* @return the node
129	dl	1.2	*/
130			private E extract() {
131			Node<E> first = head.next;
132			head = first;
133	dl	1.28	E x = first.item;
134	dl	1.2	first.item = null;
135			return x;
136			}
137
138			/**
139	tim	1.12	* Lock to prevent both puts and takes.
140	dl	1.2	*/
141			private void fullyLock() {
142			putLock.lock();
143			takeLock.lock();
144	tim	1.1	}
145	dl	1.2
146			/**
147	tim	1.12	* Unlock to allow both puts and takes.
148	dl	1.2	*/
149			private void fullyUnlock() {
150			takeLock.unlock();
151			putLock.unlock();
152			}
153
154
155			/**
156	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
157	dholmes	1.8	* {@link Integer#MAX_VALUE}.
158	dl	1.2	*/
159			public LinkedBlockingQueue() {
160			this(Integer.MAX_VALUE);
161			}
162
163			/**
164	tim	1.16	* Creates a <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity.
165			*
166	dholmes	1.8	* @param capacity the capacity of this queue.
167			* @throws IllegalArgumentException if <tt>capacity</tt> is not greater
168	tim	1.16	* than zero.
169	dl	1.2	*/
170			public LinkedBlockingQueue(int capacity) {
171	dholmes	1.8	if (capacity <= 0) throw new IllegalArgumentException();
172	dl	1.2	this.capacity = capacity;
173	dl	1.6	last = head = new Node<E>(null);
174	dl	1.2	}
175
176			/**
177	dholmes	1.13	* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of
178	dholmes	1.14	* {@link Integer#MAX_VALUE}, initially containing the elements of the
179	tim	1.12	* given collection,
180	dholmes	1.8	* added in traversal order of the collection's iterator.
181	dholmes	1.9	* @param c the collection of elements to initially contain
182			* @throws NullPointerException if <tt>c</tt> or any element within it
183			* is <tt>null</tt>
184	dl	1.2	*/
185	dholmes	1.10	public LinkedBlockingQueue(Collection<? extends E> c) {
186	dl	1.2	this(Integer.MAX_VALUE);
187	tim	1.12	for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
188			add(it.next());
189	dl	1.2	}
190
191	dholmes	1.9
192	dholmes	1.8	// this doc comment is overridden to remove the reference to collections
193			// greater in size than Integer.MAX_VALUE
194	tim	1.12	/**
195	dl	1.20	* Returns the number of elements in this queue.
196			*
197			* @return the number of elements in this queue.
198	dholmes	1.8	*/
199	dl	1.2	public int size() {
200			return count.get();
201	tim	1.1	}
202	dl	1.2
203	dholmes	1.8	// this doc comment is a modified copy of the inherited doc comment,
204			// without the reference to unlimited queues.
205	tim	1.12	/**
206	dholmes	1.13	* Returns the number of elements that this queue can ideally (in
207	dholmes	1.8	* the absence of memory or resource constraints) accept without
208			* blocking. This is always equal to the initial capacity of this queue
209			* less the current <tt>size</tt> of this queue.
210			* <p>Note that you <em>cannot</em> always tell if
211			* an attempt to <tt>add</tt> an element will succeed by
212			* inspecting <tt>remainingCapacity</tt> because it may be the
213			* case that a waiting consumer is ready to <tt>take</tt> an
214			* element out of an otherwise full queue.
215			*/
216	dl	1.2	public int remainingCapacity() {
217			return capacity - count.get();
218			}
219
220	dholmes	1.22	/**
221			* Adds the specified element to the tail of this queue, waiting if
222			* necessary for space to become available.
223	dl	1.23	* @param o the element to add
224			* @throws InterruptedException if interrupted while waiting.
225	dholmes	1.22	* @throws NullPointerException if the specified element is <tt>null</tt>.
226			*/
227	dholmes	1.14	public void put(E o) throws InterruptedException {
228			if (o == null) throw new NullPointerException();
229	dl	1.2	// Note: convention in all put/take/etc is to preset
230			// local var holding count negative to indicate failure unless set.
231	tim	1.12	int c = -1;
232	dl	1.31	final ReentrantLock putLock = this.putLock;
233			final AtomicInteger count = this.count;
234	dl	1.2	putLock.lockInterruptibly();
235			try {
236			/*
237			* Note that count is used in wait guard even though it is
238			* not protected by lock. This works because count can
239			* only decrease at this point (all other puts are shut
240			* out by lock), and we (or some other waiting put) are
241			* signalled if it ever changes from
242			* capacity. Similarly for all other uses of count in
243			* other wait guards.
244			*/
245			try {
246	tim	1.12	while (count.get() == capacity)
247	dl	1.2	notFull.await();
248	tim	1.17	} catch (InterruptedException ie) {
249	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
250			throw ie;
251			}
252	dholmes	1.14	insert(o);
253	dl	1.2	c = count.getAndIncrement();
254	dl	1.6	if (c + 1 < capacity)
255	dl	1.2	notFull.signal();
256	tim	1.17	} finally {
257	dl	1.2	putLock.unlock();
258			}
259	tim	1.12	if (c == 0)
260	dl	1.2	signalNotEmpty();
261	tim	1.1	}
262	dl	1.2
263	dholmes	1.22	/**
264			* Inserts the specified element at the tail of this queue, waiting if
265			* necessary up to the specified wait time for space to become available.
266	dl	1.23	* @param o the element to add
267			* @param timeout how long to wait before giving up, in units of
268			* <tt>unit</tt>
269			* @param unit a <tt>TimeUnit</tt> determining how to interpret the
270			* <tt>timeout</tt> parameter
271			* @return <tt>true</tt> if successful, or <tt>false</tt> if
272			* the specified waiting time elapses before space is available.
273			* @throws InterruptedException if interrupted while waiting.
274	dholmes	1.22	* @throws NullPointerException if the specified element is <tt>null</tt>.
275			*/
276	dholmes	1.14	public boolean offer(E o, long timeout, TimeUnit unit)
277	dholmes	1.8	throws InterruptedException {
278	tim	1.12
279	dholmes	1.14	if (o == null) throw new NullPointerException();
280	dl	1.2	long nanos = unit.toNanos(timeout);
281			int c = -1;
282	dl	1.31	final ReentrantLock putLock = this.putLock;
283			final AtomicInteger count = this.count;
284	dholmes	1.8	putLock.lockInterruptibly();
285	dl	1.2	try {
286			for (;;) {
287			if (count.get() < capacity) {
288	dholmes	1.14	insert(o);
289	dl	1.2	c = count.getAndIncrement();
290	dl	1.6	if (c + 1 < capacity)
291	dl	1.2	notFull.signal();
292			break;
293			}
294			if (nanos <= 0)
295			return false;
296			try {
297			nanos = notFull.awaitNanos(nanos);
298	tim	1.17	} catch (InterruptedException ie) {
299	dl	1.2	notFull.signal(); // propagate to a non-interrupted thread
300			throw ie;
301			}
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 true;
309	tim	1.1	}
310	dl	1.2
311	dl	1.23	/**
312			* Inserts the specified element at the tail of this queue if possible,
313			* returning immediately if this queue is full.
314			*
315			* @param o the element to add.
316			* @return <tt>true</tt> if it was possible to add the element to
317			* this queue, else <tt>false</tt>
318			* @throws NullPointerException if the specified element is <tt>null</tt>
319			*/
320	dholmes	1.14	public boolean offer(E o) {
321			if (o == null) throw new NullPointerException();
322	dl	1.31	final AtomicInteger count = this.count;
323	dl	1.2	if (count.get() == capacity)
324			return false;
325	tim	1.12	int c = -1;
326	dl	1.31	final ReentrantLock putLock = this.putLock;
327	dholmes	1.8	putLock.lock();
328	dl	1.2	try {
329			if (count.get() < capacity) {
330	dholmes	1.14	insert(o);
331	dl	1.2	c = count.getAndIncrement();
332	dl	1.6	if (c + 1 < capacity)
333	dl	1.2	notFull.signal();
334			}
335	tim	1.17	} finally {
336	dl	1.2	putLock.unlock();
337			}
338	tim	1.12	if (c == 0)
339	dl	1.2	signalNotEmpty();
340			return c >= 0;
341	tim	1.1	}
342	dl	1.2
343
344			public E take() throws InterruptedException {
345			E x;
346			int c = -1;
347	dl	1.31	final AtomicInteger count = this.count;
348			final ReentrantLock takeLock = this.takeLock;
349	dl	1.2	takeLock.lockInterruptibly();
350			try {
351			try {
352	tim	1.12	while (count.get() == 0)
353	dl	1.2	notEmpty.await();
354	tim	1.17	} catch (InterruptedException ie) {
355	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
356			throw ie;
357			}
358
359			x = extract();
360			c = count.getAndDecrement();
361			if (c > 1)
362			notEmpty.signal();
363	tim	1.17	} finally {
364	dl	1.2	takeLock.unlock();
365			}
366	tim	1.12	if (c == capacity)
367	dl	1.2	signalNotFull();
368			return x;
369			}
370
371			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
372			E x = null;
373			int c = -1;
374	dholmes	1.8	long nanos = unit.toNanos(timeout);
375	dl	1.31	final AtomicInteger count = this.count;
376			final ReentrantLock takeLock = this.takeLock;
377	dl	1.2	takeLock.lockInterruptibly();
378			try {
379			for (;;) {
380			if (count.get() > 0) {
381			x = extract();
382			c = count.getAndDecrement();
383			if (c > 1)
384			notEmpty.signal();
385			break;
386			}
387			if (nanos <= 0)
388			return null;
389			try {
390			nanos = notEmpty.awaitNanos(nanos);
391	tim	1.17	} catch (InterruptedException ie) {
392	dl	1.2	notEmpty.signal(); // propagate to a non-interrupted thread
393			throw ie;
394			}
395			}
396	tim	1.17	} finally {
397	dl	1.2	takeLock.unlock();
398			}
399	tim	1.12	if (c == capacity)
400	dl	1.2	signalNotFull();
401			return x;
402			}
403
404			public E poll() {
405	dl	1.31	final AtomicInteger count = this.count;
406	dl	1.2	if (count.get() == 0)
407			return null;
408			E x = null;
409	tim	1.12	int c = -1;
410	dl	1.31	final ReentrantLock takeLock = this.takeLock;
411	dl	1.30	takeLock.lock();
412	dl	1.2	try {
413			if (count.get() > 0) {
414			x = extract();
415			c = count.getAndDecrement();
416			if (c > 1)
417			notEmpty.signal();
418			}
419	tim	1.17	} finally {
420	dl	1.2	takeLock.unlock();
421			}
422	tim	1.12	if (c == capacity)
423	dl	1.2	signalNotFull();
424			return x;
425	tim	1.1	}
426	dl	1.2
427
428			public E peek() {
429			if (count.get() == 0)
430			return null;
431	dl	1.31	final ReentrantLock takeLock = this.takeLock;
432	dholmes	1.8	takeLock.lock();
433	dl	1.2	try {
434			Node<E> first = head.next;
435			if (first == null)
436			return null;
437			else
438			return first.item;
439	tim	1.17	} finally {
440	dl	1.2	takeLock.unlock();
441			}
442	tim	1.1	}
443
444	dholmes	1.9	public boolean remove(Object o) {
445			if (o == null) return false;
446	dl	1.2	boolean removed = false;
447			fullyLock();
448			try {
449			Node<E> trail = head;
450			Node<E> p = head.next;
451			while (p != null) {
452	dholmes	1.9	if (o.equals(p.item)) {
453	dl	1.2	removed = true;
454			break;
455			}
456			trail = p;
457			p = p.next;
458			}
459			if (removed) {
460			p.item = null;
461			trail.next = p.next;
462			if (count.getAndDecrement() == capacity)
463			notFull.signalAll();
464			}
465	tim	1.17	} finally {
466	dl	1.2	fullyUnlock();
467			}
468			return removed;
469	tim	1.1	}
470	dl	1.2
471			public Object[] toArray() {
472			fullyLock();
473			try {
474			int size = count.get();
475	tim	1.12	Object[] a = new Object[size];
476	dl	1.2	int k = 0;
477	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
478	dl	1.2	a[k++] = p.item;
479			return a;
480	tim	1.17	} finally {
481	dl	1.2	fullyUnlock();
482			}
483	tim	1.1	}
484	dl	1.2
485			public <T> T[] toArray(T[] a) {
486			fullyLock();
487			try {
488			int size = count.get();
489			if (a.length < size)
490	dl	1.4	a = (T[])java.lang.reflect.Array.newInstance
491			(a.getClass().getComponentType(), size);
492	tim	1.12
493	dl	1.2	int k = 0;
494	tim	1.12	for (Node p = head.next; p != null; p = p.next)
495	dl	1.2	a[k++] = (T)p.item;
496			return a;
497	tim	1.17	} finally {
498	dl	1.2	fullyUnlock();
499			}
500	tim	1.1	}
501	dl	1.2
502			public String toString() {
503			fullyLock();
504			try {
505			return super.toString();
506	tim	1.17	} finally {
507	dl	1.2	fullyUnlock();
508			}
509	tim	1.1	}
510	dl	1.2
511	dl	1.24	public void clear() {
512			fullyLock();
513			try {
514			head.next = null;
515			if (count.getAndSet(0) == capacity)
516			notFull.signalAll();
517			} finally {
518			fullyUnlock();
519			}
520			}
521
522			public int drainTo(Collection<? super E> c) {
523			if (c == null)
524			throw new NullPointerException();
525			if (c == this)
526			throw new IllegalArgumentException();
527			Node first;
528			fullyLock();
529			try {
530			first = head.next;
531			head.next = null;
532			if (count.getAndSet(0) == capacity)
533			notFull.signalAll();
534			} finally {
535			fullyUnlock();
536			}
537			// Transfer the elements outside of locks
538			int n = 0;
539	dl	1.29	for (Node<E> p = first; p != null; p = p.next) {
540			c.add(p.item);
541	dl	1.24	p.item = null;
542			++n;
543			}
544			return n;
545			}
546
547			public int drainTo(Collection<? super E> c, int maxElements) {
548			if (c == null)
549			throw new NullPointerException();
550			if (c == this)
551			throw new IllegalArgumentException();
552			if (maxElements <= 0)
553			return 0;
554			fullyLock();
555			try {
556			int n = 0;
557	dl	1.29	Node<E> p = head.next;
558	dl	1.24	while (p != null && n < maxElements) {
559	dl	1.29	c.add(p.item);
560	dl	1.24	p.item = null;
561			p = p.next;
562			++n;
563			}
564			if (n != 0) {
565			head.next = p;
566			if (count.getAndAdd(-n) == capacity)
567			notFull.signalAll();
568			}
569			return n;
570			} finally {
571			fullyUnlock();
572			}
573			}
574
575	dholmes	1.14	/**
576			* Returns an iterator over the elements in this queue in proper sequence.
577	dl	1.15	* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
578			* will never throw {@link java.util.ConcurrentModificationException},
579			* and guarantees to traverse elements as they existed upon
580			* construction of the iterator, and may (but is not guaranteed to)
581			* reflect any modifications subsequent to construction.
582	dholmes	1.14	*
583			* @return an iterator over the elements in this queue in proper sequence.
584			*/
585	dl	1.2	public Iterator<E> iterator() {
586			return new Itr();
587	tim	1.1	}
588	dl	1.2
589			private class Itr implements Iterator<E> {
590	tim	1.12	/*
591	dl	1.4	* Basic weak-consistent iterator. At all times hold the next
592			* item to hand out so that if hasNext() reports true, we will
593			* still have it to return even if lost race with a take etc.
594			*/
595	dl	1.31	private Node<E> current;
596			private Node<E> lastRet;
597			private E currentElement;
598	tim	1.12
599	dl	1.2	Itr() {
600	dl	1.31	final ReentrantLock putLock = LinkedBlockingQueue.this.putLock;
601			final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock;
602			putLock.lock();
603			takeLock.lock();
604	dl	1.2	try {
605			current = head.next;
606	dl	1.4	if (current != null)
607			currentElement = current.item;
608	tim	1.17	} finally {
609	dl	1.31	takeLock.unlock();
610			putLock.unlock();
611	dl	1.2	}
612			}
613	tim	1.12
614			public boolean hasNext() {
615	dl	1.2	return current != null;
616			}
617
618	tim	1.12	public E next() {
619	dl	1.31	final ReentrantLock putLock = LinkedBlockingQueue.this.putLock;
620			final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock;
621			putLock.lock();
622			takeLock.lock();
623	dl	1.2	try {
624			if (current == null)
625			throw new NoSuchElementException();
626	dl	1.4	E x = currentElement;
627	dl	1.2	lastRet = current;
628			current = current.next;
629	dl	1.4	if (current != null)
630			currentElement = current.item;
631	dl	1.2	return x;
632	tim	1.17	} finally {
633	dl	1.31	takeLock.unlock();
634			putLock.unlock();
635	dl	1.2	}
636			}
637
638	tim	1.12	public void remove() {
639	dl	1.2	if (lastRet == null)
640	tim	1.12	throw new IllegalStateException();
641	dl	1.31	final ReentrantLock putLock = LinkedBlockingQueue.this.putLock;
642			final ReentrantLock takeLock = LinkedBlockingQueue.this.takeLock;
643			putLock.lock();
644			takeLock.lock();
645	dl	1.2	try {
646			Node<E> node = lastRet;
647			lastRet = null;
648			Node<E> trail = head;
649			Node<E> p = head.next;
650			while (p != null && p != node) {
651			trail = p;
652			p = p.next;
653			}
654			if (p == node) {
655			p.item = null;
656			trail.next = p.next;
657			int c = count.getAndDecrement();
658			if (c == capacity)
659			notFull.signalAll();
660			}
661	tim	1.17	} finally {
662	dl	1.31	takeLock.unlock();
663			putLock.unlock();
664	dl	1.2	}
665			}
666	tim	1.1	}
667	dl	1.2
668			/**
669			* Save the state to a stream (that is, serialize it).
670			*
671			* @serialData The capacity is emitted (int), followed by all of
672			* its elements (each an <tt>Object</tt>) in the proper order,
673			* followed by a null
674	dl	1.6	* @param s the stream
675	dl	1.2	*/
676			private void writeObject(java.io.ObjectOutputStream s)
677			throws java.io.IOException {
678
679	tim	1.12	fullyLock();
680	dl	1.2	try {
681			// Write out any hidden stuff, plus capacity
682			s.defaultWriteObject();
683
684			// Write out all elements in the proper order.
685	tim	1.12	for (Node<E> p = head.next; p != null; p = p.next)
686	dl	1.2	s.writeObject(p.item);
687
688			// Use trailing null as sentinel
689			s.writeObject(null);
690	tim	1.17	} finally {
691	dl	1.2	fullyUnlock();
692			}
693	tim	1.1	}
694
695	dl	1.2	/**
696	dholmes	1.8	* Reconstitute this queue instance from a stream (that is,
697	dl	1.2	* deserialize it).
698	dl	1.6	* @param s the stream
699	dl	1.2	*/
700			private void readObject(java.io.ObjectInputStream s)
701			throws java.io.IOException, ClassNotFoundException {
702	tim	1.12	// Read in capacity, and any hidden stuff
703			s.defaultReadObject();
704	dl	1.2
705	dl	1.19	count.set(0);
706			last = head = new Node<E>(null);
707
708	dl	1.6	// Read in all elements and place in queue
709	dl	1.2	for (;;) {
710			E item = (E)s.readObject();
711			if (item == null)
712			break;
713			add(item);
714			}
715	tim	1.1	}
716			}