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 {@link 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();
    }


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

    /**
     * Create 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);
    }

    /**
     * Create a <tt>LinkedBlockingQueue</tt> with a capacity of
     * {@link Integer#MAX_VALUE}, initially holding 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<E> c) {
        this(Integer.MAX_VALUE);
        for (Iterator<E> it = c.iterator(); it.hasNext();) 
            add(it.next());
    }


    // Have to override just to update the javadoc for @throws

    /**
     * @throws IllegalStateException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean add(E o) {
        return super.add(o);
    }

    /**
     * @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
    /** 
     * Return 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.
    /** 
     * Return 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();
    }

    /**
     * Add the specified element to the tail of this queue, waiting if 
     * necessary for space to become available.
     * @throws NullPointerException {@inheritDoc}
     */
    public void put(E x) throws InterruptedException {
        if (x == 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(x);
            c = count.getAndIncrement();
            if (c + 1 < capacity)
                notFull.signal();
        }
        finally {
            putLock.unlock();
        }
        if (c == 0) 
            signalNotEmpty();
    }

    /**
     * Add 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 x, long timeout, TimeUnit unit) 
        throws InterruptedException {
       
        if (x == null) throw new NullPointerException();
        long nanos = unit.toNanos(timeout);
        int c = -1;
        putLock.lockInterruptibly();
        try {
            for (;;) {
                if (count.get() < capacity) {
                    insert(x);
                    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;
    }

   /** 
    * Add 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 x) {
        if (x == null) throw new NullPointerException();
        if (count.get() == capacity)
            return false;
        int c = -1; 
        putLock.lock();
        try {
            if (count.get() < capacity) {
                insert(x);
                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();
        }
    }

    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:	1.9
Committed:	Thu Jul 31 07:18:02 2003 UTC (20 years, 10 months ago) by dholmes
Branch:	MAIN
Changes since 1.8:	+29 -7 lines
Log Message:	Continued updates to explicit and inherited doc comments. Consistency over remove(null) Some inherited doc is still not right.
#	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	1.8	* An optionally-bounded {@link BlockingQueue blocking queue} based on
14			* linked nodes.
15			* This queue orders elements FIFO (first-in-first-out).
16			* The <em>head</em> of the queue is that element that has been on the
17			* 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	dl	1.3	*
23			* <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	dl	1.3	*
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			* takes signalling puts. Operations such as remove(Object) and
47			* 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			* Lock to prevent both puts and takes.
133			*/
134			private void fullyLock() {
135			putLock.lock();
136			takeLock.lock();
137	tim	1.1	}
138	dl	1.2
139			/**
140			* Unlock to allow both puts and takes.
141			*/
142			private void fullyUnlock() {
143			takeLock.unlock();
144			putLock.unlock();
145			}
146
147
148			/**
149	dholmes	1.8	* Create a <tt>LinkedBlockingQueue</tt> with a capacity of
150			* {@link Integer#MAX_VALUE}.
151	dl	1.2	*/
152			public LinkedBlockingQueue() {
153			this(Integer.MAX_VALUE);
154			}
155
156			/**
157	dholmes	1.8	* Create a <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity
158			* @param capacity the capacity of this queue.
159			* @throws IllegalArgumentException if <tt>capacity</tt> is not greater
160			* than zero.
161	dl	1.2	*/
162			public LinkedBlockingQueue(int capacity) {
163	dholmes	1.8	if (capacity <= 0) throw new IllegalArgumentException();
164	dl	1.2	this.capacity = capacity;
165	dl	1.6	last = head = new Node<E>(null);
166	dl	1.2	}
167
168			/**
169	dholmes	1.9	* Create a <tt>LinkedBlockingQueue</tt> with a capacity of
170	dholmes	1.8	* {@link Integer#MAX_VALUE}, initially holding the elements of the
171			* given collection,
172			* added in traversal order of the collection's iterator.
173	dholmes	1.9	* @param c the collection of elements to initially contain
174			* @throws NullPointerException if <tt>c</tt> or any element within it
175			* is <tt>null</tt>
176	dl	1.2	*/
177	dholmes	1.9	public LinkedBlockingQueue(Collection<E> c) {
178	dl	1.2	this(Integer.MAX_VALUE);
179	dholmes	1.9	for (Iterator<E> it = c.iterator(); it.hasNext();)
180	dl	1.2	add(it.next());
181			}
182
183	dholmes	1.9
184			// Have to override just to update the javadoc for @throws
185
186			/**
187			* @throws IllegalStateException {@inheritDoc}
188			* @throws NullPointerException {@inheritDoc}
189			*/
190			public boolean add(E o) {
191			return super.add(o);
192			}
193
194			/**
195			* @throws IllegalStateException {@inheritDoc}
196			* @throws NullPointerException {@inheritDoc}
197			*/
198			public boolean addAll(Collection<? extends E> c) {
199			return super.addAll(c);
200			}
201
202
203	dholmes	1.8	// this doc comment is overridden to remove the reference to collections
204			// greater in size than Integer.MAX_VALUE
205			/**
206			* Return the number of elements in this collection.
207			*/
208	dl	1.2	public int size() {
209			return count.get();
210	tim	1.1	}
211	dl	1.2
212	dholmes	1.8	// this doc comment is a modified copy of the inherited doc comment,
213			// without the reference to unlimited queues.
214			/**
215			* Return the number of elements that this queue can ideally (in
216			* the absence of memory or resource constraints) accept without
217			* blocking. This is always equal to the initial capacity of this queue
218			* less the current <tt>size</tt> of this queue.
219			* <p>Note that you <em>cannot</em> always tell if
220			* an attempt to <tt>add</tt> an element will succeed by
221			* inspecting <tt>remainingCapacity</tt> because it may be the
222			* case that a waiting consumer is ready to <tt>take</tt> an
223			* element out of an otherwise full queue.
224			*/
225	dl	1.2	public int remainingCapacity() {
226			return capacity - count.get();
227			}
228
229	dholmes	1.8	/**
230			* Add the specified element to the tail of this queue, waiting if
231			* necessary for space to become available.
232			* @throws NullPointerException {@inheritDoc}
233			*/
234	dl	1.2	public void put(E x) throws InterruptedException {
235	dl	1.6	if (x == null) throw new NullPointerException();
236	dl	1.2	// Note: convention in all put/take/etc is to preset
237			// local var holding count negative to indicate failure unless set.
238			int c = -1;
239			putLock.lockInterruptibly();
240			try {
241			/*
242			* Note that count is used in wait guard even though it is
243			* not protected by lock. This works because count can
244			* only decrease at this point (all other puts are shut
245			* out by lock), and we (or some other waiting put) are
246			* signalled if it ever changes from
247			* capacity. Similarly for all other uses of count in
248			* other wait guards.
249			*/
250			try {
251			while (count.get() == capacity)
252			notFull.await();
253			}
254			catch (InterruptedException ie) {
255			notFull.signal(); // propagate to a non-interrupted thread
256			throw ie;
257			}
258			insert(x);
259			c = count.getAndIncrement();
260	dl	1.6	if (c + 1 < capacity)
261	dl	1.2	notFull.signal();
262			}
263			finally {
264			putLock.unlock();
265			}
266			if (c == 0)
267			signalNotEmpty();
268	tim	1.1	}
269	dl	1.2
270	dholmes	1.8	/**
271			* Add the specified element to the tail of this queue, waiting if
272			* necessary up to the specified wait time for space to become available.
273			* @throws NullPointerException {@inheritDoc}
274			*/
275			public boolean offer(E x, long timeout, TimeUnit unit)
276			throws InterruptedException {
277
278	dl	1.6	if (x == null) throw new NullPointerException();
279	dl	1.2	long nanos = unit.toNanos(timeout);
280			int c = -1;
281	dholmes	1.8	putLock.lockInterruptibly();
282	dl	1.2	try {
283			for (;;) {
284			if (count.get() < capacity) {
285			insert(x);
286			c = count.getAndIncrement();
287	dl	1.6	if (c + 1 < capacity)
288	dl	1.2	notFull.signal();
289			break;
290			}
291			if (nanos <= 0)
292			return false;
293			try {
294			nanos = notFull.awaitNanos(nanos);
295			}
296			catch (InterruptedException ie) {
297			notFull.signal(); // propagate to a non-interrupted thread
298			throw ie;
299			}
300			}
301			}
302			finally {
303			putLock.unlock();
304			}
305			if (c == 0)
306			signalNotEmpty();
307			return true;
308	tim	1.1	}
309	dl	1.2
310	dholmes	1.8	/**
311			* Add the specified element to the tail of this queue if possible,
312			* returning immediately if this queue is full.
313			*
314			* @throws NullPointerException {@inheritDoc}
315			*/
316	tim	1.1	public boolean offer(E x) {
317	dl	1.6	if (x == null) throw new NullPointerException();
318	dl	1.2	if (count.get() == capacity)
319			return false;
320			int c = -1;
321	dholmes	1.8	putLock.lock();
322	dl	1.2	try {
323			if (count.get() < capacity) {
324			insert(x);
325			c = count.getAndIncrement();
326	dl	1.6	if (c + 1 < capacity)
327	dl	1.2	notFull.signal();
328			}
329			}
330			finally {
331			putLock.unlock();
332			}
333			if (c == 0)
334			signalNotEmpty();
335			return c >= 0;
336	tim	1.1	}
337	dl	1.2
338
339			public E take() throws InterruptedException {
340			E x;
341			int c = -1;
342			takeLock.lockInterruptibly();
343			try {
344			try {
345			while (count.get() == 0)
346			notEmpty.await();
347			}
348			catch (InterruptedException ie) {
349			notEmpty.signal(); // propagate to a non-interrupted thread
350			throw ie;
351			}
352
353			x = extract();
354			c = count.getAndDecrement();
355			if (c > 1)
356			notEmpty.signal();
357			}
358			finally {
359			takeLock.unlock();
360			}
361			if (c == capacity)
362			signalNotFull();
363			return x;
364			}
365
366			public E poll(long timeout, TimeUnit unit) throws InterruptedException {
367			E x = null;
368			int c = -1;
369	dholmes	1.8	long nanos = unit.toNanos(timeout);
370	dl	1.2	takeLock.lockInterruptibly();
371			try {
372			for (;;) {
373			if (count.get() > 0) {
374			x = extract();
375			c = count.getAndDecrement();
376			if (c > 1)
377			notEmpty.signal();
378			break;
379			}
380			if (nanos <= 0)
381			return null;
382			try {
383			nanos = notEmpty.awaitNanos(nanos);
384			}
385			catch (InterruptedException ie) {
386			notEmpty.signal(); // propagate to a non-interrupted thread
387			throw ie;
388			}
389			}
390			}
391			finally {
392			takeLock.unlock();
393			}
394			if (c == capacity)
395			signalNotFull();
396			return x;
397			}
398
399			public E poll() {
400			if (count.get() == 0)
401			return null;
402			E x = null;
403			int c = -1;
404			takeLock.tryLock();
405			try {
406			if (count.get() > 0) {
407			x = extract();
408			c = count.getAndDecrement();
409			if (c > 1)
410			notEmpty.signal();
411			}
412			}
413			finally {
414			takeLock.unlock();
415			}
416			if (c == capacity)
417			signalNotFull();
418			return x;
419	tim	1.1	}
420	dl	1.2
421
422			public E peek() {
423			if (count.get() == 0)
424			return null;
425	dholmes	1.8	takeLock.lock();
426	dl	1.2	try {
427			Node<E> first = head.next;
428			if (first == null)
429			return null;
430			else
431			return first.item;
432			}
433			finally {
434			takeLock.unlock();
435			}
436	tim	1.1	}
437
438	dholmes	1.9	public boolean remove(Object o) {
439			if (o == null) return false;
440	dl	1.2	boolean removed = false;
441			fullyLock();
442			try {
443			Node<E> trail = head;
444			Node<E> p = head.next;
445			while (p != null) {
446	dholmes	1.9	if (o.equals(p.item)) {
447	dl	1.2	removed = true;
448			break;
449			}
450			trail = p;
451			p = p.next;
452			}
453			if (removed) {
454			p.item = null;
455			trail.next = p.next;
456			if (count.getAndDecrement() == capacity)
457			notFull.signalAll();
458			}
459			}
460			finally {
461			fullyUnlock();
462			}
463			return removed;
464	tim	1.1	}
465	dl	1.2
466			public Object[] toArray() {
467			fullyLock();
468			try {
469			int size = count.get();
470			Object[] a = new Object[size];
471			int k = 0;
472			for (Node<E> p = head.next; p != null; p = p.next)
473			a[k++] = p.item;
474			return a;
475			}
476			finally {
477			fullyUnlock();
478			}
479	tim	1.1	}
480	dl	1.2
481			public <T> T[] toArray(T[] a) {
482			fullyLock();
483			try {
484			int size = count.get();
485			if (a.length < size)
486	dl	1.4	a = (T[])java.lang.reflect.Array.newInstance
487			(a.getClass().getComponentType(), size);
488
489	dl	1.2	int k = 0;
490			for (Node p = head.next; p != null; p = p.next)
491			a[k++] = (T)p.item;
492			return a;
493			}
494			finally {
495			fullyUnlock();
496			}
497	tim	1.1	}
498	dl	1.2
499			public String toString() {
500			fullyLock();
501			try {
502			return super.toString();
503			}
504			finally {
505			fullyUnlock();
506			}
507	tim	1.1	}
508	dl	1.2
509			public Iterator<E> iterator() {
510			return new Itr();
511	tim	1.1	}
512	dl	1.2
513			private class Itr implements Iterator<E> {
514	dl	1.4	/*
515			* Basic weak-consistent iterator. At all times hold the next
516			* item to hand out so that if hasNext() reports true, we will
517			* still have it to return even if lost race with a take etc.
518			*/
519	dl	1.2	Node<E> current;
520			Node<E> lastRet;
521	dl	1.4	E currentElement;
522	dl	1.2
523			Itr() {
524			fullyLock();
525			try {
526			current = head.next;
527	dl	1.4	if (current != null)
528			currentElement = current.item;
529	dl	1.2	}
530			finally {
531			fullyUnlock();
532			}
533			}
534
535			public boolean hasNext() {
536			return current != null;
537			}
538
539			public E next() {
540			fullyLock();
541			try {
542			if (current == null)
543			throw new NoSuchElementException();
544	dl	1.4	E x = currentElement;
545	dl	1.2	lastRet = current;
546			current = current.next;
547	dl	1.4	if (current != null)
548			currentElement = current.item;
549	dl	1.2	return x;
550			}
551			finally {
552			fullyUnlock();
553			}
554
555			}
556
557			public void remove() {
558			if (lastRet == null)
559			throw new IllegalStateException();
560			fullyLock();
561			try {
562			Node<E> node = lastRet;
563			lastRet = null;
564			Node<E> trail = head;
565			Node<E> p = head.next;
566			while (p != null && p != node) {
567			trail = p;
568			p = p.next;
569			}
570			if (p == node) {
571			p.item = null;
572			trail.next = p.next;
573			int c = count.getAndDecrement();
574			if (c == capacity)
575			notFull.signalAll();
576			}
577			}
578			finally {
579			fullyUnlock();
580			}
581			}
582	tim	1.1	}
583	dl	1.2
584			/**
585			* Save the state to a stream (that is, serialize it).
586			*
587			* @serialData The capacity is emitted (int), followed by all of
588			* its elements (each an <tt>Object</tt>) in the proper order,
589			* followed by a null
590	dl	1.6	* @param s the stream
591	dl	1.2	*/
592			private void writeObject(java.io.ObjectOutputStream s)
593			throws java.io.IOException {
594
595			fullyLock();
596			try {
597			// Write out any hidden stuff, plus capacity
598			s.defaultWriteObject();
599
600			// Write out all elements in the proper order.
601			for (Node<E> p = head.next; p != null; p = p.next)
602			s.writeObject(p.item);
603
604			// Use trailing null as sentinel
605			s.writeObject(null);
606			}
607			finally {
608			fullyUnlock();
609			}
610	tim	1.1	}
611
612	dl	1.2	/**
613	dholmes	1.8	* Reconstitute this queue instance from a stream (that is,
614	dl	1.2	* deserialize it).
615	dl	1.6	* @param s the stream
616	dl	1.2	*/
617			private void readObject(java.io.ObjectInputStream s)
618			throws java.io.IOException, ClassNotFoundException {
619			// Read in capacity, and any hidden stuff
620			s.defaultReadObject();
621
622	dl	1.6	// Read in all elements and place in queue
623	dl	1.2	for (;;) {
624			E item = (E)s.readObject();
625			if (item == null)
626			break;
627			add(item);
628			}
629	tim	1.1	}
630			}
631	dholmes	1.8
632
633
634
635	tim	1.1