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<? extends 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:	1.10
Committed:	Mon Aug 4 02:00:37 2003 UTC (20 years, 10 months ago) by dholmes
Branch:	MAIN
Changes since 1.9:	+1 -1 lines
Log Message:	Added wildcards
#	Content
1	/*
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	package java.util.concurrent;
8	import java.util.concurrent.atomic.*;
9	import java.util.concurrent.locks.*;
10	import java.util.*;
11
12	/**
13	* 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	*
23	* <p> The optional capacity bound constructor argument serves as a
24	* way to prevent excessive queue expansion. The capacity, if unspecified,
25	* is equal to {@link Integer#MAX_VALUE}. Linked nodes are
26	* dynamically created upon each insertion unless this would bring the
27	* queue above capacity.
28	*
29	* @since 1.5
30	* @author Doug Lea
31	*
32	**/
33	public class LinkedBlockingQueue<E> extends AbstractQueue<E>
34	implements BlockingQueue<E>, java.io.Serializable {
35
36	/*
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	/**
51	* Linked list node class
52	*/
53	static class Node<E> {
54	/** The item, volatile to ensure barrier separating write and read */
55	volatile E item;
56	Node<E> next;
57	Node(E x) { item = x; }
58	}
59
60	/** The capacity bound, or Integer.MAX_VALUE if none */
61	private final int capacity;
62
63	/** Current number of elements */
64	private transient final AtomicInteger count = new AtomicInteger(0);
65
66	/** Head of linked list */
67	private transient Node<E> head;
68
69	/** Tail of linked list */
70	private transient Node<E> last;
71
72	/** Lock held by take, poll, etc */
73	private final ReentrantLock takeLock = new ReentrantLock();
74
75	/** Wait queue for waiting takes */
76	private final Condition notEmpty = takeLock.newCondition();
77
78	/** Lock held by put, offer, etc */
79	private final ReentrantLock putLock = new ReentrantLock();
80
81	/** Wait queue for waiting puts */
82	private final Condition notFull = putLock.newCondition();
83
84	/**
85	* Signal a waiting take. Called only from put/offer (which do not
86	* otherwise ordinarily lock takeLock.)
87	*/
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	* Create a node and link it at end of queue
113	* @param x the item
114	*/
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	* @return the node
122	*/
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	}
138
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	* Create a <tt>LinkedBlockingQueue</tt> with a capacity of
150	* {@link Integer#MAX_VALUE}.
151	*/
152	public LinkedBlockingQueue() {
153	this(Integer.MAX_VALUE);
154	}
155
156	/**
157	* 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	*/
162	public LinkedBlockingQueue(int capacity) {
163	if (capacity <= 0) throw new IllegalArgumentException();
164	this.capacity = capacity;
165	last = head = new Node<E>(null);
166	}
167
168	/**
169	* Create a <tt>LinkedBlockingQueue</tt> with a capacity of
170	* {@link Integer#MAX_VALUE}, initially holding the elements of the
171	* given collection,
172	* added in traversal order of the collection's iterator.
173	* @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	*/
177	public LinkedBlockingQueue(Collection<? extends E> c) {
178	this(Integer.MAX_VALUE);
179	for (Iterator<E> it = c.iterator(); it.hasNext();)
180	add(it.next());
181	}
182
183
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	// 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	public int size() {
209	return count.get();
210	}
211
212	// 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	public int remainingCapacity() {
226	return capacity - count.get();
227	}
228
229	/**
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	public void put(E x) throws InterruptedException {
235	if (x == null) throw new NullPointerException();
236	// 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	if (c + 1 < capacity)
261	notFull.signal();
262	}
263	finally {
264	putLock.unlock();
265	}
266	if (c == 0)
267	signalNotEmpty();
268	}
269
270	/**
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	if (x == null) throw new NullPointerException();
279	long nanos = unit.toNanos(timeout);
280	int c = -1;
281	putLock.lockInterruptibly();
282	try {
283	for (;;) {
284	if (count.get() < capacity) {
285	insert(x);
286	c = count.getAndIncrement();
287	if (c + 1 < capacity)
288	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	}
309
310	/**
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	public boolean offer(E x) {
317	if (x == null) throw new NullPointerException();
318	if (count.get() == capacity)
319	return false;
320	int c = -1;
321	putLock.lock();
322	try {
323	if (count.get() < capacity) {
324	insert(x);
325	c = count.getAndIncrement();
326	if (c + 1 < capacity)
327	notFull.signal();
328	}
329	}
330	finally {
331	putLock.unlock();
332	}
333	if (c == 0)
334	signalNotEmpty();
335	return c >= 0;
336	}
337
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	long nanos = unit.toNanos(timeout);
370	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	}
420
421
422	public E peek() {
423	if (count.get() == 0)
424	return null;
425	takeLock.lock();
426	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	}
437
438	public boolean remove(Object o) {
439	if (o == null) return false;
440	boolean removed = false;
441	fullyLock();
442	try {
443	Node<E> trail = head;
444	Node<E> p = head.next;
445	while (p != null) {
446	if (o.equals(p.item)) {
447	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	}
465
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	}
480
481	public <T> T[] toArray(T[] a) {
482	fullyLock();
483	try {
484	int size = count.get();
485	if (a.length < size)
486	a = (T[])java.lang.reflect.Array.newInstance
487	(a.getClass().getComponentType(), size);
488
489	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	}
498
499	public String toString() {
500	fullyLock();
501	try {
502	return super.toString();
503	}
504	finally {
505	fullyUnlock();
506	}
507	}
508
509	public Iterator<E> iterator() {
510	return new Itr();
511	}
512
513	private class Itr implements Iterator<E> {
514	/*
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	Node<E> current;
520	Node<E> lastRet;
521	E currentElement;
522
523	Itr() {
524	fullyLock();
525	try {
526	current = head.next;
527	if (current != null)
528	currentElement = current.item;
529	}
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	E x = currentElement;
545	lastRet = current;
546	current = current.next;
547	if (current != null)
548	currentElement = current.item;
549	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	}
583
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	* @param s the stream
591	*/
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	}
611
612	/**
613	* Reconstitute this queue instance from a stream (that is,
614	* deserialize it).
615	* @param s the stream
616	*/
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	// Read in all elements and place in queue
623	for (;;) {
624	E item = (E)s.readObject();
625	if (item == null)
626	break;
627	add(item);
628	}
629	}
630	}
631
632
633
634
635