util/concurrent/ArrayBlockingQueue.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.locks.*;
import java.util.*;

/**
 * A bounded {@link BlockingQueue blocking queue} backed by an array.
 * 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.
 *
 * <p>This is a classic &quot;bounded buffer&quot;, in which a fixed-sized
 * array holds
 * elements inserted by producers and extracted by consumers.  Once
 * created, the capacity can not be increased.  Attempts to offer an
 * element to a full queue will result in the offer operation
 * blocking; attempts to retrieve an element from an empty queue will
 * similarly block.
 *
 * <p> This class supports an optional fairness policy for ordering
 * threads blocked on an insertion or removal.  By default, this
 * ordering is not guaranteed. However, an <tt>ArrayBlockingQueue</tt>
 * constructed with fairness set to <tt>true</tt> grants blocked
 * threads access in FIFO order. Fairness generally substantially
 * decreases throughput but reduces variablility and avoids
 * starvation.
 *
 * @since 1.5
 * @author Doug Lea
 */
public class ArrayBlockingQueue<E> extends AbstractQueue<E>
        implements BlockingQueue<E>, java.io.Serializable {

    /** The queued items */
    private transient final E[] items;
    /** items index for next take, poll or remove */
    private transient int takeIndex;
    /** items index for next put, offer, or add. */
    private transient int putIndex;
    /** Number of items in the queue */
    private int count;

    /**
     * An array used only during deserialization, to hold
     * items read back in from the stream, and then used
     * as "items" by readResolve via the private constructor.
     */
    private transient E[] deserializedItems;

    /*
     * Concurrency control via the classic two-condition algorithm
     * found in any textbook.
     */

    /** Main lock guarding all access */
    private final ReentrantLock lock;
    /** Condition for waiting takes */
    private final Condition notEmpty;
    /** Condition for wiating puts */
    private final Condition notFull;

    // Internal helper methods

    /**
     * Circularly increment i.
     */
    int inc(int i) {
        return (++i == items.length)? 0 : i;
    }

    /**
     * Insert element at current put position, advance, and signal.
     * Call only when holding lock.
     */
    private void insert(E x) {
        items[putIndex] = x;
        putIndex = inc(putIndex);
        ++count;
        notEmpty.signal();
    }

    /**
     * Extract element at current take position, advance, and signal.
     * Call only when holding lock.
     */
    private E extract() {
        E x = items[takeIndex];
        items[takeIndex] = null;
        takeIndex = inc(takeIndex);
        --count;
        notFull.signal();
        return x;
    }

    /**
     * Utility for remove and iterator.remove: Delete item at position i.
     * Call only when holding lock.
     */
    void removeAt(int i) {
        // if removing front item, just advance
        if (i == takeIndex) {
            items[takeIndex] = null;
            takeIndex = inc(takeIndex);
        }
        else {
            // slide over all others up through putIndex.
            for (;;) {
                int nexti = inc(i);
                if (nexti != putIndex) {
                    items[i] = items[nexti];
                    i = nexti;
                }
                else {
                    items[i] = null;
                    putIndex = i;
                    break;
                }
            }
        }
        --count;
        notFull.signal();
    }

    /**
     * Internal constructor also used by readResolve.
     * Sets all final fields, plus count.
     * @param cap the capacity
     * @param array the array to use or null if should create new one
     * @param count the number of items in the array, where indices 0
     * to count-1 hold items.
     * @param lk the lock to use with this queue
     */
    private ArrayBlockingQueue(int cap, E[] array, int count,
                               ReentrantLock lk) {
        if (cap <= 0)
            throw new IllegalArgumentException();
        if (array == null)
            this.items = (E[]) new Object[cap];
        else
            this.items = array;
        this.putIndex = count;
        this.count = count;
        lock = lk;
        notEmpty = lock.newCondition();
        notFull =  lock.newCondition();
    }

    /**
     * Create an <tt>ArrayBlockingQueue</tt> with the given (fixed)
     * capacity and default access policy.
     * @param capacity the capacity of this queue
     * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
     */
    public ArrayBlockingQueue(int capacity) {
        this(capacity, null, 0, new ReentrantLock());
    }

    /**
     * Create an <tt>ArrayBlockingQueue</tt> with the given (fixed)
     * capacity and the specified access policy.
     * @param capacity the capacity of this queue
     * @param fair if <tt>true</tt> then queue accesses for threads blocked
     * on insertion or removal, are processed in FIFO order; if <tt>false</tt>
     * the access order is unspecified.
     * @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
     */
    public ArrayBlockingQueue(int capacity, boolean fair) {
        this(capacity, null, 0, new ReentrantLock(fair));
    }

    /**
     * Create an <tt>ArrayBlockingQueue</tt> with the given (fixed)
     * capacity, the specified access policy and initially holding the
     * elements of the given collection,
     * added in traversal order of the collection's iterator.
     * @param capacity the capacity of this queue
     * @param fair if <tt>true</tt> then queue accesses for threads blocked
     * on insertion or removal, are processed in FIFO order; if <tt>false</tt>
     * the access order is unspecified.
     * @param c the collection of elements to initially contain
     * @throws IllegalArgumentException if <tt>capacity</tt> is less than
     * <tt>c.size()</tt>, or less than 1.
     * @throws NullPointerException if <tt>c</tt> or any element within it
     * is <tt>null</tt>
     */
    public ArrayBlockingQueue(int capacity, boolean fair, 
                              Collection<? extends E> c) {
        this(capacity, null, 0, new ReentrantLock(fair));

        if (capacity < c.size())
            throw new IllegalArgumentException();

        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);
    }

   /**
    * 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();
        lock.lock();
        try {
            if (count == items.length)
                return false;
            else {
                insert(x);
                return true;
            }
        }
        finally {
            lock.unlock();
        }
    }

    /**
     * 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();

        lock.lockInterruptibly();
        try {
            long nanos = unit.toNanos(timeout);
            for (;;) {
                if (count != items.length) {
                    insert(x);
                    return true;
                }
                if (nanos <= 0)
                    return false;
                try {
                    nanos = notFull.awaitNanos(nanos);
                }
                catch (InterruptedException ie) {
                    notFull.signal(); // propagate to non-interrupted thread
                    throw ie;
                }
            }
        }
        finally {
            lock.unlock();
        }
    }


    public E poll() {
        lock.lock();
        try {
            if (count == 0)
                return null;
            E x = extract();
            return x;
        }
        finally {
            lock.unlock();
        }
    }

    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        lock.lockInterruptibly();
        try {
            long nanos = unit.toNanos(timeout);
            for (;;) {
                if (count != 0) {
                    E x = extract();
                    return x;
                }
                if (nanos <= 0)
                    return null;
                try {
                    nanos = notEmpty.awaitNanos(nanos);
                }
                catch (InterruptedException ie) {
                    notEmpty.signal(); // propagate to non-interrupted thread
                    throw ie;
                }

            }
        }
        finally {
            lock.unlock();
        }
    }


    public boolean remove(Object x) {
        if (x == null) return false;
        lock.lock();
        try {
            int i = takeIndex;
            int k = 0;
            for (;;) {
                if (k++ >= count)
                    return false;
                if (x.equals(items[i])) {
                    removeAt(i);
                    return true;
                }
                i = inc(i);
            }

        }
        finally {
            lock.unlock();
        }
    }

    public E peek() {
        lock.lock();
        try {
            return (count == 0) ? null : items[takeIndex];
        }
        finally {
            lock.unlock();
        }
    }

    public E take() throws InterruptedException {
        lock.lockInterruptibly();
        try {
            try {
                while (count == 0)
                    notEmpty.await();
            }
            catch (InterruptedException ie) {
                notEmpty.signal(); // propagate to non-interrupted thread
                throw ie;
            }
            E x = extract();
            return x;
        }
        finally {
            lock.unlock();
        }
    }

    /**
     * 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();

        lock.lockInterruptibly();
        try {
            try {
                while (count == items.length)
                    notFull.await();
            }
            catch (InterruptedException ie) {
                notFull.signal(); // propagate to non-interrupted thread
                throw ie;
            }
            insert(x);
        }
        finally {
            lock.unlock();
        }
    }

    // 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() {
        lock.lock();
        try {
            return count;
        }
        finally {
            lock.unlock();
        }
    }

    // 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() {
        lock.lock();
        try {
            return items.length - count;
        }
        finally {
            lock.unlock();
        }
    }


    public boolean contains(Object x) {
        if (x == null) return false;
        lock.lock();
        try {
            int i = takeIndex;
            int k = 0;
            while (k++ < count) {
                if (x.equals(items[i]))
                    return true;
                i = inc(i);
            }
            return false;
        }
        finally {
            lock.unlock();
        }
    }

    public Object[] toArray() {
        lock.lock();
        try {
            E[] a = (E[]) new Object[count];
            int k = 0;
            int i = takeIndex;
            while (k < count) {
                a[k++] = items[i];
                i = inc(i);
            }
            return a;
        }
        finally {
            lock.unlock();
        }
    }

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

            int k = 0;
            int i = takeIndex;
            while (k < count) {
                a[k++] = (T)items[i];
                i = inc(i);
            }
            if (a.length > count)
                a[count] = null;
            return a;
        }
        finally {
            lock.unlock();
        }
    }

    public String toString() {
        lock.lock();
        try {
            return super.toString();
        }
        finally {
            lock.unlock();
        }
    }

    /**
     * Returns an iterator over the elements in this queue in proper sequence.
     *
     * @return an iterator over the elements in this queue in proper sequence.
     */
    public Iterator<E> iterator() {
        lock.lock();
        try {
            return new Itr();
        }
        finally {
            lock.unlock();
        }
    }

    /**
     * Iterator for ArrayBlockingQueue
     */
    private class Itr implements Iterator<E> {
        /**
         * Index of element to be returned by next,
         * or a negative number if no such.
         */
        private int nextIndex;

        /**
         * nextItem holds on to item fields because once we claim
         * that an element exists in hasNext(), we must return it in
         * the following next() call even if it was in the process of
         * being removed when hasNext() was called.
         **/
        private E nextItem;

        /**
         * Index of element returned by most recent call to next.
         * Reset to -1 if this element is deleted by a call to remove.
         */
        private int lastRet;

        Itr() {
            lastRet = -1;
            if (count == 0)
                nextIndex = -1;
            else {
                nextIndex = takeIndex;
                nextItem = items[takeIndex];
            }
        }

        public boolean hasNext() {
            /*
             * No sync. We can return true by mistake here
             * only if this iterator passed across threads,
             * which we don't support anyway.
             */
            return nextIndex >= 0;
        }

        /**
         * Check whether nextIndex is valid; if so setting nextItem.
         * Stops iterator when either hits putIndex or sees null item.
         */
        private void checkNext() {
            if (nextIndex == putIndex) {
                nextIndex = -1;
                nextItem = null;
            }
            else {
                nextItem = items[nextIndex];
                if (nextItem == null)
                    nextIndex = -1;
            }
        }

        public E next() {
            lock.lock();
            try {
                if (nextIndex < 0)
                    throw new NoSuchElementException();
                lastRet = nextIndex;
                E x = nextItem;
                nextIndex = inc(nextIndex);
                checkNext();
                return x;
            }
            finally {
                lock.unlock();
            }
        }

        public void remove() {
            lock.lock();
            try {
                int i = lastRet;
                if (i == -1)
                    throw new IllegalStateException();
                lastRet = -1;

                int ti = takeIndex;
                removeAt(i);
                // back up cursor (reset to front if was first element)
                nextIndex = (i == ti) ? takeIndex : i;
                checkNext();
            }
            finally {
                lock.unlock();
            }
        }
    }

    /**
     * Save the state to a stream (that is, serialize it).
     *
     * @serialData The maximumSize is emitted (int), followed by all of
     * its elements (each an <tt>E</tt>) in the proper order.
     * @param s the stream
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {

        // Write out element count, and any hidden stuff
        s.defaultWriteObject();
        // Write out maximumSize == items length
        s.writeInt(items.length);

        // Write out all elements in the proper order.
        int i = takeIndex;
        int k = 0;
        while (k++ < count) {
            s.writeObject(items[i]);
            i = inc(i);
        }
    }

    /**
     * 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 size, and any hidden stuff
        s.defaultReadObject();
        int size = count;

        // Read in array length and allocate array
        int arrayLength = s.readInt();

        // We use deserializedItems here because "items" is final
        deserializedItems = (E[]) new Object[arrayLength];

        // Read in all elements in the proper order into deserializedItems
        for (int i = 0; i < size; i++)
            deserializedItems[i] = (E)s.readObject();
    }

    /**
     * Throw away the object created with readObject, and replace it
     * with a usable ArrayBlockingQueue.
     * @return the ArrayBlockingQueue
     */
    private Object readResolve() throws java.io.ObjectStreamException {
        E[] array = deserializedItems;
        deserializedItems = null;
        return new ArrayBlockingQueue<E>(array.length, array, count, lock);
    }
}
Revision:	1.18
Committed:	Mon Aug 4 01:58:13 2003 UTC (20 years, 10 months ago) by dholmes
Branch:	MAIN
Changes since 1.17:	+2 -1 lines
Log Message:	Fixed 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.locks.*;
9	import java.util.*;
10
11	/**
12	* A bounded {@link BlockingQueue blocking queue} backed by an array.
13	* This queue orders elements FIFO (first-in-first-out).
14	* The <em>head</em> of the queue is that element that has been on the
15	* queue the longest time.
16	* The <em>tail</em> of the queue is that element that has been on the
17	* queue the shortest time.
18	*
19	* <p>This is a classic "bounded buffer", in which a fixed-sized
20	* array holds
21	* elements inserted by producers and extracted by consumers. Once
22	* created, the capacity can not be increased. Attempts to offer an
23	* element to a full queue will result in the offer operation
24	* blocking; attempts to retrieve an element from an empty queue will
25	* similarly block.
26	*
27	* <p> This class supports an optional fairness policy for ordering
28	* threads blocked on an insertion or removal. By default, this
29	* ordering is not guaranteed. However, an <tt>ArrayBlockingQueue</tt>
30	* constructed with fairness set to <tt>true</tt> grants blocked
31	* threads access in FIFO order. Fairness generally substantially
32	* decreases throughput but reduces variablility and avoids
33	* starvation.
34	*
35	* @since 1.5
36	* @author Doug Lea
37	*/
38	public class ArrayBlockingQueue<E> extends AbstractQueue<E>
39	implements BlockingQueue<E>, java.io.Serializable {
40
41	/** The queued items */
42	private transient final E[] items;
43	/** items index for next take, poll or remove */
44	private transient int takeIndex;
45	/** items index for next put, offer, or add. */
46	private transient int putIndex;
47	/** Number of items in the queue */
48	private int count;
49
50	/**
51	* An array used only during deserialization, to hold
52	* items read back in from the stream, and then used
53	* as "items" by readResolve via the private constructor.
54	*/
55	private transient E[] deserializedItems;
56
57	/*
58	* Concurrency control via the classic two-condition algorithm
59	* found in any textbook.
60	*/
61
62	/** Main lock guarding all access */
63	private final ReentrantLock lock;
64	/** Condition for waiting takes */
65	private final Condition notEmpty;
66	/** Condition for wiating puts */
67	private final Condition notFull;
68
69	// Internal helper methods
70
71	/**
72	* Circularly increment i.
73	*/
74	int inc(int i) {
75	return (++i == items.length)? 0 : i;
76	}
77
78	/**
79	* Insert element at current put position, advance, and signal.
80	* Call only when holding lock.
81	*/
82	private void insert(E x) {
83	items[putIndex] = x;
84	putIndex = inc(putIndex);
85	++count;
86	notEmpty.signal();
87	}
88
89	/**
90	* Extract element at current take position, advance, and signal.
91	* Call only when holding lock.
92	*/
93	private E extract() {
94	E x = items[takeIndex];
95	items[takeIndex] = null;
96	takeIndex = inc(takeIndex);
97	--count;
98	notFull.signal();
99	return x;
100	}
101
102	/**
103	* Utility for remove and iterator.remove: Delete item at position i.
104	* Call only when holding lock.
105	*/
106	void removeAt(int i) {
107	// if removing front item, just advance
108	if (i == takeIndex) {
109	items[takeIndex] = null;
110	takeIndex = inc(takeIndex);
111	}
112	else {
113	// slide over all others up through putIndex.
114	for (;;) {
115	int nexti = inc(i);
116	if (nexti != putIndex) {
117	items[i] = items[nexti];
118	i = nexti;
119	}
120	else {
121	items[i] = null;
122	putIndex = i;
123	break;
124	}
125	}
126	}
127	--count;
128	notFull.signal();
129	}
130
131	/**
132	* Internal constructor also used by readResolve.
133	* Sets all final fields, plus count.
134	* @param cap the capacity
135	* @param array the array to use or null if should create new one
136	* @param count the number of items in the array, where indices 0
137	* to count-1 hold items.
138	* @param lk the lock to use with this queue
139	*/
140	private ArrayBlockingQueue(int cap, E[] array, int count,
141	ReentrantLock lk) {
142	if (cap <= 0)
143	throw new IllegalArgumentException();
144	if (array == null)
145	this.items = (E[]) new Object[cap];
146	else
147	this.items = array;
148	this.putIndex = count;
149	this.count = count;
150	lock = lk;
151	notEmpty = lock.newCondition();
152	notFull = lock.newCondition();
153	}
154
155	/**
156	* Create an <tt>ArrayBlockingQueue</tt> with the given (fixed)
157	* capacity and default access policy.
158	* @param capacity the capacity of this queue
159	* @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
160	*/
161	public ArrayBlockingQueue(int capacity) {
162	this(capacity, null, 0, new ReentrantLock());
163	}
164
165	/**
166	* Create an <tt>ArrayBlockingQueue</tt> with the given (fixed)
167	* capacity and the specified access policy.
168	* @param capacity the capacity of this queue
169	* @param fair if <tt>true</tt> then queue accesses for threads blocked
170	* on insertion or removal, are processed in FIFO order; if <tt>false</tt>
171	* the access order is unspecified.
172	* @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
173	*/
174	public ArrayBlockingQueue(int capacity, boolean fair) {
175	this(capacity, null, 0, new ReentrantLock(fair));
176	}
177
178	/**
179	* Create an <tt>ArrayBlockingQueue</tt> with the given (fixed)
180	* capacity, the specified access policy and initially holding the
181	* elements of the given collection,
182	* added in traversal order of the collection's iterator.
183	* @param capacity the capacity of this queue
184	* @param fair if <tt>true</tt> then queue accesses for threads blocked
185	* on insertion or removal, are processed in FIFO order; if <tt>false</tt>
186	* the access order is unspecified.
187	* @param c the collection of elements to initially contain
188	* @throws IllegalArgumentException if <tt>capacity</tt> is less than
189	* <tt>c.size()</tt>, or less than 1.
190	* @throws NullPointerException if <tt>c</tt> or any element within it
191	* is <tt>null</tt>
192	*/
193	public ArrayBlockingQueue(int capacity, boolean fair,
194	Collection<? extends E> c) {
195	this(capacity, null, 0, new ReentrantLock(fair));
196
197	if (capacity < c.size())
198	throw new IllegalArgumentException();
199
200	for (Iterator<E> it = c.iterator(); it.hasNext();)
201	add(it.next());
202	}
203
204	// Have to override just to update the javadoc for @throws
205
206	/**
207	* @throws IllegalStateException {@inheritDoc}
208	* @throws NullPointerException {@inheritDoc}
209	*/
210	public boolean add(E o) {
211	return super.add(o);
212	}
213
214	/**
215	* @throws IllegalStateException {@inheritDoc}
216	* @throws NullPointerException {@inheritDoc}
217	*/
218	public boolean addAll(Collection<? extends E> c) {
219	return super.addAll(c);
220	}
221
222	/**
223	* Add the specified element to the tail of this queue if possible,
224	* returning immediately if this queue is full.
225	*
226	* @throws NullPointerException {@inheritDoc}
227	*/
228	public boolean offer(E x) {
229	if (x == null) throw new NullPointerException();
230	lock.lock();
231	try {
232	if (count == items.length)
233	return false;
234	else {
235	insert(x);
236	return true;
237	}
238	}
239	finally {
240	lock.unlock();
241	}
242	}
243
244	/**
245	* Add the specified element to the tail of this queue, waiting if
246	* necessary up to the specified wait time for space to become available.
247	* @throws NullPointerException {@inheritDoc}
248	*/
249	public boolean offer(E x, long timeout, TimeUnit unit)
250	throws InterruptedException {
251
252	if (x == null) throw new NullPointerException();
253
254	lock.lockInterruptibly();
255	try {
256	long nanos = unit.toNanos(timeout);
257	for (;;) {
258	if (count != items.length) {
259	insert(x);
260	return true;
261	}
262	if (nanos <= 0)
263	return false;
264	try {
265	nanos = notFull.awaitNanos(nanos);
266	}
267	catch (InterruptedException ie) {
268	notFull.signal(); // propagate to non-interrupted thread
269	throw ie;
270	}
271	}
272	}
273	finally {
274	lock.unlock();
275	}
276	}
277
278
279	public E poll() {
280	lock.lock();
281	try {
282	if (count == 0)
283	return null;
284	E x = extract();
285	return x;
286	}
287	finally {
288	lock.unlock();
289	}
290	}
291
292	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
293	lock.lockInterruptibly();
294	try {
295	long nanos = unit.toNanos(timeout);
296	for (;;) {
297	if (count != 0) {
298	E x = extract();
299	return x;
300	}
301	if (nanos <= 0)
302	return null;
303	try {
304	nanos = notEmpty.awaitNanos(nanos);
305	}
306	catch (InterruptedException ie) {
307	notEmpty.signal(); // propagate to non-interrupted thread
308	throw ie;
309	}
310
311	}
312	}
313	finally {
314	lock.unlock();
315	}
316	}
317
318
319	public boolean remove(Object x) {
320	if (x == null) return false;
321	lock.lock();
322	try {
323	int i = takeIndex;
324	int k = 0;
325	for (;;) {
326	if (k++ >= count)
327	return false;
328	if (x.equals(items[i])) {
329	removeAt(i);
330	return true;
331	}
332	i = inc(i);
333	}
334
335	}
336	finally {
337	lock.unlock();
338	}
339	}
340
341	public E peek() {
342	lock.lock();
343	try {
344	return (count == 0) ? null : items[takeIndex];
345	}
346	finally {
347	lock.unlock();
348	}
349	}
350
351	public E take() throws InterruptedException {
352	lock.lockInterruptibly();
353	try {
354	try {
355	while (count == 0)
356	notEmpty.await();
357	}
358	catch (InterruptedException ie) {
359	notEmpty.signal(); // propagate to non-interrupted thread
360	throw ie;
361	}
362	E x = extract();
363	return x;
364	}
365	finally {
366	lock.unlock();
367	}
368	}
369
370	/**
371	* Add the specified element to the tail of this queue, waiting if
372	* necessary for space to become available.
373	* @throws NullPointerException {@inheritDoc}
374	*/
375	public void put(E x) throws InterruptedException {
376
377	if (x == null) throw new NullPointerException();
378
379	lock.lockInterruptibly();
380	try {
381	try {
382	while (count == items.length)
383	notFull.await();
384	}
385	catch (InterruptedException ie) {
386	notFull.signal(); // propagate to non-interrupted thread
387	throw ie;
388	}
389	insert(x);
390	}
391	finally {
392	lock.unlock();
393	}
394	}
395
396	// this doc comment is overridden to remove the reference to collections
397	// greater in size than Integer.MAX_VALUE
398	/**
399	* Return the number of elements in this collection.
400	*/
401	public int size() {
402	lock.lock();
403	try {
404	return count;
405	}
406	finally {
407	lock.unlock();
408	}
409	}
410
411	// this doc comment is a modified copy of the inherited doc comment,
412	// without the reference to unlimited queues.
413	/**
414	* Return the number of elements that this queue can ideally (in
415	* the absence of memory or resource constraints) accept without
416	* blocking. This is always equal to the initial capacity of this queue
417	* less the current <tt>size</tt> of this queue.
418	* <p>Note that you <em>cannot</em> always tell if
419	* an attempt to <tt>add</tt> an element will succeed by
420	* inspecting <tt>remainingCapacity</tt> because it may be the
421	* case that a waiting consumer is ready to <tt>take</tt> an
422	* element out of an otherwise full queue.
423	*/
424	public int remainingCapacity() {
425	lock.lock();
426	try {
427	return items.length - count;
428	}
429	finally {
430	lock.unlock();
431	}
432	}
433
434
435	public boolean contains(Object x) {
436	if (x == null) return false;
437	lock.lock();
438	try {
439	int i = takeIndex;
440	int k = 0;
441	while (k++ < count) {
442	if (x.equals(items[i]))
443	return true;
444	i = inc(i);
445	}
446	return false;
447	}
448	finally {
449	lock.unlock();
450	}
451	}
452
453	public Object[] toArray() {
454	lock.lock();
455	try {
456	E[] a = (E[]) new Object[count];
457	int k = 0;
458	int i = takeIndex;
459	while (k < count) {
460	a[k++] = items[i];
461	i = inc(i);
462	}
463	return a;
464	}
465	finally {
466	lock.unlock();
467	}
468	}
469
470	public <T> T[] toArray(T[] a) {
471	lock.lock();
472	try {
473	if (a.length < count)
474	a = (T[])java.lang.reflect.Array.newInstance(
475	a.getClass().getComponentType(),
476	count
477	);
478
479	int k = 0;
480	int i = takeIndex;
481	while (k < count) {
482	a[k++] = (T)items[i];
483	i = inc(i);
484	}
485	if (a.length > count)
486	a[count] = null;
487	return a;
488	}
489	finally {
490	lock.unlock();
491	}
492	}
493
494	public String toString() {
495	lock.lock();
496	try {
497	return super.toString();
498	}
499	finally {
500	lock.unlock();
501	}
502	}
503
504	/**
505	* Returns an iterator over the elements in this queue in proper sequence.
506	*
507	* @return an iterator over the elements in this queue in proper sequence.
508	*/
509	public Iterator<E> iterator() {
510	lock.lock();
511	try {
512	return new Itr();
513	}
514	finally {
515	lock.unlock();
516	}
517	}
518
519	/**
520	* Iterator for ArrayBlockingQueue
521	*/
522	private class Itr implements Iterator<E> {
523	/**
524	* Index of element to be returned by next,
525	* or a negative number if no such.
526	*/
527	private int nextIndex;
528
529	/**
530	* nextItem holds on to item fields because once we claim
531	* that an element exists in hasNext(), we must return it in
532	* the following next() call even if it was in the process of
533	* being removed when hasNext() was called.
534	**/
535	private E nextItem;
536
537	/**
538	* Index of element returned by most recent call to next.
539	* Reset to -1 if this element is deleted by a call to remove.
540	*/
541	private int lastRet;
542
543	Itr() {
544	lastRet = -1;
545	if (count == 0)
546	nextIndex = -1;
547	else {
548	nextIndex = takeIndex;
549	nextItem = items[takeIndex];
550	}
551	}
552
553	public boolean hasNext() {
554	/*
555	* No sync. We can return true by mistake here
556	* only if this iterator passed across threads,
557	* which we don't support anyway.
558	*/
559	return nextIndex >= 0;
560	}
561
562	/**
563	* Check whether nextIndex is valid; if so setting nextItem.
564	* Stops iterator when either hits putIndex or sees null item.
565	*/
566	private void checkNext() {
567	if (nextIndex == putIndex) {
568	nextIndex = -1;
569	nextItem = null;
570	}
571	else {
572	nextItem = items[nextIndex];
573	if (nextItem == null)
574	nextIndex = -1;
575	}
576	}
577
578	public E next() {
579	lock.lock();
580	try {
581	if (nextIndex < 0)
582	throw new NoSuchElementException();
583	lastRet = nextIndex;
584	E x = nextItem;
585	nextIndex = inc(nextIndex);
586	checkNext();
587	return x;
588	}
589	finally {
590	lock.unlock();
591	}
592	}
593
594	public void remove() {
595	lock.lock();
596	try {
597	int i = lastRet;
598	if (i == -1)
599	throw new IllegalStateException();
600	lastRet = -1;
601
602	int ti = takeIndex;
603	removeAt(i);
604	// back up cursor (reset to front if was first element)
605	nextIndex = (i == ti) ? takeIndex : i;
606	checkNext();
607	}
608	finally {
609	lock.unlock();
610	}
611	}
612	}
613
614	/**
615	* Save the state to a stream (that is, serialize it).
616	*
617	* @serialData The maximumSize is emitted (int), followed by all of
618	* its elements (each an <tt>E</tt>) in the proper order.
619	* @param s the stream
620	*/
621	private void writeObject(java.io.ObjectOutputStream s)
622	throws java.io.IOException {
623
624	// Write out element count, and any hidden stuff
625	s.defaultWriteObject();
626	// Write out maximumSize == items length
627	s.writeInt(items.length);
628
629	// Write out all elements in the proper order.
630	int i = takeIndex;
631	int k = 0;
632	while (k++ < count) {
633	s.writeObject(items[i]);
634	i = inc(i);
635	}
636	}
637
638	/**
639	* Reconstitute this queue instance from a stream (that is,
640	* deserialize it).
641	* @param s the stream
642	*/
643	private void readObject(java.io.ObjectInputStream s)
644	throws java.io.IOException, ClassNotFoundException {
645	// Read in size, and any hidden stuff
646	s.defaultReadObject();
647	int size = count;
648
649	// Read in array length and allocate array
650	int arrayLength = s.readInt();
651
652	// We use deserializedItems here because "items" is final
653	deserializedItems = (E[]) new Object[arrayLength];
654
655	// Read in all elements in the proper order into deserializedItems
656	for (int i = 0; i < size; i++)
657	deserializedItems[i] = (E)s.readObject();
658	}
659
660	/**
661	* Throw away the object created with readObject, and replace it
662	* with a usable ArrayBlockingQueue.
663	* @return the ArrayBlockingQueue
664	*/
665	private Object readResolve() throws java.io.ObjectStreamException {
666	E[] array = deserializedItems;
667	deserializedItems = null;
668	return new ArrayBlockingQueue<E>(array.length, array, count, lock);
669	}
670	}