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 {@linkplain 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. New elements
 * are inserted at the tail of the queue, and the queue retrieval
 * operations obtain elements at the head of the queue.
 *
 * <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 decreases
 * throughput but reduces variability and avoids starvation.
 *
 * <p>This class implements all of the <em>optional</em> methods
 * of the {@link Collection} and {@link Iterator} interfaces.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public class ArrayBlockingQueue<E> extends AbstractQueue<E>
        implements BlockingQueue<E>, java.io.Serializable {

    /**
     * Seialization ID. This class relies on default serialzation even
     * for the items array is default-serialized, even if it is
     * empty. Otherwise it could not be declared final, which is
     * necessary here.
     */
    private static final long serialVersionUID = -817911632652898426L;

    /** The queued items  */
    private 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;

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

    /** Main lock guarding all access */
    private final ReentrantLock lock;
    /** Condition for waiting takes */
    private final ReentrantLock.ConditionObject notEmpty;
    /** Condition for waiting puts */
    private final ReentrantLock.ConditionObject 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() {
        final E[] items = this.items;
        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) {
        final E[] items = this.items;
        // 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();
    }

    /**
     * Creates 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, false);
    }

    /**
     * Creates 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) {
        if (capacity <= 0)
            throw new IllegalArgumentException();
        this.items = (E[]) new Object[capacity];
        lock = new ReentrantLock(fair);
        notEmpty = lock.newCondition();
        notFull =  lock.newCondition();
    }

    /**
     * Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
     * capacity, the specified access policy and initially containing 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, fair);
        if (capacity < c.size())
            throw new IllegalArgumentException();

        for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
            add(it.next());
    }

    /**
     * Inserts the specified element at the tail of this queue if possible,
     * returning immediately if this queue is full.
     *
     * @param o the element to add.
     * @return <tt>true</tt> if it was possible to add the element to
     *         this queue, else <tt>false</tt>
     * @throws NullPointerException if the specified element is <tt>null</tt>
     */
    public boolean offer(E o) {
        if (o == null) throw new NullPointerException();
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            if (count == items.length)
                return false;
            else {
                insert(o);
                return true;
            }
        } finally {
            lock.unlock();
        }
    }

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

        if (o == null) throw new NullPointerException();
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            long nanos = unit.toNanos(timeout);
            for (;;) {
                if (count != items.length) {
                    insert(o);
                    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() {
        final ReentrantLock lock = this.lock;
        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 {
        final ReentrantLock lock = this.lock;
        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 o) {
        if (o == null) return false;
        final E[] items = this.items;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int i = takeIndex;
            int k = 0;
            for (;;) {
                if (k++ >= count)
                    return false;
                if (o.equals(items[i])) {
                    removeAt(i);
                    return true;
                }
                i = inc(i);
            }

        } finally {
            lock.unlock();
        }
    }

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

    public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        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();
        }
    }

    /**
     * Adds the specified element to the tail of this queue, waiting if
     * necessary for space to become available.
     * @param o the element to add
     * @throws InterruptedException if interrupted while waiting.
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     */
    public void put(E o) throws InterruptedException {
        if (o == null) throw new NullPointerException();
        final E[] items = this.items;
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            try {
                while (count == items.length)
                    notFull.await();
            } catch (InterruptedException ie) {
                notFull.signal(); // propagate to non-interrupted thread
                throw ie;
            }
            insert(o);
        } finally {
            lock.unlock();
        }
    }

    // this doc comment is overridden to remove the reference to collections
    // greater in size than Integer.MAX_VALUE
    /**
     * Returns the number of elements in this queue.
     *
     * @return  the number of elements in this queue.
     */
    public int size() {
        final ReentrantLock lock = this.lock;
        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.
    /**
     * Returns the number of elements that this queue can ideally (in
     * the absence of memory or resource constraints) accept without
     * blocking. This is always equal to the initial capacity of this queue
     * less the current <tt>size</tt> of this queue.
     * <p>Note that you <em>cannot</em> always tell if
     * an attempt to <tt>add</tt> an element will succeed by
     * inspecting <tt>remainingCapacity</tt> because it may be the
     * case that a waiting consumer is ready to <tt>take</tt> an
     * element out of an otherwise full queue.
     */
    public int remainingCapacity() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return items.length - count;
        } finally {
            lock.unlock();
        }
    }


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

    public Object[] toArray() {
        final E[] items = this.items;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            Object[] a = 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) {
        final E[] items = this.items;
        final ReentrantLock lock = this.lock;
        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() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return super.toString();
        } finally {
            lock.unlock();
        }
    }


    public void clear() {
        final E[] items = this.items;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int i = takeIndex;
            int k = count;
            while (k-- > 0) {
                items[i] = null;
                i = inc(i);
            }
            count = 0;
            putIndex = 0;
            takeIndex = 0;
            notFull.signalAll();
        } finally {
            lock.unlock();
        }
    }

    public int drainTo(Collection<? super E> c) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        final E[] items = this.items;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int i = takeIndex;
            int n = 0;
            int max = count;
            while (n < max) {
                c.add(items[i]);
                items[i] = null;
                i = inc(i);
                ++n;
            }
            if (n > 0) {
                count = 0;
                putIndex = 0;
                takeIndex = 0;
                notFull.signalAll();
            }
            return n;
        } finally {
            lock.unlock();
        }
    }


    public int drainTo(Collection<? super E> c, int maxElements) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        if (maxElements <= 0)
            return 0;
        final E[] items = this.items;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            int i = takeIndex;
            int n = 0;
            int sz = count;
            int max = (maxElements < count)? maxElements : count;
            while (n < max) {
                c.add(items[i]);
                items[i] = null;
                i = inc(i);
                ++n;
            }
            if (n > 0) {
                count -= n;
                takeIndex = i;
                notFull.signalAll();
            }
            return n;
        } finally {
            lock.unlock();
        }
    }


    /**
     * Returns an iterator over the elements in this queue in proper sequence.
     * The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
     * will never throw {@link java.util.ConcurrentModificationException},
     * and guarantees to traverse elements as they existed upon
     * construction of the iterator, and may (but is not guaranteed to)
     * reflect any modifications subsequent to construction.
     *
     * @return an iterator over the elements in this queue in proper sequence.
     */
    public Iterator<E> iterator() {
        final ReentrantLock lock = this.lock;
        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() {
            final ReentrantLock lock = ArrayBlockingQueue.this.lock;
            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() {
            final ReentrantLock lock = ArrayBlockingQueue.this.lock;
            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();
            }
        }
    }
}
Revision:	1.36
Committed:	Tue Dec 23 19:38:09 2003 UTC (20 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.35:	+49 -99 lines
Log Message:	cache finals across volatiles; avoid readResolve; doc improvments; timed invokeAll interleaves
#	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 {@linkplain BlockingQueue blocking queue} backed by an
13	* array. This queue orders elements FIFO (first-in-first-out). The
14	* <em>head</em> of the queue is that element that has been on the
15	* queue the longest time. The <em>tail</em> of the queue is that
16	* element that has been on the queue the shortest time. New elements
17	* are inserted at the tail of the queue, and the queue retrieval
18	* operations obtain elements at the head of the queue.
19	*
20	* <p>This is a classic "bounded buffer", in which a fixed-sized
21	* array holds
22	* elements inserted by producers and extracted by consumers. Once
23	* created, the capacity can not be increased. Attempts to offer an
24	* element to a full queue will result in the offer operation
25	* blocking; attempts to retrieve an element from an empty queue will
26	* similarly block.
27	*
28	* <p> This class supports an optional fairness policy for ordering
29	* threads blocked on an insertion or removal. By default, this
30	* ordering is not guaranteed. However, an <tt>ArrayBlockingQueue</tt>
31	* constructed with fairness set to <tt>true</tt> grants blocked
32	* threads access in FIFO order. Fairness generally decreases
33	* throughput but reduces variability and avoids starvation.
34	*
35	* <p>This class implements all of the <em>optional</em> methods
36	* of the {@link Collection} and {@link Iterator} interfaces.
37	*
38	* @since 1.5
39	* @author Doug Lea
40	* @param <E> the type of elements held in this collection
41	*/
42	public class ArrayBlockingQueue<E> extends AbstractQueue<E>
43	implements BlockingQueue<E>, java.io.Serializable {
44
45	/**
46	* Seialization ID. This class relies on default serialzation even
47	* for the items array is default-serialized, even if it is
48	* empty. Otherwise it could not be declared final, which is
49	* necessary here.
50	*/
51	private static final long serialVersionUID = -817911632652898426L;
52
53	/** The queued items */
54	private final E[] items;
55	/** items index for next take, poll or remove */
56	private transient int takeIndex;
57	/** items index for next put, offer, or add. */
58	private transient int putIndex;
59	/** Number of items in the queue */
60	private int count;
61
62	/*
63	* Concurrency control uses the classic two-condition algorithm
64	* found in any textbook.
65	*/
66
67	/** Main lock guarding all access */
68	private final ReentrantLock lock;
69	/** Condition for waiting takes */
70	private final ReentrantLock.ConditionObject notEmpty;
71	/** Condition for waiting puts */
72	private final ReentrantLock.ConditionObject notFull;
73
74	// Internal helper methods
75
76	/**
77	* Circularly increment i.
78	*/
79	int inc(int i) {
80	return (++i == items.length)? 0 : i;
81	}
82
83	/**
84	* Insert element at current put position, advance, and signal.
85	* Call only when holding lock.
86	*/
87	private void insert(E x) {
88	items[putIndex] = x;
89	putIndex = inc(putIndex);
90	++count;
91	notEmpty.signal();
92	}
93
94	/**
95	* Extract element at current take position, advance, and signal.
96	* Call only when holding lock.
97	*/
98	private E extract() {
99	final E[] items = this.items;
100	E x = items[takeIndex];
101	items[takeIndex] = null;
102	takeIndex = inc(takeIndex);
103	--count;
104	notFull.signal();
105	return x;
106	}
107
108	/**
109	* Utility for remove and iterator.remove: Delete item at position i.
110	* Call only when holding lock.
111	*/
112	void removeAt(int i) {
113	final E[] items = this.items;
114	// if removing front item, just advance
115	if (i == takeIndex) {
116	items[takeIndex] = null;
117	takeIndex = inc(takeIndex);
118	} else {
119	// slide over all others up through putIndex.
120	for (;;) {
121	int nexti = inc(i);
122	if (nexti != putIndex) {
123	items[i] = items[nexti];
124	i = nexti;
125	} else {
126	items[i] = null;
127	putIndex = i;
128	break;
129	}
130	}
131	}
132	--count;
133	notFull.signal();
134	}
135
136	/**
137	* Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
138	* capacity and default access policy.
139	* @param capacity the capacity of this queue
140	* @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
141	*/
142	public ArrayBlockingQueue(int capacity) {
143	this(capacity, false);
144	}
145
146	/**
147	* Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
148	* capacity and the specified access policy.
149	* @param capacity the capacity of this queue
150	* @param fair if <tt>true</tt> then queue accesses for threads blocked
151	* on insertion or removal, are processed in FIFO order; if <tt>false</tt>
152	* the access order is unspecified.
153	* @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
154	*/
155	public ArrayBlockingQueue(int capacity, boolean fair) {
156	if (capacity <= 0)
157	throw new IllegalArgumentException();
158	this.items = (E[]) new Object[capacity];
159	lock = new ReentrantLock(fair);
160	notEmpty = lock.newCondition();
161	notFull = lock.newCondition();
162	}
163
164	/**
165	* Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
166	* capacity, the specified access policy and initially containing the
167	* elements of the given collection,
168	* added in traversal order of the collection's iterator.
169	* @param capacity the capacity of this queue
170	* @param fair if <tt>true</tt> then queue accesses for threads blocked
171	* on insertion or removal, are processed in FIFO order; if <tt>false</tt>
172	* the access order is unspecified.
173	* @param c the collection of elements to initially contain
174	* @throws IllegalArgumentException if <tt>capacity</tt> is less than
175	* <tt>c.size()</tt>, or less than 1.
176	* @throws NullPointerException if <tt>c</tt> or any element within it
177	* is <tt>null</tt>
178	*/
179	public ArrayBlockingQueue(int capacity, boolean fair,
180	Collection<? extends E> c) {
181	this(capacity, fair);
182	if (capacity < c.size())
183	throw new IllegalArgumentException();
184
185	for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
186	add(it.next());
187	}
188
189	/**
190	* Inserts the specified element at the tail of this queue if possible,
191	* returning immediately if this queue is full.
192	*
193	* @param o the element to add.
194	* @return <tt>true</tt> if it was possible to add the element to
195	* this queue, else <tt>false</tt>
196	* @throws NullPointerException if the specified element is <tt>null</tt>
197	*/
198	public boolean offer(E o) {
199	if (o == null) throw new NullPointerException();
200	final ReentrantLock lock = this.lock;
201	lock.lock();
202	try {
203	if (count == items.length)
204	return false;
205	else {
206	insert(o);
207	return true;
208	}
209	} finally {
210	lock.unlock();
211	}
212	}
213
214	/**
215	* Inserts the specified element at the tail of this queue, waiting if
216	* necessary up to the specified wait time for space to become available.
217	* @param o the element to add
218	* @param timeout how long to wait before giving up, in units of
219	* <tt>unit</tt>
220	* @param unit a <tt>TimeUnit</tt> determining how to interpret the
221	* <tt>timeout</tt> parameter
222	* @return <tt>true</tt> if successful, or <tt>false</tt> if
223	* the specified waiting time elapses before space is available.
224	* @throws InterruptedException if interrupted while waiting.
225	* @throws NullPointerException if the specified element is <tt>null</tt>.
226	*/
227	public boolean offer(E o, long timeout, TimeUnit unit)
228	throws InterruptedException {
229
230	if (o == null) throw new NullPointerException();
231	final ReentrantLock lock = this.lock;
232	lock.lockInterruptibly();
233	try {
234	long nanos = unit.toNanos(timeout);
235	for (;;) {
236	if (count != items.length) {
237	insert(o);
238	return true;
239	}
240	if (nanos <= 0)
241	return false;
242	try {
243	nanos = notFull.awaitNanos(nanos);
244	} catch (InterruptedException ie) {
245	notFull.signal(); // propagate to non-interrupted thread
246	throw ie;
247	}
248	}
249	} finally {
250	lock.unlock();
251	}
252	}
253
254
255	public E poll() {
256	final ReentrantLock lock = this.lock;
257	lock.lock();
258	try {
259	if (count == 0)
260	return null;
261	E x = extract();
262	return x;
263	} finally {
264	lock.unlock();
265	}
266	}
267
268	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
269	final ReentrantLock lock = this.lock;
270	lock.lockInterruptibly();
271	try {
272	long nanos = unit.toNanos(timeout);
273	for (;;) {
274	if (count != 0) {
275	E x = extract();
276	return x;
277	}
278	if (nanos <= 0)
279	return null;
280	try {
281	nanos = notEmpty.awaitNanos(nanos);
282	} catch (InterruptedException ie) {
283	notEmpty.signal(); // propagate to non-interrupted thread
284	throw ie;
285	}
286
287	}
288	} finally {
289	lock.unlock();
290	}
291	}
292
293
294	public boolean remove(Object o) {
295	if (o == null) return false;
296	final E[] items = this.items;
297	final ReentrantLock lock = this.lock;
298	lock.lock();
299	try {
300	int i = takeIndex;
301	int k = 0;
302	for (;;) {
303	if (k++ >= count)
304	return false;
305	if (o.equals(items[i])) {
306	removeAt(i);
307	return true;
308	}
309	i = inc(i);
310	}
311
312	} finally {
313	lock.unlock();
314	}
315	}
316
317	public E peek() {
318	final ReentrantLock lock = this.lock;
319	lock.lock();
320	try {
321	return (count == 0) ? null : items[takeIndex];
322	} finally {
323	lock.unlock();
324	}
325	}
326
327	public E take() throws InterruptedException {
328	final ReentrantLock lock = this.lock;
329	lock.lockInterruptibly();
330	try {
331	try {
332	while (count == 0)
333	notEmpty.await();
334	} catch (InterruptedException ie) {
335	notEmpty.signal(); // propagate to non-interrupted thread
336	throw ie;
337	}
338	E x = extract();
339	return x;
340	} finally {
341	lock.unlock();
342	}
343	}
344
345	/**
346	* Adds the specified element to the tail of this queue, waiting if
347	* necessary for space to become available.
348	* @param o the element to add
349	* @throws InterruptedException if interrupted while waiting.
350	* @throws NullPointerException if the specified element is <tt>null</tt>.
351	*/
352	public void put(E o) throws InterruptedException {
353	if (o == null) throw new NullPointerException();
354	final E[] items = this.items;
355	final ReentrantLock lock = this.lock;
356	lock.lockInterruptibly();
357	try {
358	try {
359	while (count == items.length)
360	notFull.await();
361	} catch (InterruptedException ie) {
362	notFull.signal(); // propagate to non-interrupted thread
363	throw ie;
364	}
365	insert(o);
366	} finally {
367	lock.unlock();
368	}
369	}
370
371	// this doc comment is overridden to remove the reference to collections
372	// greater in size than Integer.MAX_VALUE
373	/**
374	* Returns the number of elements in this queue.
375	*
376	* @return the number of elements in this queue.
377	*/
378	public int size() {
379	final ReentrantLock lock = this.lock;
380	lock.lock();
381	try {
382	return count;
383	} finally {
384	lock.unlock();
385	}
386	}
387
388	// this doc comment is a modified copy of the inherited doc comment,
389	// without the reference to unlimited queues.
390	/**
391	* Returns the number of elements that this queue can ideally (in
392	* the absence of memory or resource constraints) accept without
393	* blocking. This is always equal to the initial capacity of this queue
394	* less the current <tt>size</tt> of this queue.
395	* <p>Note that you <em>cannot</em> always tell if
396	* an attempt to <tt>add</tt> an element will succeed by
397	* inspecting <tt>remainingCapacity</tt> because it may be the
398	* case that a waiting consumer is ready to <tt>take</tt> an
399	* element out of an otherwise full queue.
400	*/
401	public int remainingCapacity() {
402	final ReentrantLock lock = this.lock;
403	lock.lock();
404	try {
405	return items.length - count;
406	} finally {
407	lock.unlock();
408	}
409	}
410
411
412	public boolean contains(Object o) {
413	if (o == null) return false;
414	final E[] items = this.items;
415	final ReentrantLock lock = this.lock;
416	lock.lock();
417	try {
418	int i = takeIndex;
419	int k = 0;
420	while (k++ < count) {
421	if (o.equals(items[i]))
422	return true;
423	i = inc(i);
424	}
425	return false;
426	} finally {
427	lock.unlock();
428	}
429	}
430
431	public Object[] toArray() {
432	final E[] items = this.items;
433	final ReentrantLock lock = this.lock;
434	lock.lock();
435	try {
436	Object[] a = new Object[count];
437	int k = 0;
438	int i = takeIndex;
439	while (k < count) {
440	a[k++] = items[i];
441	i = inc(i);
442	}
443	return a;
444	} finally {
445	lock.unlock();
446	}
447	}
448
449	public <T> T[] toArray(T[] a) {
450	final E[] items = this.items;
451	final ReentrantLock lock = this.lock;
452	lock.lock();
453	try {
454	if (a.length < count)
455	a = (T[])java.lang.reflect.Array.newInstance(
456	a.getClass().getComponentType(),
457	count
458	);
459
460	int k = 0;
461	int i = takeIndex;
462	while (k < count) {
463	a[k++] = (T)items[i];
464	i = inc(i);
465	}
466	if (a.length > count)
467	a[count] = null;
468	return a;
469	} finally {
470	lock.unlock();
471	}
472	}
473
474	public String toString() {
475	final ReentrantLock lock = this.lock;
476	lock.lock();
477	try {
478	return super.toString();
479	} finally {
480	lock.unlock();
481	}
482	}
483
484
485	public void clear() {
486	final E[] items = this.items;
487	final ReentrantLock lock = this.lock;
488	lock.lock();
489	try {
490	int i = takeIndex;
491	int k = count;
492	while (k-- > 0) {
493	items[i] = null;
494	i = inc(i);
495	}
496	count = 0;
497	putIndex = 0;
498	takeIndex = 0;
499	notFull.signalAll();
500	} finally {
501	lock.unlock();
502	}
503	}
504
505	public int drainTo(Collection<? super E> c) {
506	if (c == null)
507	throw new NullPointerException();
508	if (c == this)
509	throw new IllegalArgumentException();
510	final E[] items = this.items;
511	final ReentrantLock lock = this.lock;
512	lock.lock();
513	try {
514	int i = takeIndex;
515	int n = 0;
516	int max = count;
517	while (n < max) {
518	c.add(items[i]);
519	items[i] = null;
520	i = inc(i);
521	++n;
522	}
523	if (n > 0) {
524	count = 0;
525	putIndex = 0;
526	takeIndex = 0;
527	notFull.signalAll();
528	}
529	return n;
530	} finally {
531	lock.unlock();
532	}
533	}
534
535
536	public int drainTo(Collection<? super E> c, int maxElements) {
537	if (c == null)
538	throw new NullPointerException();
539	if (c == this)
540	throw new IllegalArgumentException();
541	if (maxElements <= 0)
542	return 0;
543	final E[] items = this.items;
544	final ReentrantLock lock = this.lock;
545	lock.lock();
546	try {
547	int i = takeIndex;
548	int n = 0;
549	int sz = count;
550	int max = (maxElements < count)? maxElements : count;
551	while (n < max) {
552	c.add(items[i]);
553	items[i] = null;
554	i = inc(i);
555	++n;
556	}
557	if (n > 0) {
558	count -= n;
559	takeIndex = i;
560	notFull.signalAll();
561	}
562	return n;
563	} finally {
564	lock.unlock();
565	}
566	}
567
568
569	/**
570	* Returns an iterator over the elements in this queue in proper sequence.
571	* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
572	* will never throw {@link java.util.ConcurrentModificationException},
573	* and guarantees to traverse elements as they existed upon
574	* construction of the iterator, and may (but is not guaranteed to)
575	* reflect any modifications subsequent to construction.
576	*
577	* @return an iterator over the elements in this queue in proper sequence.
578	*/
579	public Iterator<E> iterator() {
580	final ReentrantLock lock = this.lock;
581	lock.lock();
582	try {
583	return new Itr();
584	} finally {
585	lock.unlock();
586	}
587	}
588
589	/**
590	* Iterator for ArrayBlockingQueue
591	*/
592	private class Itr implements Iterator<E> {
593	/**
594	* Index of element to be returned by next,
595	* or a negative number if no such.
596	*/
597	private int nextIndex;
598
599	/**
600	* nextItem holds on to item fields because once we claim
601	* that an element exists in hasNext(), we must return it in
602	* the following next() call even if it was in the process of
603	* being removed when hasNext() was called.
604	**/
605	private E nextItem;
606
607	/**
608	* Index of element returned by most recent call to next.
609	* Reset to -1 if this element is deleted by a call to remove.
610	*/
611	private int lastRet;
612
613	Itr() {
614	lastRet = -1;
615	if (count == 0)
616	nextIndex = -1;
617	else {
618	nextIndex = takeIndex;
619	nextItem = items[takeIndex];
620	}
621	}
622
623	public boolean hasNext() {
624	/*
625	* No sync. We can return true by mistake here
626	* only if this iterator passed across threads,
627	* which we don't support anyway.
628	*/
629	return nextIndex >= 0;
630	}
631
632	/**
633	* Check whether nextIndex is valid; if so setting nextItem.
634	* Stops iterator when either hits putIndex or sees null item.
635	*/
636	private void checkNext() {
637	if (nextIndex == putIndex) {
638	nextIndex = -1;
639	nextItem = null;
640	} else {
641	nextItem = items[nextIndex];
642	if (nextItem == null)
643	nextIndex = -1;
644	}
645	}
646
647	public E next() {
648	final ReentrantLock lock = ArrayBlockingQueue.this.lock;
649	lock.lock();
650	try {
651	if (nextIndex < 0)
652	throw new NoSuchElementException();
653	lastRet = nextIndex;
654	E x = nextItem;
655	nextIndex = inc(nextIndex);
656	checkNext();
657	return x;
658	} finally {
659	lock.unlock();
660	}
661	}
662
663	public void remove() {
664	final ReentrantLock lock = ArrayBlockingQueue.this.lock;
665	lock.lock();
666	try {
667	int i = lastRet;
668	if (i == -1)
669	throw new IllegalStateException();
670	lastRet = -1;
671
672	int ti = takeIndex;
673	removeAt(i);
674	// back up cursor (reset to front if was first element)
675	nextIndex = (i == ti) ? takeIndex : i;
676	checkNext();
677	} finally {
678	lock.unlock();
679	}
680	}
681	}
682	}