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.*;

/**
 * A bounded blocking queue backed by an array.  The implementation is
 * a classic "bounded buffer", in which a fixed-sized array holds
 * elements inserted by producers and extracted by
 * consumers.  Once created, the capacity can not be increased.
 * Array-based queues typically have more predictable
 * performance than linked queues but lower throughput in most
 * concurrent applications.
 *
 * 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.  Threads blocked on an insertion or
 * removal will be services in FIFO order.
 * @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 gurding all access */
    private final FairReentrantLock lock = new FairReentrantLock();
    /** Condition wor waiting takes */
    private final Condition notEmpty = lock.newCondition();
    /** Condition for wiating puts */
    private final Condition notFull =  lock.newCondition();

    // Internal helper methods

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

    /**
     * Insert element at current put position and advance.
     */
    private void insert(E x) {
        items[putIndex] = x;
        putIndex = inc(putIndex);
        ++count;
    }
    
    /**
     * Extract element at current take position and advance.
     */
    private  E extract() {
        E x = items[takeIndex];
        items[takeIndex] = null;
        takeIndex = inc(takeIndex);
        --count;
        return x;
    }

    /**
     * Utility for remove and iterator.remove: Delete item at position
     * i by sliding over all others up through putIndex.
     */
    void removeAt(int i) {
        for (;;) {
            int nexti = inc(i);
            items[i] = items[nexti];
            if (nexti != putIndex) 
                i = nexti;
            else {
                items[nexti] = null;
                putIndex = i;
                --count;
                return;
            }
        }
    }

    /**
     * Internal constructor also used by readResolve. 
     * Sets all final fields, plus count.
     * @param cap the maximumSize 
     * @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.
     */
    private ArrayBlockingQueue(int cap, E[] array, int count) {
        if (cap <= 0) 
            throw new IllegalArgumentException();
        if (array == null)
            this.items = new E[cap];
        else
            this.items = array;
        this.putIndex = count;
        this.count = count;
    }
    
    /**
     * Creates a new ArrayBlockingQueue with the given (fixed) capacity.
     * @param maximumSize the capacity
     */
    public ArrayBlockingQueue(int maximumSize) {
        this(maximumSize, null, 0);
    }

    /**
     * Creates a new ArrayBlockingQueue with the given (fixed)
     * capacity, and initially contianing the given elements, added in
     * iterator traversal order.
     * @param maximumSize the capacity
     * @param initialElements the items to hold initially.
     * @throws IllegalArgumentException if the given capacity is
     * less than the number of initialElements.
     */
    public ArrayBlockingQueue(int maximumSize, Collection<E> initialElements) {
        this(maximumSize, null, 0);
        int n = 0;
        for (Iterator<E> it = initialElements.iterator(); it.hasNext();) {
            if (++n >= items.length)
                throw new IllegalArgumentException();
            items[n] = it.next();
        }
        putIndex = count = n;
    }

    /** Return the number of elements currently in the queue */
    public int size() {
        lock.lock();
        try {
            return count;
        }
        finally {
            lock.unlock();
        }
    }

    /** Return the remaining capacity of the queue, which is the
     * number of elements that can be inserted before the queue is
     * full. */
    public int remainingCapacity() {
        lock.lock();
        try {
            return items.length - count;
        }
        finally {
            lock.unlock();
        }
    }


    /** Insert a new element into the queue, blocking if the queue is full. */
    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);
            notEmpty.signal();
        }
        finally {
            lock.unlock();
        }
    }

    /** Remove and return the first element from the queue, blocking
     * if the queue is empty. 
     */
    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();
            notFull.signal();
            return x;
        }
        finally {
            lock.unlock();
        }
    }

   /** Attempt to insert a new element into the queue, but return
    * immediately without inserting the element if the queue is full.
    * @return <tt>true</tt> if the element was inserted successfully,
    * <tt>false</tt> otherwise
    */
    public boolean offer(E x) {
        if (x == null) throw new NullPointerException();
        lock.lock();
        try {
            if (count == items.length) 
                return false;
            else {
                insert(x);
                notEmpty.signal();
                return true;
            }
        }
        finally {
            lock.unlock(); 
        }
    }

    /** Attempt to retrieve the first insert element from the queue,
     * but return immediately if the queue is empty.
     * @return The first element of the queue if the queue is not
     * empty, or <tt>null</tt> otherwise.
     */
    public E poll() {
        lock.lock();
        try {
            if (count == 0)
                return null;
            E x = extract();
            notFull.signal();
            return x;
        }
        finally {
            lock.unlock(); 
        }
    }

    /** Attempt to insert a new element into the queue.  If the queue
     * is full, wait up to the specified amount of time before giving
     * up.
     * @param x the element to be inserted
     * @param timeout how long to wait before giving up, in units of
     * <tt>unit</tt>
     * @param unit a TimeUnit determining how to interpret the timeout
     * parameter
     * @return <tt>true</tt> if the element was inserted successfully,
     * <tt>false</tt> otherwise
     * @throws InterruptedException if interrupted while waiting
     */
    public boolean offer(E x, long timeout, TimeUnit unit) throws InterruptedException {
        if (x == null) throw new NullPointerException();
        lock.lockInterruptibly();
        long nanos = unit.toNanos(timeout);
        try {
            for (;;) {
                if (count != items.length) {
                    insert(x);
                    notEmpty.signal();
                    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();
        }
    }

    /**
     * Attempt to retrieve the first insert element from the queue.
     * If the queue is empty, wait up to the specified amount of time
     * before giving up.
     * @param timeout how long to wait before giving up, in units of
     * <tt>unit</tt>
     * @param unit a TimeUnit determining how to interpret the timeout
     * parameter
     * @return The first element of the queue if an item was
     * successfully retrieved, or <tt>null</tt> otherwise.
     * @throws InterruptedException if interrupted while waiting
     *
     */
    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        lock.lockInterruptibly();
        long nanos = unit.toNanos(timeout);
        try {
            for (;;) {
                if (count != 0) {
                    E x = extract();
                    notFull.signal();
                    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();
        }
    }

    /** Return, but do not remove, the first element from the queue,
     * if the queue is not empty.  This will return the same result as
     * <tt>poll</tt>, but will not remove it from the queue.
     * @return The first element of the queue if the queue is not
     * empty, or <tt>null</tt> otherwise.
     */
    public E peek() {
        lock.lock();
        try {
            return (count == 0) ? null : items[takeIndex];
        }
        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 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 = new E[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 valied; 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;
                
                nextIndex = i;   // back up cursor
                removeAt(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 the 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 = new E[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(array.length, array, count);
    }
}
Revision:	1.8
Committed:	Tue Jun 24 14:34:47 2003 UTC (20 years, 11 months ago) by dl
Branch:	MAIN
Changes since 1.7:	+35 -68 lines
Log Message:	Added missing javadoc tags; minor reformatting
#	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.*;
9
10	/**
11	* A bounded blocking queue backed by an array. The implementation is
12	* a classic "bounded buffer", in which a fixed-sized array holds
13	* elements inserted by producers and extracted by
14	* consumers. Once created, the capacity can not be increased.
15	* Array-based queues typically have more predictable
16	* performance than linked queues but lower throughput in most
17	* concurrent applications.
18	*
19	* Attempts to offer an element to a full queue will result
20	* in the offer operation blocking; attempts to retrieve an element from
21	* an empty queue will similarly block. Threads blocked on an insertion or
22	* removal will be services in FIFO order.
23	* @since 1.5
24	* @author Doug Lea
25	*/
26	public class ArrayBlockingQueue<E> extends AbstractQueue<E>
27	implements BlockingQueue<E>, java.io.Serializable {
28
29	/** The queued items */
30	private transient final E[] items;
31	/** items index for next take, poll or remove */
32	private transient int takeIndex;
33	/** items index for next put, offer, or add. */
34	private transient int putIndex;
35	/** Number of items in the queue */
36	private int count;
37
38	/**
39	* An array used only during deserialization, to hold
40	* items read back in from the stream, and then used
41	* as "items" by readResolve via the private constructor.
42	*/
43	private transient E[] deserializedItems;
44
45	/*
46	* Concurrency control via the classic two-condition algorithm
47	* found in any textbook.
48	*/
49
50	/** Main lock gurding all access */
51	private final FairReentrantLock lock = new FairReentrantLock();
52	/** Condition wor waiting takes */
53	private final Condition notEmpty = lock.newCondition();
54	/** Condition for wiating puts */
55	private final Condition notFull = lock.newCondition();
56
57	// Internal helper methods
58
59	/**
60	* Circularly increment i.
61	*/
62	int inc(int i) {
63	return (++i == items.length)? 0 : i;
64	}
65
66	/**
67	* Insert element at current put position and advance.
68	*/
69	private void insert(E x) {
70	items[putIndex] = x;
71	putIndex = inc(putIndex);
72	++count;
73	}
74
75	/**
76	* Extract element at current take position and advance.
77	*/
78	private E extract() {
79	E x = items[takeIndex];
80	items[takeIndex] = null;
81	takeIndex = inc(takeIndex);
82	--count;
83	return x;
84	}
85
86	/**
87	* Utility for remove and iterator.remove: Delete item at position
88	* i by sliding over all others up through putIndex.
89	*/
90	void removeAt(int i) {
91	for (;;) {
92	int nexti = inc(i);
93	items[i] = items[nexti];
94	if (nexti != putIndex)
95	i = nexti;
96	else {
97	items[nexti] = null;
98	putIndex = i;
99	--count;
100	return;
101	}
102	}
103	}
104
105	/**
106	* Internal constructor also used by readResolve.
107	* Sets all final fields, plus count.
108	* @param cap the maximumSize
109	* @param array the array to use or null if should create new one
110	* @param count the number of items in the array, where indices 0
111	* to count-1 hold items.
112	*/
113	private ArrayBlockingQueue(int cap, E[] array, int count) {
114	if (cap <= 0)
115	throw new IllegalArgumentException();
116	if (array == null)
117	this.items = new E[cap];
118	else
119	this.items = array;
120	this.putIndex = count;
121	this.count = count;
122	}
123
124	/**
125	* Creates a new ArrayBlockingQueue with the given (fixed) capacity.
126	* @param maximumSize the capacity
127	*/
128	public ArrayBlockingQueue(int maximumSize) {
129	this(maximumSize, null, 0);
130	}
131
132	/**
133	* Creates a new ArrayBlockingQueue with the given (fixed)
134	* capacity, and initially contianing the given elements, added in
135	* iterator traversal order.
136	* @param maximumSize the capacity
137	* @param initialElements the items to hold initially.
138	* @throws IllegalArgumentException if the given capacity is
139	* less than the number of initialElements.
140	*/
141	public ArrayBlockingQueue(int maximumSize, Collection<E> initialElements) {
142	this(maximumSize, null, 0);
143	int n = 0;
144	for (Iterator<E> it = initialElements.iterator(); it.hasNext();) {
145	if (++n >= items.length)
146	throw new IllegalArgumentException();
147	items[n] = it.next();
148	}
149	putIndex = count = n;
150	}
151
152	/** Return the number of elements currently in the queue */
153	public int size() {
154	lock.lock();
155	try {
156	return count;
157	}
158	finally {
159	lock.unlock();
160	}
161	}
162
163	/** Return the remaining capacity of the queue, which is the
164	* number of elements that can be inserted before the queue is
165	* full. */
166	public int remainingCapacity() {
167	lock.lock();
168	try {
169	return items.length - count;
170	}
171	finally {
172	lock.unlock();
173	}
174	}
175
176
177	/** Insert a new element into the queue, blocking if the queue is full. */
178	public void put(E x) throws InterruptedException {
179	if (x == null) throw new NullPointerException();
180	lock.lockInterruptibly();
181	try {
182	try {
183	while (count == items.length)
184	notFull.await();
185	}
186	catch (InterruptedException ie) {
187	notFull.signal(); // propagate to non-interrupted thread
188	throw ie;
189	}
190	insert(x);
191	notEmpty.signal();
192	}
193	finally {
194	lock.unlock();
195	}
196	}
197
198	/** Remove and return the first element from the queue, blocking
199	* if the queue is empty.
200	*/
201	public E take() throws InterruptedException {
202	lock.lockInterruptibly();
203	try {
204	try {
205	while (count == 0)
206	notEmpty.await();
207	}
208	catch (InterruptedException ie) {
209	notEmpty.signal(); // propagate to non-interrupted thread
210	throw ie;
211	}
212	E x = extract();
213	notFull.signal();
214	return x;
215	}
216	finally {
217	lock.unlock();
218	}
219	}
220
221	/** Attempt to insert a new element into the queue, but return
222	* immediately without inserting the element if the queue is full.
223	* @return <tt>true</tt> if the element was inserted successfully,
224	* <tt>false</tt> otherwise
225	*/
226	public boolean offer(E x) {
227	if (x == null) throw new NullPointerException();
228	lock.lock();
229	try {
230	if (count == items.length)
231	return false;
232	else {
233	insert(x);
234	notEmpty.signal();
235	return true;
236	}
237	}
238	finally {
239	lock.unlock();
240	}
241	}
242
243	/** Attempt to retrieve the first insert element from the queue,
244	* but return immediately if the queue is empty.
245	* @return The first element of the queue if the queue is not
246	* empty, or <tt>null</tt> otherwise.
247	*/
248	public E poll() {
249	lock.lock();
250	try {
251	if (count == 0)
252	return null;
253	E x = extract();
254	notFull.signal();
255	return x;
256	}
257	finally {
258	lock.unlock();
259	}
260	}
261
262	/** Attempt to insert a new element into the queue. If the queue
263	* is full, wait up to the specified amount of time before giving
264	* up.
265	* @param x the element to be inserted
266	* @param timeout how long to wait before giving up, in units of
267	* <tt>unit</tt>
268	* @param unit a TimeUnit determining how to interpret the timeout
269	* parameter
270	* @return <tt>true</tt> if the element was inserted successfully,
271	* <tt>false</tt> otherwise
272	* @throws InterruptedException if interrupted while waiting
273	*/
274	public boolean offer(E x, long timeout, TimeUnit unit) throws InterruptedException {
275	if (x == null) throw new NullPointerException();
276	lock.lockInterruptibly();
277	long nanos = unit.toNanos(timeout);
278	try {
279	for (;;) {
280	if (count != items.length) {
281	insert(x);
282	notEmpty.signal();
283	return true;
284	}
285	if (nanos <= 0)
286	return false;
287	try {
288	nanos = notFull.awaitNanos(nanos);
289	}
290	catch (InterruptedException ie) {
291	notFull.signal(); // propagate to non-interrupted thread
292	throw ie;
293	}
294	}
295	}
296	finally {
297	lock.unlock();
298	}
299	}
300
301	/**
302	* Attempt to retrieve the first insert element from the queue.
303	* If the queue is empty, wait up to the specified amount of time
304	* before giving up.
305	* @param timeout how long to wait before giving up, in units of
306	* <tt>unit</tt>
307	* @param unit a TimeUnit determining how to interpret the timeout
308	* parameter
309	* @return The first element of the queue if an item was
310	* successfully retrieved, or <tt>null</tt> otherwise.
311	* @throws InterruptedException if interrupted while waiting
312	*
313	*/
314	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
315	lock.lockInterruptibly();
316	long nanos = unit.toNanos(timeout);
317	try {
318	for (;;) {
319	if (count != 0) {
320	E x = extract();
321	notFull.signal();
322	return x;
323	}
324	if (nanos <= 0)
325	return null;
326	try {
327	nanos = notEmpty.awaitNanos(nanos);
328	}
329	catch (InterruptedException ie) {
330	notEmpty.signal(); // propagate to non-interrupted thread
331	throw ie;
332	}
333
334	}
335	}
336	finally {
337	lock.unlock();
338	}
339	}
340
341	/** Return, but do not remove, the first element from the queue,
342	* if the queue is not empty. This will return the same result as
343	* <tt>poll</tt>, but will not remove it from the queue.
344	* @return The first element of the queue if the queue is not
345	* empty, or <tt>null</tt> otherwise.
346	*/
347	public E peek() {
348	lock.lock();
349	try {
350	return (count == 0) ? null : items[takeIndex];
351	}
352	finally {
353	lock.unlock();
354	}
355	}
356
357
358	public boolean remove(Object x) {
359	if (x == null) return false;
360	lock.lock();
361	try {
362	int i = takeIndex;
363	int k = 0;
364	for (;;) {
365	if (k++ >= count)
366	return false;
367	if (x.equals(items[i])) {
368	removeAt(i);
369	return true;
370	}
371	i = inc(i);
372	}
373
374	}
375	finally {
376	lock.unlock();
377	}
378	}
379
380	public boolean contains(Object x) {
381	if (x == null) return false;
382	lock.lock();
383	try {
384	int i = takeIndex;
385	int k = 0;
386	while (k++ < count) {
387	if (x.equals(items[i]))
388	return true;
389	i = inc(i);
390	}
391	return false;
392	}
393	finally {
394	lock.unlock();
395	}
396	}
397
398	public Object[] toArray() {
399	lock.lock();
400	try {
401	E[] a = new E[count];
402	int k = 0;
403	int i = takeIndex;
404	while (k < count) {
405	a[k++] = items[i];
406	i = inc(i);
407	}
408	return a;
409	}
410	finally {
411	lock.unlock();
412	}
413	}
414
415	public <T> T[] toArray(T[] a) {
416	lock.lock();
417	try {
418	if (a.length < count)
419	a = (T[])java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), count);
420
421	int k = 0;
422	int i = takeIndex;
423	while (k < count) {
424	a[k++] = (T)items[i];
425	i = inc(i);
426	}
427	if (a.length > count)
428	a[count] = null;
429	return a;
430	}
431	finally {
432	lock.unlock();
433	}
434	}
435
436	public String toString() {
437	lock.lock();
438	try {
439	return super.toString();
440	}
441	finally {
442	lock.unlock();
443	}
444	}
445
446	/**
447	* Returns an iterator over the elements in this queue in proper sequence.
448	*
449	* @return an iterator over the elements in this queue in proper sequence.
450	*/
451	public Iterator<E> iterator() {
452	lock.lock();
453	try {
454	return new Itr();
455	}
456	finally {
457	lock.unlock();
458	}
459	}
460
461	/**
462	* Iterator for ArrayBlockingQueue
463	*/
464	private class Itr implements Iterator<E> {
465	/**
466	* Index of element to be returned by next,
467	* or a negative number if no such.
468	*/
469	private int nextIndex;
470
471	/**
472	* nextItem holds on to item fields because once we claim
473	* that an element exists in hasNext(), we must return it in
474	* the following next() call even if it was in the process of
475	* being removed when hasNext() was called.
476	**/
477	private E nextItem;
478
479	/**
480	* Index of element returned by most recent call to next.
481	* Reset to -1 if this element is deleted by a call to remove.
482	*/
483	private int lastRet;
484
485	Itr() {
486	lastRet = -1;
487	if (count == 0)
488	nextIndex = -1;
489	else {
490	nextIndex = takeIndex;
491	nextItem = items[takeIndex];
492	}
493	}
494
495	public boolean hasNext() {
496	/*
497	* No sync. We can return true by mistake here
498	* only if this iterator passed across threads,
499	* which we don't support anyway.
500	*/
501	return nextIndex >= 0;
502	}
503
504	/**
505	* Check whether nextIndex is valied; if so setting nextItem.
506	* Stops iterator when either hits putIndex or sees null item.
507	*/
508	private void checkNext() {
509	if (nextIndex == putIndex) {
510	nextIndex = -1;
511	nextItem = null;
512	}
513	else {
514	nextItem = items[nextIndex];
515	if (nextItem == null)
516	nextIndex = -1;
517	}
518	}
519
520	public E next() {
521	lock.lock();
522	try {
523	if (nextIndex < 0)
524	throw new NoSuchElementException();
525	lastRet = nextIndex;
526	E x = nextItem;
527	nextIndex = inc(nextIndex);
528	checkNext();
529	return x;
530	}
531	finally {
532	lock.unlock();
533	}
534	}
535
536	public void remove() {
537	lock.lock();
538	try {
539	int i = lastRet;
540	if (i == -1)
541	throw new IllegalStateException();
542	lastRet = -1;
543
544	nextIndex = i; // back up cursor
545	removeAt(i);
546	checkNext();
547	}
548	finally {
549	lock.unlock();
550	}
551	}
552	}
553
554	/**
555	* Save the state to a stream (that is, serialize it).
556	*
557	* @serialData The maximumSize is emitted (int), followed by all of
558	* its elements (each an <tt>E</tt>) in the proper order.
559	* @param s the stream
560	*/
561	private void writeObject(java.io.ObjectOutputStream s)
562	throws java.io.IOException {
563
564	// Write out element count, and any hidden stuff
565	s.defaultWriteObject();
566	// Write out maximumSize == items length
567	s.writeInt(items.length);
568
569	// Write out all elements in the proper order.
570	int i = takeIndex;
571	int k = 0;
572	while (k++ < count) {
573	s.writeObject(items[i]);
574	i = inc(i);
575	}
576	}
577
578	/**
579	* Reconstitute the Queue instance from a stream (that is,
580	* deserialize it).
581	* @param s the stream
582	*/
583	private void readObject(java.io.ObjectInputStream s)
584	throws java.io.IOException, ClassNotFoundException {
585	// Read in size, and any hidden stuff
586	s.defaultReadObject();
587	int size = count;
588
589	// Read in array length and allocate array
590	int arrayLength = s.readInt();
591
592	// We use deserializedItems here because "items" is final
593	deserializedItems = new E[arrayLength];
594
595	// Read in all elements in the proper order into deserializedItems
596	for (int i = 0; i < size; i++)
597	deserializedItems[i] = (E)s.readObject();
598	}
599
600	/**
601	* Throw away the object created with readObject, and replace it
602	* with a usable ArrayBlockingQueue.
603	* @return the ArrayBlockingQueue
604	*/
605	private Object readResolve() throws java.io.ObjectStreamException {
606	E[] array = deserializedItems;
607	deserializedItems = null;
608	return new ArrayBlockingQueue(array.length, array, count);
609	}
610	}