util/concurrent/ArrayBlockingQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

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 cannot be
 * increased.  Attempts to <tt>put</tt> an element into a full queue
 * will result in the operation blocking; attempts to <tt>take</tt> an
 * element from an empty queue will similarly block.
 *
 * <p> This class supports an optional fairness policy for ordering
 * waiting producer and consumer threads.  By default, this ordering
 * is not guaranteed. However, a queue constructed with fairness set
 * to <tt>true</tt> grants threads access in FIFO order. Fairness
 * generally decreases throughput but reduces variability and avoids
 * starvation.
 *
 * <p>This class and its iterator implement all of the
 * <em>optional</em> methods of the {@link Collection} and {@link
 * Iterator} interfaces.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @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 {

    /**
     * Serialization ID. This class relies on default serialization
     * even for the items array, which 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  */
    final E[] items;
    /** items index for next take, poll or remove */
    int takeIndex;
    /** items index for next put, offer, or add. */
    int putIndex;
    /** Number of items in the queue */
    int count;

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

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

    // Internal helper methods

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

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

    /**
     * Extracts element at current take position, advances, and signals.
     * 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 the specified collection or any
     *         of its elements are null
     */
    public ArrayBlockingQueue(int capacity, boolean fair,
                              Collection<? extends E> c) {
        this(capacity, fair);
        if (capacity < c.size())
            throw new IllegalArgumentException();

        for (E e : c)
            add(e);
    }

    /**
     * Inserts the specified element at the tail of this queue if it is
     * possible to do so immediately without exceeding the queue's capacity,
     * returning <tt>true</tt> upon success and throwing an
     * <tt>IllegalStateException</tt> if this queue is full.
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     * @throws IllegalStateException if this queue is full
     * @throws NullPointerException if the specified element is null
     */
    public boolean add(E e) {
        return super.add(e);
    }

    /**
     * Inserts the specified element at the tail of this queue if it is
     * possible to do so immediately without exceeding the queue's capacity,
     * returning <tt>true</tt> upon success and <tt>false</tt> if this queue
     * is full.  This method is generally preferable to method {@link #add},
     * which can fail to insert an element only by throwing an exception.
     *
     * @throws NullPointerException if the specified element is null
     */
    public boolean offer(E e) {
        if (e == null) throw new NullPointerException();
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            if (count == items.length)
                return false;
            else {
                insert(e);
                return true;
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Inserts the specified element at the tail of this queue, waiting
     * for space to become available if the queue is full.
     *
     * @throws InterruptedException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     */
    public void put(E e) throws InterruptedException {
        if (e == null) throw new NullPointerException();
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            while (count == items.length)
                notFull.await();
            insert(e);
        } finally {
            lock.unlock();
        }
    }

    /**
     * Inserts the specified element at the tail of this queue, waiting
     * up to the specified wait time for space to become available if
     * the queue is full.
     *
     * @throws InterruptedException {@inheritDoc}
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean offer(E e, long timeout, TimeUnit unit)
        throws InterruptedException {

        if (e == null) throw new NullPointerException();
        long nanos = unit.toNanos(timeout);
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            while (count == items.length) {
                if (nanos <= 0)
                    return false;
                nanos = notFull.awaitNanos(nanos);
            }
            insert(e);
            return true;
        } finally {
            lock.unlock();
        }
    }

    public E poll() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return (count == 0) ? null : extract();
        } finally {
            lock.unlock();
        }
    }

    public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            while (count == 0)
                notEmpty.await();
            return extract();
        } finally {
            lock.unlock();
        }
    }

    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        long nanos = unit.toNanos(timeout);
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            while (count == 0) {
                if (nanos <= 0)
                    return null;
                nanos = notEmpty.awaitNanos(nanos);
            }
            return extract();
        } finally {
            lock.unlock();
        }
    }

    public E peek() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return (count == 0) ? null : items[takeIndex];
        } 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 additional 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 insert
     * an element will succeed by inspecting <tt>remainingCapacity</tt>
     * because it may be the case that another thread is about to
     * insert or remove an element.
     */
    public int remainingCapacity() {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            return items.length - count;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Removes a single instance of the specified element from this queue,
     * if it is present.  More formally, removes an element <tt>e</tt> such
     * that <tt>o.equals(e)</tt>, if this queue contains one or more such
     * elements.
     * Returns <tt>true</tt> if this queue contained the specified element
     * (or equivalently, if this queue changed as a result of the call).
     *
     * @param o element to be removed from this queue, if present
     * @return <tt>true</tt> if this queue changed as a result of the call
     */
    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();
        }
    }

    /**
     * Returns <tt>true</tt> if this queue contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this queue contains
     * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
     *
     * @param o object to be checked for containment in this queue
     * @return <tt>true</tt> if this queue contains the specified element
     */
    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();
        }
    }

    /**
     * Returns an array containing all of the elements in this queue, in
     * proper sequence.
     *
     * <p>The returned array will be "safe" in that no references to it are
     * maintained by this queue.  (In other words, this method must allocate
     * a new array).  The caller is thus free to modify the returned array.
     *
     * <p>This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all of the elements in this queue
     */
    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();
        }
    }

    /**
     * Returns an array containing all of the elements in this queue, in
     * proper sequence; the runtime type of the returned array is that of
     * the specified array.  If the queue fits in the specified array, it
     * is returned therein.  Otherwise, a new array is allocated with the
     * runtime type of the specified array and the size of this queue.
     *
     * <p>If this queue fits in the specified array with room to spare
     * (i.e., the array has more elements than this queue), the element in
     * the array immediately following the end of the queue is set to
     * <tt>null</tt>.
     *
     * <p>Like the {@link #toArray()} method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs.
     *
     * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
     * The following code can be used to dump the queue into a newly
     * allocated array of <tt>String</tt>:
     *
     * <pre>
     *     String[] y = x.toArray(new String[0]);</pre>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
     * <tt>toArray()</tt>.
     *
     * @param a the array into which the elements of the queue are to
     *          be stored, if it is big enough; otherwise, a new array of the
     *          same runtime type is allocated for this purpose
     * @return an array containing all of the elements in this queue
     * @throws ArrayStoreException if the runtime type of the specified array
     *         is not a supertype of the runtime type of every element in
     *         this queue
     * @throws NullPointerException if the specified array is null
     */
    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();
        }
    }

    /**
     * Atomically removes all of the elements from this queue.
     * The queue will be empty after this call returns.
     */
    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();
        }
    }

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    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();
        }
    }

    /**
     * @throws UnsupportedOperationException {@inheritDoc}
     * @throws ClassCastException            {@inheritDoc}
     * @throws NullPointerException          {@inheritDoc}
     * @throws IllegalArgumentException      {@inheritDoc}
     */
    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 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;
        }

        /**
         * Checks 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:	1.59
Committed:	Fri Jul 23 16:35:02 2010 UTC (13 years, 10 months ago) by jsr166
Branch:	MAIN
Changes since 1.58:	+9 -14 lines
Log Message:	hand-inline empty() and full() methods, to appease hotspot
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/licenses/publicdomain
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
21	* fixed-sized array holds elements inserted by producers and
22	* extracted by consumers. Once created, the capacity cannot be
23	* increased. Attempts to <tt>put</tt> an element into a full queue
24	* will result in the operation blocking; attempts to <tt>take</tt> an
25	* element from an empty queue will similarly block.
26	*
27	* <p> This class supports an optional fairness policy for ordering
28	* waiting producer and consumer threads. By default, this ordering
29	* is not guaranteed. However, a queue constructed with fairness set
30	* to <tt>true</tt> grants threads access in FIFO order. Fairness
31	* generally decreases throughput but reduces variability and avoids
32	* starvation.
33	*
34	* <p>This class and its iterator implement all of the
35	* <em>optional</em> methods of the {@link Collection} and {@link
36	* Iterator} interfaces.
37	*
38	* <p>This class is a member of the
39	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
40	* Java Collections Framework</a>.
41	*
42	* @since 1.5
43	* @author Doug Lea
44	* @param <E> the type of elements held in this collection
45	*/
46	public class ArrayBlockingQueue<E> extends AbstractQueue<E>
47	implements BlockingQueue<E>, java.io.Serializable {
48
49	/**
50	* Serialization ID. This class relies on default serialization
51	* even for the items array, which is default-serialized, even if
52	* it is empty. Otherwise it could not be declared final, which is
53	* necessary here.
54	*/
55	private static final long serialVersionUID = -817911632652898426L;
56
57	/** The queued items */
58	final E[] items;
59	/** items index for next take, poll or remove */
60	int takeIndex;
61	/** items index for next put, offer, or add. */
62	int putIndex;
63	/** Number of items in the queue */
64	int count;
65
66	/*
67	* Concurrency control uses the classic two-condition algorithm
68	* found in any textbook.
69	*/
70
71	/** Main lock guarding all access */
72	final ReentrantLock lock;
73	/** Condition for waiting takes */
74	private final Condition notEmpty;
75	/** Condition for waiting puts */
76	private final Condition notFull;
77
78	// Internal helper methods
79
80	/**
81	* Circularly increment i.
82	*/
83	final int inc(int i) {
84	return (++i == items.length) ? 0 : i;
85	}
86
87	/**
88	* Inserts element at current put position, advances, and signals.
89	* Call only when holding lock.
90	*/
91	private void insert(E x) {
92	items[putIndex] = x;
93	putIndex = inc(putIndex);
94	++count;
95	notEmpty.signal();
96	}
97
98	/**
99	* Extracts element at current take position, advances, and signals.
100	* Call only when holding lock.
101	*/
102	private E extract() {
103	final E[] items = this.items;
104	E x = items[takeIndex];
105	items[takeIndex] = null;
106	takeIndex = inc(takeIndex);
107	--count;
108	notFull.signal();
109	return x;
110	}
111
112	/**
113	* Utility for remove and iterator.remove: Delete item at position i.
114	* Call only when holding lock.
115	*/
116	void removeAt(int i) {
117	final E[] items = this.items;
118	// if removing front item, just advance
119	if (i == takeIndex) {
120	items[takeIndex] = null;
121	takeIndex = inc(takeIndex);
122	} else {
123	// slide over all others up through putIndex.
124	for (;;) {
125	int nexti = inc(i);
126	if (nexti != putIndex) {
127	items[i] = items[nexti];
128	i = nexti;
129	} else {
130	items[i] = null;
131	putIndex = i;
132	break;
133	}
134	}
135	}
136	--count;
137	notFull.signal();
138	}
139
140	/**
141	* Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
142	* capacity and default access policy.
143	*
144	* @param capacity the capacity of this queue
145	* @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
146	*/
147	public ArrayBlockingQueue(int capacity) {
148	this(capacity, false);
149	}
150
151	/**
152	* Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
153	* capacity and the specified access policy.
154	*
155	* @param capacity the capacity of this queue
156	* @param fair if <tt>true</tt> then queue accesses for threads blocked
157	* on insertion or removal, are processed in FIFO order;
158	* if <tt>false</tt> the access order is unspecified.
159	* @throws IllegalArgumentException if <tt>capacity</tt> is less than 1
160	*/
161	public ArrayBlockingQueue(int capacity, boolean fair) {
162	if (capacity <= 0)
163	throw new IllegalArgumentException();
164	this.items = (E[]) new Object[capacity];
165	lock = new ReentrantLock(fair);
166	notEmpty = lock.newCondition();
167	notFull = lock.newCondition();
168	}
169
170	/**
171	* Creates an <tt>ArrayBlockingQueue</tt> with the given (fixed)
172	* capacity, the specified access policy and initially containing the
173	* elements of the given collection,
174	* added in traversal order of the collection's iterator.
175	*
176	* @param capacity the capacity of this queue
177	* @param fair if <tt>true</tt> then queue accesses for threads blocked
178	* on insertion or removal, are processed in FIFO order;
179	* if <tt>false</tt> the access order is unspecified.
180	* @param c the collection of elements to initially contain
181	* @throws IllegalArgumentException if <tt>capacity</tt> is less than
182	* <tt>c.size()</tt>, or less than 1.
183	* @throws NullPointerException if the specified collection or any
184	* of its elements are null
185	*/
186	public ArrayBlockingQueue(int capacity, boolean fair,
187	Collection<? extends E> c) {
188	this(capacity, fair);
189	if (capacity < c.size())
190	throw new IllegalArgumentException();
191
192	for (E e : c)
193	add(e);
194	}
195
196	/**
197	* Inserts the specified element at the tail of this queue if it is
198	* possible to do so immediately without exceeding the queue's capacity,
199	* returning <tt>true</tt> upon success and throwing an
200	* <tt>IllegalStateException</tt> if this queue is full.
201	*
202	* @param e the element to add
203	* @return <tt>true</tt> (as specified by {@link Collection#add})
204	* @throws IllegalStateException if this queue is full
205	* @throws NullPointerException if the specified element is null
206	*/
207	public boolean add(E e) {
208	return super.add(e);
209	}
210
211	/**
212	* Inserts the specified element at the tail of this queue if it is
213	* possible to do so immediately without exceeding the queue's capacity,
214	* returning <tt>true</tt> upon success and <tt>false</tt> if this queue
215	* is full. This method is generally preferable to method {@link #add},
216	* which can fail to insert an element only by throwing an exception.
217	*
218	* @throws NullPointerException if the specified element is null
219	*/
220	public boolean offer(E e) {
221	if (e == null) throw new NullPointerException();
222	final ReentrantLock lock = this.lock;
223	lock.lock();
224	try {
225	if (count == items.length)
226	return false;
227	else {
228	insert(e);
229	return true;
230	}
231	} finally {
232	lock.unlock();
233	}
234	}
235
236	/**
237	* Inserts the specified element at the tail of this queue, waiting
238	* for space to become available if the queue is full.
239	*
240	* @throws InterruptedException {@inheritDoc}
241	* @throws NullPointerException {@inheritDoc}
242	*/
243	public void put(E e) throws InterruptedException {
244	if (e == null) throw new NullPointerException();
245	final ReentrantLock lock = this.lock;
246	lock.lockInterruptibly();
247	try {
248	while (count == items.length)
249	notFull.await();
250	insert(e);
251	} finally {
252	lock.unlock();
253	}
254	}
255
256	/**
257	* Inserts the specified element at the tail of this queue, waiting
258	* up to the specified wait time for space to become available if
259	* the queue is full.
260	*
261	* @throws InterruptedException {@inheritDoc}
262	* @throws NullPointerException {@inheritDoc}
263	*/
264	public boolean offer(E e, long timeout, TimeUnit unit)
265	throws InterruptedException {
266
267	if (e == null) throw new NullPointerException();
268	long nanos = unit.toNanos(timeout);
269	final ReentrantLock lock = this.lock;
270	lock.lockInterruptibly();
271	try {
272	while (count == items.length) {
273	if (nanos <= 0)
274	return false;
275	nanos = notFull.awaitNanos(nanos);
276	}
277	insert(e);
278	return true;
279	} finally {
280	lock.unlock();
281	}
282	}
283
284	public E poll() {
285	final ReentrantLock lock = this.lock;
286	lock.lock();
287	try {
288	return (count == 0) ? null : extract();
289	} finally {
290	lock.unlock();
291	}
292	}
293
294	public E take() throws InterruptedException {
295	final ReentrantLock lock = this.lock;
296	lock.lockInterruptibly();
297	try {
298	while (count == 0)
299	notEmpty.await();
300	return extract();
301	} finally {
302	lock.unlock();
303	}
304	}
305
306	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
307	long nanos = unit.toNanos(timeout);
308	final ReentrantLock lock = this.lock;
309	lock.lockInterruptibly();
310	try {
311	while (count == 0) {
312	if (nanos <= 0)
313	return null;
314	nanos = notEmpty.awaitNanos(nanos);
315	}
316	return extract();
317	} finally {
318	lock.unlock();
319	}
320	}
321
322	public E peek() {
323	final ReentrantLock lock = this.lock;
324	lock.lock();
325	try {
326	return (count == 0) ? null : items[takeIndex];
327	} finally {
328	lock.unlock();
329	}
330	}
331
332	// this doc comment is overridden to remove the reference to collections
333	// greater in size than Integer.MAX_VALUE
334	/**
335	* Returns the number of elements in this queue.
336	*
337	* @return the number of elements in this queue
338	*/
339	public int size() {
340	final ReentrantLock lock = this.lock;
341	lock.lock();
342	try {
343	return count;
344	} finally {
345	lock.unlock();
346	}
347	}
348
349	// this doc comment is a modified copy of the inherited doc comment,
350	// without the reference to unlimited queues.
351	/**
352	* Returns the number of additional elements that this queue can ideally
353	* (in the absence of memory or resource constraints) accept without
354	* blocking. This is always equal to the initial capacity of this queue
355	* less the current <tt>size</tt> of this queue.
356	*
357	* <p>Note that you <em>cannot</em> always tell if an attempt to insert
358	* an element will succeed by inspecting <tt>remainingCapacity</tt>
359	* because it may be the case that another thread is about to
360	* insert or remove an element.
361	*/
362	public int remainingCapacity() {
363	final ReentrantLock lock = this.lock;
364	lock.lock();
365	try {
366	return items.length - count;
367	} finally {
368	lock.unlock();
369	}
370	}
371
372	/**
373	* Removes a single instance of the specified element from this queue,
374	* if it is present. More formally, removes an element <tt>e</tt> such
375	* that <tt>o.equals(e)</tt>, if this queue contains one or more such
376	* elements.
377	* Returns <tt>true</tt> if this queue contained the specified element
378	* (or equivalently, if this queue changed as a result of the call).
379	*
380	* @param o element to be removed from this queue, if present
381	* @return <tt>true</tt> if this queue changed as a result of the call
382	*/
383	public boolean remove(Object o) {
384	if (o == null) return false;
385	final E[] items = this.items;
386	final ReentrantLock lock = this.lock;
387	lock.lock();
388	try {
389	int i = takeIndex;
390	int k = 0;
391	for (;;) {
392	if (k++ >= count)
393	return false;
394	if (o.equals(items[i])) {
395	removeAt(i);
396	return true;
397	}
398	i = inc(i);
399	}
400
401	} finally {
402	lock.unlock();
403	}
404	}
405
406	/**
407	* Returns <tt>true</tt> if this queue contains the specified element.
408	* More formally, returns <tt>true</tt> if and only if this queue contains
409	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
410	*
411	* @param o object to be checked for containment in this queue
412	* @return <tt>true</tt> if this queue contains the specified element
413	*/
414	public boolean contains(Object o) {
415	if (o == null) return false;
416	final E[] items = this.items;
417	final ReentrantLock lock = this.lock;
418	lock.lock();
419	try {
420	int i = takeIndex;
421	int k = 0;
422	while (k++ < count) {
423	if (o.equals(items[i]))
424	return true;
425	i = inc(i);
426	}
427	return false;
428	} finally {
429	lock.unlock();
430	}
431	}
432
433	/**
434	* Returns an array containing all of the elements in this queue, in
435	* proper sequence.
436	*
437	* <p>The returned array will be "safe" in that no references to it are
438	* maintained by this queue. (In other words, this method must allocate
439	* a new array). The caller is thus free to modify the returned array.
440	*
441	* <p>This method acts as bridge between array-based and collection-based
442	* APIs.
443	*
444	* @return an array containing all of the elements in this queue
445	*/
446	public Object[] toArray() {
447	final E[] items = this.items;
448	final ReentrantLock lock = this.lock;
449	lock.lock();
450	try {
451	Object[] a = new Object[count];
452	int k = 0;
453	int i = takeIndex;
454	while (k < count) {
455	a[k++] = items[i];
456	i = inc(i);
457	}
458	return a;
459	} finally {
460	lock.unlock();
461	}
462	}
463
464	/**
465	* Returns an array containing all of the elements in this queue, in
466	* proper sequence; the runtime type of the returned array is that of
467	* the specified array. If the queue fits in the specified array, it
468	* is returned therein. Otherwise, a new array is allocated with the
469	* runtime type of the specified array and the size of this queue.
470	*
471	* <p>If this queue fits in the specified array with room to spare
472	* (i.e., the array has more elements than this queue), the element in
473	* the array immediately following the end of the queue is set to
474	* <tt>null</tt>.
475	*
476	* <p>Like the {@link #toArray()} method, this method acts as bridge between
477	* array-based and collection-based APIs. Further, this method allows
478	* precise control over the runtime type of the output array, and may,
479	* under certain circumstances, be used to save allocation costs.
480	*
481	* <p>Suppose <tt>x</tt> is a queue known to contain only strings.
482	* The following code can be used to dump the queue into a newly
483	* allocated array of <tt>String</tt>:
484	*
485	* <pre>
486	* String[] y = x.toArray(new String[0]);</pre>
487	*
488	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
489	* <tt>toArray()</tt>.
490	*
491	* @param a the array into which the elements of the queue are to
492	* be stored, if it is big enough; otherwise, a new array of the
493	* same runtime type is allocated for this purpose
494	* @return an array containing all of the elements in this queue
495	* @throws ArrayStoreException if the runtime type of the specified array
496	* is not a supertype of the runtime type of every element in
497	* this queue
498	* @throws NullPointerException if the specified array is null
499	*/
500	public <T> T[] toArray(T[] a) {
501	final E[] items = this.items;
502	final ReentrantLock lock = this.lock;
503	lock.lock();
504	try {
505	if (a.length < count)
506	a = (T[])java.lang.reflect.Array.newInstance(
507	a.getClass().getComponentType(),
508	count
509	);
510
511	int k = 0;
512	int i = takeIndex;
513	while (k < count) {
514	a[k++] = (T)items[i];
515	i = inc(i);
516	}
517	if (a.length > count)
518	a[count] = null;
519	return a;
520	} finally {
521	lock.unlock();
522	}
523	}
524
525	public String toString() {
526	final ReentrantLock lock = this.lock;
527	lock.lock();
528	try {
529	return super.toString();
530	} finally {
531	lock.unlock();
532	}
533	}
534
535	/**
536	* Atomically removes all of the elements from this queue.
537	* The queue will be empty after this call returns.
538	*/
539	public void clear() {
540	final E[] items = this.items;
541	final ReentrantLock lock = this.lock;
542	lock.lock();
543	try {
544	int i = takeIndex;
545	int k = count;
546	while (k-- > 0) {
547	items[i] = null;
548	i = inc(i);
549	}
550	count = 0;
551	putIndex = 0;
552	takeIndex = 0;
553	notFull.signalAll();
554	} finally {
555	lock.unlock();
556	}
557	}
558
559	/**
560	* @throws UnsupportedOperationException {@inheritDoc}
561	* @throws ClassCastException {@inheritDoc}
562	* @throws NullPointerException {@inheritDoc}
563	* @throws IllegalArgumentException {@inheritDoc}
564	*/
565	public int drainTo(Collection<? super E> c) {
566	if (c == null)
567	throw new NullPointerException();
568	if (c == this)
569	throw new IllegalArgumentException();
570	final E[] items = this.items;
571	final ReentrantLock lock = this.lock;
572	lock.lock();
573	try {
574	int i = takeIndex;
575	int n = 0;
576	int max = count;
577	while (n < max) {
578	c.add(items[i]);
579	items[i] = null;
580	i = inc(i);
581	++n;
582	}
583	if (n > 0) {
584	count = 0;
585	putIndex = 0;
586	takeIndex = 0;
587	notFull.signalAll();
588	}
589	return n;
590	} finally {
591	lock.unlock();
592	}
593	}
594
595	/**
596	* @throws UnsupportedOperationException {@inheritDoc}
597	* @throws ClassCastException {@inheritDoc}
598	* @throws NullPointerException {@inheritDoc}
599	* @throws IllegalArgumentException {@inheritDoc}
600	*/
601	public int drainTo(Collection<? super E> c, int maxElements) {
602	if (c == null)
603	throw new NullPointerException();
604	if (c == this)
605	throw new IllegalArgumentException();
606	if (maxElements <= 0)
607	return 0;
608	final E[] items = this.items;
609	final ReentrantLock lock = this.lock;
610	lock.lock();
611	try {
612	int i = takeIndex;
613	int n = 0;
614	int sz = count;
615	int max = (maxElements < count) ? maxElements : count;
616	while (n < max) {
617	c.add(items[i]);
618	items[i] = null;
619	i = inc(i);
620	++n;
621	}
622	if (n > 0) {
623	count -= n;
624	takeIndex = i;
625	notFull.signalAll();
626	}
627	return n;
628	} finally {
629	lock.unlock();
630	}
631	}
632
633
634	/**
635	* Returns an iterator over the elements in this queue in proper sequence.
636	* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that
637	* will never throw {@link ConcurrentModificationException},
638	* and guarantees to traverse elements as they existed upon
639	* construction of the iterator, and may (but is not guaranteed to)
640	* reflect any modifications subsequent to construction.
641	*
642	* @return an iterator over the elements in this queue in proper sequence
643	*/
644	public Iterator<E> iterator() {
645	final ReentrantLock lock = this.lock;
646	lock.lock();
647	try {
648	return new Itr();
649	} finally {
650	lock.unlock();
651	}
652	}
653
654	/**
655	* Iterator for ArrayBlockingQueue
656	*/
657	private class Itr implements Iterator<E> {
658	/**
659	* Index of element to be returned by next,
660	* or a negative number if no such.
661	*/
662	private int nextIndex;
663
664	/**
665	* nextItem holds on to item fields because once we claim
666	* that an element exists in hasNext(), we must return it in
667	* the following next() call even if it was in the process of
668	* being removed when hasNext() was called.
669	*/
670	private E nextItem;
671
672	/**
673	* Index of element returned by most recent call to next.
674	* Reset to -1 if this element is deleted by a call to remove.
675	*/
676	private int lastRet;
677
678	Itr() {
679	lastRet = -1;
680	if (count == 0)
681	nextIndex = -1;
682	else {
683	nextIndex = takeIndex;
684	nextItem = items[takeIndex];
685	}
686	}
687
688	public boolean hasNext() {
689	/*
690	* No sync. We can return true by mistake here
691	* only if this iterator passed across threads,
692	* which we don't support anyway.
693	*/
694	return nextIndex >= 0;
695	}
696
697	/**
698	* Checks whether nextIndex is valid; if so setting nextItem.
699	* Stops iterator when either hits putIndex or sees null item.
700	*/
701	private void checkNext() {
702	if (nextIndex == putIndex) {
703	nextIndex = -1;
704	nextItem = null;
705	} else {
706	nextItem = items[nextIndex];
707	if (nextItem == null)
708	nextIndex = -1;
709	}
710	}
711
712	public E next() {
713	final ReentrantLock lock = ArrayBlockingQueue.this.lock;
714	lock.lock();
715	try {
716	if (nextIndex < 0)
717	throw new NoSuchElementException();
718	lastRet = nextIndex;
719	E x = nextItem;
720	nextIndex = inc(nextIndex);
721	checkNext();
722	return x;
723	} finally {
724	lock.unlock();
725	}
726	}
727
728	public void remove() {
729	final ReentrantLock lock = ArrayBlockingQueue.this.lock;
730	lock.lock();
731	try {
732	int i = lastRet;
733	if (i == -1)
734	throw new IllegalStateException();
735	lastRet = -1;
736
737	int ti = takeIndex;
738	removeAt(i);
739	// back up cursor (reset to front if was first element)
740	nextIndex = (i == ti) ? takeIndex : i;
741	checkNext();
742	} finally {
743	lock.unlock();
744	}
745	}
746	}
747	}