android-platform-libcore/luni/src/main/java/java/util/concurrent/ArrayBlockingQueue.java - nest-cam/4320010/android-platform-libcore - Git at Google

 /*
  * 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.AbstractQueue;
 import java.util.Collection;
 import java.util.ConcurrentModificationException;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 import java.util.concurrent.locks.Condition;
 import java.util.concurrent.locks.ReentrantLock;

 // BEGIN android-note
 // removed link to collections framework docs
 // END android-note

 /**
  * 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.
  *
  * @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  */
     private final E[] items;
     /** items index for next take, poll or remove */
     private int takeIndex;
     /** items index for next put, offer, or add. */
     private 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 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 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(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 {
             for (;;) {
                 if (count != items.length) {
                     insert(e);
                     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 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();
         }
     }

     public E poll(long timeout, TimeUnit unit) throws InterruptedException {
         long nanos = unit.toNanos(timeout);
         final ReentrantLock lock = this.lock;
         lock.lockInterruptibly();
         try {
             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 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();
             }
         }
     }
 }
	/*
	* 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.AbstractQueue;
	import java.util.Collection;
	import java.util.ConcurrentModificationException;
	import java.util.Iterator;
	import java.util.NoSuchElementException;
	import java.util.concurrent.locks.Condition;
	import java.util.concurrent.locks.ReentrantLock;

	// BEGIN android-note
	// removed link to collections framework docs
	// END android-note

	/**
	* 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 "bounded buffer", 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.
	*
	* @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 */
	private final E[] items;
	/** items index for next take, poll or remove */
	private int takeIndex;
	/** items index for next put, offer, or add. */
	private 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 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 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(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 {
	for (;;) {
	if (count != items.length) {
	insert(e);
	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 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();
	}
	}

	public E poll(long timeout, TimeUnit unit) throws InterruptedException {
	long nanos = unit.toNanos(timeout);
	final ReentrantLock lock = this.lock;
	lock.lockInterruptibly();
	try {
	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 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();
	}
	}
	}
	}