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//
// ========================================================================
// Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.util;
import java.util.AbstractList;
import java.util.NoSuchElementException;
import java.util.Queue;
/* ------------------------------------------------------------ */
/**
* Queue backed by circular array.
*
* This partial Queue implementation (also with {@link #remove()} for stack operation)
* is backed by a growable circular array.
*
* @param
*/
public class ArrayQueue extends AbstractList implements Queue
{
public static final int DEFAULT_CAPACITY = 64;
public static final int DEFAULT_GROWTH = 32;
protected final Object _lock;
protected final int _growCapacity;
protected Object[] _elements;
protected int _nextE;
protected int _nextSlot;
protected int _size;
/* ------------------------------------------------------------ */
public ArrayQueue()
{
this(DEFAULT_CAPACITY, -1);
}
/* ------------------------------------------------------------ */
public ArrayQueue(Object lock)
{
this(DEFAULT_CAPACITY, -1,lock);
}
/* ------------------------------------------------------------ */
public ArrayQueue(int capacity)
{
this(capacity, -1);
}
/* ------------------------------------------------------------ */
public ArrayQueue(int initCapacity, int growBy)
{
this(initCapacity, growBy, null);
}
/* ------------------------------------------------------------ */
public ArrayQueue(int initCapacity, int growBy, Object lock)
{
_lock = lock == null ? this : lock;
_growCapacity = growBy;
_elements = new Object[initCapacity];
}
/* ------------------------------------------------------------ */
public Object lock()
{
return _lock;
}
/* ------------------------------------------------------------ */
public int getCapacity()
{
synchronized (_lock)
{
return _elements.length;
}
}
/* ------------------------------------------------------------ */
@Override
public boolean add(E e)
{
if (!offer(e))
throw new IllegalStateException("Full");
return true;
}
/* ------------------------------------------------------------ */
public boolean offer(E e)
{
synchronized (_lock)
{
return enqueue(e);
}
}
/* ------------------------------------------------------------ */
private boolean enqueue(E e)
{
if (_size == _elements.length && !grow())
return false;
_size++;
_elements[_nextSlot++] = e;
if (_nextSlot == _elements.length)
_nextSlot = 0;
return true;
}
/* ------------------------------------------------------------ */
/**
* Add without synchronization or bounds checking
*
* @param e the element to add
* @see #add(Object)
*/
public void addUnsafe(E e)
{
if (!enqueue(e))
throw new IllegalStateException("Full");
}
/* ------------------------------------------------------------ */
public E element()
{
synchronized (_lock)
{
if (isEmpty())
throw new NoSuchElementException();
return at(_nextE);
}
}
/* ------------------------------------------------------------ */
@SuppressWarnings("unchecked")
private E at(int index)
{
return (E)_elements[index];
}
/* ------------------------------------------------------------ */
public E peek()
{
synchronized (_lock)
{
if (_size == 0)
return null;
return at(_nextE);
}
}
/* ------------------------------------------------------------ */
public E peekUnsafe()
{
if (_size == 0)
return null;
return at(_nextE);
}
/* ------------------------------------------------------------ */
public E poll()
{
synchronized (_lock)
{
if (_size == 0)
return null;
return dequeue();
}
}
/* ------------------------------------------------------------ */
public E pollUnsafe()
{
if (_size == 0)
return null;
return dequeue();
}
/* ------------------------------------------------------------ */
private E dequeue()
{
E e = at(_nextE);
_elements[_nextE] = null;
_size--;
if (++_nextE == _elements.length)
_nextE = 0;
return e;
}
/* ------------------------------------------------------------ */
public E remove()
{
synchronized (_lock)
{
if (_size == 0)
throw new NoSuchElementException();
return dequeue();
}
}
/* ------------------------------------------------------------ */
@Override
public void clear()
{
synchronized (_lock)
{
_size = 0;
_nextE = 0;
_nextSlot = 0;
}
}
/* ------------------------------------------------------------ */
@Override
public boolean isEmpty()
{
synchronized (_lock)
{
return _size == 0;
}
}
/* ------------------------------------------------------------ */
@Override
public int size()
{
synchronized (_lock)
{
return _size;
}
}
/* ------------------------------------------------------------ */
@Override
public E get(int index)
{
synchronized (_lock)
{
if (index < 0 || index >= _size)
throw new IndexOutOfBoundsException("!(" + 0 + "<" + index + "<=" + _size + ")");
return getUnsafe(index);
}
}
/* ------------------------------------------------------------ */
/**
* Get without synchronization or bounds checking.
*
* @param index index of the element to return
* @return the element at the specified index
* @see #get(int)
*/
public E getUnsafe(int index)
{
int i = (_nextE + index) % _elements.length;
return at(i);
}
/* ------------------------------------------------------------ */
@Override
public E remove(int index)
{
synchronized (_lock)
{
if (index < 0 || index >= _size)
throw new IndexOutOfBoundsException("!(" + 0 + "<" + index + "<=" + _size + ")");
int i = (_nextE + index) % _elements.length;
E old = at(i);
if (i < _nextSlot)
{
// 0 _elements.length
// _nextE........._nextSlot
System.arraycopy(_elements, i + 1, _elements, i, _nextSlot - i);
_nextSlot--;
_size--;
}
else
{
// 0 _elements.length
// ......_nextSlot _nextE..........
System.arraycopy(_elements, i + 1, _elements, i, _elements.length - i - 1);
if (_nextSlot > 0)
{
_elements[_elements.length - 1] = _elements[0];
System.arraycopy(_elements, 1, _elements, 0, _nextSlot - 1);
_nextSlot--;
}
else
_nextSlot = _elements.length - 1;
_size--;
}
return old;
}
}
/* ------------------------------------------------------------ */
@Override
public E set(int index, E element)
{
synchronized (_lock)
{
if (index < 0 || index >= _size)
throw new IndexOutOfBoundsException("!(" + 0 + "<" + index + "<=" + _size + ")");
int i = _nextE + index;
if (i >= _elements.length)
i -= _elements.length;
E old = at(i);
_elements[i] = element;
return old;
}
}
/* ------------------------------------------------------------ */
@Override
public void add(int index, E element)
{
synchronized (_lock)
{
if (index < 0 || index > _size)
throw new IndexOutOfBoundsException("!(" + 0 + "<" + index + "<=" + _size + ")");
if (_size == _elements.length && !grow())
throw new IllegalStateException("Full");
if (index == _size)
{
add(element);
}
else
{
int i = _nextE + index;
if (i >= _elements.length)
i -= _elements.length;
_size++;
_nextSlot++;
if (_nextSlot == _elements.length)
_nextSlot = 0;
if (i < _nextSlot)
{
// 0 _elements.length
// _nextE.....i..._nextSlot
// 0 _elements.length
// ..i..._nextSlot _nextE..........
System.arraycopy(_elements, i, _elements, i + 1, _nextSlot - i);
_elements[i] = element;
}
else
{
// 0 _elements.length
// ......_nextSlot _nextE.....i....
if (_nextSlot > 0)
{
System.arraycopy(_elements, 0, _elements, 1, _nextSlot);
_elements[0] = _elements[_elements.length - 1];
}
System.arraycopy(_elements, i, _elements, i + 1, _elements.length - i - 1);
_elements[i] = element;
}
}
}
}
/* ------------------------------------------------------------ */
protected boolean grow()
{
synchronized (_lock)
{
if (_growCapacity <= 0)
return false;
Object[] elements = new Object[_elements.length + _growCapacity];
int split = _elements.length - _nextE;
if (split > 0)
System.arraycopy(_elements, _nextE, elements, 0, split);
if (_nextE != 0)
System.arraycopy(_elements, 0, elements, split, _nextSlot);
_elements = elements;
_nextE = 0;
_nextSlot = _size;
return true;
}
}
}