org.eclipse.jetty.util.ArrayQueue Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of ehcache Show documentation
Show all versions of ehcache Show documentation
Ehcache is an open source, standards-based cache used to boost performance,
offload the database and simplify scalability. Ehcache is robust, proven and full-featured and
this has made it the most widely-used Java-based cache.
//
// ========================================================================
// Copyright (c) 1995-2013 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(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 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 (isEmpty())
return null;
return at(_nextE);
}
}
/* ------------------------------------------------------------ */
public E poll()
{
synchronized (_lock)
{
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;
}
}
}