/*
============================================================================
The Apache Software License, Version 1.1
============================================================================
Copyright (C) 1999-2003 The Apache Software Foundation. All rights reserved.
Redistribution and use in source and binary forms, with or without modifica-
tion, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.
3. The end-user documentation included with the redistribution, if any, must
include the following acknowledgment: "This product includes software
developed by the Apache Software Foundation (http://www.apache.org/)."
Alternately, this acknowledgment may appear in the software itself, if
and wherever such third-party acknowledgments normally appear.
4. The names "Jakarta", "Avalon", "Excalibur" and "Apache Software Foundation"
must not be used to endorse or promote products derived from this software
without prior written permission. For written permission, please contact
apache@apache.org.
5. Products derived from this software may not be called "Apache", nor may
"Apache" appear in their name, without prior written permission of the
Apache Software Foundation.
THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
APACHE SOFTWARE FOUNDATION OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLU-
DING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
This software consists of voluntary contributions made by many individuals
on behalf of the Apache Software Foundation. For more information on the
Apache Software Foundation, please see <http://www.apache.org/>.
*/
package org.apache.excalibur.event.impl;
import org.apache.commons.collections.Buffer;
import org.apache.commons.collections.UnboundedFifoBuffer;
import org.apache.excalibur.event.EnqueuePredicate;
import org.apache.excalibur.event.PreparedEnqueue;
import org.apache.excalibur.event.SinkException;
import org.apache.excalibur.event.SinkFullException;
import EDU.oswego.cs.dl.util.concurrent.ReentrantLock;
/**
* The default queue implementation is a variable size queue. This queue is
* thread safe, however the overhead in synchronization costs a few extra
* milliseconds.
*
* @author <a href="mailto:bloritsch@apache.org">Berin Loritsch</a>
*/
public final class DefaultQueue extends AbstractQueue
{
private final Buffer m_elements;
private final ReentrantLock m_mutex;
protected int m_reserve;
private final int m_maxSize;
/**
* Construct a new DefaultQueue with the specified number of elements.
* if the number of elements is greater than zero, then the
* <code>Queue</code> is bounded by that number. Otherwise, the
* <code>Queue</code> is not bounded at all.
*
* @param size The maximum number of elements in the <code>Queue</code>.
* Any number less than 1 means there is no limit.
*/
public DefaultQueue( int size )
{
this( new ThresholdEnqueuePredicate( size ) );
}
public DefaultQueue( EnqueuePredicate predicate )
{
setEnqueuePredicate( predicate );
m_mutex = new ReentrantLock();
m_elements = new UnboundedFifoBuffer();
m_reserve = 0;
m_maxSize = -1;
}
/**
* Create an unbounded DefaultQueue.
*/
public DefaultQueue()
{
this( new NullEnqueuePredicate() );
}
/**
* Return the number of elements currently in the <code>Queue</code>.
*
* @return <code>int</code> representing the number of elements (including the reserved ones).
*/
public int size()
{
return m_elements.size() + m_reserve;
}
/**
* Return the maximum number of elements that will fit in the
* <code>Queue</code>. A number below 1 indecates an unbounded
* <code>Queue</code>, which means there is no limit.
*
* @return <code>int</code> representing the maximum number of elements
*/
public int maxSize()
{
return m_maxSize;
}
public PreparedEnqueue prepareEnqueue( final Object[] elements )
throws SinkException
{
PreparedEnqueue enqueue = null;
try
{
m_mutex.acquire();
try
{
if( getEnqueuePredicate().accept(elements, this) )
{
enqueue = new DefaultPreparedEnqueue( this, elements );
}
else
{
throw new SinkFullException( "Not enough room to enqueue these elements." );
}
}
finally
{
m_mutex.release();
}
}
catch( InterruptedException ie )
{
if ( null == enqueue )
{
throw new SinkException("The mutex was interrupted before it could be released");
}
}
return enqueue;
}
public boolean tryEnqueue( final Object element )
{
boolean success = false;
try
{
m_mutex.acquire();
try
{
success = getEnqueuePredicate().accept( element, this );
if ( success )
{
m_elements.add( element );
}
}
finally
{
m_mutex.release();
}
}
catch( InterruptedException ie )
{
}
return success;
}
public void enqueue( final Object[] elements )
throws SinkException
{
final int len = elements.length;
try
{
m_mutex.acquire();
try
{
if( ! getEnqueuePredicate().accept( elements, this ) )
{
throw new SinkFullException( "Not enough room to enqueue these elements." );
}
for( int i = 0; i < len; i++ )
{
m_elements.add( elements[ i ] );
}
}
finally
{
m_mutex.release();
}
}
catch( InterruptedException ie )
{
}
}
public void enqueue( final Object element )
throws SinkException
{
try
{
m_mutex.acquire();
try
{
if( ! getEnqueuePredicate().accept(element, this) )
{
throw new SinkFullException( "Not enough room to enqueue these elements." );
}
m_elements.add( element );
}
finally
{
m_mutex.release();
}
}
catch( InterruptedException ie )
{
}
}
public Object[] dequeue( final int numElements )
{
getDequeueInterceptor().before(this);
Object[] elements = EMPTY_ARRAY;
try
{
if( m_mutex.attempt( m_timeout ) )
{
try
{
elements = retrieveElements( m_elements,
Math.min( size(),
numElements ) );
}
finally
{
m_mutex.release();
}
}
}
catch( InterruptedException ie )
{
//TODO: exception handling
}
getDequeueInterceptor().after(this);
return elements;
}
public Object[] dequeueAll()
{
getDequeueInterceptor().before(this);
Object[] elements = EMPTY_ARRAY;
try
{
if( m_mutex.attempt( m_timeout ) )
{
try
{
elements = retrieveElements( m_elements, size() );
}
finally
{
m_mutex.release();
}
}
}
catch( InterruptedException ie )
{
// TODO: exception hanlding
}
getDequeueInterceptor().after(this);
return elements;
}
/**
* Removes the given number of elements from the given <code>buf</code>
* and returns them in an array. Trusts the caller to pass in a buffer
* full of <code>Object</code>s and with at least
* <code>count</code> elements available.
* <p>
* @param buf to remove elements from, the caller is responsible
* for synchronizing access
* @param count number of elements to remove/return
* @return requested number of elements
*/
private static Object[] retrieveElements( Buffer buf, int count )
{
Object[] elements = new Object[ count ];
for( int i = 0; i < count; i++ )
{
elements[ i ] = buf.remove();
}
return elements;
}
public Object dequeue()
{
getDequeueInterceptor().before(this);
Object element = null;
try
{
if( m_mutex.attempt( m_timeout ) )
{
try
{
if( size() > 0 )
{
element = m_elements.remove();
}
}
finally
{
m_mutex.release();
}
}
}
catch( InterruptedException ie )
{
// TODO: exception handling
}
getDequeueInterceptor().after(this);
return element;
}
private static final class DefaultPreparedEnqueue implements PreparedEnqueue
{
private final DefaultQueue m_parent;
private Object[] m_elements;
private DefaultPreparedEnqueue( DefaultQueue parent, Object[] elements )
{
m_parent = parent;
m_elements = elements;
m_parent.m_reserve += elements.length;
}
public void commit()
{
if( null == m_elements )
{
throw new IllegalStateException( "This PreparedEnqueue has already been processed!" );
}
try
{
m_parent.m_reserve -= m_elements.length;
m_parent.enqueue( m_elements );
m_elements = null;
}
catch( Exception e )
{
throw new IllegalStateException( "Default enqueue did not happen--should be impossible" );
// will never happen
}
}
public void abort()
{
if( null == m_elements )
{
throw new IllegalStateException( "This PreparedEnqueue has already been processed!" );
}
m_parent.m_reserve -= m_elements.length;
m_elements = null;
}
}
}