/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
* implied.
*
* See the License for the specific language governing permissions and
* limitations under the License.
*/
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:dev@avalon.apache.org">Avalon Development Team</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;
}
}
}