/*
* 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.log.output;
import java.util.LinkedList;
import org.apache.log.ErrorAware;
import org.apache.log.ErrorHandler;
import org.apache.log.LogEvent;
import org.apache.log.LogTarget;
/**
* An asynchronous LogTarget that sends entries on in another thread.
* It is the responsibility of the user of this class to start
* the thread etc.
*
* <pre>
* LogTarget mySlowTarget = ...;
* AsyncLogTarget asyncTarget = new AsyncLogTarget( mySlowTarget );
* Thread thread = new Thread( asyncTarget );
* thread.setPriority( Thread.MIN_PRIORITY );
* thread.start();
*
* logger.setLogTargets( new LogTarget[] { asyncTarget } );
* </pre>
*
* @author <a href="mailto:dev@avalon.apache.org">Avalon Development Team</a>
* @author Peter Donald
*/
public class AsyncLogTarget
extends AbstractWrappingTarget
implements Runnable
{
private final LinkedList m_list;
private final int m_queueSize;
/**
* Creation of a new async log target.
* @param logTarget the underlying target
*/
public AsyncLogTarget( final LogTarget logTarget )
{
this( logTarget, 15 );
}
/**
* Creation of a new async log target.
* @param logTarget the underlying target
* @param queueSize the queue size
*/
public AsyncLogTarget( final LogTarget logTarget, final int queueSize )
{
this( logTarget, queueSize, false );
}
/**
* Creation of a new async log target.
* @param logTarget the underlying target
* @param closeTarget close the underlying target when this target is closed. This flag
* has no effect unless the logTarget implements Closeable.
*/
public AsyncLogTarget( final LogTarget logTarget, final boolean closeTarget )
{
this( logTarget, 15, closeTarget );
}
/**
* Creation of a new async log target.
* @param logTarget the underlying target
* @param queueSize the queue size
* @param closeTarget close the underlying target when this target is closed. This flag
* has no effect unless the logTarget implements Closeable.
*/
public AsyncLogTarget( final LogTarget logTarget, final int queueSize, final boolean closeTarget )
{
super( logTarget, closeTarget );
m_list = new LinkedList();
m_queueSize = queueSize;
open();
}
/**
* Provide component with ErrorHandler.
*
* @param errorHandler the errorHandler
*/
public synchronized void setErrorHandler( final ErrorHandler errorHandler )
{
super.setErrorHandler( errorHandler );
if( this.getLogTarget() instanceof ErrorAware )
{
( (ErrorAware)this.getLogTarget() ).setErrorHandler( errorHandler );
}
}
/**
* Process a log event by adding it to queue.
*
* @param event the log event
*/
public void doProcessEvent( final LogEvent event )
{
synchronized( m_list )
{
int size = m_list.size();
while( m_queueSize <= size )
{
try
{
m_list.wait();
}
catch( final InterruptedException ie )
{
//This really should not occur ...
//Maybe we should log it though for
//now lets ignore it
}
size = m_list.size();
}
m_list.addFirst( event );
if( size == 0 )
{
//tell the "server" thread to wake up
//if it is waiting for a queue to contain some items
m_list.notify();
}
}
}
/**
* Thread startup.
*/
public void run()
{
//set this variable when thread is interupted
//so we know we can shutdown thread soon.
boolean interupted = false;
while( true )
{
LogEvent event = null;
synchronized( m_list )
{
while( null == event )
{
final int size = m_list.size();
if( size > 0 )
{
event = (LogEvent)m_list.removeLast();
if( size == m_queueSize )
{
//tell the "client" thread to wake up
//if it is waiting for a queue position to open up
m_list.notify();
}
}
else if( interupted || Thread.interrupted() )
{
//ie there is nothing in queue and thread is interrupted
//thus we stop thread
return;
}
else
{
try
{
m_list.wait();
}
catch( final InterruptedException ie )
{
//Ignore this and let it be dealt in next loop
//Need to set variable as the exception throw cleared status
interupted = true;
}
}
}
}
try
{
//actually process an event
this.getLogTarget().processEvent( event );
}
catch( final Throwable throwable )
{
getErrorHandler().error( "Unknown error writing event.", throwable, event );
}
}
}
}