/*
* Copyright (C) The Apache Software Foundation. All rights reserved.
*
* This software is published under the terms of the Apache Software License
* version 1.1, a copy of which has been included with this distribution in
* the LICENSE file.
*/
package org.apache.log.output;
import java.util.LinkedList;
import org.apache.log.ErrorHandler;
import org.apache.log.ErrorAware;
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:peter@apache.org">Peter Donald</a>
*/
public class AsyncLogTarget
extends AbstractTarget
implements Runnable
{
private final LinkedList m_list;
private final int m_queueSize;
private final LogTarget m_logTarget;
public AsyncLogTarget( final LogTarget logTarget )
{
this( logTarget, 15 );
}
public AsyncLogTarget( final LogTarget logTarget, final int queueSize )
{
m_logTarget = logTarget;
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( m_logTarget instanceof ErrorAware )
{
((ErrorAware)m_logTarget).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 )
{
final 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
}
}
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();
}
}
}
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
m_logTarget.processEvent( event );
}
catch( final Throwable throwable )
{
getErrorHandler().error( "Unknown error writing event.", throwable, event );
}
}
}
}