We use the RollingFileAppender under Windows NT and simultaneously open the log 
file in a log viewer.
Under these conditions, the appender no longer works because renaming a file 
that has been opened is not permitted, possibly resulting in a loss of data.
There are not any problems under linux.
We have found a way of solving this and use this derived appender.
It is based on the idea that a rollover does not take place in case the file 
has been opened by a second application.
This is tested through a renameTo using the original file name.We use the 
RollingFileAppender under Windows NT and simultaneously open the log file in a 
log viewer.
Under these conditions, the appender no longer works because renaming a file 
that has been opened is not permitted, possibly resulting in a loss of data.
There are not any problems under linux.
We have found a way of solving this and use this derived appender.
It is based on the idea that a rollover does not take place in case the file 
has been opened by a second application.
This is tested through a renameTo using the original file name.

Our derived appender class:

package org.apache.log4j;

import java.io.File;
import java.io.IOException;


public class RollingFileAppenderEx extends RollingFileAppender 
{
  public
  RollingFileAppenderEx() 
  {
  	super();
  }
  
  public
  synchronized
  boolean canRename()
  {
  	boolean bRet = false;
  	File file;
	try 
	{	
		file = new File(fileName);
		this.closeFile();
		bRet = file.renameTo(file);
		this.setFile(fileName, true);
	}
	catch(IOException e){}
	return bRet;
  }
  
  public
  synchronized
  void rollOver() 
  {
  	if (canRename() == true)
	{
		super.rollOver();
	}		
  }
}