Bug 195335 Multithreads issue
a static hashmap in class HTMLServerImageHandler has not been synchronized which may leads to that the same images are handled(eg: write to disk) multiple times.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/HTMLServerImageHandler.java
{
			return image.getReportRunnable( ).hashCode( ) + image.getID( );
		}
		return image.getID( );
	}
	/**
	 * get image
	 * 
	 * @param out
	 *            the output stream of image
	 * @param imageDir
	 *            the image directory
	 * @param imageID
	 *            id of image
	 * @throws IOException
	 */
	public void getImage( OutputStream out, String imageDir, String imageID )
			throws EngineException
	{
		File image = new File( imageDir, imageID );
		if ( !image.exists( ) )
		{
			throw new EngineException(
					MessageConstants.MISSING_IMAGE_FILE_ERROR ); 
		}
		InputStream in = null;
		try
		{
			in = new FileInputStream( image );
			byte[] buffer = new byte[1024];