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 (String) map.get( mapID );
			}
		}
		String ret = null;
		if ( context != null && ( context instanceof HTMLRenderContext ) )
		{
			HTMLRenderContext myContext = (HTMLRenderContext) context;
			String imageURL = myContext.getBaseImageURL( );
			String imageDir = myContext.getImageDirectory( );
			if ( imageURL == null || imageURL.length( ) == 0
					|| imageDir == null || imageDir.length( ) == 0 )
			{
				log.log( Level.SEVERE, "imageURL or ImageDIR is not set!" ); 
				return null;
			}
			String fileName;
			File file;
			String extension = image.getExtension( );
			if ( extension != null && extension.length( ) > 0 )
			{
				fileName = createUniqueFileName( imageDir, prefix, extension ); 
			}
			else
			{
				fileName = createUniqueFileName( imageDir, prefix );
			}
			file = new File( imageDir, fileName ); 
			try
			{
				image.writeImage( file );