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 a Java File Object
	 */
	protected String createUniqueFileName( String imageDir, String prefix,
			String postfix )
	{
		File file = null;
		postfix = ( postfix == null ? "" : postfix );
		String uniCount = null;
		do
		{
			uniCount = genUniqueCount( );
			file = new File( imageDir + "/" + prefix + uniCount + postfix ); 
		} while ( file.exists( ) );
		
		return prefix + uniCount + postfix;
	}
	/**
	 * Generating unique string which contains following parts
	 * <li> the hashcode of the image handler
	 * <li> creation time of the image handler
	 * <li> image count created by the image handler
	 * @return return the unique count for filename
	 */
	synchronized private String genUniqueCount( )
	{
		count++;
		return handlerId + count;
	}
	/*
	 * (non-Javadoc)