robertodimarco on "[Plugin: WooCommerce - excelling eCommerce] Update stock after clicking "add to cart""

Hello!
I need this hack, please help me!
I sell single product, so I need the inventory is updated immediately after click on add to cart button, to display the message "out of stock" on the product page. I do not want two people make an order on the same single product. I hope I was clear, I usat google trad. Thank you!

http://wordpress.org/extend/plugins/woocommerce/