Usually on long flights such as that there are self service snacks (chips, candy, and the like) available mid-flight..the FA sets them out on a cart or tray near the galley and you can help yourself. I have not flown IAD-DXB but I suspect that flight is long enough to where they also have hot sandwiches available mid-flight if you request it from the FA. They would not do an "official" mid flight snack service where they come down the aisle with a cart.