What should one do if while performing Ghusl, one of the causes of ghusl occurs, such as touching a dead body or becoming Junub?

If the cause for the second Ghusl, is the same as the cause if the first, the Ghusl must be performed again, for example while performing Ghusl for Janabah one becomes Junub again. However if the cause of the second Ghusl is different to that of the first, such as while performing Ghusl for Janabah one touches a dead body, in which case one can make intention to complete the first Ghusl thereafter perform the new one, or invalidate the previous Ghusl and perform a new Ghusl with the intention of all outstanding Ghusl.