Does masturbating WHILE bathing/ghusl invalidate the bath?

If mani was released ghusl is obligatory if madhiy was realesed then wudu is obligatory for becomming ritually pure. Also mastrbuation is haram beccause of clear evidence Masturbation (for both men and women) is haraam (forbidden) in Islam based on the following evidence: First from the Quraan: Imam Shafii stated that masturbation is forbidden based on the following verses from the Quraan (interpretation of the meaning): "And those who guard their chastity (i.e. private parts, from illegal sexual acts). Except from their wives or (the captives and slaves) that their right hands possess, - for them, they are free from blame. But whoever seeks beyond that, then those are the transgressors." 23.5-7 Here the verses are clear in forbidding all illegal sexual acts (including masturbation) except for the wives or that their right hand possess. And whoever seeks beyond that is the transgressor. "And let those who find not the financial means for marriage keep themselves chaste, until Allah enriches them of His bounty." 24.33. This verse also clearly orders whoever does not have the financial means to marry to keep himself chaste and be patient in facing temptations (including masturbation) until Allah enriches them of His bounty. Secondly, from the sunnah of the Prophet (peace be upon him): Abdullaah ibn Masood said, "We were with the Prophet while we were young and had no wealth whatsoever. So Allaahs Messenger said, "O young people! Whoever among you can marry, should marry, because it helps him lower his gaze and guard his modesty (i.e. his private parts from committing illegal sexual intercourse etc.), and whoever is not able to marry, should fast, as fasting diminishes his sexual power." Bukhari:5066. The hadeeth orders men who are not able to marry to fast despite the hardship encountered in doing so, and not to masturbate despite the ease with which it can be done. There are additional evidences that can be cited to support this ruling on masturbation, but due to the limited space we will not go through them here. Copy pasted from islamqa most trusted islamic web.

Ghusl is only valid if it was performed after the reason for which it was ordered. Allah the Almighty says :

... And if you are in a state of janabah, then purify yourselves.... (5:6)

Here the Arabic original uses the past form and says:

وإن كنتم جنبا فاطهروا

So "are" is rather "were" and the emphasize is on what happened earlier. As the verb كان always refers to a past (or something which has already started).

This means one first has to have a wet dream or intercourse (legal or illegal) or seemen emission from whatever reason or the menses or child bed bleeding ended before starting to do ghusl. If any or more precisely some of these happens during a ghusl this ghusl is invalid and must be restarted.

So in your case your ghusl is only valid if you started it (newly) after masturbation.