2.7. Calling Violation during the throwing motion

The following situation led to a discussion in our last game:

A player catches an upline pass on the sideline and immediately steps into a throwing motion. During the throw he realizes there are people on the sideline obstructing the throw. He calls violation during the throwing motion, throws and the result is a turnover.

Resolution A: the thrower called the violation during the throwing motion thus in posession. The call is valid and the disc goes back

Resolution B: the thrower should have stopped his throwing motion upon realizing there is a violation. in completing the throw he accepted the violation and thus the turnover stands.

Is one of these correct? Otherwise what is the correct solution?

Extra: If the violation is called by the thrower after the throw is this a turnover?

Thanks in advance for the answer.