Reverse Polish Notation Algorithm Multi-threaded?

Question

Algorithms

Good afternoon, I need to implement multi-threaded, parsing reverse Polish notation to normal and vice versa.
Tell me where to dig what literature to read?
A single-threaded algorithm has been implemented repeatedly, but with a multi-threaded implementation, there are no ideas.

Answer 1

If there is a single-threaded implementation, what prevents it from being converted into a multi-threaded one?
What is the problem?