How to run two different commands (functions) at the same time in shell

I am writing a shell script (on git) where i need to run two command at the same time, simultaneously. The situation is something like

  1. The script start to run
  2. It contains a function which run for 10 sec. It generates a new output every second. It means 10 output for 10 sec run.
  3. Another function which runs for 10 sec. The input for this function is the output of above function.

The problem is i can not go to the second function until first function execution is over.

Until both function run mutually i can not get the desired out. What to do?

Any help in this regard is welcome.

Background functions.

Thanks @Henrik_Iivonen,
I am going to implement this for my code, in my leisure time.