Are all 100 lines of same type? If they are same than just start 20 threads and import txt file as a resource set up to use each line 1 time.
If its 20 x 5 different lines, you could import txt file as a list and than split that list to 20 parts with list commands, After that you could start asynchronus functions, each with its set of 5 enteries from original 100 line text file.
Or if its 20 x 5 different lines, you could rearange txt file so all 5 enteries are in same line and deal with it like in first case, to avoid asynchronous functions all together.