How does one execute asynchronous tasks in Python 3.4?

You should read about pool.map_async, I've used it many times to perform asynchronous tasks. Basically what you need to do is write a function which is passed 2 arguments, the in_file and the out_file, instantiate the pool and associate it with the function and its list of tuples arguments [(in_file1,out_file1), (in_file2,out_file2)...].

Caution! while the files may not overlap you are still using an IO device which incurs a lot of overhead in terms of waiting for read and write, so try to separate the reading and writing of file from the main logic, i.e. read the file, process all of the data and store it on ram, write the file out.

EDIT1: appearantly in python3 they have starmap, which to my understanding lets you pass an iterable of iterables, the iterables are parsed as arguments. So I changed the code to use starmap. Also you should consider adding a timeout to one iteration, you can do that using the get method.

I'll include some example code (it's in python2 but the logic/syntax is easily transferable):

import multiprocessing as mp

def foo(in_file, out_file):
    in_data = ""
    # this is just an example of how to read file
    with open(in_file, "rb") as f:
        for line in f:
            in_data += line
    ...
    out_data = process(in_data)
    ...
    with open(out_file,'wb') as f:
        f.write(out_data)


def main():
    files =[("/infile1", "/outfile1"), ("/infile2", "/outfile2"), ...]
    # you should choose how many processes you wish to instantiate.
    # leaving it blank will assume the number of threads/core available.
    pool = mp.Pool(processes=4)
    pool.starmap_async(foo,files)