Python multithreading,multi processing

It depends on your code and the type of the problem you are trying to solve. Python GIL applies to CPU-bound threads, i.e. threads that want to do CPU-intensive tasks*.

However, if your threads are I/O-bound, i.e. spend most of the time waiting for input/output, the GIL would not be a problem because while waiting for the I/O operation to complete, threads can do not need a lock on the Python interpreter. An example would be waiting for a network operation to complete (downloading a file, for example). You can easily fire multiple threads and download the files simultaneously.

*footnote: even for CPU-bound tasks, the GIL only applies to Python code. If a thread uses a C-extension (i.e. library written in C), it won't need the GIL while executing, because it won't be running Python instructions.

Edit: Reading your comment saying that you will be invoking the POS simulator functions via sockets... that's an I/O operation. While the server will be executing function calls, Python (the client) will simply wait doing nothing, and the threads will not need to hold GIL most of the time.

This should give you an idea of how it's done.

import multiprocessing
import threading

def thread():
    pass


def process():
    threads = []
    for i in range(30):
        t = threading.Thread(target=thread)
        threads.append(t)
        t.start()
    for t in threads:
        t.join()

if __name__ == '__main__':
    processes = []
    for i in range(16):
        p = multiprocessing.Process(target=process)
        processes.append(p)
        p.start()
    for p in processes:
        p.join()