Create a new subdirectory for each walker - Emcee/MCMC

Question

I am using the Emcee python package to fit some models to data. My python code is a wrapper to a separate piece of software. My code generates the input file to this software at each step in the MCMC chain.

For each iteration, I need to:

1. Copy the folder containing the software to a new folder with a unique path
2. Generate the input file within that folder
3. Run the software
4. Compare the output to the data

I am having trouble with Step 1. I have set up a function called model() which creates the new folder and input file for each iteration:

def model(theta):
    id_number = random.randint(100000)     
    os.system('cp -R original/model/path/ new/model/path/{}/'.format(id_number))

    # then actually generate input and run the model using theta...

The idea is that each walker copies the folder over with a unique ID, then generates an input file and runs the software from that particular unique location. However, the code doesn't seem to create a new folder for each individual walker. At the moment, the folder is successfully copied with a unique ID once, then all the walkers attempt to generate input files and run the software from that folder at the same time. I am not sure why this is.

The emcee part of my code is as follows:

from multiprocessing import Pool
import multiprocessing as mp
mp.set_start_method('fork')

def main(p0,nwalkers,niter,ndim,lnprob,data):
    with Pool() as pool:
        sampler = emcee.EnsembleSampler(nwalkers, ndim, lnprob, args=data, pool=pool)
        pos, prob, state = sampler.run_mcmc(p0, niter, progress=True)

        return sampler, pos, prob, state
    
sampler, pos, prob, state = main(p0, nwalkers, niter, ndim, lnprob, data)

A similar question was asked here, but I wasn't able to get this to work.