Streamlit session_state with multiprocesssing

[ferdy]

@Beni

I’m curious to know whether there’s a workaround or it’s a limitation that we have to deal with it (i.e. either using session_state or multiprocessing, and not both).

Create a session state variable to save your work. Run other processes as normal but save the result to session state when done.

import concurrent.futures
from concurrent.futures import ProcessPoolExecutor
import time

import streamlit as st


if 'save' not in st.session_state:
    st.session_state.save = []


def task(v):
    """session state does not work here"""
    time.sleep(1)
    return v * v


if __name__ == '__main__':
    num_workers = 2
    jobs = [1, 2, 3, 4, 5, 6, 7, 8, 9]
    processed_jobs = []

    start = st.button('start work')

    if start:
        with ProcessPoolExecutor(max_workers=num_workers) as executor:
            for j in jobs:
                pj = executor.submit(task, j)
                processed_jobs.append(pj)

            for future in concurrent.futures.as_completed(processed_jobs):
                try:
                    res = future.result()
                    st.write(f'res: {res}')

                    # Incrementally save the completed task so far.
                    st.session_state.save.append(res)

                except concurrent.futures.process.BrokenProcessPool as ex:
                    raise Exception(ex)

    if len(st.session_state.save):
        st.write('#### Completed Jobs')
        st.write(f'{st.session_state.save}')

Output