airflow: Error: 'daemonic processes are not allowed to have children', after upgradeing to airflow:2.0.1

Apache Airflow version: 2.0.1

Kubernetes version (if you are using kubernetes) (use kubectl version): /

Environment:

• OS (e.g. from /etc/os-release): Ubuntu 18.04
• Kernel (e.g. uname -a): Linux ivan-pc 5.4.0-66-generic #74~18.04.2-Ubuntu SMP Fri Feb 5 11:17:31 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

What happened: I am using LocalExecutor, and I was using it on Apache/Airflow 1.10.12 the same way. I mean I had one PythonOperator which runs python method which runs multiprocessing job using ProcessPoolExecutor (concurrent.futures). And on earlier version it ran successfully without any problems, but now I get this error:

[2021-03-18 15:38:37,552] {taskinstance.py:1455} ERROR - daemonic processes are not allowed to have children
Traceback (most recent call last):
  File "/home/airflow/.local/lib/python3.6/site-packages/airflow/models/taskinstance.py", line 1112, in _run_raw_task
    self._prepare_and_execute_task_with_callbacks(context, task)
  File "/home/airflow/.local/lib/python3.6/site-packages/airflow/models/taskinstance.py", line 1285, in _prepare_and_execute_task_with_callbacks
    result = self._execute_task(context, task_copy)
  File "/home/airflow/.local/lib/python3.6/site-packages/airflow/models/taskinstance.py", line 1315, in _execute_task
    result = task_copy.execute(context=context)
  File "/home/airflow/.local/lib/python3.6/site-packages/airflow/operators/python.py", line 117, in execute
    return_value = self.execute_callable()
  File "/home/airflow/.local/lib/python3.6/site-packages/airflow/operators/python.py", line 128, in execute_callable
    return self.python_callable(*self.op_args, **self.op_kwargs)
  File "/home/airflow/Edmond/edmond/backend/main_parts/run_algorithm_o_book.py", line 15, in run_algorithm_o_book
    alg_o_output = run_o(k_output, capacity, OModelBook, config)
  File "/home/airflow/Edmond/edmond/models/O/model.py", line 388, in run_o
    for mid_result in executor.map(_run, args):
  File "/usr/local/lib/python3.6/concurrent/futures/process.py", line 496, in map
    timeout=timeout)
  File "/usr/local/lib/python3.6/concurrent/futures/_base.py", line 575, in map
    fs = [self.submit(fn, *args) for args in zip(*iterables)]
  File "/usr/local/lib/python3.6/concurrent/futures/_base.py", line 575, in <listcomp>
    fs = [self.submit(fn, *args) for args in zip(*iterables)]
  File "/usr/local/lib/python3.6/concurrent/futures/process.py", line 466, in submit
    self._start_queue_management_thread()
  File "/usr/local/lib/python3.6/concurrent/futures/process.py", line 427, in _start_queue_management_thread
    self._adjust_process_count()
  File "/usr/local/lib/python3.6/concurrent/futures/process.py", line 446, in _adjust_process_count
    p.start()
  File "/usr/local/lib/python3.6/multiprocessing/process.py", line 103, in start
    'daemonic processes are not allowed to have children'
AssertionError: daemonic processes are not allowed to have children

What you expected to happen: I expected it to run as it was running on Airflow 1.10.12

How to reproduce it: Run airflow using docker-compose like this:

version: '3.8'
x-airflow-common:
  &airflow-common
  image: edmond_image
  env_file:
    - compose-services.env
  volumes:
    - ./dags:/opt/airflow/dags
    - ./logs:/opt/airflow/logs
    - ./scripts:/opt/airflow/scripts
    - ./notebooks:/home/airflow/Edmond/notebooks
    - ./data:/home/airflow/Edmond/data
  depends_on:
    - postgres
  restart: always

services:
  postgres:
    image: postgres:13
    environment:
      POSTGRES_USER: airflow
      POSTGRES_PASSWORD: airflow
      POSTGRES_DB: airflow

  airflow-webserver:
    <<: *airflow-common
    command: webserver
    ports:
      - 8090:8080

  airflow-scheduler:
    <<: *airflow-common
    command: scheduler

  airflow-init:
    <<: *airflow-common
    restart: on-failure
    environment:
      _AIRFLOW_DB_UPGRADE: 'true'
      _AIRFLOW_WWW_USER_CREATE: 'true'
      _AIRFLOW_WWW_USER_USERNAME: 'Admin'
      _AIRFLOW_WWW_USER_PASSWORD: 'Admin'

And inside run python operator which runs ProcessPoolExecutor from concurrent.futures

Anything else we need to know: This problem occurs every time I run python operator with multiprocessing. I have searched everywhere without any luck. There seems to be a similar error when using Celery Executor but it doesn’t help (as I am using LocalExecutor) and there is no import collisions.