multiprocessing after a prefect test hangs

[atombear]

Bug summary

on linux, though not on darwin, the following example hangs with pytest file.py

contents of file.py

import prefect
from prefect.testing.utilities import prefect_test_harness
from multiprocessing import Process

def thread_func():
    print("HI")
    return 10

@prefect.task
def task():
    return 1

@prefect.flow
def flow():
    return task.submit()

def test():
    with prefect_test_harness():
        flow()

    p = Process(target=thread_func)
    p.start()
    print("ENDING")
    p.join()

Version info

Version:              3.4.22
API version:          0.8.4
Python version:       3.11.13
Git commit:           6a6d114f
Built:                Fri, Oct 3, 2025 06:15 PM
OS/Arch:              linux/x86_64
Profile:              default
Server type:          server
Pydantic version:     2.11.10
Server:
  Database:           postgresql
  PostgreSQL version: 14.17

Additional context

No response

[zzstoatzz]

hi @atombear - would you be willing to try out the branch above? i'm not sure if that's the solution we'll go with, but it appears to work and it'd be good to get confirmation from you

[atombear]

@zzstoatzz yes, the problematic code now completes successfully!