Executor not shut down (ARCH2040)

Key python.async.executor-not-shutdown · Severity warning · Category async

Creating a ThreadPoolExecutor or similar pool without calling shutdown() or using it as a context manager leaks non-daemon threads and prevents the process from exiting cleanly.

Incorrect

from concurrent.futures import ThreadPoolExecutor

def run(tasks):
    pool = ThreadPoolExecutor(max_workers=4)  # never shut down
    return list(pool.map(work, tasks))

Correct

from concurrent.futures import ThreadPoolExecutor

def run(tasks):
    with ThreadPoolExecutor(max_workers=4) as pool:
        return list(pool.map(work, tasks))

Fix

Use the executor inside a with block, or call shutdown() when you are done with it.