from concurrent.futures import *
from threading import Event
from sys import setswitchinterval

setswitchinterval(1e-6)
pool = ThreadPoolExecutor(100)
event = Event()

def do_nothing():
    event.wait()

fs = {pool.submit(do_nothing) for i in range(1000)}
event.set()
wait(fs, return_when=ALL_COMPLETED)