import os
from concurrent.futures import ThreadPoolExecutor

def new_process(arg):
    pid = os.fork()
    if pid == 0:
        exec_fn("/bin/true", "/bin/true")
    else:
        pid, status = os.waitpid(pid, 0)

with ThreadPoolExecutor(max_workers=4) as executor:
    futures = [executor.submit(new_process, None)
               for i in range(0, 4)]
    for fut in futures:
        fut.result()