Python threading: can I sleep on two threading.Event()s simultaneously?

Question

If I have two threading.Event() objects, and wish to sleep until either one of them is set, is there an efficient way to do that in python? Clearly I could do

Answer 1

This is an old question, but I hope this helps someone coming from Google.
The accepted answer is fairly old and will cause an infinite loop for twice-"orified" events.

Here is an implementation using concurrent.futures

import concurrent.futures
from concurrent.futures import ThreadPoolExecutor

def wait_for_either(events, timeout=None, t_pool=None):
    '''blocks untils one of the events gets set

    PARAMETERS
    events (list): list of threading.Event objects
    timeout (float): timeout for events (used for polling)
    t_pool (concurrent.futures.ThreadPoolExecutor): optional
    '''

    if any(event.is_set() for event in events):
        # sanity check
        pass
    else:
        t_pool = t_pool or ThreadPoolExecutor(max_workers=len(events))
        tasks = []
        for event in events:
            tasks.append(t_pool.submit(event.wait))

        concurrent.futures.wait(tasks, timeout=timeout, return_when='FIRST_COMPLETED')
        # cleanup
        for task in tasks:
            try:
                task.result(timeout=0)
            except concurrent.futures.TimeoutError:
                pass

Testing the function

import threading
import time
from datetime import datetime, timedelta

def bomb(myevent, sleep_s):
    '''set event after sleep_s seconds'''
    with lock:
        print('explodes in ', datetime.now() + timedelta(seconds=sleep_s))
    time.sleep(sleep_s)
    myevent.set()
    with lock:
        print('BOOM!')

lock = threading.RLock()  # so prints don't get jumbled
a = threading.Event()
b = threading.Event()

t_pool = ThreadPoolExecutor(max_workers=2)

threading.Thread(target=bomb, args=(event1, 5), daemon=True).start()
threading.Thread(target=bomb, args=(event2, 120), daemon=True).start()

with lock:
    print('1 second timeout, no ThreadPool', datetime.now())

wait_for_either([a, b], timeout=1)

with lock:
    print('wait_event_or done', datetime.now())
    print('=' * 15)

with lock:
    print('wait for event1', datetime.now())

wait_for_either([a, b], t_pool=t_pool)

with lock:
    print('wait_event_or done', datetime.now())