Anything better than asyncio.as_completed() and asyncio.wait() to manage execution of large amount of tasks?

Valery Khamenya khamenya at
Sun Jul 20 14:16:24 CEST 2014

Hi Maxime,

many thanks for your great solution. It would be so great to have it in
stock asyncio and use it out-of-the-box...
I've made 4 fixes to it that are rather of "cosmetic" nature. Here is the
final version:

import asyncio
from concurrent import futures

def as_completed_with_max_workers(tasks, *, loop=None, max_workers=5,
    loop = loop if loop is not None else asyncio.get_event_loop()
    workers = []
    pending = set()
    done = asyncio.Queue(maxsize=max_workers, loop=loop) # Valery: respect
the "loop" parameter
    exhausted = False
    timeout_handle = None # Valery: added to see, if we indeed have to call

    def _worker():
        nonlocal exhausted
        while not exhausted:
                t = next(tasks)
                yield from t
                yield from done.put(t)
            except StopIteration:
                exhausted = True

    def _on_timeout():
        for f in workers:
        # Wake up _wait_for_one()

    def _wait_for_one():
        f = yield from done.get()
        if f is None:
            raise futures.TimeoutError()
        return f.result()

    workers = [asyncio.async(_worker(), loop=loop) for _ in
range(max_workers)] # Valery: respect the "loop" parameter

    if workers and timeout is not None:
        timeout_handle = loop.call_later(timeout, _on_timeout)

    while not exhausted or pending or not done.empty():
        yield _wait_for_one()

    if timeout_handle: # Valery: call timeout_handle.cancel() only if it is

best regards
Valery A.Khamenya
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