Guarantee asyncio execution order

Question

I have seen other answers on here stating that asyncio doesn't guarantee execution order, only that the order of the outputs will match that of the inputs.

Is there a way I can guarantee the execution order

For example, if I have a list of the functions I want to run, will calling create task on each of them before calling gather work? Is there something else I can do to achieve this?

Answer 1

You could do this with asyncio.Event:

async def perform_task(listen_event, push_event):
    await do_some_paralell_work()
    await listen_event.wait()
    await do_some_work_in_order()
    if push_event:
        await push-event.set()

async def main():
    events = [asyncio.Event() for i in range(100)]
    tasks = [asyncio.Task(events[i], events[i+1] if i<100 else None) for i in range(100)]
    events[0].set()
    await asyncio.gather(*tasks)

This should let the parallel work run in parallel but then run the final statement in order

Answer 2

You probably want to read the section on asyncio syncrhonization. You have have one task wait on an Event that is set by another task.