Le 14/06/2018 à 04:09, Nathaniel Smith a écrit : > How about: > > async def wait_to_run(async_fn, *args): > await wait_for_something() > return await async_fn(*args) > > task = loop.create_task(wait_to_run(myfunc, ...)) >
It's quite elegant, although figuring out the wait_for_something() is going to be tricky. > ----- > > Whatever strategy you use, you should also think about what semantics > you want if one of these delayed tasks is cancelled before it starts. > > For regular, non-delayed tasks, Trio makes sure that even if it gets > cancelled before it starts, then it still gets scheduled and runs until > the first cancellation point. This is necessary for correct resource > hand-off between tasks: > > async def some_task(handle): > with handle: > await ... > > If we skipped running this task entirely, then the handle wouldn't be > closed properly; scheduling it once allows the with block to run, and > then get cleaned up by the cancellation exception. I'm not sure but I > think asyncio handles pre-cancellation in a similar way. (Yury, do you > know? > > Now, in delayed task case, there's a similar issue. If you want to keep > the same solution, then you might want to instead write: > > # asyncio > async def wait_to_run(async_fn, *args): > try: > await wait_for_something() > except asyncio.CancelledError: > # have to create a subtask to make it cancellable > subtask = loop.create_task(async_fn(*args)) > # then cancel it immediately > subtask.cancel() > # and wait for the cancellation to be processed > return await subtask > else: > return await async_fn(*args) > > In trio, this could be simplified to > > # trio > async def wait_to_run(async_fn, *args): > try: > await wait_for_something() > except trio.Cancelled: > pass > return await async_fn(*args) > > (This works because of trio's "stateful cancellation" – if the whole > thing is cancelled, then as soon as async_fn hits a cancellation point > the exception will be re-delivered.) Thanks for the tip. It schedules it in all cases, but I don't know what asyncio does with it. I'll add a unit test for that. _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
