I looked a bit more. The only thing that ever waits is the caller in the for-loop (for f in as_completed(...): x = yield from f; ...). It will always wait for _wait_for_one(), which in turn will always wait for done.get(). So if the above yield-from is cancelled, _wait_for_one() is cancelled, which in turn cancels the Queue.get() call. If this is cancelled, the corresponding put_nowait() call may well cancelled (I stopped following the code carefully) but this is called from the completion callback for a completed future, so that future isn't cancellable, and there's nothing that cancels the futures still in the todo queue.
I'm skeptical that it's desirable to cancel the original futures though. Have you thought through the use case? (Admittedly I haven't.) On Tue, Mar 3, 2015 at 11:01 AM, Gustavo Carneiro <[email protected]> wrote: > > > On 2 March 2015 at 10:12, Victor Stinner <[email protected]> wrote: > >> Hi, >> >> To answer Luciano's question on as_completed(), I read the source code >> of the function. It's not clear to me what happens on timeout. >> >> >> Should we abort something on timeout? The documentation doesn't >> explain if tasks are cancelled or if an exception is set. In the code, >> it's clear that the task is not touched. It's probably just a >> documentation issue. >> > > I think it should cancel the wrapped task. I think this is what the > programmer will want most of the time, and in case he doesn't want it he > can use shield() to prevent it. > > Also it makes it consistent with wait_for: > > https://code.google.com/p/tulip/issues/detail?id=107 > http://bugs.python.org/issue23219 > > >> >> >> Coroutine objects are wrapped into tasks: on timeout, these temporary >> tasks may be destroyed before their completion. A warning is emited in >> this case. The warning is useless, since the caller doesn't have >> access to all these temporary tasks. As gather(), we should probably >> set the _log_destroy_pending attribute of these tasks to False. What >> do you think? > > >> Victor >> > > > > -- > Gustavo J. A. M. Carneiro > Gambit Research > "The universe is always one step beyond logic." -- Frank Herbert > -- --Guido van Rossum (python.org/~guido)
