Yury Selivanov <yseliva...@gmail.com> added the comment:
>> There's no clear reason to complicate the Task<->coroutine relationship by >> allowing to inject arbitrary exceptions into running coroutines. > My comment was more about CancelledError rather than arbitrary exceptions. > You didn't reply to the part of my response saying that Task.cancel() doesn't > let you communicate why the task was ended, [..] I didn't reply because you didn't clearly articulate why the cancellation reason is important :) AFAIK no other async framework allows you to do this. So what are those real-world cases that can explain why asyncio should support this functionality? > [..] which is something the removed API's let you do. Unfortunately they didn't. They never worked properly; IIRC Task.set_exception had never worked at all. The fact they were available at all was a simple oversight. > Task.set_exception() and Task.set_result() both give you a way to > unconditionally end a task. With cancel() though, the docs say, > "Task.cancel() does not guarantee that the Task will be cancelled." [1] Yes, because Task can only signal its coroutine that it was requested to be cancelled. The coroutine may choose to ignore that by swallowing CancelledError. > The reason you might want to unconditionally end a task is if e.g. you > already called Task.cancel() and it is still running after waiting a certain > amount of time. Well, if you want to unconditionally end tasks you shouldn't write coroutines that ignore CancelledErrors. If you do, then you clearly *do not want* the coroutine to be cancelled, and thus there's no use case for set_exception. Finally, asyncio has queues, which can be used to build two-way communication channels between coroutines and implement whatever advanced cancellation mechanism you want. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue32363> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
