[issue21163] asyncio task possibly incorrectly garbage collected

[Guido van Rossum]

Guido van Rossum added the comment:

Thanks for understanding. 

It's definitely subtle: there is also some code in asyncio that logs an error when a Future holding an exception becomes unreachable before anyone has asked for it; this has been a valuable debugging tool, and it depends on *not* holding references to Futures.

Regarding the difference between Python 3.3 and 3.4, I don't know the exact reason, but GC definitely gets more precise with each new revision, and there are also some differences in how exactly the debug feature I just mentioned is implemented (look for _tb_logger in asyncio/futures.py).

OTOH it does seem a little odd to just GC a coroutine that hasn't exited yet, and I'm not 100% convinced there *isn't* a bug here. The more I think about it, the more I think that it's suspicious that it's always the *first* iteration that gets GC'ed. So I'd like to keep this open as a reminder.

Finally, I'm not sure the analogy with threads holds -- a thread manages OS resources that really do have to be destroyed explicitly, but that's not so for tasks, and any cleanup you do need can be handled using try/finally. (In general drawing analogies between threads and asyncio tasks/coroutines is probably one of the less fruitful lines of thinking about the latter; there are more differences than similarities.)

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resolution: invalid -> remind

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21163>
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