[issue30491] Add a lightweight mechanism for detecting un-awaited coroutine objects
Yury Selivanov
report at bugs.python.org
Wed Jan 24 00:06:30 EST 2018
Yury Selivanov <yselivanov at gmail.com> added the comment:
Guido,
This is another feature for native coroutines that Nathaniel proposes for 3.7.
Here's a summary (this issue has too many messages):
1. It adds a new mechanism to detect un-awaited coroutines (i.e. when a user forgets to use await).
2. To enable the mechanism, which is disabled by default, a "sys. set_unawaited_coroutine_tracking_enabled()" function needs to be called by a framework.
3. "sys.get_unawaited_coroutines()" returns a list of not-yet-awaited native-coroutine objects that were created since the previous call to "get_unawaited_coroutines()".
4. In Trio, the APIs are designed to accept *coroutine functions*. So in Trio, a user either writes "await coro()" or passes "coro" to a Trio API. Nathaniel wants Trio to check periodically if there are any un-awaited coroutines and raise an error, which should improve Trio usability.
5. Another potential user of this new functionality is pytest-asyncio. It can use the API to warn the user that a test created some coroutines that were never awaited.
6. asyncio/tornado/curio/twisted will not be able to use this API.
7. Effectively, the previously merged origin-tracking API (the one with which we replaced set_coroutine_wrapper) achieves the same goal. The only downside is that the warning won't be raised until GC. On other interpreters like PyPy it can take a while before a coroutine gets GCed.
8. The patch adds two pointers to native coroutines objects to maintain a doubly-linked list of them.
9. The performance impact is visible in micro-benchmarks, but is unlikely be visible in real applications. Still, it's about 3-4% slowdown for both generators and coroutines.
10. The PR itself is in a good shape, although I'll still make a review pass if you approve this feature to go in 3.7.
What do you think?
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