| msg296931 - (view) |
Author: Dima Tisnek (Dima.Tisnek) * |
Date: 2017-06-26 18:55 |
| MRE ``` import asyncio async def generator(): while True: x = yield 42 print("received", x) await asyncio.sleep(0.1) async def user(name, g): print("sending", name) await g.asend(name) async def helper(): g = generator() await g.asend(None) await asyncio.gather(*(user(f"user-{x}", g) for x in range(3))) if __name__ == "__main__": asyncio.get_event_loop().run_until_complete(helper()) ``` Produces output: ``` sending user-0 received user-0 sending user-1 sending user-2 received None received None ``` Expected output (some variance allowed): ``` sending user-0 received user-0 sending user-1 sending user-2 received user-1 received user-2 ``` Initial report / discussion: https://mail.python.org/pipermail/async-sig/2017-June/000293.html |
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| msg296932 - (view) |
Author: Dima Tisnek (Dima.Tisnek) * |
Date: 2017-06-26 19:03 |
| @Yuri, this bug doesn't require `gather`, here's a version with futures and explicit await's instead. It produces same output: ``` import asyncio async def generator(): while True: x = yield 42 print("received", x) await asyncio.sleep(0.1) async def user(name, g): print("sending", name) await g.asend(name) async def helper(): g = generator() await g.asend(None) u0 = asyncio.ensure_future(user("user-0", g)) u1 = asyncio.ensure_future(user("user-1", g)) u2 = asyncio.ensure_future(user("user-2", g)) await u0 await u1 await u2 if __name__ == "__main__": asyncio.get_event_loop().run_until_complete(helper()) ``` Same with `asyncio.get_event_loop().create_task` as well. |
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| msg297022 - (view) |
Author: Chris Jerdonek (chris.jerdonek) *  |
Date: 2017-06-27 11:27 |
| Note that the example can be further simplified by replacing user() with: async def send_hello(g): print("sending: hello") await g.asend("hello") Then the output is: sending: hello received hello sending: hello sending: hello received None received None |
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| msg317563 - (view) |
Author: Jan Češpivo (jan.cespivo) |
Date: 2018-05-24 11:49 |
| I've reproduced the problem also in 3.7 branch. ``` import asyncio loop = asyncio.get_event_loop() async def consumer(): while True: await asyncio.sleep(0) message = yield print('received', message) async def amain(): agenerator = consumer() await agenerator.asend(None) fa = asyncio.create_task(agenerator.asend('A')) fb = asyncio.create_task(agenerator.asend('B')) await fa await fb loop.run_until_complete(amain()) ``` Output: ``` received A received None ``` If the line `await asyncio.sleep(0)` is omitted the output is ok: ``` received A received B ``` |
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| msg317603 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2018-05-24 18:39 |
| Thanks Jan. Thanks a lot for a short script to reproduce this bug. The actual problem here is that asynchronous generators don't control their 'asend' and 'athrow' coroutines in any way. So if you have two of them iterating *in parallel* they will cause their asynchronous generator to be in an inconsistent state. The most obvious solution to this problem is to prohibit iterating 'asend'/'athrow' objects in parallel by throwing an exception. Nathaniel, what are your thoughts on this? |
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| msg317605 - (view) |
Author: Nathaniel Smith (njs) * |
Date: 2018-05-24 19:14 |
| My thoughts: https://bugs.python.org/issue32526#msg309783 |
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| msg317607 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2018-05-24 19:19 |
| Thanks, I'll look into adding ag_running properly. |
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| msg353543 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2019-09-30 05:59 |
| New changeset fc4a044a3c54ce21e9ed150f7d769fb479d34c49 by Yury Selivanov in branch 'master': bpo-30773: Fix ag_running; prohibit running athrow/asend/aclose in parallel (#7468) https://github.com/python/cpython/commit/fc4a044a3c54ce21e9ed150f7d769fb479d34c49 |
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| msg353544 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2019-09-30 06:19 |
| New changeset 2f87a7dc5a1ad7f37787f0adee242c931643f878 by Yury Selivanov (Miss Islington (bot)) in branch '3.8': bpo-30773: Fix ag_running; prohibit running athrow/asend/aclose in parallel (GH-7468) (#16486) https://github.com/python/cpython/commit/2f87a7dc5a1ad7f37787f0adee242c931643f878 |
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