49 lines
2.5 KiB
Markdown
49 lines
2.5 KiB
Markdown
 
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# CPython bug reports: asyncio.wait_for() timeout does not kill the awaited process
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## Metadata
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| Field | Value |
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| Institute | Molodetz Institute — Research & Retrieval Division |
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| Subject | async-pty-process-testing |
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| Document type | Source Dossier |
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| Tier | 1 |
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| Source title | bugs.python.org msg233486, and companion msg357930 |
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| Source URL | https://bugs.python.org/msg233486 |
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| Source publisher / author | Python core development bug tracker (bugs.python.org / BPO) |
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| Source type | other (official bug tracker message) |
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| Source date (published) | Unknown — not stated |
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| Date researched | 2026-10-09 |
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| Researched by | tai (agent), model: Claude Sonnet 5, on behalf of retoor |
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| Research method | web search synthesis |
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| Confidence | High |
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| Status | Active |
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## Summary
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Official CPython bug tracker messages confirming that `asyncio.wait_for()` timing out does not, by itself, terminate the coroutine/process it was waiting on — the awaited operation can continue running in the background after the `TimeoutError` is raised to the caller.
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## Key findings
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- A bug report describes `wait_for()` timing out while the process it was waiting on continued living in the background — the timeout only stops *waiting*, it does not reach into and stop the underlying operation.
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- This is documented as a known, discussed behavior in CPython's own bug tracker (two related messages), not a one-off misunderstanding.
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## Pros / strengths
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- Primary-source, from the language's own bug tracker — about as authoritative as a finding in this subject gets.
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- Directly actionable: it tells you precisely what `wait_for()` does *not* do for you, closing a dangerous assumption gap.
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## Cons / limitations / caveats
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- Only the two referenced messages were reviewed, not the full bug thread's eventual resolution or whether later Python versions changed this behavior.
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## Relevance to tai
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This is the specific reason `tai_test.py.TestCase.execute()` never treats a caught `asyncio.TimeoutError` (from the `asyncio.wait_for(self.run(), timeout=self.timeout)` wrapping every test) as sufficient cleanup on its own. The `finally` block unconditionally calls `await proc.terminate()` for every spawned process, precisely because this source confirms the timeout itself does nothing to stop the process — only the explicit `terminate()` call (with its own `killpg` escalation and reap) does.
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## Changelog
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| Date | Change |
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| 2026-10-09 | Initial dossier created. |
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