118 lines
4.1 KiB
Markdown
118 lines
4.1 KiB
Markdown
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---
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model: claude-opus-4-7[1m]
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service: claude
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session: subints-phase-b2-destroy-race-fix
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timestamp: 2026-04-18T04:25:26Z
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git_ref: 26fb820
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scope: code
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substantive: true
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raw_file: 20260418T042526Z_26fb820_prompt_io.raw.md
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---
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## Prompt
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Follow-up to Phase B.2 (`5cd6df58`) after the user
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observed intermittent mid-suite hangs when running
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the tractor test suite under `--spawn-backend=subint`
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on py3.14. The specific sequence of prompts over
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several turns:
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1. User pointed at the `test_context_stream_semantics.py`
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suite as the first thing to make run clean under
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`--spawn-backend=subint`.
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2. After a series of `timeout`-terminated runs that
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gave no diagnostic info, user nudged me to stop
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relying on `timeout` and get actual runtime
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diagnostics ("the suite hangs indefinitely, so i
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don't think this `timeout 30` is helping you at
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all.."). Switched to
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`faulthandler.dump_traceback_later(...)` and a
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resource-tracker fixture to rule out leaks.
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3. Captured a stack pinning the hang on
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`_interpreters.destroy(interp_id)` in the subint
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teardown finally block.
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4. Proposed dedicated-OS-thread fix. User greenlit.
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5. Implemented + verified on-worktree; user needed
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to be pointed at the *worktree*'s `./py313` venv
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because bare `pytest` was picking up the main
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repo's venv (running un-patched `_subint.py`) and
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still hanging.
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Running theme over the whole exchange: this patch
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only closes the *destroy race*. The user and I also
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traced through the deeper cancellation story — SIGINT
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can't reach subints, legacy-mode shares the GIL,
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portal-cancel dies when the IPC channel is already
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broken — and agreed the next step is a bounded
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hard-kill in `subint_proc`'s teardown plus a
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dedicated cancellation test suite. Those land as
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separate commits.
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## Response summary
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Produced the `tractor/spawn/_subint.py` patch landed
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as commit `26fb8206` ("Fix subint destroy race via
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dedicated OS thread"). One file, +110/-84 LOC.
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Mechanism: swap `trio.to_thread.run_sync(_interpreters
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.exec, ...)` for a plain `threading.Thread(target=...
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, daemon=False)`. The trio thread cache recycles
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workers — so the OS thread that ran `_interpreters
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.exec()` remained alive in the cache holding a
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stale subint tstate, blocking
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`_interpreters.destroy()` in the finally indefinitely.
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A dedicated one-shot thread exits naturally after
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the sync target returns, releasing tstate and
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unblocking destroy.
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Coordination across the trio↔thread boundary:
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- `trio.lowlevel.current_trio_token()` captured at
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`subint_proc` entry
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- driver thread signals `subint_exited.set()` back
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to parent trio via `trio.from_thread.run_sync(...,
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trio_token=token)` (synchronous from the thread's
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POV; the call returns after trio has run `.set()`)
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- `trio.RunFinishedError` swallowed in that path for
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the process-teardown case where parent trio already
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exited
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- teardown `finally` off-loads the sync
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`driver_thread.join()` via `to_thread.run_sync` (a
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cache thread carries no subint tstate — safe)
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## Files changed
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See `git diff 26fb820~1..26fb820 --stat`:
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```
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tractor/spawn/_subint.py | 194 +++++++++++++++++++------------
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1 file changed, 110 insertions(+), 84 deletions(-)
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```
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Validation:
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- `test_parent_cancels[chk_ctx_result_before_exit=True-
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cancel_method=ctx-child_returns_early=False]`
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(the specific test that was hanging for the user)
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— passed in 1.06s.
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- Full `tests/test_context_stream_semantics.py` under
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subint — 61 passed in 100.35s (clean-cache re-run:
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100.82s).
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- Trio backend regression subset — 69 passed / 1
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skipped / 89.19s — no regressions from this change.
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## Files changed
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Beyond the `_subint.py` patch, the raw log also
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records the cancellation-semantics research that
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spanned this conversation but did not ship as code
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in *this* commit. Preserving it inline under "Non-
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code output" because it directly informs the
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Phase B.3 hard-kill impl that will follow (and any
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upstream CPython bug reports we end up filing).
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## Human edits
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None — committed as generated. The commit message
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itself was also AI-drafted via `/commit-msg` and
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rewrapped via the project's `rewrap.py --width 67`
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tooling; user landed it without edits.
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