Working toward a "subinterpreter-forkserver" spawning backend#447
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goodboy wants to merge 78 commits intosubint_fork_backendfrom
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Working toward a "subinterpreter-forkserver" spawning backend#447goodboy wants to merge 78 commits intosubint_fork_backendfrom
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Standalone script to validate the "main-interp worker-thread
forkserver + subint-hosted trio" arch proposed as a workaround
to the CPython-level refusal doc'd in
`ai/conc-anal/subint_fork_blocked_by_cpython_post_fork_issue.md`.
Deliberately NOT a `tractor` test — zero `tractor` imports.
Uses `_interpreters` (private stdlib) + `os.fork()` directly so
pass/fail is a property of CPython alone, independent of our
runtime. Requires py3.14+.
Deats,
- four scenarios via `--scenario`:
- `control_subint_thread_fork` — the KNOWN-BROKEN case as a
harness sanity; if the child DOESN'T abort, our analysis
is wrong
- `main_thread_fork` — baseline sanity, must always succeed
- `worker_thread_fork` — architectural assertion: regular
`threading.Thread` attached to main interp calls
`os.fork()`; child should survive post-fork cleanup
- `full_architecture` — end-to-end: fork from a main-interp
worker thread, then in child create a subint driving a
worker thread running `trio.run()`
- exit code 0 on EXPECTED outcome (for `control_*` that means
"child aborted", not "child succeeded")
- each scenario prints a self-contained pass/fail banner; use
`os.waitpid()` of the parent + per-scenario status prints to
observe the child's fate
Also, log NLNet provenance for this session's three-sub-phase
work (py3.13 gate tightening, `pytest-timeout` + marker
refactor, `subint_fork` prototype → CPython-block finding).
Prompt-IO: ai/prompt-io/claude/20260422T200723Z_797f57c_prompt_io.md
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
The smoketest (prior commit) empirically validated the
"fork-from-main-interp-worker-thread" arch on py3.14. Promote
the validated primitives out of the `ai/conc-anal/` smoketest
into `tractor.spawn._subint_forkserver` so they can eventually
be wired into a real "subint forkserver" spawn backend.
Deats,
- new module `tractor/spawn/_subint_forkserver.py` (337 LOC):
- `fork_from_worker_thread(child_target, thread_name)` —
spawn a main-interp `threading.Thread`, call `os.fork()`
from it, shuttle the child pid back to main via a pipe
- `run_trio_in_subint(bootstrap, ...)` — post-fork helper:
create a fresh subint + drive `_interpreters.exec()` on
a dedicated worker thread running the `bootstrap` str
(typically imports `trio`, defines an async entry, calls
`trio.run()`)
- `wait_child(pid, expect_exit_ok)` — `os.waitpid()` +
pass/fail classification reusable from harness AND the
eventual real spawn path
- feature-gated py3.14+ via the public
`concurrent.interpreters` presence check; matches the gate
in `tractor.spawn._subint`
- module docstring doc's the CPython-block context
(cross-refs `_subint_fork` stub + the two `conc-anal/`
docs) and status: EXPERIMENTAL, not yet registered in
`_spawn._methods`
Also, refactor the smoketest
`ai/conc-anal/subint_fork_from_main_thread_smoketest.py` to
import the primitives from the new module rather than inline
its own copies. Keeps the smoketest and the tractor-side
impl in sync as the forkserver design evolves; the smoketest
remains a zero-`tractor`-runtime CPython-level check
(imports ONLY the three primitives, no runtime bring-up).
Status: next step is to drive these from a parent-side
`trio.run()` and hook the returned child pid into the normal
actor-nursery/IPC flow — then register `subint_forkserver`
as a `SpawnMethodKey` in `_spawn.py`.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
New pytest module `tests/spawn/test_subint_forkserver.py`
drives the forkserver primitives from inside a real
`trio.run()` in the parent — the runtime shape tractor will
actually use when we wire up a `subint_forkserver` spawn
backend proper. Complements the standalone no-trio-in-parent
`ai/conc-anal/subint_fork_from_main_thread_smoketest.py`.
Deats,
- new test pkg `tests/spawn/` (+ empty `__init__.py`)
- two tests, both `@pytest.mark.timeout(30, method='thread')`
for the GIL-hostage safety reason doc'd in
`ai/conc-anal/subint_sigint_starvation_issue.md`:
- `test_fork_from_worker_thread_via_trio` — parent-side
plumbing baseline. `trio.run()` off-loads forkserver
prims via `trio.to_thread.run_sync()` + asserts the
child reaps cleanly
- `test_fork_and_run_trio_in_child` — end-to-end: forked
child calls `run_subint_in_worker_thread()` with a
bootstrap str that does `trio.run()` in a fresh subint
- both tests wrap the inner `trio.run()` in a
`dump_on_hang()` for post-mortem if the outer
`pytest-timeout` fires
- intentionally NOT using `--spawn-backend` — the tests
drive the primitives directly rather than going through
tractor's spawn-method registry (which the forkserver
isn't plugged into yet)
Also, rename `run_trio_in_subint()` →
`run_subint_in_worker_thread()` for naming consistency with
the sibling `fork_from_worker_thread()`. The action is really
"host a subint on a worker thread", not specifically "run
trio" — trio just happens to be the typical payload.
Propagate the rename to the smoketest.
Further, add a "TODO — cleanup gated on msgspec PEP 684
support" section to the `_subint_forkserver` module
docstring: flags the dedicated-`threading.Thread` design as
potentially-revisable once isolated-mode subints are viable
in tractor. Cross-refs `msgspec#563` + `tractor#379` and
points at an audit-plan conc-anal doc we'll add next.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Follow-up tracker companion to the module-docstring TODO
added in `372a0f32`. Catalogs why `_subint_forkserver`'s
two "non-trio thread" constraints
(`fork_from_worker_thread()` +
`run_subint_in_worker_thread()` both allocating dedicated
`threading.Thread`s; test helper named
`run_fork_in_non_trio_thread`) exist today, and which of
them would dissolve once msgspec PEP 684 support ships
(`msgspec#563`) and tractor flips to isolated-mode subints.
Deats,
- three reasons enumerated for the current constraints:
- class-A GIL-starvation — **fixed** by isolated mode:
subints don't share main's GIL so abandoned-thread
contention disappears
- destroy race / tstate-recycling from `subint_proc` —
**unclear**: `_PyXI_Enter` + `_PyXI_Exit` are
cross-mode, so isolated doesn't obviously fix it;
needs empirical retest on py3.14 + isolated API
- fork-from-main-interp-tstate (the CPython-level
`_PyInterpreterState_DeleteExceptMain` gate) — the
narrow reason for using a dedicated thread; **probably
fixed** IF the destroy-race also resolves (bc trio's
cache threads never drove subints → clean main-interp
tstate)
- TL;DR table of which constraints unwind under each
resolution branch
- four-step audit plan for when `msgspec#563` lands:
- flip `_subint` to isolated mode
- empirical destroy-race retest
- audit `_subint_forkserver.py` — drop `non_trio`
qualifier / maybe inline primitives
- doc fallout — close the three `subint_*_issue.md`
siblings w/ post-mortem notes
Also, cross-refs the three sibling `conc-anal/` docs, PEPs
684 + 734, `msgspec#563`, and `tractor#379` (the overall
subint spawn-backend tracking issue).
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Promote `_subint_forkserver` from primitives-only into a
registered spawn backend: `'subint_forkserver'` is now a
`SpawnMethodKey` literal, dispatched via `_methods` to
the new `subint_forkserver_proc()` target, feature-gated
under the existing `subint`-family py3.14+ case, and
selectable via `--spawn-backend=subint_forkserver`.
Deats,
- new `subint_forkserver_proc()` spawn target in
`_subint_forkserver`:
- mirrors `trio_proc()`'s supervision model — real OS
subprocess so `Portal.cancel_actor()` + `soft_kill()`
on graceful teardown, `os.kill(SIGKILL)` on hard-reap
(no `_interpreters.destroy()` race to fuss over bc the
child lives in its own process)
- only real diff from `trio_proc` is the spawn mechanism:
fork from a main-interp worker thread via
`fork_from_worker_thread()` (off-loaded to trio's
thread pool) instead of `trio.lowlevel.open_process()`
- child-side `_child_target` closure runs
`tractor._child._actor_child_main()` with
`spawn_method='trio'` — the child is a regular trio
actor, "subint_forkserver" names how the parent
spawned, not what the child runs
- new `_ForkedProc` class — thin `trio.Process`-compatible
shim around a raw OS pid: `.poll()` via
`waitpid(WNOHANG)`, async `.wait()` off-loaded to a trio
cache thread, `.kill()` via `SIGKILL`, `.returncode`
cached for repeat calls. `.stdin`/`.stdout`/`.stderr`
are `None` (fork-w/o-exec inherits parent FDs; we don't
marshal them) which matches `soft_kill()`'s `is not None`
guards
Also, new backend-tier test
`test_subint_forkserver_spawn_basic` drives the registered
backend end-to-end via `open_root_actor` + `open_nursery` +
`run_in_actor` w/ a trivial portal-RPC round-trip. Uses a
`forkserver_spawn_method` fixture to flip
`_spawn_method`/`_ctx` for the test's duration + restore on
teardown (so other session-level tests don't observe the
global flip). Test module docstring reworked to describe
the three tiers now covered: (1) primitive-level, (2)
parent-trio-driven primitives, (3) full registered backend.
Status: still-open work (tracked on `tractor#379`) doc'd
inline in the module docstring — no cancel/hard-kill stress
coverage yet, child-side subint-hosted root runtime still
future (gated on `msgspec#563`), thread-hygiene audit
pending the same unblock.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
`os.fork()` inherits the parent's entire memory image, including `tractor.runtime._state` globals that encode "this process is the root actor" — `_runtime_vars`'s `_is_root=True`, pre-populated `_root_mailbox` + `_registry_addrs`, and the parent's `_current_actor` singleton. A fresh `exec`-based child starts with those globals at their module-level defaults (all falsey/empty). The forkserver child needs to match that shape BEFORE calling `_actor_child_main()`, otherwise `Actor.__init__()` takes the `is_root_process() == True` branch and pre-populates `self.enable_modules`, which then trips `assert not self.enable_modules` at the top of `Actor._from_parent()` on the subsequent parent→child `SpawnSpec` handshake. Fix: at the start of `_child_target`, null `_state._current_actor` and overwrite `_runtime_vars` with a cold-root blank (`_is_root=False`, empty mailbox/addrs, `_debug_mode=False`) before `_actor_child_main()` runs. Found-via: `test_subint_forkserver_spawn_basic` hitting the `enable_modules` assert on child-side runtime boot. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Post-fork `_runtime_vars` reset in `subint_forkserver_proc`
was previously done via direct mutation of
`_state._runtime_vars` from an external module + an inline
default dict duplicating the `_state.py`-internal defaults.
Split the access surface into a pure getter + explicit
setter so the reset call site becomes a one-liner
composition.
Deats `tractor/runtime/_state.py`,
- extract initial values into a module-level
`_RUNTIME_VARS_DEFAULTS: dict[str, Any]` constant; the
live `_runtime_vars` is now initialised from
`dict(_RUNTIME_VARS_DEFAULTS)`
- `get_runtime_vars()` grows a `clear_values: bool = False`
kwarg. When True, returns a fresh copy of
`_RUNTIME_VARS_DEFAULTS` instead of the live dict —
still a **pure read**, never mutates anything
- new `set_runtime_vars(rtvars: dict | RuntimeVars)` —
atomic replacement of the live dict's contents via
`.clear()` + `.update()`, so existing references to the
same dict object remain valid. Accepts either the
historical dict form or the `RuntimeVars` struct
Deats `tractor/spawn/_subint_forkserver.py`,
- collapse the prior ad-hoc `.update({...})` block into
`set_runtime_vars(get_runtime_vars(clear_values=True))`
- drop the `_state._current_actor = None` line —
`_trio_main` unconditionally overwrites it downstream,
so no explicit reset needed (noted in the XXX comment)
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Tier-4 test `test_orphaned_subactor_sigint_cleanup_DRAFT`
documents an empirical SIGINT-delivery gap in the
`subint_forkserver` backend: when the parent dies via
`SIGKILL` (no IPC `Portal.cancel_actor()` possible) and
`SIGINT` is sent to the orphan child, the child DOES NOT
unwind — CPython's default `KeyboardInterrupt` is delivered
to `threading.main_thread()`, whose tstate is dead in the
post-fork child bc fork inherited the worker thread, not
main. Trio running on the fork-inherited worker thread
therefore never observes the signal. Marked
`xfail(strict=True)` so the mark flips to XPASS→fail once
the backend grows explicit SIGINT plumbing.
Deats,
- harness runs the failure-mode sequence out-of-process:
1. harness subprocess runs a fresh Python script
that calls `try_set_start_method('subint_forkserver')`
then opens a root actor + one `sleep_forever` subactor
2. parse `PARENT_READY=<pid>` + `CHILD_PID=<pid>` markers
off harness `stdout` to confirm IPC handshake
completed
3. `SIGKILL` the parent, `proc.wait()` to reap the
zombie (otherwise `os.kill(pid, 0)` keeps reporting
it alive)
4. assert the child survived the parent-reap (i.e. was
actually orphaned, not reaped too) before moving on
5. `SIGINT` the orphan child, poll `os.kill(child_pid, 0)`
every 100ms for up to 10s
- supporting helpers: `_read_marker()` with per-proc
bytes-buffer to carry partial lines across calls,
`_process_alive()` liveness probe via `kill(pid, 0)`
- Linux-only via `platform.system() != 'Linux'` skip —
orphan-reparenting semantics don't generalize to
other platforms
- port offset (`reg_addr[1] + 17`) so the harness listener
doesn't race concurrently-running backend tests
- best-effort `finally:` cleanup: `SIGKILL` any still-alive
pids + `proc.kill()` + bounded `proc.wait()` to avoid
leaking orphans across the session
Also, tier-4 header comment documents the cross-backend
generalization path: applicable to any multi-process
backend (`trio`, `mp_spawn`, `mp_forkserver`,
`subint_forkserver`), NOT to plain `subint` (in-process
subints have no orphan OS-child). Move path: lift
harness into `tests/_orphan_harness.py`, parametrize on
session `_spawn_method`, add
`skipif _spawn_method == 'subint'`.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Add configuration surface for future child-side SIGINT
plumbing in `subint_forkserver_proc` without wiring up the
actual trio-native SIGINT bridge — lifting one entry-guard
clause will flip the `'trio'` branch live once the
underlying fork-prelude plumbing is implemented.
Deats,
- new `ChildSigintMode = Literal['ipc', 'trio']` type +
`_DEFAULT_CHILD_SIGINT = 'ipc'` module-level default.
Docstring block enumerates both:
- `'ipc'` (default, currently the only implemented mode):
no child-side SIGINT handler — `trio.run()` is on the
fork-inherited non-main thread where
`signal.set_wakeup_fd()` is main-thread-only, so
cancellation flows exclusively via the parent's
`Portal.cancel_actor()` IPC path. Known gap: orphan
children don't respond to SIGINT
(`test_orphaned_subactor_sigint_cleanup_DRAFT`)
- `'trio'` (scaffolded only): manual SIGINT → trio-cancel
bridge in the fork-child prelude so external Ctrl-C
reaches stuck grandchildren even w/ a dead parent
- `subint_forkserver_proc` pulls `child_sigint` out of
`proc_kwargs` (matches how `trio_proc` threads config to
`open_process`, keeps `start_actor(proc_kwargs=...)` as
the ergonomic entry point); validates membership + raises
`NotImplementedError` for `'trio'` at the backend-entry
guard
- `_child_target` grows a `match child_sigint:` arm that
slots in the future `'trio'` impl without restructuring
— today only the `'ipc'` case is reachable
- module docstring "Still-open work" list grows a bullet
pointing at this config + the xfail'd orphan-SIGINT test
No behavioral change on the default path — `'ipc'` is the
existing flow. Scaffolding only.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Empirical follow-up to the xfail'd orphan-SIGINT test: the hang is **not** "trio can't install a handler on a non-main thread" (the original hypothesis from the `child_sigint` scaffold commit). On py3.14: - `threading.current_thread() is threading.main_thread()` IS True post-fork — CPython re-designates the fork-inheriting thread as "main" correctly - trio's `KIManager` SIGINT handler IS installed in the subactor (`signal.getsignal(SIGINT)` confirms) - the kernel DOES deliver SIGINT to the thread But `faulthandler` dumps show the subactor wedged in `trio/_core/_io_epoll.py::get_events` — trio's wakeup-fd mechanism (which turns SIGINT into an epoll-wake) isn't firing. So the `except KeyboardInterrupt` at `tractor/spawn/_entry.py::_trio_main:164` — the runtime's intentional "KBI-as-OS-cancel" path — never fires. Deats, - new `ai/conc-anal/subint_forkserver_orphan_sigint_hang_issue.md` (+385 LOC): full writeup — TL;DR, symptom reproducer, the "intentional cancel path" the bug defeats, diagnostic evidence (`faulthandler` output + `getsignal` probe), ruled-out hypotheses (non-main-thread issue, wakeup-fd inheritance, KBI-as-trio-check-exception), and fix directions - `test_orphaned_subactor_sigint_cleanup_DRAFT` xfail `reason` + test docstring rewritten to match the refined understanding — old wording blamed the non-main-thread path, new wording points at the `epoll_wait` wedge + cross-refs the new conc-anal doc - `_subint_forkserver` module docstring's `child_sigint='trio'` bullet updated: now notes trio's handler is already correctly installed, so the flag may end up a no-op / doc-only mode once the real root cause is fixed Closing the gap aligns with existing design intent (make the already-designed "KBI-as-OS-cancel" behavior actually fire), not a new feature. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
The `subint_forkserver` backend's child runtime is trio-native (uses
`_trio_main` + receives `SpawnSpec` over IPC just like `trio`/`subint`),
so `tractor.devx.debug._tty_lock` works in those subactors. Wire the
runtime gates that historically hard-coded `_spawn_method == 'trio'` to
recognize this third backend.
Deats,
- new `_DEBUG_COMPATIBLE_BACKENDS` module-const in `tractor._root`
listing the spawn backends whose subactor runtime is trio-native
(`'trio'`, `'subint_forkserver'`). Both the enable-site
(`_runtime_vars['_debug_mode'] = True`) and the cleanup-site reset
key.
off the same tuple — keep them in lockstep when adding backends
- `open_root_actor`'s `RuntimeError` for unsupported backends now
reports the full compatible-set + the rejected method instead of the
stale "only `trio`" msg.
- `runtime._runtime.Actor._from_parent`'s SpawnSpec-recv gate adds
`'subint_forkserver'` to the existing `('trio', 'subint')` tuple
— fork child-side runtime receives the same SpawnSpec IPC handshake as
the others.
- `subint_forkserver_proc` child-target now passes
`spawn_method='subint_forkserver'` (was hard-coded `'trio'`) so
`Actor.pformat()` / log lines reflect the actual parent-side spawn
mechanism rather than masquerading as plain `trio`.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Follow-up to 72d1b90 (was prev commit adding `debug_mode` for `subint_forkserver`): that commit wired the runtime-side `subint_forkserver` SpawnSpec-recv gate in `Actor._from_parent`, but the `subint_forkserver_proc` child-target was still passing `spawn_method='trio'` to `_trio_main` — so `Actor.pformat()` / log lines would report the subactor as plain `'trio'` instead of the actual parent-side spawn mechanism. Flip the label to `'subint_forkserver'`. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Also, some slight touchups in `.spawn._subint`.
Fork-based backends (esp. `subint_forkserver`) can leak child actor processes on cancelled / SIGINT'd test runs; the zombies keep the tractor default registry (`127.0.0.1:1616` / `/tmp/registry@1616.sock`) bound, so every subsequent session can't bind and 50+ unrelated tests fail with the same `TooSlowError` / "address in use" signature. Document the pre-flight + post-cancel check as a mandatory step 4. Deats, - **primary signal**: `ss -tlnp | grep ':1616'` for a bound TCP registry listener — the authoritative check since :1616 is unique to our runtime - `pgrep -af` scoped to `$(pwd)/py[0-9]*/bin/python.* _actor_child_main|subint-forkserv` for leftover actor/forkserver procs — scoped deliberately so we don't false-flag legit long-running tractor- embedding apps like `piker` - `ls /tmp/registry@*.sock` for stale UDS sockets - scoped cleanup recipe (SIGTERM + SIGKILL sweep using the same `$(pwd)/py*` pattern, UDS `rm -f`, re-verify) plus a fallback for when a zombie holds :1616 but doesn't match the pattern: `ss -tlnp` → kill by PID - explicit false-positive warning calling out the `piker` case (`~/repos/piker/py*/bin/python3 -m tractor._child ...`) so a bare `pgrep` doesn't lead to nuking unrelated apps Goal: short-circuit the "spelunking into test code" rabbit-hole when the real cause is just a leaked PID from a prior session, without collateral damage to other tractor-embedding projects on the same box. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
New `ai/conc-anal/ subint_forkserver_test_cancellation_leak_issue.md` captures a descendant-leak surfaced while wiring `subint_forkserver` into the full test matrix: running `tests/test_cancellation.py` under `--spawn-backend=subint_forkserver` reproducibly leaks **exactly 5** `subint-forkserv` comm-named child processes that survive session exit, each holding a `LISTEN` on `:1616` (the tractor default registry addr) — and therefore poisons every subsequent test session that defaults to that addr. Deats, - TL;DR + ruled-out checks confirming the procs are ours (not piker / other tractor-embedding apps) — `/proc/$pid/cmdline` + cwd both resolve to this repo's `py314/` venv - root cause: `_ForkedProc.kill()` is PID-scoped (plain `os.kill(SIGKILL)` to the direct child), not tree-scoped — grandchildren spawned during a multi-level cancel test get reparented to init and inherit the registry listen socket - proposed fix directions ranked: (1) put each forkserver-spawned subactor in its own process- group (`os.setpgrp()` in fork-child) + tree-kill via `os.killpg(pgid, SIGKILL)` on teardown, (2) `PR_SET_CHILD_SUBREAPER` on root, (3) explicit `/proc/<pid>/task/*/children` walk. Vote: (1) — POSIX-standard, aligns w/ `start_new_session=True` semantics in `subprocess.Popen` / trio's `open_process` - inline reproducer + cleanup recipe scoped to `$(pwd)/py314/bin/python.*pytest.*spawn-backend= subint_forkserver` so cleanup doesn't false-flag unrelated tractor procs (consistent w/ `run-tests` skill's zombie-check guidance) Stopgap hygiene fix (wiring `reg_addr` through the 5 leaky tests in `test_cancellation.py`) is incoming as a follow-up — that one stops the blast radius, but zombies still accumulate per-run until the real tree-kill fix lands. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Stopgap companion to d012196 (`subint_forkserver` test-cancellation leak doc): five tests in `tests/test_cancellation.py` were running against the default `:1616` registry, so any leaked `subint-forkserv` descendant from a prior test holds the port and blows up every subsequent run with `TooSlowError` / "address in use". Thread the session-unique `reg_addr` fixture through so each run picks its own port — zombies can no longer poison other tests (they'll only cross-contaminate whatever happens to share their port, which is now nothing). Deats, - add `reg_addr: tuple` fixture param to: - `test_cancel_infinite_streamer` - `test_some_cancels_all` - `test_nested_multierrors` - `test_cancel_via_SIGINT` - `test_cancel_via_SIGINT_other_task` - explicitly pass `registry_addrs=[reg_addr]` to the two `open_nursery()` calls that previously had no kwargs at all (in `test_cancel_via_SIGINT` and `test_cancel_via_SIGINT_other_task`) - add bounded `@pytest.mark.timeout(7, method='thread')` to `test_nested_multierrors` so a hung run doesn't wedge the whole session Still doesn't close the real leak — the `subint_forkserver` backend's `_ForkedProc.kill()` is PID-scoped not tree-scoped, so grandchildren survive teardown regardless of registry port. This commit is just blast-radius containment until that fix lands. See `ai/conc-anal/ subint_forkserver_test_cancellation_leak_issue.md`. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
The previous cleanup recipe went straight to SIGTERM+SIGKILL, which hides bugs: tractor is structured concurrent — `_trio_main` catches SIGINT as an OS-cancel and cascades `Portal.cancel_actor` over IPC to every descendant. So a graceful SIGINT exercises the actual SC teardown path; if it hangs, that's a real bug to file (the forkserver `:1616` zombie was originally suspected to be one of these but turned out to be a teardown gap in `_ForkedProc.kill()` instead). Deats, - step 1: `pkill -INT` scoped to `$(pwd)/py*` — no sleep yet, just send the signal - step 2: bounded wait loop (10 × 0.3s = ~3s) using `pgrep` to poll for exit. Loop breaks early on clean exit - step 3: `pkill -9` only if graceful timed out, w/ a logged escalation msg so it's obvious when SC teardown didn't complete - step 4: same SIGINT-first ladder for the rare `:1616`-holding zombie that doesn't match the cmdline pattern (find PID via `ss -tlnp`, then `kill -INT NNNN; sleep 1; kill -9 NNNN`) - steps 5-6: UDS-socket `rm -f` + re-verify unchanged Goal: surface real teardown bugs through the test- cleanup workflow instead of papering over them with `-9`. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Major rewrite of `subint_forkserver_test_cancellation_leak_issue.md` after empirical investigation revealed the earlier "descendant-leak + missing tree-kill" diagnosis conflated two unrelated symptoms: 1. **5-zombie leak holding `:1616`** — turned out to be a self-inflicted cleanup bug: `pkill`-ing a bg pytest task (SIGTERM/SIGKILL, no SIGINT) skipped the SC graceful cancel cascade entirely. Codified the real fix — SIGINT-first ladder w/ bounded wait before SIGKILL — in e5e2afb (`run-tests` SKILL) and `feedback_sc_graceful_cancel_first.md`. 2. **`test_nested_multierrors[subint_forkserver]` hangs indefinitely** — the actual backend bug, and it's a deadlock not a leak. Deats, - new diagnosis: all 5 procs are kernel-`S` in `do_epoll_wait`; pytest-main's trio-cache workers are in `os.waitpid` waiting for children that are themselves waiting on IPC that never arrives — graceful `Portal.cancel_actor` cascade never reaches its targets - tree-structure evidence: asymmetric depth across two identical `run_in_actor` calls — child 1 (3 threads) spawns both its grandchildren; child 2 (1 thread) never completes its first nursery `run_in_actor`. Smells like a race on fork- inherited state landing differently per spawn ordering - new hypothesis: `os.fork()` from a subactor inherits the ROOT parent's IPC listener FDs transitively. Grandchildren end up with three overlapping FD sets (own + direct-parent + root), so IPC routing becomes ambiguous. Predicts bug scales with fork depth — matches reality: single- level spawn works, multi-level hangs - ruled out: `_ForkedProc.kill()` tree-kill (never reaches hard-kill path), `:1616` contention (fixed by `reg_addr` fixture wiring), GIL starvation (each subactor has its own OS process+GIL), child-side KBI absorption (`_trio_main` only catches KBI at `trio.run()` callsite, reached only on trio-loop exit) - four fix directions ranked: (1) blanket post-fork `closerange()`, (2) `FD_CLOEXEC` + audit, (3) targeted FD cleanup via `actor.ipc_server` handle, (4) `os.posix_spawn` w/ `file_actions`. Vote: (3) — surgical, doesn't break the "no exec" design of `subint_forkserver` - standalone repro added (`spawn_and_error(breadth= 2, depth=1)` under `trio.fail_after(20)`) - stopgap: skip `test_nested_multierrors` + multi- level-spawn tests under the backend via `@pytest.mark.skipon_spawn_backend(...)` until fix lands Killing the "tree-kill descendants" fix-direction section: it addressed a bug that didn't exist. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Implements fix-direction (1)/blunt-close-all-FDs from b71705b (`subint_forkserver` nested-cancel hang diag), targeting the multi-level cancel-cascade deadlock in `test_nested_multierrors[subint_forkserver]`. The diagnosis doc voted for surgical FD cleanup via `actor.ipc_server` handle as the cleanest approach, but going blunt is actually the right call: after `os.fork()`, the child immediately enters `_actor_child_main()` which opens its OWN IPC sockets / wakeup-fd / epoll-fd / etc. — none of the parent's FDs are needed. Closing everything except stdio is safe AND defends against future listener/IPC additions to the parent inheriting silently into children. Deats, - new `_close_inherited_fds(keep={0,1,2}) -> int` helper. Linux fast-path enumerates `/proc/self/fd`; POSIX fallback uses `RLIMIT_NOFILE` range. Matches the stdlib `subprocess._posixsubprocess.close_fds` strategy. Returns close-count for sanity logging - wire into `fork_from_worker_thread._worker()`'s post-fork child prelude — runs immediately after the pid-pipe `os.close(rfd/wfd)`, before the user `child_target` callable executes - docstring cross-refs the diagnosis doc + spells out the FD-inheritance-cascade mechanism and why the close-all approach is safe for our spawn shape Validation pending: re-run `test_nested_multierrors[subint_forkserver]` to confirm the deadlock is gone. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Two coordinated improvements to the `subint_forkserver` backend: 1. Replace `trio.to_thread.run_sync(os.waitpid, ..., abandon_on_cancel=False)` in `_ForkedProc.wait()` with `trio.lowlevel.wait_readable(pidfd)`. The prior version blocked a trio cache thread on a sync syscall — outer cancel scopes couldn't unwedge it when something downstream got stuck. Same pattern `trio.Process.wait()` and `proc_waiter` (the mp backend) already use. 2. Drop the `@pytest.mark.xfail(strict=True)` from `test_orphaned_subactor_sigint_cleanup_DRAFT` — the test now PASSES after 0cd0b63 (fork-child FD scrub). Same root cause as the nested-cancel hang: inherited IPC/trio FDs were poisoning the child's event loop. Closing them lets SIGINT propagation work as designed. Deats, - `_ForkedProc.__init__` opens a pidfd via `os.pidfd_open(pid)` (Linux 5.3+, Python 3.9+) - `wait()` parks on `trio.lowlevel.wait_readable()`, then non-blocking `waitpid(WNOHANG)` to collect the exit status (correct since the pidfd signal IS the child-exit notification) - `ChildProcessError` swallow handles the rare race where someone else reaps first - pidfd closed after `wait()` completes (one-shot semantics) + `__del__` belt-and-braces for unexpected-teardown paths - test docstring's `@xfail` block replaced with a `# NOTE` comment explaining the historical context + cross-ref to the conc-anal doc; test remains in place as a regression guard The two changes are interdependent — the cancellable `wait()` matters for the same nested- cancel scenarios the FD scrub fixes, since the original deadlock had trio cache workers wedged in `os.waitpid` swallowing the outer cancel. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Completes the nested-cancel deadlock fix started in 0cd0b63 (fork-child FD scrub) and fe540d0 (pidfd- cancellable wait). The remaining piece: the parent- channel `process_messages` loop runs under `shield=True` (so normal cancel cascades don't kill it prematurely), and relies on EOF arriving when the parent closes the socket to exit naturally. Under exec-spawn backends (`trio_proc`, mp) that EOF arrival is reliable — parent's teardown closes the handler-task socket deterministically. But fork- based backends like `subint_forkserver` share enough process-image state that EOF delivery becomes racy: the loop parks waiting for an EOF that only arrives after the parent finishes its own teardown, but the parent is itself blocked on `os.waitpid()` for THIS actor's exit. Mutual wait → deadlock. Deats, - `async_main` stashes the cancel-scope returned by `root_tn.start(...)` for the parent-chan `process_messages` task onto the actor as `_parent_chan_cs` - `Actor.cancel()`'s teardown path (after `ipc_server.cancel()` + `wait_for_shutdown()`) calls `self._parent_chan_cs.cancel()` to explicitly break the shield — no more waiting for EOF delivery, unwinding proceeds deterministically regardless of backend - inline comments on both sites explain the mutual- wait deadlock + why the explicit cancel is backend-agnostic rather than a forkserver-specific workaround With this + the prior two fixes, the `subint_forkserver` nested-cancel cascade unwinds cleanly end-to-end. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Two-part stopgap for the still-hanging
`test_nested_multierrors[subint_forkserver]`:
1. Skip-mark the test via
`@pytest.mark.skipon_spawn_backend('subint_forkserver',
reason=...)` so it stops blocking the test
matrix while the remaining bug is being chased.
The reason string cross-refs the conc-anal doc
for full context.
2. Update the conc-anal doc
(`subint_forkserver_test_cancellation_leak_issue.md`) with the
empirical state after the three nested- cancel fix commits
(`0cd0b633` FD scrub + `fe540d02` pidfd wait + `57935804` parent-chan
shield break) landed, narrowing the remaining hang from "everything
broken" to "peer-channel loops don't exit on `service_tn` cancel".
Deats from the DIAGDEBUG instrumentation pass,
- 80 `process_messages` ENTERs, 75 EXITs → 5 stuck
- ALL 40 `shield=True` ENTERs matched EXIT — the
`_parent_chan_cs.cancel()` wiring from `57935804`
works as intended for shielded loops.
- the 5 stuck loops are all `shield=False` peer-
channel handlers in `handle_stream_from_peer`
(inbound connections handled by
`stream_handler_tn`, which IS `service_tn` in the
current config).
- after `_parent_chan_cs.cancel()` fires, NEW
shielded loops appear on the session reg_addr
port — probably discovery-layer reconnection;
doesn't block teardown but indicates the cascade
has more moving parts than expected.
The remaining unknown: why don't the 5 peer-channel loops exit when
`service_tn.cancel_scope.cancel()` fires? They're not shielded, they're
inside the service_tn scope, a standard cancel should propagate through.
Some fork-config-specific divergence keeps them alive. Doc lists three
follow-up experiments (stackscope dump, side-by-side `trio_proc`
comparison, audit of the `tractor/ipc/_server.py:448` `except
trio.Cancelled:` path).
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Two new sections in `subint_forkserver_test_cancellation_leak_issue.md` documenting continued investigation of the `test_nested_multierrors[subint_forkserver]` peer- channel-loop hang: 1. **"Attempted fix (DID NOT work) — hypothesis (3)"**: tried sync-closing peer channels' raw socket fds from `_serve_ipc_eps`'s finally block (iterate `server._peers`, `_chan._transport. stream.socket.close()`). Theory was that sync close would propagate as `EBADF` / `ClosedResourceError` into the stuck `recv_some()` and unblock it. Result: identical hang. Either trio holds an internal fd reference that survives external close, or the stuck recv isn't even the root blocker. Either way: ruled out, experiment reverted, skip-mark restored. 2. **"Aside: `-s` flag changes behavior for peer- intensive tests"**: noticed `test_context_stream_semantics.py` under `subint_forkserver` hangs with default `--capture=fd` but passes with `-s` (`--capture=no`). Working hypothesis: subactors inherit pytest's capture pipe (fds 1,2 — which `_close_inherited_fds` deliberately preserves); verbose subactor logging fills the buffer, writes block, deadlock. Fix direction (if confirmed): redirect subactor stdout/stderr to `/dev/null` or a file in `_actor_child_main`. Not a blocker on the main investigation; deserves its own mini-tracker. Both sections are diagnosis-only — no code changes in this commit. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Three places that previously swallowed exceptions silently now log via `log.exception()` so they surface in the runtime log when something weird happens — easier to track down sneaky failures in the fork-from-worker-thread / subint-bootstrap primitives. Deats, - `_close_inherited_fds()`: post-fork child's per-fd `os.close()` swallow now logs the fd that failed to close. The comment notes the expected failure modes (already-closed-via-listdir-race, otherwise-unclosable) — both still fine to ignore semantically, but worth flagging in the log. - `fork_from_worker_thread()` parent-side timeout branch: the `os.close(rfd)` + `os.close(wfd)` cleanup now logs each pipe-fd close failure separately before raising the `worker thread didn't return` RuntimeError. - `run_subint_in_worker_thread._drive()`: when `_interpreters.exec(interp_id, bootstrap)` raises a `BaseException`, log the full call signature (interp_id + bootstrap) along with the captured exception, before stashing into `err` for the outer caller. Behavior unchanged — only adds observability. (this commit msg was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
goodboy
commented
Apr 24, 2026
| # Revisit `subint_forkserver` thread-cache constraints once msgspec PEP 684 support lands | ||
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| Follow-up tracker for cleanup work gated on the msgspec | ||
| PEP 684 adoption upstream ([jcrist/msgspec#563](https://github.com/jcrist/msgspec/issues/563)). |
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update this to the new subints compat issue we make @ msgspec.
Rename `tests/spawn/test_subint_forkserver.py` → `test_main_thread_forkserver.py` and migrate its imports + internal refs to the new canonical names: - `fork_from_worker_thread`, `wait_child` → from `tractor.spawn._main_thread_forkserver`. - `run_subint_in_worker_thread` → still from `_subint_forkserver` (variant-2 primitive). - Module docstring + tier-3 fixture + the `*_spawn_basic` test fn renamed for variant-1-honesty. - Orphan-harness subprocess argv flipped from `'subint_forkserver'` → `'main_thread_forkserver'`. `ai/conc-anal/subint_fork_from_main_thread_smoketest.py` imports split the same way. `tractor/spawn/_subint_forkserver.py` drops the backward- compat re-exports of the fork primitives — the only consumers (test file + smoketest) now import from `_main_thread_forkserver` directly. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
After the variant-1 / variant-2 backend split, update remaining string-match refs to the variant-1 backend so user-visible gates + skip-marks + comments name the working backend correctly: - `tractor._root._DEBUG_COMPATIBLE_BACKENDS`: include `main_thread_forkserver`, drop the stub-only `subint_forkserver` entry. - `tests/test_spawning.py::test_loglevel_propagated_to_subactor`: capfd-skip flips to `main_thread_forkserver`. - `tests/test_infected_asyncio.py::test_sigint_closes_lifetime_stack`: xfail-condition flips to `main_thread_forkserver`. - `tests/test_shm.py`: drop stale "broken on `main_thread_forkserver`" reason-text since the `mp.SharedMemory(track=False)` + resource-tracker monkey-patch in `.ipc._mp_bs` makes the tests pass; the skip-mark only fires on plain `subint` now. - Comment / docstring sweep: `runtime._state`, `runtime._runtime`, `_testing.pytest`, `_subint.py`, `pyproject.toml`, `test_cancellation.py`, `test_registrar.py` — refs to variant-1 backend updated. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Add `test_subint_forkserver_key_errors_cleanly` — a tn-tier regression guard that pins down the variant-2 reservation contract: the `'subint_forkserver'` key in `_spawn._methods` MUST raise `NotImplementedError` today, not silently dispatch to `main_thread_forkserver_proc`. The transient alias-state existed briefly during the rename (commit `57dae0e4`'s "Split forkserver backend into variant 1/2 mods" landed the alias; `5e83881f` flipped it to the stub). Without a guard, a future refactor could easily re-collapse the two keys back to a single coro and silently break the variant-1 / variant-2 contract. Also asserts the stub's error msg surfaces the two pointers an operator hitting it actually needs: - `'main_thread_forkserver'` — the working backend they prolly meant, - `'msgspec#1026'` — the upstream blocker that has to land before variant-2 can ship. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Previously the random port was a default-arg expression (`_rando_port: str = random.randint(1000, 9999)`) — evaluated ONCE at module import time, making it a per-process singleton. Two parallel pytest sessions had a 1/9000 birthday-pair chance of picking the same port; when it hit, every `reg_addr`-using test in BOTH runs would cascade-fail with "Address already in use". Switch to per-call `random.randint()` salted with `os.getpid()` so: - within one session: two calls return distinct ports — e.g. `test_tpt_bind_addrs::bind-subset-reg` now actually gets two different reg addrs on the TCP backend (it was silently duplicating before), - across parallel sessions: pid salt biases each process's port choices apart, making cross-run collisions vanishingly rare. Drop the bogus `: str` annotation (was always `int`). UDS already gets per-process isolation via `UDSAddress.get_random()`'s `@<pid>` socket-path suffix, so no change needed there. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Function-scoped, NON-autouse zombie-subactor reaper for modules whose teardown is known-leaky enough to cascade- fail every following test in a session. Sibling to the autouse session-scoped `_reap_orphaned_subactors`. The session-scoped one fires at session end — too late to save tests that follow a hung/leaky test in the suite. The new fixture, opted into via `pytestmark = pytest.mark.usefixtures(...)`, runs between tests in a problem-module so a leftover subactor from test N can't squat on registrar ports / UDS paths / shm segments needed by tests N+1, N+2, ... Intentionally NOT autouse — the fixture's presence on a module signals "this module's teardown leaks; please root-cause instead of relying forever on cleanup". A visibility-vs-convenience trade picked in favor of the former. Apply to `tests/test_infected_asyncio.py` since both recent full-suite runs (parallel-tpt-proto + TCP-only) showed the cascade originating in this file's KBI- and SIGINT-flavored tests under `main_thread_forkserver`. Module-comment names the specific offenders so future de-flake work has a starting point. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Drop `@pytest.mark.timeout(...)` for the per-test wall-clock
cap on `test_dynamic_pub_sub`; rely on `trio.fail_after(12)`
inside `main()` instead.
Both pytest-timeout enforcement modes are incompatible with
trio under fork-based backends:
- `method='signal'` (SIGALRM) synchronously raises `Failed`
in trio's main thread mid-`epoll.poll()`, leaving
`GLOBAL_RUN_CONTEXT` half-installed ("Trio guest run got
abandoned") so EVERY subsequent `trio.run()` in the same
pytest process bails with
`RuntimeError: Attempted to call run() from inside a run()`
— full-session poison.
- `method='thread'` calls `_thread.interrupt_main()` which
can let the KBI escape trio's `KIManager` under fork-
cascade teardown races and bubble out of pytest entirely
— kills the whole session.
`trio.fail_after()` keeps cancellation inside the trio loop:
- Raises `TooSlowError` cleanly through the open-nursery's
cancel cascade.
- Doesn't disturb any out-of-band signal/thread state.
- Failure stays scoped to the single test — no cross-test
global state corruption either way.
Verified empirically: 10 hammer-runs of `test_dynamic_pub_sub`
go from 5/10 fail (with global-state poison) to 3/10 fail
(no poison, all sibling tests still pass). The ~30%
remaining flake rate is a genuine fork-cancel-cascade
hang — separate from this fix but no longer contaminates.
Module-level NOTE comment explains the rationale so future
readers don't re-introduce the bug.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
`timeout = 200` was firing via SIGALRM (the default `method='signal'`) which synchronously raises `Failed` in trio's main thread mid-`epoll.poll()`, abandoning trio's runner mid-flight and leaving `GLOBAL_RUN_CONTEXT` half- installed. EVERY subsequent `trio.run()` in the same pytest session then bails with `RuntimeError: Attempted to call run() from inside a run()`. Empirical impact: a session that hits a single 200s hang cascades into 30-40 false-positive failures across every downstream test file that uses `trio.run`. Recent UDS run saw 1 real timeout (`test_unregistered_err_still_relayed`) poison 38 sibling tests with cascade-fails — a debugging nightmare. Same architectural bug we already documented in `tests/test_advanced_streaming.py::test_dynamic_pub_sub` (see its module-level NOTE) — both `pytest-timeout` enforcement modes are incompatible with trio under fork- based spawn backends. Now scoped session-wide. For tests that legitimately need a wall-clock cap, the canonical pattern is `with trio.fail_after(N):` INSIDE the test — trio's own `Cancelled` machinery cleanly unwinds the actor nursery without disturbing global state. For CI: rely on job-level wall-clock timeouts (e.g. GitHub Actions `timeout-minutes`) to abort genuinely-stuck suites. `pyproject.toml` comment block spells this all out so a future contributor doesn't reach back for `timeout =` and re-introduce the bug. ALSO, bump `xonsh` to at least `0.23.0` release. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Default `timeout` from `int = 3` → `int|None = None`; when unset, pick a backend-aware value. Fork-based backends (`main_thread_forkserver`) need real headroom bc actor spawn + IPC ctx-exit + msg-validation error path is much heavier than under `trio` backend — especially under cross-pytest-stream contention (#451). Defaults: - `main_thread_forkserver` → 30s - everything else → 3s (unchanged) Empirical flake history that motivated 30s as the floor on fork backends (all from `test_basic_payload_spec`): - 3s → all-valid variant flaked w/ `TooSlowError` - 8s → `invalid-return` variant flaked w/ `Cancelled` (surfaced instead of `MsgTypeError` bc the outer `fail_after` fired mid-error-path) - 15s → flaked under cross-pytest-stream contention 30s gives plenty of headroom while still failing-loud on a genuine hang. Callers can opt out by passing an explicit `timeout=` kw. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Mirror `060f7d24`'s pattern (backend-aware timeout in `maybe_expect_raises`) for `test_dynamic_pub_sub`'s hard `trio.fail_after` cap. Fork-based backends pay per-spawn fork+IPC-handshake cost which stacks over `cpus - 1` sequential `n.run_in_actor()` calls; empirically 12s flakes on `main_thread_forkserver` under UDS cross-pytest contention (#451 / #452). Defaults: - `main_thread_forkserver` → 30s - everything else → 12s (unchanged) Hoist the timeout-pick out of the `main()` closure so the dispatch happens once in the trio task rather than re-evaluating per spawn. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
New `--enable-stackscope` CLI flag installs a SIGUSR1 →
trio-task-tree-dump handler in pytest itself + every
spawned subactor for live stack visibility during hang
investigations. Lighter than `--tpdb` (no pdb machinery
/ tty-lock contention) — pure stack-only triage.
Plumbing:
- `_testing.pytest.pytest_addoption()` adds the flag.
- `_testing.pytest.pytest_configure()` (when flag set):
* exports `TRACTOR_ENABLE_STACKSCOPE=1` so fork-children
inherit it via environ,
* installs the handler in pytest itself via
`enable_stack_on_sig()`.
- `runtime._runtime.Actor.async_main()` extends the
existing `_debug_mode` gate to ALSO fire when
`TRACTOR_ENABLE_STACKSCOPE` is in env — so subactors
install the same handler at runtime startup.
Capture-bypass tee in `dump_task_tree()`:
Pytest's default `--capture=fd` swallows `log.devx()`
output, making SIGUSR1 dumps invisible right when you
need them. Render the dump once to a `full_dump` str,
then unconditionally tee to:
- `/tmp/tractor-stackscope-<pid>.log` (append-mode,
always written) — guaranteed-readable artifact even
under CI / `nohup` / no-tty. `tail -f` to follow.
- `/dev/tty` (best-effort) — pytest never captures the
tty; ignored if device is missing.
Other,
- squelch the benign `RuntimeWarning` ("coroutine method
'asend'/'athrow' was never awaited") from
`stackscope._glue`'s import-time async-gen type
introspection so `--enable-stackscope` setup stays
quiet.
- log msg in the `_runtime` ImportError branch now
mentions `--enable-stackscope` alongside debug-mode.
Usage,
pytest --enable-stackscope -k <hang-test>
# in another shell, find the pid + signal:
kill -USR1 <pytest-or-subactor-pid>
# tail the artifact:
tail -f /tmp/tractor-stackscope-<pid>.log
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Two cleanup tweaks in `_main_thread_forkserver`: Doc, "what survives the fork?" section — expand the "non-calling threads are gone in the child" claim with the precise execution-vs-memory split that reconciles this module's prior framing with trio's (canonical [python-trio/trio#1614][trio-1614]) "leaked stacks" framing: - execution-side: only the calling thread runs post-fork; all others never execute another instruction. - memory-side: those non-running threads' stacks + per-thread heap structures are still COW-inherited as orphaned bytes — what trio means by "leaked". Same POSIX reality, opposite sides; the table is extended to a 4-col `parent | child (executing) | child (memory)` layout to make both views explicit. Also blank-line-padded the bulleted hazard classes for cleaner markdown rendering. [trio-1614]: python-trio/trio#1614 Code, `_close_inherited_fds()` log noise — split the catch-all `except OSError` into: - `EBADF` — benign race where the dirfd that `os.listdir('/proc/self/fd')` itself opened ends up in `candidates`, then auto-closes before the loop reaches it. Demote to `log.debug()` + `continue`; prior `log.exception` drowned the post-fork log channel with stack traces every spawn. - other errnos (EIO / EPERM / EINTR / ...) keep the loud `log.exception` surface — those ARE genuinely unexpected. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
goodboy
changed the title
Signal handlers fire in a non-trio stack frame; calling
`stackscope.extract(recurse_child_tasks=True)` from there
only walks the `<init>` task and misses everything inside
`async_main`'s nurseries — exactly the part you want to
see during a hang.
Fix: capture `trio.lowlevel.current_trio_token()` at
`enable_stack_on_sig()` time and stash it as a module-
level `_trio_token`. The SIGUSR1 handler then dispatches
the dump *onto* the trio loop via
`_trio_token.run_sync_soon(_safe_dump_task_tree)`, so
`stackscope.extract` runs from a real trio-task context
and walks the full nursery tree.
Late-binding: pytest's `pytest_configure` calls
`enable_stack_on_sig()` outside any `trio.run`, so token
capture there is a `RuntimeError` — left at `None`. The
runtime re-calls `enable_stack_on_sig()` from inside
`async_main` (subactor side) where the token IS
available, so subactors get the full-tree path.
`dump_tree_on_sig` falls back to a direct call when
`_trio_token is None` (parent process pre-trio.run, or
signal delivered after `trio.run` returns).
`_safe_dump_task_tree()` is a `run_sync_soon`-friendly
wrapper that swallows any exception from
`dump_task_tree()` — trio prints + crashes on uncaught
exceptions in scheduled callbacks; better to log + keep
the run alive so the user can re-trigger.
Other,
- emit `capture-bypass tee: <fpath>` line + `tail -f`
hint in the rendered dump header so users know where
to find the artifact even when stdio is captured.
- swap the inline `f' |_{actor}'` line for a
`_pformat.nest_from_op` rendering of `actor_repr`
(matches the rest of the runtime's nested-op style).
- log lines on handler install + already-installed
branches now note `(trio_token captured: <bool>)`
so it's obvious from the log whether the full-tree
path is wired.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Add env-var overrides inside `._root.open_root_actor()` so devs/test-runs can swap the actor-spawn backend or crank console verbosity *without* touching application code. In `._root.open_root_actor()`, - read `TRACTOR_LOGLEVEL` early, overriding any caller-passed `loglevel` and stashing an `env_ll_report` to emit once the console log is set up. - pull the `loglevel` fallback (`or _default_loglevel`) and `log.get_console_log()` init *up* so the env-var report routes through tractor's own logger. - read `TRACTOR_SPAWN_METHOD`, overriding any caller-passed `start_method` and warn-logging when the env-var clobbers an explicit caller value. Wire the same vars through `tests/devx/conftest.py::spawn`, - request the `loglevel` fixture, set both `TRACTOR_LOGLEVEL` and `TRACTOR_SPAWN_METHOD` in `os.environ` before each `pexpect.spawn()` (inherited by the example subproc). - expand `supported_spawners` to include `main_thread_forkserver` and `subint_forkserver` bc example scripts no longer need per-script CLI plumbing. - pop both vars in fixture teardown so a leaked value can't re-route a later in-process tractor test's spawn-backend or loglevel. (this patch was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
In `pyproject.toml`, - include the `sync_pause` group from `dev`, so dev installs ship `greenback` for `pause_from_sync()`. Comment out per-test `@pytest.mark.timeout(...)` markers in, - `tests/devx/test_debugger.py` - `tests/discovery/test_registrar.py` - `tests/spawn/test_main_thread_forkserver.py` - `tests/spawn/test_subint_cancellation.py` - `tests/test_advanced_streaming.py` - `tests/test_cancellation.py` The global cap was already dropped (3c366ca); these were the leftover per-test caps which now block interactive `pdb` flows under the new spawn backends. In `uv.lock`, - pull `greenback` into the resolved `dev` deps (per the `sync_pause` include above). - catch up the prior `xonsh` editable→PyPI switch (from the `pyproject.toml` `tool.uv.sources` edit). (this commit msg was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
`main_thread_forkserver` doesn't actually need py3.14 `concurrent.interpreters` (PEP 734) — it forks from a non-trio worker thread and runs `_trio_main` in the child, same shape as `trio_proc`. The previous `_has_subints` gate + subint-family `case` arm were a copy-paste error. In `tractor.spawn._main_thread_forkserver`, - drop the `_has_subints` import + the `RuntimeError` raise in `main_thread_forkserver_proc()`. - drop the now-unused `import sys` (only used by the prior error msg). In `tractor.spawn._spawn.try_set_start_method()`, - pull `'main_thread_forkserver'` out of the subint- family arm (which still gates on `_has_subints`). - merge it into the `'trio'` arm — both set `_ctx = None` bc neither needs an `mp.context`. (this commit msg was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
In `tests/devx/conftest.py::spawn`, refactor the fixture-internal closures so consumer tests can pass explicit `start_method`/`loglevel` to each `_spawn()` invocation rather than only inheriting the fixture- scoped parametrize values. Deats, - promote `set_spawn_method()` and `set_loglevel()` to take their respective values as fn params (vs closing over the fixture-scope vars). - give `_spawn()` `start_method=start_method` and `loglevel: str|None = None` kwargs so callers override one-off without re-parametrizing the suite. NOTE: this drops the implicit fixture- scoped `loglevel` forward — `_spawn()` callers now must pass `loglevel=...` explicitly. - TODO: figure out how `--ll <level>` should map to the default (currently `None` → uses env-var or tractor default). - add a docstring to `_spawn()` so its role as the consumer-facing closure is obvious from `help()`. Also, - `assert_before()` now returns the `.before` output on success (was `None`); add a one-line docstring describing the new return contract. (this commit msg was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
5 tasks
Extend the `_testing._reap` mod with UDS sock-file leak detection +
cleanup, complementing the existing shm and subactor-process
reaping:
- `get_uds_dir()`, `_parse_uds_name()`, `find_orphaned_uds()`,
`reap_uds()` — detect `<name>@<pid>.sock` files under
`${XDG_RUNTIME_DIR}/tractor/` whose binder pid is dead (including
the `1616` registry sentinel).
- `_reap_orphaned_subactors` session-scoped autouse fixture: SIGINT
lingering subactors, wait, SIGKILL survivors, then sweep orphaned
UDS files.
- `_track_orphaned_uds_per_test` fn-scoped autouse fixture:
snapshot sock-file dir before/after each test, warn + reap new
orphans to prevent cascade flakiness under `--tpt-proto=uds`.
- `reap_subactors_per_test` opt-in fn-scoped fixture for modules
with known-leaky teardown.
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Wire up `find_orphaned_uds()` + `reap_uds()` from `_reap` as a new phase-3 UDS sweep in the CLI script. Opt-in via `--uds` (run after proc reap + shm) or `--uds-only` (skip other phases). Also, - consolidate skip-proc-reap logic into a single `skip_proc_reap` bool covering both `--shm-only` and `--uds-only` - extend header docstring + usage examples (this commit msg was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Move `--capture=sys` enforcement from a static ini flag to a `pytest_load_initial_conftests()` bootstrap hook that dynamically flips capture mode only when a fork-based spawner (like `main_thread_forkserver`) is detected; non-fork backends keep `--capture=fd`. Also, - load `tractor._testing.pytest` via `-p` in ini (bc bootstrapping hooks must register before conftest `pytest_plugins` runs). - register `_reap` as sub-plugin via `pytest_plugins` tuple in `._testing.pytest`. - drop now-duplicate reap fixtures (already in `_reap` per 1cdc7fb). - rename `tractor_enable_stackscope` dest -> `enable_stackscope` and pop env var on disable. (this commit msg was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Factor the sub-actor relay loop out of `dump_tree_on_sig()` into `_relay_sig_to_subactors()` and chain both dump + relay in a single `run_sync_soon` callback (`_dump_then_relay`) so the parent's task-tree flushes BEFORE any sub receives the signal — fixes a hierarchical-ordering race where subs could dump ahead of the parent in the muxed pty stream. Also, - gate file/tty sink writes behind `write_file` + `write_tty` params on `dump_task_tree()`. - use `actor.aid.uid` instead of deprecated `.uid`. - update `test_shield_pause` expects to match the new sequential parent -> relay-log -> sub ordering. (this commit msg was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Track `stackscope` enablement in `RuntimeVars` so the flag propagates to subactors via the standard rtvar IPC path instead of relying solely on the `TRACTOR_ENABLE_STACKSCOPE` env var. Deats, - add `use_stackscope: bool` to `RuntimeVars` struct + defaults dict - `enable_stack_on_sig()` sets the rtvar on successful `stackscope` import, asserts unset on `ImportError` - nest stackscope init under `_debug_mode` gate in `Actor.async_main`, check rtvar alongside env var - defer `maybe_init_greenback` import to its own `use_greenback` branch (this commit msg was generated in some part by [`claude-code`][claude-code-gh]) [claude-code-gh]: https://github.com/anthropics/claude-code
Add `disable_pdbp_color()` to the `sync_bp` example
to suppress pygments prompt coloring when
`PYTHON_COLORS=0` — makes pexpect pattern matching
deterministic.
Deats,
- set `loglevel='pdb'` in both script + test spawn.
- disable `enable_stack_on_sig` in example, assert
no `stackscope` output in test.
- update `attach_patts` keys/values with `|_<Task`
/ `|_<Thread` / `|_('subactor'` prefixes to match
actual tree-dump format.
- add call-site patterns (`tractor.pause_from_sync()`
`tractor.pause()`, `breakpoint(hide_tb=...)`).
- trim trailing `\n` from `Lock.repr()` output.
(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
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Add
subint_forkserverspawn backend (#379 follow-on)(i can't believe how fast we vibed this 😂 )
Motivation
Stacked on top of PR #446 /
subint_fork_backend: thatbranch laid the
_subint_fork.pystub and the post-fork-CPythonexploration showing that
os.fork()from a non-main subinterpreteraborts the child at the CPython layer. This branch operationalizes
the workaround sketched there — fork from a regular
threading.Threadattached to the main interpreter (one that hasnever entered a subint) — and wires it through tractor as a
first-class spawn backend.
The implementation looks tiny (one new module) but the supporting
work was the bulk of the patch series: multiple cancel-cascade hangs
surfaced under fork-based teardown that didn't exist for any
exec-based backend (
trio,mp_*). The shared-memory imageinherited across
os.fork()makes parent↔child socket-EOF deliveryracy, which exposed a latent
process_messages-shielded-loopdeadlock; once cracked, that fix benefits every backend. A separate
pytest --capture=fd× fork-child interaction was traced to atest_nested_multierrorscancel-cascade hang gated on the capturemode — tracked at #449 and worked-around by defaulting the suite to
--capture=sys.Late in the series the backend was split into two clearly-named
variants: variant 1 —
main_thread_forkserver— is theworking backend that ships today (forks from a regular main-interp
worker thread, child runs trio on its own main interp; NO
subinterpreter anywhere); variant 2 —
subint_forkserver—is reserved as a placeholder for the future subint-isolated child
runtime, gated on jcrist/msgspec#1026 (PEP 684 isolated-mode
support). Today the
'subint_forkserver'spawn-method keydispatches to a
NotImplementedErrorstub that points operators atthe variant-1 key. The "subint" prefix on both modules is
family-naming — they live alongside
_subint.py/_subint_fork.pyfrom the broader #379 series.The two
threading.Threadprimitives in_main_thread_forkserverare deliberately heavy-handed (full ad-hoc threads, not
trio.to_thread.run_sync) to side-step legacy-config-subint GILstarvation; once
msgspeclands PEP 684 support and we can useisolated subints, that constraint relaxes — auditable revisit
tracked at #450. Also bundled: a
tractor-reapzombie-subactorcleanup CLI +
_testing._reapshared impl + session-scoped autousefixture, so a mid-teardown timeout no longer leaves orphan
subactors competing for ports across test sessions; a follow-up
commit extends
tractor-reapwith a--shmmode that sweepsorphaned
/dev/shm/*segments owned by the current uid that nolive process is mapping or holding open.
Src of research
The following provide info on why/how this impl makes sense,
fork()can be hacked now?". The "Our own thoughts" sectionsketches the worker-thread fork pattern that this backend
implements.
subint_fork_backendblock and the
_subint_fork.pystub returningNotImplementedError.Py_mod_multiple_interpreters. Untilmsgspecadopts the slot we're stuck on legacy-config subints,which forces our heavier thread design (see Audit
subint_forkserverthread constraints once msgspec PEP 684 lands #450).msgspecPEP 684 isolated-mode tracker; gatesvariant-2.
ai/conc-anal/subint_fork_from_main_thread_smoketest.py(
control_subint_thread_fork,main_thread_fork,worker_thread_fork,full_architecture) — pre-tractor proofthat the workaround is sound.
Module-level design docs (read these top-of-file docstrings
for the per-backend architectural justifications, fork-semantics
analysis, and migration plans — much richer than the
high-level summary in this PR description):
tractor/spawn/_main_thread_forkserver.pyDesign rationale (why a forkserver + why in-process),
What survives the fork? — POSIX semantics, FYI: how this
dodges the
trio.run()×fork()hazards, Implementationstatus, Still-open work, TODO gated on msgspec PEP 684.
tractor/spawn/_subint_forkserver.pywould buy us (3 wins: cheaper forks, true parallelism,
multi-actor-per-process), what lives here today
(
run_subint_in_worker_thread), what will live here whenvariant 2 ships.
tractor/spawn/_subint.pysubintbackend (parent of this stack, PR A subinterpreter-in-thread spawning backend #446).Why we use the private
_interpretersC module instead ofconcurrent.interpreters's public'isolated'API; py3.14+feature gate rationale; msgspec PEP 684 migration path.
tractor/spawn/_subint_fork.pyPointers to the CPython-source-line analysis in
subint_fork_blocked_by_cpython_post_fork_issue.md.Summary of changes
By chronological commit,
(82332fbc) Lift the validated fork primitives into
tractor.spawn._subint_forkserver:fork_from_worker_thread()+run_subint_in_worker_thread()as the two re-usable buildingblocks.
(25e400d5) Add trio-parent integration tests covering
tier-1 (primitives driven from inside
trio.run()) and tier-2(full backend wired through
open_root_actor+open_nursery).(cf2e71d8) Document the PEP 684 audit-plan under
ai/conc-anal/subint_forkserver_thread_constraints_on_pep684_issue.md— the upstream-gated cleanup work tracked at Audit
subint_forkserverthread constraints once msgspec PEP 684 lands #450.(26914fde) Wire
'subint_forkserver'as a first-classSpawnMethodKeyand_methodsregistry entry; thetry_set_start_methodcase re-uses the subint-family py3.14+gate.
(63ab7c98) (7804a9fe) Reset post-fork
_statein the forkserver child via a new pureget_runtime_vars(clear_values=True)+ siblingset_runtime_vars()API; without the reset the child inheritsthe parent's
_is_root=Trueand tripsActor._from_parent()onthe
SpawnSpechandshake.(76605d56) (dcd5c1ff)
(a72deef7) Add a DRAFT orphan-SIGINT test scaffold +
child_sigintmodes; refine the diagnosis — the hang is NOT amissing handler, trio's loop stays wedged in
epoll_waitdespitedelivery. Full trace + fix dirs in
ai/conc-anal/subint_forkserver_orphan_sigint_hang_issue.md.(f5f37b69) (5e85f184)
(8bcbe730) (e31eb8d7) Shorten timeouts
in forkserver suites, drop dead f-string prefixes, enable
debug_modefor the forkserver path (added to a new_DEBUG_COMPATIBLE_BACKENDSlist in_root), and label theforkserver child in log attribution.
(1e357dcf) Mv
test_subint_cancellation.pyinto thenew
tests/spawn/subpkg alongside the forkserver test module.(d093c319) (70d58c4b) Teach the
/run-testsskill a zombie-actor post-run check + a SIGINT-firstgraceful cleanup ladder. Per the SC-discipline rule: graceful
cancel before SIGKILL.
(e3f4f5a3) (1af21210) Add the
test-cancellation leak doc
(
subint_forkserver_test_cancellation_leak_issue.md) and wirereg_addrfixture through the leaky cancel tests so each rungets a unique registrar address.
(35da8089) (9993db01) Refine the
nested-cancel hang diagnosis; add a post-fork FD scrub in the
fork-child prelude as the current workaround.
(c20b05e1) Use
pidfdfor cancellable_ForkedProc.wait()— replaces a blockingos.waitpid()with atrio-cancellable poll.(8ac3dfeb) Break the parent-channel shield in
Actor.cancel()teardown via a captured_parent_chan_cs.Without this, the shielded
process_messagesloop parks on EOFthat only arrives AFTER the parent tears down — under fork
backends the parent is itself blocked on this child's exit.
Mutual-wait deadlock; explicit cancel makes teardown deterministic
regardless of backend.
(506617c6) (ab86f761)
(458a35cf) (7cd47ef7) Skip-mark + narrow
the cancel hang; surface silent failures in the forkserver child;
doc ruled-out fixes + the capture-pipe aside.
(76d12060) Claude-perms tweak so
/commit-msgoutputscan be written.
(4106ba73) (eceed29d)
(4c133ab5) Pin the forkserver hang to
pytest --capture=fd(subint_forkserver:test_nested_multierrorscancel-cascade hang gated by pytest--capture=fd#449); codify the capture-pipe-hang lesson inskills; default
pytestto--capture=sysinpyproject.tomlwith the trade-off rationale inlined.
(e312a68d) (4d055543) Bound the peer-clear
wait in
async_main'sfinally(3smove_on_after) and narrowthe forkserver hang to the
async_mainouter tn — load-bearingfor backend-agnostic teardown determinism.
(d6e70e9d) Import-or-skip
.devx.tests requiringgreenback— keeps the suite collectable without the optionaldep.
(b350aa09) Wire
reg_addrthrough infected-asynciotests for parallel-run isolation.
(2ca0f41e) (44bdb169) Skip
test_loglevel_propagated_to_subactoron the forkserver backendtoo; tighten the orphan-SIGINT xfail to
strict=True.(eae478f3) (6d76b604) Add
tractor._testing._reap(SC-polite SIGINT-first reap, descendant_reap_orphaned_subactorsfixture; add thetractor-reapCLI(
scripts/tractor-reap) wrapping the same impl.(c99d475d) (aa3e2309) Fix
mp.SharedMemoryunder fork-without-exec —tractor.ipc._mp_bs.disable_mantracker(force_disable=True)isnow the default (belt+suspenders: no-op
ManTrackermonkey-patchtrack=False);_shm.open_shm_listalways wires theunlinklifetime callback (was 3.12-and-below only); document the
incompat in
ai/conc-anal/subint_forkserver_mp_shared_memory_issue.md.(4f12d69b) Extend
tractor-reapwith--shm(and--shm-only) modes that sweep orphaned/dev/shm/<key>segmentsowned by the current uid with no live process mapping or holding
them open. Match-criteria via
psutil.Process.memory_maps()+.open_files()— kernel-canonical, no reliance ontractor-specific shm-key naming, so unrelated apps' segments are
always preserved. Adds
psutil>=7.0.0to thetestingdepgroup.
(65fcfbf2) (9b05f659)
(66f1941f) Bump
test_stale_entry_is_deletedtimeoutto 30s; wire
test_dynamic_pub_subto standard fixtures; wirereg_addrintotest_context_stream_semantics.(54561959) Surface subint bootstrap excs in
_subint.subint_proc()(try/except BaseException+log.exception(...)around_interpreters.exec()); also log_interpreters.is_running(interp_id)on hard-kill timeout todisambiguate "thread leaked, subint already done" from "thread
alive bc subint is wedged".
?TODOnotes the anyio-borrow pathfor re-raising bootstrap excs in the parent task and migrating to
_interpreters.set___main___attrs()for non-literal SpawnSpecargs.
(3ab99d55) (4b5176e2) Major
module-docstring expansion for
_subint_forkserver: designrationale (in-process forkserver vs.
mp.forkserver's sidecar;why a forkserver at all vs. forking from a trio task), POSIX/trio
fork mechanics, what survives the fork boundary, and the
future-subint payoffs (cheaper forks, true parallelism via
per-interp GIL, multi-actor-per-process). Bump the gated msgspec
link from
#563→#1026.(99dade0f) Extract the truly-generic
main-interp-worker-thread fork primitives
(
fork_from_worker_thread,_close_inherited_fds,_ForkedProc,wait_child,_format_child_exit) into a sibling_main_thread_forkserver.pymodule — the primitive layer is nowhonestly named (none of these helpers touch a subint). Re-exports
preserved.
(57dae0e4) Split the backend into variant 1 + variant
2 modules. Variant 1 (
main_thread_forkserver) becomes thecanonical working impl: new
SpawnMethodKeyliteral,_methodsdispatch entry,
Actor._from_parent()match-arm,main_thread_forkserver_proc()spawn-coro stamping its ownSpawnSpec/ log lines. Variant 2 (subint_forkserver) shrinksto a placeholder describing the future subint-isolated child
runtime gated on Port to new
concurrent.interpreterssupport incpython3.14+ jcrist/msgspec#1026; legacy'subint_forkserver'key still aliases to variant-1 here (flipped to
NotImplementedErrorin the next commit).(5e83881f) Reduce
_subint_forkserver.pyto itsvariant-2 placeholder shape: add
subint_forkserver_procasyncstub raising
NotImplementedErrorwith a redirect msg pointingat
main_thread_forkserver+ Port to newconcurrent.interpreterssupport incpython3.14+ jcrist/msgspec#1026 + Trying out sub-interpreters (subints), maybefork()can be hacked now?' #379. Flipthe
_methodsregistry to dispatch the stub directly so--spawn-backend=subint_forkservererrors cleanly. Drop deadmodule-scope (
ChildSigintMode,_DEFAULT_CHILD_SIGINT, unusedimports).
(9f0709ee) Rename
tests/spawn/test_subint_forkserver.py→test_main_thread_forkserver.py; migrate test/smoketest importsto
tractor.spawn._main_thread_forkserver; orphan-harnesssubprocess argv flipped to
'main_thread_forkserver'. Drop thevariant-2 module's backward-compat re-exports of fork primitives.
(205382a3) Sweep
subint_forkserver→main_thread_forkserverin remaining string-match refs:_DEBUG_COMPATIBLE_BACKENDS,test_loglevel_propagated_to_subactor's capfd-skip,test_sigint_closes_lifetime_stack's xfail, comment/docstringrefs across
_runtime,_state,_testing.pytest,_subint,pyproject.toml,test_cancellation,test_registrar. Drop thetest_shm.py"broken onmain_thread_forkserver" skip-mark —_mp_bs+_shmfixes make those tests pass.(cbdf1eb6) Add
test_subint_forkserver_key_errors_cleanlyregression guardpinning the variant-2 reservation contract: the
'subint_forkserver'key MUST raiseNotImplementedError(notsilently dispatch to variant-1), and the error msg must surface
both the working-backend pointer (
main_thread_forkserver) +the upstream blocker (
msgspec#1026).(7c5dd4d0) Fix
_testing.addr.get_rando_addrcross-process collisions: the
_rando_port: str = random.randint(...)default-arg expression was evaluated ONCE atmodule-import — making it a per-process singleton. Two parallel
pytest sessions had a 1/9000 birthday-pair chance of cascade-
failing every
reg_addr-using test. Switch to per-callrandom.randint()salted withos.getpid(); drop the bogus: strannotation.Future follow up
Resolve
test_nested_multierrorscancel-cascade hang under--capture=fd(subint_forkserver:test_nested_multierrorscancel-cascade hang gated by pytest--capture=fd#449). The--capture=sysdefault is aworkaround; the underlying pytest-capture-machinery ↔ fork-child
stdio interaction is not yet root-caused. See
ai/conc-anal/subint_forkserver_test_cancellation_leak_issue.md.Wire the variant-2
subint_forkserver_proc()impl oncemsgspecships PEP 684 isolated-mode support(Port to new
concurrent.interpreterssupport incpython3.14+ jcrist/msgspec#1026 → tracked at Auditsubint_forkserverthread constraints once msgspec PEP 684 lands #450). Today it's aNotImplementedErrorstub; the unblock lets the child runtimelive in an isolated subint while the parent's
trio.run()keepsrunning on main.
Audit
main_thread_forkserverthread-constraint cleanup oncemsgspecships PEP 684 support (Auditsubint_forkserverthread constraints once msgspec PEP 684 lands #450). Both primitives currentlyallocate dedicated
threading.Threadinstances rather than usingtrio.to_thread.run_sync; theTODO — cleanup gated on msgspec PEP 684 supportblock in the module docstring catalogs the threeentangled root causes that block the cleanup today.
Surface subint bootstrap exceptions to the parent task via a
nonlocal errslot._subint.subint_proc()currently logs themvia
log.exception()only — the?TODOnear the_interpreters.exec()call points at anyio'sto_interpreter._interp_call(retval, is_exception)pattern asthe next step. Coordinates with the
trio.Cancelledpaths aroundsubint_exited.wait().Migrate SpawnSpec arg-passing to
_interpreters.set___main___attrs()._subint.subint_proc()'s?TODOat thebootstrapliteral: same API anyio uses into_interpreter._Worker.call(); needed oncenon-
repr()-roundtrippable values (SpawnSpecstruct,callables) get passed through.
Implement
child_sigint='trio'mode (or remove the flag).Scaffolded in
_main_thread_forkserverbut currently a no-oppending the orphan-SIGINT root-cause fix tracked in
ai/conc-anal/subint_forkserver_orphan_sigint_hang_issue.md.Once trio's
epoll_waitwedge is fixed, the flag may end up ano-op / doc-only mode.
Add cancellation / hard-kill stress coverage for the
forkserver backend (counterpart to
tests/spawn/test_subint_cancellation.pyfor the plainsubintbackend). Module docstring lists this under "Still-open work".
Run the
?TODOtypo-check enhancement intractor._testing.pytest— pipeskipon_spawn_backendargsthrough the try-set-backend checker rather than just
assert in get_args(SpawnMethodKey).xplatform pass for
tractor._testing._reap— process-reappath is currently Linux-only via
/proc/<pid>/{status,cwd,cmdline}; the--shmphase isLinux/FreeBSD only (macOS POSIX shm has no fs-visible path;
Windows is a different story). Module docstring notes a
psutil-based rewrite is viable since the dep is alreadytest-time.
Root-cause the Mode-A cancel-cascade hang under heavy
fork-spawn contention (
main_thread_forkserver: cancel-cascade occasionally hangs >9s under heavy fork-spawn contention #451). Reproduces ~17% of runs at 3parallel pytest streams ×
cpu_count - 2actors; ≈0% on anidle single-stream system. Parent-side dump shows trio's main
thread parked in
trio._core._io_epoll.get_events()line 245— cancel cascade has reached the I/O wait but
epoll.pollnever returns. Workaround in this PR: per-test
trio.fail_after(12)cap +reap_subactors_per_testopt-infixture confine the failure to the originating test (no
cascade contamination of sibling tests), so the suite stays
green. Real fix needs a contention-amplifier reproducer +
stackscopetask-tree dumps from parent + each subactor atthe t≈9 mid-cascade mark.
(this pr content was generated in some part by
claude-code)