Initial prototype for a one-cancels-one style supervisor, nursery thing..
Tyler Goodlet
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# tractor: structured concurrent "actors".
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# Copyright 2018-eternity Tyler Goodlet.
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Affero General Public License for more details.
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <https://www.gnu.org/licenses/>.
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'''
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Erlang-style (ish) "one-cancels-one" nursery.
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'''
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from __future__ import annotations
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from contextlib import (
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asynccontextmanager as acm,
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contextmanager as cm,
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nullcontext,
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)
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from typing import ContextManager
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from outcome import (
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Outcome,
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acapture,
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)
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import pdbp
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from msgspec import Struct
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import trio
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from trio._core._run import (
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Task,
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CancelScope,
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Nursery,
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)
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class MaybeOutcome(Struct):
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_ready: Event = trio.Event()
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_outcome: Outcome | None = None
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_result: Any | None = None
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@property
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def result(self) -> Any:
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'''
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Either Any or None depending on whether the Outcome has compeleted.
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'''
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if self._outcome is None:
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raise RuntimeError(
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# f'Task {task.name} is not complete.\n'
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f'Outcome is not complete.\n'
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'wait on `await MaybeOutcome.unwrap()` first!'
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)
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return self._result
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def _set_outcome(
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self,
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outcome: Outcome,
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):
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self._outcome = outcome
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self._result = outcome.unwrap()
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self._ready.set()
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# TODO: maybe a better name like,
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# - .wait_and_unwrap()
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# - .wait_unwrap()
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# - .aunwrap() ?
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async def unwrap(self) -> Any:
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if self._ready.is_set():
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return self._result
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await self._ready.wait()
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out = self._outcome
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if out is None:
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raise ValueError(f'{out} is not an outcome!?')
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return self.result
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class TaskHandle(Struct):
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task: Task
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cs: CancelScope
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exited: Event | None = None
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_outcome: Outcome | None = None
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class ScopePerTaskNursery(Struct):
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_n: Nursery
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_scopes: dict[
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Task,
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tuple[CancelScope, Outcome]
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] = {}
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scope_manager: ContextManager | None = None
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async def start_soon(
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self,
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async_fn,
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*args,
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name=None,
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scope_manager: ContextManager | None = None,
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) -> tuple[CancelScope, Task]:
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# NOTE: internals of a nursery don't let you know what
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# the most recently spawned task is by order.. so we'd
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# have to either change that or do set ops.
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# pre_start_tasks: set[Task] = n._children.copy()
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# new_tasks = n._children - pre_start_Tasks
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# assert len(new_tasks) == 1
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# task = new_tasks.pop()
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n: Nursery = self._n
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cs = CancelScope()
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new_task: Task | None = None
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to_return: tuple[Any] | None = None
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maybe_outcome = MaybeOutcome()
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sm = self.scope_manager
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if sm is None:
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mngr = nullcontext([cs])
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else:
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mngr = sm(
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nursery=n,
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scope=cs,
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maybe_outcome=maybe_outcome,
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)
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async def _start_wrapped_in_scope(
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task_status: TaskStatus[
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tuple[CancelScope, Task]
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] = trio.TASK_STATUS_IGNORED,
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) -> None:
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nonlocal maybe_outcome
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nonlocal to_return
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with cs:
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task = trio.lowlevel.current_task()
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self._scopes[cs] = task
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# TODO: instead we should probably just use
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# `Outcome.send(mngr)` here no and inside a custom
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# decorator `@trio.cancel_scope_manager` enforce
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# that it's a single yield generator?
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with mngr as to_return:
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# TODO: relay through whatever the
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# started task passes back via `.started()` ?
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# seems like that won't work with also returning
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# a "task handle"?
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task_status.started()
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# invoke underlying func now that cs is entered.
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outcome = await acapture(async_fn, *args)
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# TODO: instead, mngr.send(outcome) so that we don't
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# tie this `.start_soon()` impl to the
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# `MaybeOutcome` type? Use `Outcome.send(mngr)`
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# right?
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maybe_outcome._set_outcome(outcome)
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await n.start(_start_wrapped_in_scope)
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assert to_return is not None
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# TODO: better way to concat the values delivered by the user
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# provided `.scope_manager` and the outcome?
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return tuple([maybe_outcome] + to_return)
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# TODO: maybe just make this a generator with a single yield that also
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# delivers a value (of some std type) from the yield expression?
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# @trio.cancel_scope_manager
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@cm
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def add_task_handle_and_crash_handling(
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nursery: Nursery,
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scope: CancelScope,
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maybe_outcome: MaybeOutcome,
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) -> Generator[None, list[Any]]:
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cs: CancelScope = CancelScope()
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# if you need it you can ask trio for the task obj
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task: Task = trio.lowlevel.current_task()
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print(f'Spawning task: {task.name}')
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try:
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# yields back when task is terminated, cancelled, returns?
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with cs:
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# the yielded values here are what are returned to the
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# nursery's `.start_soon()` caller
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# TODO: actually make this work so that `MaybeOutcome` isn't
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# tied to the impl of `.start_soon()` on our custom nursery!
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task_outcome: Outcome = yield [cs]
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except Exception as err:
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# Adds "crash handling" from `pdbp` by entering
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# a REPL on std errors.
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pdbp.xpm()
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raise
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@acm
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async def open_nursery(
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scope_manager = None,
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**kwargs,
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):
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async with trio.open_nursery(**kwargs) as nurse:
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yield ScopePerTaskNursery(
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nurse,
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scope_manager=scope_manager,
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)
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async def sleep_then_err():
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await trio.sleep(1)
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assert 0
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async def sleep_then_return_val(val: str):
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await trio.sleep(0.2)
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return val
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if __name__ == '__main__':
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async def main():
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async with open_nursery(
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scope_manager=add_task_handle_and_crash_handling,
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) as sn:
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for _ in range(3):
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outcome, cs = await sn.start_soon(trio.sleep_forever)
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# extra task we want to engage in debugger post mortem.
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err_outcome, *_ = await sn.start_soon(sleep_then_err)
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val: str = 'yoyoyo'
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val_outcome, cs = await sn.start_soon(sleep_then_return_val, val)
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res = await val_outcome.unwrap()
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assert res == val
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print(f'GOT EXPECTED TASK VALUE: {res}')
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print('WAITING FOR CRASH..')
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trio.run(main)
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