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Propagate any spawned asyncio task error upwards
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This should mostly maintain top level SC principles for any task spawned
using `tractor.to_asyncio.run()`. When the `asyncio` task completes make
sure to cancel the pertaining `trio` cancel scope and raise any error
that may have resulted.

Resolves #120
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goodboy committed Aug 10, 2021
1 parent 4e520fe commit f23ace5
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99 changes: 99 additions & 0 deletions tractor/to_asyncio.py
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"""
Infection apis for ``asyncio`` loops running ``trio`` using guest mode.
"""
import asyncio
import inspect
from typing import (
Any,
Callable,
AsyncGenerator,
Awaitable,
Union,
)

import trio

from ._state import current_actor


__all__ = ['run']


async def _invoke(
from_trio: trio.abc.ReceiveChannel,
to_trio: asyncio.Queue,
coro: Awaitable,
) -> Union[AsyncGenerator, Awaitable]:
"""Await or stream awaiable object based on type into
``trio`` memory channel.
"""
async def stream_from_gen(c):
async for item in c:
to_trio.send_nowait(item)

async def just_return(c):
to_trio.send_nowait(await c)

if inspect.isasyncgen(coro):
return await stream_from_gen(coro)
elif inspect.iscoroutine(coro):
return await coro


async def run(
func: Callable,
qsize: int = 2**10,
**kwargs,
) -> Any:
"""Run an ``asyncio`` async function or generator in a task, return
or stream the result back to ``trio``.
"""
assert current_actor()._infected_aio

# ITC (inter task comms)
from_trio = asyncio.Queue(qsize)
to_trio, from_aio = trio.open_memory_channel(qsize)

# allow target func to accept/stream results manually
kwargs['to_trio'] = to_trio
kwargs['from_trio'] = to_trio

coro = func(**kwargs)

cancel_scope = trio.CancelScope()

# start the asyncio task we submitted from trio
# TODO: try out ``anyio`` asyncio based tg here
task = asyncio.create_task(_invoke(from_trio, to_trio, coro))
err = None

# XXX: I'm not sure this actually does anything...
def cancel_trio(task):
"""Cancel the calling ``trio`` task on error.
"""
nonlocal err
err = task.exception()
cancel_scope.cancel()

task.add_done_callback(cancel_trio)

# determine return type async func vs. gen
if inspect.isasyncgen(coro):
# simple async func
async def result():
with cancel_scope:
return await from_aio.get()
if cancel_scope.cancelled_caught and err:
raise err

elif inspect.iscoroutine(coro):
# asycn gen
async def result():
with cancel_scope:
async with from_aio:
async for item in from_aio:
yield item
if cancel_scope.cancelled_caught and err:
raise err

return result()

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