First draft "infected `asyncio` mode"

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. This interface uses `trio`'s "guest-mode" to run
`asyncio` loop using a special entrypoint which is handed to Python
during process spawn.

tractor/_actor.py

@@ -361,6 +361,9 @@ class Actor:
     # syncs for setup/teardown sequences
     _server_down: Optional[trio.Event] = None
 
+    # if started on ``asycio`` running ``trio`` in guest mode
+    _infected_aio: bool = False
+
     def __init__(
         self,
         name: str,
@@ -1459,6 +1462,9 @@ class Actor:
         log.runtime(f"Handshake with actor {uid}@{chan.raddr} complete")
         return uid
 
+    def is_infected_aio(self) -> bool:
+        return self._infected_aio
+
 
 class Arbiter(Actor):
     '''

tractor/_entry.py

@@ -26,6 +26,7 @@ import trio  # type: ignore
 
 from .log import get_console_log, get_logger
 from . import _state
+from .to_asyncio import run_as_asyncio_guest
 
 
 log = get_logger(__name__)
@@ -62,6 +63,10 @@ def _mp_main(
         parent_addr=parent_addr
     )
     try:
+        if infect_asyncio:
+            actor._infected_aio = True
+            run_as_asyncio_guest(trio_main)
+        else:
             trio.run(trio_main)
     except KeyboardInterrupt:
         pass  # handle it the same way trio does?

tractor/to_asyncio.py

@@ -0,0 +1,150 @@
+"""
+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 .log import get_logger
+from ._state import current_actor
+
+log = get_logger(__name__)
+
+
+__all__ = ['run_task']
+
+
+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_task(
+    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()
+
+
+def run_as_asyncio_guest(
+    trio_main: Awaitable,
+) -> None:
+    """Entry for an "infected ``asyncio`` actor".
+
+    Uh, oh. :o
+
+    It looks like your event loop has caught a case of the ``trio``s.
+
+    :()
+
+    Don't worry, we've heard you'll barely notice. You might hallucinate
+    a few more propagating errors and feel like your digestion has
+    slowed but if anything get's too bad your parents will know about
+    it.
+
+    :)
+    """
+    async def aio_main(trio_main):
+        loop = asyncio.get_running_loop()
+
+        trio_done_fut = asyncio.Future()
+
+        def trio_done_callback(main_outcome):
+            log.info(f"trio_main finished: {main_outcome!r}")
+            trio_done_fut.set_result(main_outcome)
+
+        # start the infection: run trio on the asyncio loop in "guest mode"
+        log.info(f"Infecting asyncio process with {trio_main}")
+        trio.lowlevel.start_guest_run(
+            trio_main,
+            run_sync_soon_threadsafe=loop.call_soon_threadsafe,
+            done_callback=trio_done_callback,
+        )
+
+        (await trio_done_fut).unwrap()
+
+    # might as well if it's installed.
+    try:
+        import uvloop
+        loop = uvloop.new_event_loop()
+        asyncio.set_event_loop(loop)
+    except ImportError:
+        pass
+
+    asyncio.run(aio_main(trio_main))