482 lines
16 KiB
Python
482 lines
16 KiB
Python
"""
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Machinery for actor process spawning using multiple backends.
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"""
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import sys
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import multiprocessing as mp
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import platform
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from typing import Any, Dict, Optional
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import trio
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from trio_typing import TaskStatus
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from async_generator import asynccontextmanager
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try:
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from multiprocessing import semaphore_tracker # type: ignore
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resource_tracker = semaphore_tracker
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resource_tracker._resource_tracker = resource_tracker._semaphore_tracker
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except ImportError:
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# 3.8 introduces a more general version that also tracks shared mems
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from multiprocessing import resource_tracker # type: ignore
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from multiprocessing import forkserver # type: ignore
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from typing import Tuple
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from . import _forkserver_override
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from ._state import (
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current_actor,
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is_main_process,
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)
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from .log import get_logger
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from ._portal import Portal
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from ._actor import Actor
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from ._entry import _mp_main
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from ._exceptions import ActorFailure
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log = get_logger('tractor')
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# placeholder for an mp start context if so using that backend
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_ctx: Optional[mp.context.BaseContext] = None
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_spawn_method: str = "trio"
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if platform.system() == 'Windows':
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_ctx = mp.get_context("spawn")
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async def proc_waiter(proc: mp.Process) -> None:
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await trio.lowlevel.WaitForSingleObject(proc.sentinel)
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else:
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# *NIX systems use ``trio`` primitives as our default as well
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async def proc_waiter(proc: mp.Process) -> None:
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await trio.lowlevel.wait_readable(proc.sentinel)
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def try_set_start_method(name: str) -> Optional[mp.context.BaseContext]:
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"""Attempt to set the method for process starting, aka the "actor
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spawning backend".
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If the desired method is not supported this function will error.
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On Windows only the ``multiprocessing`` "spawn" method is offered
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besides the default ``trio`` which uses async wrapping around
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``subprocess.Popen``.
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"""
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global _ctx
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global _spawn_method
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methods = mp.get_all_start_methods()
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if 'fork' in methods:
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# forking is incompatible with ``trio``s global task tree
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methods.remove('fork')
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# supported on all platforms
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methods += ['trio']
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if name not in methods:
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raise ValueError(
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f"Spawn method `{name}` is invalid please choose one of {methods}"
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)
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elif name == 'forkserver':
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_forkserver_override.override_stdlib()
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_ctx = mp.get_context(name)
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elif name == 'trio':
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_ctx = None
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else:
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_ctx = mp.get_context(name)
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_spawn_method = name
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return _ctx
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async def exhaust_portal(
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portal: Portal,
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actor: Actor
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) -> Any:
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"""Pull final result from portal (assuming it has one).
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If the main task is an async generator do our best to consume
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what's left of it.
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"""
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try:
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log.debug(f"Waiting on final result from {actor.uid}")
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# XXX: streams should never be reaped here since they should
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# always be established and shutdown using a context manager api
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final = await portal.result()
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except (Exception, trio.MultiError) as err:
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# we reraise in the parent task via a ``trio.MultiError``
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return err
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except trio.Cancelled as err:
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# lol, of course we need this too ;P
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# TODO: merge with above?
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log.warning(f"Cancelled result waiter for {portal.actor.uid}")
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return err
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else:
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log.debug(f"Returning final result: {final}")
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return final
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async def cancel_on_completion(
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portal: Portal,
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actor: Actor,
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errors: Dict[Tuple[str, str], Exception],
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task_status: TaskStatus[trio.CancelScope] = trio.TASK_STATUS_IGNORED,
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) -> None:
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"""Cancel actor gracefully once it's "main" portal's
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result arrives.
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Should only be called for actors spawned with `run_in_actor()`.
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"""
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with trio.CancelScope() as cs:
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task_status.started(cs)
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# if this call errors we store the exception for later
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# in ``errors`` which will be reraised inside
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# a MultiError and we still send out a cancel request
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result = await exhaust_portal(portal, actor)
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if isinstance(result, Exception):
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errors[actor.uid] = result
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log.warning(
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f"Cancelling {portal.channel.uid} after error {result}"
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)
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else:
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log.runtime(
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f"Cancelling {portal.channel.uid} gracefully "
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f"after result {result}")
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# cancel the process now that we have a final result
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await portal.cancel_actor()
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async def do_hard_kill(
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proc: trio.Process,
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) -> None:
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# NOTE: this timeout used to do nothing since we were shielding
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# the ``.wait()`` inside ``new_proc()`` which will pretty much
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# never release until the process exits, now it acts as
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# a hard-kill time ultimatum.
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with trio.move_on_after(3) as cs:
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# NOTE: This ``__aexit__()`` shields internally.
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async with proc: # calls ``trio.Process.aclose()``
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log.debug(f"Terminating {proc}")
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if cs.cancelled_caught:
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# XXX: should pretty much never get here unless we have
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# to move the bits from ``proc.__aexit__()`` out and
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# into here.
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log.critical(f"HARD KILLING {proc}")
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proc.kill()
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@asynccontextmanager
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async def spawn_subactor(
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subactor: 'Actor',
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parent_addr: Tuple[str, int],
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):
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spawn_cmd = [
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sys.executable,
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"-m",
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# Hardcode this (instead of using ``_child.__name__`` to avoid a
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# double import warning: https://stackoverflow.com/a/45070583
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"tractor._child",
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# We provide the child's unique identifier on this exec/spawn
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# line for debugging purposes when viewing the process tree from
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# the OS; it otherwise can be passed via the parent channel if
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# we prefer in the future (for privacy).
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"--uid",
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str(subactor.uid),
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# Address the child must connect to on startup
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"--parent_addr",
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str(parent_addr)
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]
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if subactor.loglevel:
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spawn_cmd += [
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"--loglevel",
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subactor.loglevel
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]
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proc = await trio.open_process(spawn_cmd)
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try:
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yield proc
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finally:
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log.runtime(f"Attempting to kill {proc}")
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# XXX: do this **after** cancellation/tearfown
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# to avoid killing the process too early
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# since trio does this internally on ``__aexit__()``
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await do_hard_kill(proc)
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async def new_proc(
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name: str,
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actor_nursery: 'ActorNursery', # type: ignore # noqa
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subactor: Actor,
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errors: Dict[Tuple[str, str], Exception],
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# passed through to actor main
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bind_addr: Tuple[str, int],
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parent_addr: Tuple[str, int],
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_runtime_vars: Dict[str, Any], # serialized and sent to _child
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*,
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task_status: TaskStatus[Portal] = trio.TASK_STATUS_IGNORED
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) -> None:
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"""Create a new ``multiprocessing.Process`` using the
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spawn method as configured using ``try_set_start_method()``.
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"""
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cancel_scope = None
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# mark the new actor with the global spawn method
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subactor._spawn_method = _spawn_method
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if _spawn_method == 'trio':
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async with trio.open_nursery() as nursery:
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async with spawn_subactor(
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subactor,
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parent_addr,
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) as proc:
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log.runtime(f"Started {proc}")
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# wait for actor to spawn and connect back to us
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# channel should have handshake completed by the
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# local actor by the time we get a ref to it
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event, chan = await actor_nursery._actor.wait_for_peer(
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subactor.uid)
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portal = Portal(chan)
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actor_nursery._children[subactor.uid] = (
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subactor, proc, portal)
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# send additional init params
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await chan.send({
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"_parent_main_data": subactor._parent_main_data,
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"enable_modules": subactor.enable_modules,
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"_arb_addr": subactor._arb_addr,
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"bind_host": bind_addr[0],
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"bind_port": bind_addr[1],
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"_runtime_vars": _runtime_vars,
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})
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# track subactor in current nursery
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curr_actor = current_actor()
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curr_actor._actoruid2nursery[subactor.uid] = actor_nursery
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# resume caller at next checkpoint now that child is up
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task_status.started(portal)
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# wait for ActorNursery.wait() to be called
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with trio.CancelScope(shield=True):
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await actor_nursery._join_procs.wait()
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if portal in actor_nursery._cancel_after_result_on_exit:
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cancel_scope = await nursery.start(
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cancel_on_completion,
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portal,
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subactor,
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errors
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)
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# Wait for proc termination but **dont' yet** call
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# ``trio.Process.__aexit__()`` (it tears down stdio
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# which will kill any waiting remote pdb trace).
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# TODO: No idea how we can enforce zombie
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# reaping more stringently without the shield
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# we used to have below...
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# with trio.CancelScope(shield=True):
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# async with proc:
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# Always "hard" join sub procs since no actor zombies
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# are allowed!
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# this is a "light" (cancellable) join, the hard join is
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# in the enclosing scope (see above).
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await proc.wait()
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log.debug(f"Joined {proc}")
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# pop child entry to indicate we no longer managing this subactor
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subactor, proc, portal = actor_nursery._children.pop(subactor.uid)
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# cancel result waiter that may have been spawned in
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# tandem if not done already
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if cancel_scope:
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log.warning(
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"Cancelling existing result waiter task for "
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f"{subactor.uid}")
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cancel_scope.cancel()
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else:
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# `multiprocessing`
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# async with trio.open_nursery() as nursery:
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await mp_new_proc(
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name=name,
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actor_nursery=actor_nursery,
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subactor=subactor,
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errors=errors,
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# passed through to actor main
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bind_addr=bind_addr,
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parent_addr=parent_addr,
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_runtime_vars=_runtime_vars,
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task_status=task_status,
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)
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async def mp_new_proc(
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name: str,
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actor_nursery: 'ActorNursery', # type: ignore # noqa
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subactor: Actor,
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errors: Dict[Tuple[str, str], Exception],
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# passed through to actor main
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bind_addr: Tuple[str, int],
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parent_addr: Tuple[str, int],
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_runtime_vars: Dict[str, Any], # serialized and sent to _child
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*,
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task_status: TaskStatus[Portal] = trio.TASK_STATUS_IGNORED
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) -> None:
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async with trio.open_nursery() as nursery:
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assert _ctx
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start_method = _ctx.get_start_method()
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if start_method == 'forkserver':
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# XXX do our hackery on the stdlib to avoid multiple
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# forkservers (one at each subproc layer).
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fs = forkserver._forkserver
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curr_actor = current_actor()
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if is_main_process() and not curr_actor._forkserver_info:
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# if we're the "main" process start the forkserver
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# only once and pass its ipc info to downstream
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# children
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# forkserver.set_forkserver_preload(enable_modules)
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forkserver.ensure_running()
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fs_info = (
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fs._forkserver_address,
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fs._forkserver_alive_fd,
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getattr(fs, '_forkserver_pid', None),
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getattr(
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resource_tracker._resource_tracker, '_pid', None),
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resource_tracker._resource_tracker._fd,
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)
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else:
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assert curr_actor._forkserver_info
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fs_info = (
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fs._forkserver_address,
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fs._forkserver_alive_fd,
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fs._forkserver_pid,
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resource_tracker._resource_tracker._pid,
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resource_tracker._resource_tracker._fd,
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) = curr_actor._forkserver_info
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else:
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fs_info = (None, None, None, None, None)
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proc: mp.Process = _ctx.Process( # type: ignore
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target=_mp_main,
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args=(
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subactor,
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bind_addr,
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fs_info,
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start_method,
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parent_addr,
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),
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# daemon=True,
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name=name,
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)
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# `multiprocessing` only (since no async interface):
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# register the process before start in case we get a cancel
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# request before the actor has fully spawned - then we can wait
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# for it to fully come up before sending a cancel request
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actor_nursery._children[subactor.uid] = (subactor, proc, None)
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proc.start()
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if not proc.is_alive():
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raise ActorFailure("Couldn't start sub-actor?")
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log.runtime(f"Started {proc}")
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try:
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# wait for actor to spawn and connect back to us
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# channel should have handshake completed by the
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# local actor by the time we get a ref to it
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event, chan = await actor_nursery._actor.wait_for_peer(
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subactor.uid)
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portal = Portal(chan)
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actor_nursery._children[subactor.uid] = (subactor, proc, portal)
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# unblock parent task
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task_status.started(portal)
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# wait for ``ActorNursery`` block to signal that
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# subprocesses can be waited upon.
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# This is required to ensure synchronization
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# with user code that may want to manually await results
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# from nursery spawned sub-actors. We don't want the
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# containing nurseries here to collect results or error
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# while user code is still doing it's thing. Only after the
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# nursery block closes do we allow subactor results to be
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# awaited and reported upwards to the supervisor.
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await actor_nursery._join_procs.wait()
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finally:
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# XXX: in the case we were cancelled before the sub-proc
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# registered itself back we must be sure to try and clean
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# any process we may have started.
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reaping_cancelled: bool = False
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cancel_scope: Optional[trio.CancelScope] = None
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cancel_exc: Optional[trio.Cancelled] = None
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if portal in actor_nursery._cancel_after_result_on_exit:
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try:
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# async with trio.open_nursery() as n:
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# n.cancel_scope.shield = True
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cancel_scope = await nursery.start(
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cancel_on_completion,
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portal,
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subactor,
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errors
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)
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except trio.Cancelled as err:
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cancel_exc = err
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# if the reaping task was cancelled we may have hit
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# a race where the subproc disconnected before we
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# could send it a message to cancel (classic 2 generals)
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# in that case, wait shortly then kill the process.
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reaping_cancelled = True
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if proc.is_alive():
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with trio.move_on_after(0.1) as cs:
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cs.shield = True
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await proc_waiter(proc)
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if cs.cancelled_caught:
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proc.terminate()
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if not reaping_cancelled and proc.is_alive():
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await proc_waiter(proc)
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# TODO: timeout block here?
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proc.join()
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log.debug(f"Joined {proc}")
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# pop child entry to indicate we are no longer managing subactor
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subactor, proc, portal = actor_nursery._children.pop(subactor.uid)
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# cancel result waiter that may have been spawned in
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# tandem if not done already
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if cancel_scope:
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log.warning(
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"Cancelling existing result waiter task for "
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f"{subactor.uid}")
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cancel_scope.cancel()
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elif reaping_cancelled: # let the cancellation bubble up
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assert cancel_exc
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raise cancel_exc
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