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tractor
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Simplify to soft and hard reap sequences 

This is actually surprisingly easy to grok having gone through a lot of
pain understanding edge cases in the zombie lord dev branch. Basically
we just need to make sure actors are managed in a 2 step reap sequence.
In the "soft" reap phase we wait for the process to terminate on its own
concurrently with (maybe) waiting for its portal's final result (if it's
a `.run_in_actor()`). If this path is cancelled or errors, then we do
a "hard" reap where we timeout and send a signal to the proc to
terminate immediately. The only last remaining trick is to tie in the
root-is-debugger-aware logic to yet again avoid tty clobbers.
immediate_remote_cancels
Tyler Goodlet 2021-10-13 01:09:16 -04:00
parent 2df16c1557
commit 77ec29008d
1 changed files with 138 additions and 159 deletions
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297
tractor/_spawn.py
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@ -8,7 +8,6 @@ from typing import Any, Dict, Optional
import trio import trio
from trio_typing import TaskStatus from trio_typing import TaskStatus
from async_generator import asynccontextmanager
try: try:
from multiprocessing import semaphore_tracker # type: ignore from multiprocessing import semaphore_tracker # type: ignore
@ -123,34 +122,32 @@ async def cancel_on_completion(
portal: Portal, portal: Portal,
actor: Actor, actor: Actor,
errors: Dict[Tuple[str, str], Exception], errors: Dict[Tuple[str, str], Exception],
task_status: TaskStatus[trio.CancelScope] = trio.TASK_STATUS_IGNORED,
) -> None: ) -> None:
"""Cancel actor gracefully once it's "main" portal's """
Cancel actor gracefully once it's "main" portal's
result arrives. result arrives.
Should only be called for actors spawned with `run_in_actor()`. Should only be called for actors spawned with `run_in_actor()`.
""" """
with trio.CancelScope() as cs: # if this call errors we store the exception for later
# in ``errors`` which will be reraised inside
# a MultiError and we still send out a cancel request
result = await exhaust_portal(portal, actor)
if isinstance(result, Exception):
errors[actor.uid] = result
log.warning(
f"Cancelling {portal.channel.uid} after error {result}"
)
task_status.started(cs) else:
log.runtime(
f"Cancelling {portal.channel.uid} gracefully "
f"after result {result}")
# if this call errors we store the exception for later # cancel the process now that we have a final result
# in ``errors`` which will be reraised inside await portal.cancel_actor()
# a MultiError and we still send out a cancel request
result = await exhaust_portal(portal, actor)
if isinstance(result, Exception):
errors[actor.uid] = result
log.warning(
f"Cancelling {portal.channel.uid} after error {result}"
)
else:
log.runtime(
f"Cancelling {portal.channel.uid} gracefully "
f"after result {result}")
# cancel the process now that we have a final result
await portal.cancel_actor()
async def do_hard_kill( async def do_hard_kill(
@ -191,8 +188,6 @@ async def new_proc(
spawn method as configured using ``try_set_start_method()``. spawn method as configured using ``try_set_start_method()``.
""" """
cancel_scope = None
# mark the new actor with the global spawn method # mark the new actor with the global spawn method
subactor._spawn_method = _spawn_method subactor._spawn_method = _spawn_method
@ -258,7 +253,8 @@ async def new_proc(
async with trio.open_nursery() as nursery: async with trio.open_nursery() as nursery:
if portal in actor_nursery._cancel_after_result_on_exit: if portal in actor_nursery._cancel_after_result_on_exit:
cancel_scope = await nursery.start( # cancel_scope = await nursery.start(
nursery.start_soon(
cancel_on_completion, cancel_on_completion,
portal, portal,
subactor, subactor,
@ -271,22 +267,22 @@ async def new_proc(
# This is a "soft" (cancellable) join/reap. # This is a "soft" (cancellable) join/reap.
await proc.wait() await proc.wait()
finally: # cancel result waiter that may have been spawned in
# cancel result waiter that may have been spawned in # tandem if not done already
# tandem if not done already
if cancel_scope:
log.warning( log.warning(
"Cancelling existing result waiter task for " "Cancelling existing result waiter task for "
f"{subactor.uid}") f"{subactor.uid}")
cancel_scope.cancel() nursery.cancel_scope.cancel()
log.runtime(f"Attempting to kill {proc}") finally:
if proc.poll() is None:
log.cancel(f"Attempting to hard kill {proc}")
# The "hard" reap since no actor zombies are allowed! # The "hard" reap since no actor zombies are allowed!
# XXX: do this **after** cancellation/tearfown to avoid # XXX: do this **after** cancellation/tearfown to avoid
# killing the process too early. # killing the process too early.
with trio.CancelScope(shield=True): with trio.CancelScope(shield=True):
await do_hard_kill(proc) await do_hard_kill(proc)
log.debug(f"Joined {proc}") log.debug(f"Joined {proc}")
# pop child entry to indicate we no longer managing this subactor # pop child entry to indicate we no longer managing this subactor
@ -322,141 +318,124 @@ async def mp_new_proc(
task_status: TaskStatus[Portal] = trio.TASK_STATUS_IGNORED task_status: TaskStatus[Portal] = trio.TASK_STATUS_IGNORED
) -> None: ) -> None:
async with trio.open_nursery() as nursery:
assert _ctx assert _ctx
start_method = _ctx.get_start_method() start_method = _ctx.get_start_method()
if start_method == 'forkserver': if start_method == 'forkserver':
# XXX do our hackery on the stdlib to avoid multiple # XXX do our hackery on the stdlib to avoid multiple
# forkservers (one at each subproc layer). # forkservers (one at each subproc layer).
fs = forkserver._forkserver fs = forkserver._forkserver
curr_actor = current_actor() curr_actor = current_actor()
if is_main_process() and not curr_actor._forkserver_info: if is_main_process() and not curr_actor._forkserver_info:
# if we're the "main" process start the forkserver # if we're the "main" process start the forkserver
# only once and pass its ipc info to downstream # only once and pass its ipc info to downstream
# children # children
# forkserver.set_forkserver_preload(enable_modules) # forkserver.set_forkserver_preload(enable_modules)
forkserver.ensure_running() forkserver.ensure_running()
fs_info = ( fs_info = (
fs._forkserver_address, fs._forkserver_address,
fs._forkserver_alive_fd, fs._forkserver_alive_fd,
getattr(fs, '_forkserver_pid', None), getattr(fs, '_forkserver_pid', None),
getattr( getattr(
resource_tracker._resource_tracker, '_pid', None), resource_tracker._resource_tracker, '_pid', None),
resource_tracker._resource_tracker._fd, resource_tracker._resource_tracker._fd,
) )
else:
assert curr_actor._forkserver_info
fs_info = (
fs._forkserver_address,
fs._forkserver_alive_fd,
fs._forkserver_pid,
resource_tracker._resource_tracker._pid,
resource_tracker._resource_tracker._fd,
) = curr_actor._forkserver_info
else: else:
fs_info = (None, None, None, None, None) assert curr_actor._forkserver_info
fs_info = (
fs._forkserver_address,
fs._forkserver_alive_fd,
fs._forkserver_pid,
resource_tracker._resource_tracker._pid,
resource_tracker._resource_tracker._fd,
) = curr_actor._forkserver_info
else:
fs_info = (None, None, None, None, None)
proc: mp.Process = _ctx.Process( # type: ignore proc: mp.Process = _ctx.Process( # type: ignore
target=_mp_main, target=_mp_main,
args=( args=(
subactor, subactor,
bind_addr, bind_addr,
fs_info, fs_info,
start_method, start_method,
parent_addr, parent_addr,
), ),
# daemon=True, # daemon=True,
name=name, name=name,
) )
# `multiprocessing` only (since no async interface): # `multiprocessing` only (since no async interface):
# register the process before start in case we get a cancel # register the process before start in case we get a cancel
# request before the actor has fully spawned - then we can wait # request before the actor has fully spawned - then we can wait
# for it to fully come up before sending a cancel request # for it to fully come up before sending a cancel request
actor_nursery._children[subactor.uid] = (subactor, proc, None) actor_nursery._children[subactor.uid] = (subactor, proc, None)
proc.start() proc.start()
if not proc.is_alive(): if not proc.is_alive():
raise ActorFailure("Couldn't start sub-actor?") raise ActorFailure("Couldn't start sub-actor?")
log.runtime(f"Started {proc}") log.runtime(f"Started {proc}")
try: try:
# wait for actor to spawn and connect back to us # wait for actor to spawn and connect back to us
# channel should have handshake completed by the # channel should have handshake completed by the
# local actor by the time we get a ref to it # local actor by the time we get a ref to it
event, chan = await actor_nursery._actor.wait_for_peer( event, chan = await actor_nursery._actor.wait_for_peer(
subactor.uid) subactor.uid)
portal = Portal(chan) # except:
actor_nursery._children[subactor.uid] = (subactor, proc, portal) # TODO: in the case we were cancelled before the sub-proc
# registered itself back we must be sure to try and clean
# any process we may have started.
# unblock parent task portal = Portal(chan)
task_status.started(portal) actor_nursery._children[subactor.uid] = (subactor, proc, portal)
# wait for ``ActorNursery`` block to signal that # unblock parent task
# subprocesses can be waited upon. task_status.started(portal)
# This is required to ensure synchronization
# with user code that may want to manually await results # wait for ``ActorNursery`` block to signal that
# from nursery spawned sub-actors. We don't want the # subprocesses can be waited upon.
# containing nurseries here to collect results or error # This is required to ensure synchronization
# while user code is still doing it's thing. Only after the # with user code that may want to manually await results
# nursery block closes do we allow subactor results to be # from nursery spawned sub-actors. We don't want the
# awaited and reported upwards to the supervisor. # containing nurseries here to collect results or error
# while user code is still doing it's thing. Only after the
# nursery block closes do we allow subactor results to be
# awaited and reported upwards to the supervisor.
with trio.CancelScope(shield=True):
await actor_nursery._join_procs.wait() await actor_nursery._join_procs.wait()
finally: async with trio.open_nursery() as nursery:
# XXX: in the case we were cancelled before the sub-proc
# registered itself back we must be sure to try and clean
# any process we may have started.
reaping_cancelled: bool = False
cancel_scope: Optional[trio.CancelScope] = None
cancel_exc: Optional[trio.Cancelled] = None
if portal in actor_nursery._cancel_after_result_on_exit: if portal in actor_nursery._cancel_after_result_on_exit:
try: nursery.start_soon(
# async with trio.open_nursery() as n: cancel_on_completion,
# n.cancel_scope.shield = True portal,
cancel_scope = await nursery.start( subactor,
cancel_on_completion, errors
portal, )
subactor,
errors
)
except trio.Cancelled as err:
cancel_exc = err
# if the reaping task was cancelled we may have hit await proc_waiter(proc)
# a race where the subproc disconnected before we
# could send it a message to cancel (classic 2 generals)
# in that case, wait shortly then kill the process.
reaping_cancelled = True
if proc.is_alive():
with trio.move_on_after(0.1) as cs:
cs.shield = True
await proc_waiter(proc)
if cs.cancelled_caught:
proc.terminate()
if not reaping_cancelled and proc.is_alive():
await proc_waiter(proc)
# TODO: timeout block here?
proc.join()
log.debug(f"Joined {proc}")
# pop child entry to indicate we are no longer managing subactor
subactor, proc, portal = actor_nursery._children.pop(subactor.uid)
# cancel result waiter that may have been spawned in # cancel result waiter that may have been spawned in
# tandem if not done already # tandem if not done already
if cancel_scope: log.warning(
log.warning( "Cancelling existing result waiter task for "
"Cancelling existing result waiter task for " f"{subactor.uid}")
f"{subactor.uid}") nursery.cancel_scope.cancel()
cancel_scope.cancel()
elif reaping_cancelled: # let the cancellation bubble up finally:
assert cancel_exc # hard reap sequence
raise cancel_exc if proc.is_alive():
log.cancel(f"Attempting to hard kill {proc}")
with trio.move_on_after(0.1) as cs:
cs.shield = True
await proc_waiter(proc)
if cs.cancelled_caught:
proc.terminate()
proc.join()
log.debug(f"Joined {proc}")
# pop child entry to indicate we are no longer managing subactor
subactor, proc, portal = actor_nursery._children.pop(subactor.uid)