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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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83
tractor/_spawn.py
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@ -8,7 +8,6 @@ from typing import Any, Dict, Optional
import trio
from trio_typing import TaskStatus
from async_generator import asynccontextmanager
try:
from multiprocessing import semaphore_tracker # type: ignore
@ -123,17 +122,15 @@ async def cancel_on_completion(
portal: Portal,
actor: Actor,
errors: Dict[Tuple[str, str], Exception],
task_status: TaskStatus[trio.CancelScope] = trio.TASK_STATUS_IGNORED,
) -> None:
"""Cancel actor gracefully once it's "main" portal's
"""
Cancel actor gracefully once it's "main" portal's
result arrives.
Should only be called for actors spawned with `run_in_actor()`.
"""
with trio.CancelScope() as cs:
task_status.started(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
@ -191,8 +188,6 @@ async def new_proc(
spawn method as configured using ``try_set_start_method()``.
"""
cancel_scope = None
# mark the new actor with the global spawn method
subactor._spawn_method = _spawn_method
@ -258,7 +253,8 @@ async def new_proc(
async with trio.open_nursery() as nursery:
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,
portal,
subactor,
@ -271,16 +267,16 @@ async def new_proc(
# This is a "soft" (cancellable) join/reap.
await proc.wait()
finally:
# cancel result waiter that may have been spawned in
# tandem if not done already
if cancel_scope:
log.warning(
"Cancelling existing result waiter task for "
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!
# XXX: do this **after** cancellation/tearfown to avoid
@ -322,7 +318,7 @@ async def mp_new_proc(
task_status: TaskStatus[Portal] = trio.TASK_STATUS_IGNORED
) -> None:
async with trio.open_nursery() as nursery:
assert _ctx
start_method = _ctx.get_start_method()
if start_method == 'forkserver':
@ -386,6 +382,11 @@ async def mp_new_proc(
# local actor by the time we get a ref to it
event, chan = await actor_nursery._actor.wait_for_peer(
subactor.uid)
# except:
# 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.
portal = Portal(chan)
actor_nursery._children[subactor.uid] = (subactor, proc, portal)
@ -401,37 +402,31 @@ async def mp_new_proc(
# 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()
finally:
# 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
async with trio.open_nursery() as nursery:
if portal in actor_nursery._cancel_after_result_on_exit:
try:
# async with trio.open_nursery() as n:
# n.cancel_scope.shield = True
cancel_scope = await nursery.start(
nursery.start_soon(
cancel_on_completion,
portal,
subactor,
errors
)
except trio.Cancelled as err:
cancel_exc = err
# if the reaping task was cancelled we may have hit
# 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
await proc_waiter(proc)
# cancel result waiter that may have been spawned in
# tandem if not done already
log.warning(
"Cancelling existing result waiter task for "
f"{subactor.uid}")
nursery.cancel_scope.cancel()
finally:
# hard reap sequence
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)
@ -439,24 +434,8 @@ async def mp_new_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
# tandem if not done already
if cancel_scope:
log.warning(
"Cancelling existing result waiter task for "
f"{subactor.uid}")
cancel_scope.cancel()
elif reaping_cancelled: # let the cancellation bubble up
assert cancel_exc
raise cancel_exc