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Drop `msg` kwarg from `Context.cancel()` 

Well first off, turns out it's never used and generally speaking
doesn't seem to help much with "runtime hacking/debugging"; why would
we need to "fabricate" a msg when `.cancel()` is called to self-cancel?

Also (and since `._maybe_cancel_and_set_remote_error()` now takes an
`error: BaseException` as input and thus expects error-msg unpacking
prior to being called), we now manually set `Context._cancel_msg: dict`
just prior to any remote error assignment - so any case where we would
have fabbed a "cancel msg" near calling `.cancel()`, just do the manual
assign.

In this vein some other subtle changes:
- obviously don't set `._cancel_msg` in `.cancel()` since it's no longer
  an input.
- generally do walrus-style `error := unpack_error()` before applying
  and setting remote error-msg state.
- always raise any `._remote_error` in `.result()` instead of returning
  the exception instance and check before AND after the underlying mem
  chan read.
- add notes/todos around `raise self._remote_error from None` masking of
  (runtime) errors in `._maybe_raise_remote_err()` and use it inside
  `.result()` since we had the inverse duplicate logic there anyway..

Further, this adds and extends a ton of (internal) interface docs and
details comments around the `Context` API including many subtleties
pertaining to calling `._maybe_cancel_and_set_remote_error()`.
multihomed
Tyler Goodlet 2023-10-17 15:30:16 -04:00
parent e4a6223256
commit 534e5d150d
1 changed files with 183 additions and 105 deletions
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288
tractor/_context.py
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@ -86,30 +86,51 @@ class Context:
'''
chan: Channel
cid: str
cid: str # "context id", more or less a unique linked-task-pair id
# these are the "feeder" channels for delivering
# message values to the local task from the runtime
# msg processing loop.
# the "feeder" channels for delivering message values to the
# local task from the runtime's msg processing loop.
_recv_chan: trio.MemoryReceiveChannel
_send_chan: trio.MemorySendChannel
# the "invocation type" of the far end task-entry-point
# function, normally matching a logic block inside
# `._runtime.invoke()`.
_remote_func_type: str | None = None
# only set on the caller side
_portal: Portal | None = None # type: ignore # noqa
# NOTE: (for now) only set (a portal) on the caller side since
# the callee doesn't generally need a ref to one and should
# normally need to explicitly ask for handle to its peer if
# more the the `Context` is needed?
_portal: Portal | None = None
# NOTE: each side of the context has its own cancel scope
# which is exactly the primitive that allows for
# cross-actor-task-supervision and thus SC.
_scope: trio.CancelScope | None = None
_result: Any | int = None
_remote_error: BaseException | None = None
# cancellation state
_cancel_called: bool = False # did WE cancel the far end?
_cancelled_remote: tuple[str, str] | None = None
_cancel_msg: str | None = None
_scope: trio.CancelScope | None = None
# NOTE: this is set by the `.devx._debug` machinery
# to indicate whether code in `._runtime` should handle
# cancelled context crashes in the pdbp REPL.
# NOTE: we try to ensure assignment of a "cancel msg" since
# there's always going to be an "underlying reason" that any
# context was closed due to either a remote side error or
# a call to `.cancel()` which triggers `ContextCancelled`.
_cancel_msg: str | dict | None = None
# NOTE: this state var used by the runtime to determine if the
# `pdbp` REPL is allowed to engage on contexts terminated via
# a `ContextCancelled` due to a call to `.cancel()` triggering
# "graceful closure" on either side:
# - `._runtime._invoke()` will check this flag before engaging
# the crash handler REPL in such cases where the "callee"
# raises the cancellation,
# - `.devx._debug.lock_tty_for_child()` will set it to `False` if
# the global tty-lock has been configured to filter out some
# actors from being able to acquire the debugger lock.
_enter_debugger_on_cancel: bool = True
@property
@ -177,36 +198,71 @@ class Context:
async def _maybe_cancel_and_set_remote_error(
self,
error_msg: dict[str, Any],
error: BaseException,
) -> None:
'''
(Maybe) unpack and raise a msg error into the local scope
nursery for this context.
(Maybe) cancel this local scope due to a received remote
error (normally via an IPC msg) which the actor runtime
routes to this context.
Acts as a form of "relay" for a remote error raised
in the corresponding remote callee task.
Acts as a form of "relay" for a remote error raised in the
corresponding remote task's `Context` wherein the next time
the local task exectutes a checkpoint, a `trio.Cancelled`
will be raised and depending on the type and source of the
original remote error, and whether or not the local task
called `.cancel()` itself prior, an equivalent
`ContextCancelled` or `RemoteActorError` wrapping the
remote error may be raised here by any of,
- `Portal.open_context()`
- `Portal.result()`
- `Context.open_stream()`
- `Context.result()`
when called/closed by actor local task(s).
NOTEs & TODOs:
- It is expected that the caller has previously unwrapped
the remote error using a call to `unpack_error()` and
provides that output exception value as the input
`error` argument here.
- If this is an error message from a context opened by
`Portal.open_context()` we want to interrupt any
ongoing local tasks operating within that `Context`'s
cancel-scope so as to be notified ASAP of the remote
error and engage any caller handling (eg. for
cross-process task supervision).
- In some cases we may want to raise the remote error
immediately since there is no guarantee the locally
operating task(s) will attempt to execute a checkpoint
any time soon; in such cases there are 2 possible
approaches depending on the current task's work and
wrapping "thread" type:
- `trio`-native-and-graceful: only ever wait for tasks
to exec a next `trio.lowlevel.checkpoint()` assuming
that any such task must do so to interact with the
actor runtime and IPC interfaces.
- (NOT IMPLEMENTED) system-level-aggressive: maybe we
could eventually interrupt sync code (invoked using
`trio.to_thread` or some other adapter layer) with
a signal (a custom unix one for example?
https://stackoverflow.com/a/5744185) depending on the
task's wrapping thread-type such that long running
sync code should never cause the delay of actor
supervision tasks such as cancellation and respawn
logic.
'''
# If this is an error message from a context opened by
# ``Portal.open_context()`` we want to interrupt any ongoing
# (child) tasks within that context to be notified of the remote
# error relayed here.
#
# The reason we may want to raise the remote error immediately
# is that there is no guarantee the associated local task(s)
# will attempt to read from any locally opened stream any time
# soon.
#
# NOTE: this only applies when
# ``Portal.open_context()`` has been called since it is assumed
# (currently) that other portal APIs (``Portal.run()``,
# ``.run_in_actor()``) do their own error checking at the point
# of the call and result processing.
error = unpack_error(
error_msg,
self.chan,
)
# XXX: currently this should only be used when
# `Portal.open_context()` has been opened since it's
# assumed that other portal APIs like,
# - `Portal.run()`,
# - `ActorNursery.run_in_actor()`
# do their own error checking at their own call points and
# result processing.
# XXX: set the remote side's error so that after we cancel
# whatever task is the opener of this context it can raise
@ -236,35 +292,25 @@ class Context:
else:
log.error(
f'Remote context error for {self.chan.uid}:{self.cid}:\n'
f'{error_msg["error"]["tb_str"]}'
f'{error}'
)
# TODO: tempted to **not** do this by-reraising in a
# nursery and instead cancel a surrounding scope, detect
# the cancellation, then lookup the error that was set?
# YES! this is way better and simpler!
if (
self._scope
):
if self._scope:
# from trio.testing import wait_all_tasks_blocked
# await wait_all_tasks_blocked()
# self._cancelled_remote = self.chan.uid
self._scope.cancel()
# NOTE: this usage actually works here B)
# from .devx._debug import breakpoint
# await breakpoint()
# XXX: this will break early callee results sending
# since when `.result()` is finally called, this
# chan will be closed..
# if self._recv_chan:
# await self._recv_chan.aclose()
# this REPL usage actually works here BD
# from .devx._debug import pause
# await pause()
async def cancel(
self,
msg: str | None = None,
timeout: float = 0.616,
# timeout: float = 1000,
) -> None:
'''
@ -274,15 +320,12 @@ class Context:
Timeout quickly in an attempt to sidestep 2-generals...
'''
side = 'caller' if self._portal else 'callee'
if msg:
assert side == 'callee', 'Only callee side can provide cancel msg'
side: str = 'caller' if self._portal else 'callee'
log.cancel(
f'Cancelling {side} side of context to {self.chan.uid}'
)
log.cancel(f'Cancelling {side} side of context to {self.chan.uid}')
self._cancel_called = True
# await devx._debug.breakpoint()
# breakpoint()
self._cancel_called: bool = True
if side == 'caller':
if not self._portal:
@ -290,12 +333,13 @@ class Context:
"No portal found, this is likely a callee side context"
)
cid = self.cid
cid: str = self.cid
with trio.move_on_after(timeout) as cs:
cs.shield = True
log.cancel(
f"Cancelling stream {cid} to "
f"{self._portal.channel.uid}")
f'Cancelling stream {cid} to '
f'{self._portal.channel.uid}'
)
# NOTE: we're telling the far end actor to cancel a task
# corresponding to *this actor*. The far end local channel
@ -314,17 +358,17 @@ class Context:
# if not self._portal.channel.connected():
if not self.chan.connected():
log.cancel(
"May have failed to cancel remote task "
f"{cid} for {self._portal.channel.uid}")
'May have failed to cancel remote task '
f'{cid} for {self._portal.channel.uid}'
)
else:
log.cancel(
"Timed out on cancelling remote task "
f"{cid} for {self._portal.channel.uid}")
'Timed out on cancel request of remote task '
f'{cid} for {self._portal.channel.uid}'
)
# callee side remote task
else:
self._cancel_msg = msg
# TODO: should we have an explicit cancel message
# or is relaying the local `trio.Cancelled` as an
# {'error': trio.Cancelled, cid: "blah"} enough?
@ -335,7 +379,6 @@ class Context:
@acm
async def open_stream(
self,
allow_overruns: bool | None = False,
msg_buffer_size: int | None = None,
@ -354,10 +397,10 @@ class Context:
``Portal.open_context()``. In the future this may change but
currently there seems to be no obvious reason to support
"re-opening":
- pausing a stream can be done with a message.
- task errors will normally require a restart of the entire
scope of the inter-actor task context due to the nature of
``trio``'s cancellation system.
- pausing a stream can be done with a message.
- task errors will normally require a restart of the entire
scope of the inter-actor task context due to the nature of
``trio``'s cancellation system.
'''
actor = current_actor()
@ -439,18 +482,19 @@ class Context:
self,
err: Exception,
) -> None:
'''
Maybe raise a remote error depending on who (which task from
which actor) requested a cancellation (if any).
'''
# NOTE: whenever the context's "opener" side (task) **is**
# the side which requested the cancellation (likekly via
# ``Context.cancel()``), we don't want to re-raise that
# cancellation signal locally (would be akin to
# a ``trio.Nursery`` nursery raising ``trio.Cancelled``
# whenever ``CancelScope.cancel()`` was called) and instead
# silently reap the expected cancellation "error"-msg.
# if 'pikerd' in err.msgdata['tb_str']:
# # from . import _debug
# # await _debug.breakpoint()
# breakpoint()
# whenever ``CancelScope.cancel()`` was called) and
# instead silently reap the expected cancellation
# "error"-msg.
if (
isinstance(err, ContextCancelled)
and (
@ -461,7 +505,18 @@ class Context:
):
return err
raise err # from None
# NOTE: currently we are masking underlying runtime errors
# which are often superfluous to user handler code. not
# sure if this is still needed / desired for all operation?
# TODO: maybe we can only NOT mask if:
# - [ ] debug mode is enabled or,
# - [ ] a certain log level is set?
# - [ ] consider using `.with_traceback()` to filter out
# runtime frames from the tb explicitly?
# https://docs.python.org/3/reference/simple_stmts.html#the-raise-statement
# https://stackoverflow.com/a/24752607
__tracebackhide__: bool = True
raise err from None
async def result(self) -> Any | Exception:
'''
@ -489,12 +544,12 @@ class Context:
of the remote cancellation.
'''
__tracebackhide__: bool = True
assert self._portal, "Context.result() can not be called from callee!"
assert self._recv_chan
if re := self._remote_error:
self._maybe_raise_remote_err(re)
return re
return self._maybe_raise_remote_err(re)
if (
self._result == id(self)
@ -505,8 +560,8 @@ class Context:
# and discarding any bi dir stream msgs still
# in transit from the far end.
while True:
msg = await self._recv_chan.receive()
try:
msg = await self._recv_chan.receive()
self._result: Any = msg['return']
# NOTE: we don't need to do this right?
@ -519,17 +574,22 @@ class Context:
# NOTE: we get here if the far end was
# `ContextCancelled` in 2 cases:
# - we requested the cancellation and thus
# SHOULD NOT raise that far end error,
# - WE DID NOT REQUEST that cancel and thus
# SHOULD RAISE HERE!
# 1. we requested the cancellation and thus
# SHOULD NOT raise that far end error,
# 2. WE DID NOT REQUEST that cancel and thus
# SHOULD RAISE HERE!
except trio.Cancelled:
if not self._cancel_called:
raise self._remote_error
else:
# if we DID request the cancel we simply
# continue as normal.
raise
# CASE 2: mask the local cancelled-error(s)
# only when we are sure the remote error is the
# (likely) source cause of this local runtime
# task's cancellation.
if re := self._remote_error:
self._maybe_raise_remote_err(re)
# CASE 1: we DID request the cancel we simply
# continue to bubble up as normal.
raise
except KeyError: # as msgerr:
@ -544,7 +604,8 @@ class Context:
# internal error should never get here
assert msg.get('cid'), (
"Received internal error at portal?")
"Received internal error at portal?"
)
err = unpack_error(
msg,
@ -554,7 +615,10 @@ class Context:
err = self._maybe_raise_remote_err(err)
self._remote_error = err
return self._remote_error or self._result
if re := self._remote_error:
return self._maybe_raise_remote_err(re)
return self._result
async def started(
self,
@ -563,7 +627,7 @@ class Context:
) -> None:
'''
Indicate to calling actor's task that this linked context
has started and send ``value`` to the other side.
has started and send ``value`` to the other side via IPC.
On the calling side ``value`` is the second item delivered
in the tuple returned by ``Portal.open_context()``.
@ -571,19 +635,17 @@ class Context:
'''
if self._portal:
raise RuntimeError(
f"Caller side context {self} can not call started!")
f'Caller side context {self} can not call started!'
)
elif self._started_called:
raise RuntimeError(
f"called 'started' twice on context with {self.chan.uid}")
f'called `.started()` twice on context with {self.chan.uid}'
)
await self.chan.send({'started': value, 'cid': self.cid})
self._started_called = True
# TODO: do we need a restart api?
# async def restart(self) -> None:
# pass
async def _drain_overflows(
self,
) -> None:
@ -638,10 +700,21 @@ class Context:
self,
msg: dict,
draining: bool = False,
# draining: bool = False,
) -> bool:
'''
Deliver an IPC msg received from a transport-channel to
this context's underlying mem chan for handling by
user operating tasks; deliver a bool indicating whether the
msg was immediately sent.
If `._allow_overruns == True` (maybe) append the msg to an
"overflow queue" and start a "drainer task" (inside the
`._scope_nursery: trio.Nursery`) which ensures that such
messages are eventually sent if possible.
'''
cid = self.cid
chan = self.chan
uid = chan.uid
@ -652,8 +725,12 @@ class Context:
)
error = msg.get('error')
if error:
await self._maybe_cancel_and_set_remote_error(msg)
if error := unpack_error(
msg,
self.chan,
):
self._cancel_msg = msg
await self._maybe_cancel_and_set_remote_error(error)
if (
self._in_overrun
@ -685,6 +762,7 @@ class Context:
# the sender; the main motivation is that using bp can block the
# msg handling loop which calls into this method!
except trio.WouldBlock:
# XXX: always push an error even if the local
# receiver is in overrun state.
# await self._maybe_cancel_and_set_remote_error(msg)