Get mega-pedantic in `Portal.open_context()`
Specifically in the `.__aexit__()` phase to ensure remote, runtime-internal, and locally raised error-during-cancelled-handling exceptions are NEVER masked by a local `ContextCancelled` or any exception group of `trio.Cancelled`s. Also adds a ton of details to doc strings including extreme detail surrounding the `ContextCancelled` raising cases and their processing inside `.open_context()`'s exception handler blocks. Details, details: - internal rename `err`/`_err` stuff to just be `scope_err` since it's effectively the error bubbled up from the context's surrounding (and cross-actor) "scope". - always shield `._recv_chan.aclose()` to avoid any `Cancelled` from masking the `scope_err` with a runtime related `trio.Cancelled`. - explicitly catch the specific set of `scope_err: BaseException` that we can reasonably expect to handle instead of the catch-all parent type including exception groups, cancels and KBIs.multihomed
Tyler Goodlet
parent
7eb31f3fea
commit
63b1488ab6
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@ -15,8 +15,12 @@
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# along with this program. If not, see <https://www.gnu.org/licenses/>.
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'''
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Memory boundary "Portals": an API for structured
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concurrency linked tasks running in disparate memory domains.
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Memory "portal" contruct.
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"Memory portals" are both an API and set of IPC wrapping primitives
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for managing structured concurrency "cancel-scope linked" tasks
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running in disparate virtual memory domains - at least in different
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OS processes, possibly on different (hardware) hosts.
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'''
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from __future__ import annotations
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@ -47,6 +51,7 @@ from ._exceptions import (
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)
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from ._context import Context
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from ._streaming import MsgStream
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from .devx._debug import maybe_wait_for_debugger
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log = get_logger(__name__)
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@ -66,20 +71,21 @@ def _unwrap_msg(
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raise unpack_error(msg, channel) from None
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# TODO: maybe move this to ._exceptions?
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class MessagingError(Exception):
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'Some kind of unexpected SC messaging dialog issue'
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class Portal:
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'''
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A 'portal' to a(n) (remote) ``Actor``.
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A 'portal' to a memory-domain-separated `Actor`.
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A portal is "opened" (and eventually closed) by one side of an
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inter-actor communication context. The side which opens the portal
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is equivalent to a "caller" in function parlance and usually is
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either the called actor's parent (in process tree hierarchy terms)
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or a client interested in scheduling work to be done remotely in a
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far process.
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process which has a separate (virtual) memory domain.
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The portal api allows the "caller" actor to invoke remote routines
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and receive results through an underlying ``tractor.Channel`` as
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@ -89,9 +95,9 @@ class Portal:
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like having a "portal" between the seperate actor memory spaces.
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'''
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# the timeout for a remote cancel request sent to
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# a(n) (peer) actor.
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cancel_timeout = 0.5
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# global timeout for remote cancel requests sent to
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# connected (peer) actors.
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cancel_timeout: float = 0.5
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def __init__(self, channel: Channel) -> None:
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self.channel = channel
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@ -393,12 +399,32 @@ class Portal:
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) -> AsyncGenerator[tuple[Context, Any], None]:
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'''
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Open an inter-actor task context.
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Open an inter-actor "task context"; a remote task is
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scheduled and cancel-scope-state-linked to a `trio.run()` across
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memory boundaries in another actor's runtime.
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This is a synchronous API which allows for deterministic
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setup/teardown of a remote task. The yielded ``Context`` further
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allows for opening bidirectional streams, explicit cancellation
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and synchronized final result collection. See ``tractor.Context``.
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This is an `@acm` API which allows for deterministic setup
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and teardown of a remotely scheduled task in another remote
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actor. Once opened, the 2 now "linked" tasks run completely
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in parallel in each actor's runtime with their enclosing
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`trio.CancelScope`s kept in a synced state wherein if
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either side errors or cancels an equivalent error is
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relayed to the other side via an SC-compat IPC protocol.
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The yielded `tuple` is a pair delivering a `tractor.Context`
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and any first value "sent" by the "callee" task via a call
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to `Context.started(<value: Any>)`; this side of the
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context does not unblock until the "callee" task calls
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`.started()` in similar style to `trio.Nursery.start()`.
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When the "callee" (side that is "called"/started by a call
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to *this* method) returns, the caller side (this) unblocks
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and any final value delivered from the other end can be
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retrieved using the `Contex.result()` api.
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The yielded ``Context`` instance further allows for opening
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bidirectional streams, explicit cancellation and
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structurred-concurrency-synchronized final result-msg
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collection. See ``tractor.Context`` for more details.
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'''
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# conduct target func method structural checks
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)
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assert ctx._remote_func_type == 'context'
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msg = await ctx._recv_chan.receive()
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msg: dict = await ctx._recv_chan.receive()
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try:
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# the "first" value here is delivered by the callee's
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# ``Context.started()`` call.
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first = msg['started']
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ctx._started_called = True
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ctx._started_called: bool = True
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except KeyError:
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assert msg.get('cid'), ("Received internal error at context?")
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if not (cid := msg.get('cid')):
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raise MessagingError(
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'Received internal error at context?\n'
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'No call-id (cid) in startup msg?'
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)
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if msg.get('error'):
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# raise kerr from unpack_error(msg, self.channel)
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# NOTE: mask the key error with the remote one
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raise unpack_error(msg, self.channel) from None
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else:
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raise MessagingError(
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f'Context for {ctx.cid} was expecting a `started` message'
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f' but received a non-error msg:\n{pformat(msg)}'
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f'Context for {cid} was expecting a `started` message'
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' but received a non-error msg:\n'
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f'{pformat(msg)}'
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)
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_err: BaseException | None = None
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ctx._portal: Portal = self
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uid: tuple = self.channel.uid
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cid: str = ctx.cid
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etype: Type[BaseException] | None = None
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# deliver context instance and .started() msg value in enter
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# tuple.
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# placeholder for any exception raised in the runtime
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# or by user tasks which cause this context's closure.
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scope_err: BaseException | None = None
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try:
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async with trio.open_nursery() as nurse:
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ctx._scope_nursery = nurse
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ctx._scope = nurse.cancel_scope
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ctx._scope_nursery: trio.Nursery = nurse
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ctx._scope: trio.CancelScope = nurse.cancel_scope
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# deliver context instance and .started() msg value
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# in enter tuple.
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yield ctx, first
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# when in allow_ovveruns mode there may be lingering
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# overflow sender tasks remaining?
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# when in allow_overruns mode there may be
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# lingering overflow sender tasks remaining?
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if nurse.child_tasks:
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# ensure we are in overrun state with
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# ``._allow_overruns=True`` bc otherwise
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# XXX: ensure we are in overrun state
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# with ``._allow_overruns=True`` bc otherwise
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# there should be no tasks in this nursery!
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if (
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not ctx._allow_overruns
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):
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raise RuntimeError(
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'Context has sub-tasks but is '
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'not in `allow_overruns=True` Mode!?'
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'not in `allow_overruns=True` mode!?'
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)
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# ensure cancel of all overflow sender tasks
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# started in the ctx nursery.
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ctx._scope.cancel()
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except ContextCancelled as err:
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_err = err
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# XXX: (maybe) shield/mask context-cancellations that were
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# initiated by any of the context's 2 tasks. There are
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# subsequently 2 operating cases for a "graceful cancel"
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# of a `Context`:
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#
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# 1.*this* side's task called `Context.cancel()`, in
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# which case we mask the `ContextCancelled` from bubbling
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# to the opener (much like how `trio.Nursery` swallows
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# any `trio.Cancelled` bubbled by a call to
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# `Nursery.cancel_scope.cancel()`)
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#
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# 2.*the other* side's (callee/spawned) task cancelled due
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# to a self or peer cancellation request in which case we
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# DO let the error bubble to the opener.
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except ContextCancelled as ctxc:
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scope_err = ctxc
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# swallow and mask cross-actor task context cancels that
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# were initiated by *this* side's task.
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# CASE 1: this context was never cancelled
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# via a local task's call to `Context.cancel()`.
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if not ctx._cancel_called:
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# XXX: this should NEVER happen!
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# from .devx._debug import breakpoint
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# await breakpoint()
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raise
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# if the context was cancelled by client code
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# then we don't need to raise since user code
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# is expecting this and the block should exit.
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# CASE 2: context was cancelled by local task calling
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# `.cancel()`, we don't raise and the exit block should
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# exit silently.
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else:
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log.debug(f'Context {ctx} cancelled gracefully')
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log.debug(
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f'Context {ctx} cancelled gracefully with:\n'
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f'{ctxc}'
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)
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except (
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BaseException,
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# - a standard error in the caller/yieldee
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Exception,
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# more specifically, we need to handle these but not
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# sure it's worth being pedantic:
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# Exception,
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# trio.Cancelled,
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# KeyboardInterrupt,
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# - a runtime teardown exception-group and/or
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# cancellation request from a caller task.
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BaseExceptionGroup,
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trio.Cancelled,
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KeyboardInterrupt,
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) as err:
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etype = type(err)
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scope_err = err
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# cancel ourselves on any error.
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# XXX: request cancel of this context on any error.
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# NOTE: `Context.cancel()` is conversely NOT called in
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# the `ContextCancelled` "cancellation requested" case
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# above.
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log.cancel(
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'Context cancelled for task, sending cancel request..\n'
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'Context cancelled for task due to\n'
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f'{err}\n'
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'Sending cancel request..\n'
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f'task:{cid}\n'
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f'actor:{uid}'
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)
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try:
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await ctx.cancel()
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except trio.BrokenResourceError:
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log.warning(
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@ -528,8 +581,9 @@ class Portal:
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f'actor:{uid}'
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)
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raise
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raise # duh
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# no scope error case
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else:
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if ctx.chan.connected():
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log.info(
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@ -537,10 +591,20 @@ class Portal:
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f'task: {cid}\n'
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f'actor: {uid}'
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)
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# XXX NOTE XXX: the below call to
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# `Context.result()` will ALWAYS raise
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# a `ContextCancelled` (via an embedded call to
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# `Context._maybe_raise_remote_err()`) IFF
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# a `Context._remote_error` was set by the runtime
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# via a call to
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# `Context._maybe_cancel_and_set_remote_error()`
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# which IS SET any time the far end fails and
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# causes "caller side" cancellation via
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# a `ContextCancelled` here.
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result = await ctx.result()
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log.runtime(
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f'Context {fn_name} returned '
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f'value from callee `{result}`'
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f'Context {fn_name} returned value from callee:\n'
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f'`{result}`'
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)
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finally:
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@ -548,22 +612,73 @@ class Portal:
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# operating *in* this scope to have survived
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# we tear down the runtime feeder chan last
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# to avoid premature stream clobbers.
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if ctx._recv_chan is not None:
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# should we encapsulate this in the context api?
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await ctx._recv_chan.aclose()
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rxchan: trio.ReceiveChannel = ctx._recv_chan
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if (
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rxchan
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if etype:
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# maybe TODO: yes i know the below check is
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# touching `trio` memchan internals..BUT, there are
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# only a couple ways to avoid a `trio.Cancelled`
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# bubbling from the `.aclose()` call below:
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#
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# - catch and mask it via the cancel-scope-shielded call
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# as we are rn (manual and frowned upon) OR,
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# - specially handle the case where `scope_err` is
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# one of {`BaseExceptionGroup`, `trio.Cancelled`}
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# and then presume that the `.aclose()` call will
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# raise a `trio.Cancelled` and just don't call it
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# in those cases..
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#
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# that latter approach is more logic, LOC, and more
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# convoluted so for now stick with the first
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# psuedo-hack-workaround where we just try to avoid
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# the shielded call as much as we can detect from
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# the memchan's `._closed` state..
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#
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# XXX MOTIVATION XXX-> we generally want to raise
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# any underlying actor-runtime/internals error that
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# surfaces from a bug in tractor itself so it can
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# be easily detected/fixed AND, we also want to
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# minimize noisy runtime tracebacks (normally due
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# to the cross-actor linked task scope machinery
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# teardown) displayed to user-code and instead only
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# displaying `ContextCancelled` traces where the
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# cause of crash/exit IS due to something in
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# user/app code on either end of the context.
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and not rxchan._closed
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):
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# XXX NOTE XXX: and again as per above, we mask any
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# `trio.Cancelled` raised here so as to NOT mask
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# out any exception group or legit (remote) ctx
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# error that sourced from the remote task or its
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# runtime.
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with trio.CancelScope(shield=True):
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await ctx._recv_chan.aclose()
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# XXX: since we always (maybe) re-raise (and thus also
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# mask runtime machinery related
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# multi-`trio.Cancelled`s) any scope error which was
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# the underlying cause of this context's exit, add
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# different log msgs for each of the (2) cases.
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if scope_err is not None:
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etype: Type[BaseException] = type(scope_err)
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# CASE 2
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if ctx._cancel_called:
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log.cancel(
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f'Context {fn_name} cancelled by caller with\n{etype}'
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f'Context {fn_name} cancelled by caller with\n'
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f'{etype}'
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)
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elif _err is not None:
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# CASE 1
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else:
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log.cancel(
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f'Context for task cancelled by callee with {etype}\n'
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f'Context cancelled by callee with {etype}\n'
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f'target: `{fn_name}`\n'
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f'task:{cid}\n'
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f'actor:{uid}'
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)
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# XXX: (MEGA IMPORTANT) if this is a root opened process we
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# wait for any immediate child in debug before popping the
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# context from the runtime msg loop otherwise inside
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@ -572,10 +687,10 @@ class Portal:
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# a "stop" msg for a stream), this can result in a deadlock
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# where the root is waiting on the lock to clear but the
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# child has already cleared it and clobbered IPC.
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from .devx._debug import maybe_wait_for_debugger
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await maybe_wait_for_debugger()
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# remove the context from runtime tracking
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# FINALLY, remove the context from runtime tracking and
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# exit Bo
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self.actor._contexts.pop(
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(self.channel.uid, ctx.cid),
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None,
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Loading…
Reference in New Issue