690 lines
23 KiB
Python
690 lines
23 KiB
Python
# Copyright 2014-2016 OpenMarket Ltd
|
|
# Copyright 2018 New Vector Ltd
|
|
#
|
|
# Licensed under the Apache License, Version 2.0 (the "License");
|
|
# you may not use this file except in compliance with the License.
|
|
# You may obtain a copy of the License at
|
|
#
|
|
# http://www.apache.org/licenses/LICENSE-2.0
|
|
#
|
|
# Unless required by applicable law or agreed to in writing, software
|
|
# distributed under the License is distributed on an "AS IS" BASIS,
|
|
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
# See the License for the specific language governing permissions and
|
|
# limitations under the License.
|
|
|
|
import abc
|
|
import collections
|
|
import inspect
|
|
import itertools
|
|
import logging
|
|
from contextlib import contextmanager
|
|
from typing import (
|
|
Any,
|
|
Awaitable,
|
|
Callable,
|
|
Collection,
|
|
Dict,
|
|
Generic,
|
|
Hashable,
|
|
Iterable,
|
|
Iterator,
|
|
List,
|
|
Optional,
|
|
Set,
|
|
Tuple,
|
|
TypeVar,
|
|
Union,
|
|
cast,
|
|
overload,
|
|
)
|
|
|
|
import attr
|
|
from typing_extensions import ContextManager
|
|
|
|
from twisted.internet import defer
|
|
from twisted.internet.defer import CancelledError
|
|
from twisted.internet.interfaces import IReactorTime
|
|
from twisted.python.failure import Failure
|
|
|
|
from synapse.logging.context import (
|
|
PreserveLoggingContext,
|
|
make_deferred_yieldable,
|
|
run_in_background,
|
|
)
|
|
from synapse.util import Clock
|
|
|
|
logger = logging.getLogger(__name__)
|
|
|
|
_T = TypeVar("_T")
|
|
|
|
|
|
class AbstractObservableDeferred(Generic[_T], metaclass=abc.ABCMeta):
|
|
"""Abstract base class defining the consumer interface of ObservableDeferred"""
|
|
|
|
__slots__ = ()
|
|
|
|
@abc.abstractmethod
|
|
def observe(self) -> "defer.Deferred[_T]":
|
|
"""Add a new observer for this ObservableDeferred
|
|
|
|
This returns a brand new deferred that is resolved when the underlying
|
|
deferred is resolved. Interacting with the returned deferred does not
|
|
effect the underlying deferred.
|
|
|
|
Note that the returned Deferred doesn't follow the Synapse logcontext rules -
|
|
you will probably want to `make_deferred_yieldable` it.
|
|
"""
|
|
...
|
|
|
|
|
|
class ObservableDeferred(Generic[_T], AbstractObservableDeferred[_T]):
|
|
"""Wraps a deferred object so that we can add observer deferreds. These
|
|
observer deferreds do not affect the callback chain of the original
|
|
deferred.
|
|
|
|
If consumeErrors is true errors will be captured from the origin deferred.
|
|
|
|
Cancelling or otherwise resolving an observer will not affect the original
|
|
ObservableDeferred.
|
|
|
|
NB that it does not attempt to do anything with logcontexts; in general
|
|
you should probably make_deferred_yieldable the deferreds
|
|
returned by `observe`, and ensure that the original deferred runs its
|
|
callbacks in the sentinel logcontext.
|
|
"""
|
|
|
|
__slots__ = ["_deferred", "_observers", "_result"]
|
|
|
|
def __init__(self, deferred: "defer.Deferred[_T]", consumeErrors: bool = False):
|
|
object.__setattr__(self, "_deferred", deferred)
|
|
object.__setattr__(self, "_result", None)
|
|
object.__setattr__(self, "_observers", [])
|
|
|
|
def callback(r: _T) -> _T:
|
|
object.__setattr__(self, "_result", (True, r))
|
|
|
|
# once we have set _result, no more entries will be added to _observers,
|
|
# so it's safe to replace it with the empty tuple.
|
|
observers = self._observers
|
|
object.__setattr__(self, "_observers", ())
|
|
|
|
for observer in observers:
|
|
try:
|
|
observer.callback(r)
|
|
except Exception as e:
|
|
logger.exception(
|
|
"%r threw an exception on .callback(%r), ignoring...",
|
|
observer,
|
|
r,
|
|
exc_info=e,
|
|
)
|
|
return r
|
|
|
|
def errback(f: Failure) -> Optional[Failure]:
|
|
object.__setattr__(self, "_result", (False, f))
|
|
|
|
# once we have set _result, no more entries will be added to _observers,
|
|
# so it's safe to replace it with the empty tuple.
|
|
observers = self._observers
|
|
object.__setattr__(self, "_observers", ())
|
|
|
|
for observer in observers:
|
|
# This is a little bit of magic to correctly propagate stack
|
|
# traces when we `await` on one of the observer deferreds.
|
|
f.value.__failure__ = f # type: ignore[union-attr]
|
|
try:
|
|
observer.errback(f)
|
|
except Exception as e:
|
|
logger.exception(
|
|
"%r threw an exception on .errback(%r), ignoring...",
|
|
observer,
|
|
f,
|
|
exc_info=e,
|
|
)
|
|
|
|
if consumeErrors:
|
|
return None
|
|
else:
|
|
return f
|
|
|
|
deferred.addCallbacks(callback, errback)
|
|
|
|
def observe(self) -> "defer.Deferred[_T]":
|
|
"""Observe the underlying deferred.
|
|
|
|
This returns a brand new deferred that is resolved when the underlying
|
|
deferred is resolved. Interacting with the returned deferred does not
|
|
effect the underlying deferred.
|
|
"""
|
|
if not self._result:
|
|
d: "defer.Deferred[_T]" = defer.Deferred()
|
|
self._observers.append(d)
|
|
return d
|
|
else:
|
|
success, res = self._result
|
|
return defer.succeed(res) if success else defer.fail(res)
|
|
|
|
def observers(self) -> "Collection[defer.Deferred[_T]]":
|
|
return self._observers
|
|
|
|
def has_called(self) -> bool:
|
|
return self._result is not None
|
|
|
|
def has_succeeded(self) -> bool:
|
|
return self._result is not None and self._result[0] is True
|
|
|
|
def get_result(self) -> Union[_T, Failure]:
|
|
return self._result[1]
|
|
|
|
def __getattr__(self, name: str) -> Any:
|
|
return getattr(self._deferred, name)
|
|
|
|
def __setattr__(self, name: str, value: Any) -> None:
|
|
setattr(self._deferred, name, value)
|
|
|
|
def __repr__(self) -> str:
|
|
return "<ObservableDeferred object at %s, result=%r, _deferred=%r>" % (
|
|
id(self),
|
|
self._result,
|
|
self._deferred,
|
|
)
|
|
|
|
|
|
T = TypeVar("T")
|
|
|
|
|
|
async def concurrently_execute(
|
|
func: Callable[[T], Any], args: Iterable[T], limit: int
|
|
) -> None:
|
|
"""Executes the function with each argument concurrently while limiting
|
|
the number of concurrent executions.
|
|
|
|
Args:
|
|
func: Function to execute, should return a deferred or coroutine.
|
|
args: List of arguments to pass to func, each invocation of func
|
|
gets a single argument.
|
|
limit: Maximum number of conccurent executions.
|
|
|
|
Returns:
|
|
Deferred: Resolved when all function invocations have finished.
|
|
"""
|
|
it = iter(args)
|
|
|
|
async def _concurrently_execute_inner(value: T) -> None:
|
|
try:
|
|
while True:
|
|
await maybe_awaitable(func(value))
|
|
value = next(it)
|
|
except StopIteration:
|
|
pass
|
|
|
|
# We use `itertools.islice` to handle the case where the number of args is
|
|
# less than the limit, avoiding needlessly spawning unnecessary background
|
|
# tasks.
|
|
await yieldable_gather_results(
|
|
_concurrently_execute_inner, (value for value in itertools.islice(it, limit))
|
|
)
|
|
|
|
|
|
async def yieldable_gather_results(
|
|
func: Callable[..., Awaitable[T]], iter: Iterable, *args: Any, **kwargs: Any
|
|
) -> List[T]:
|
|
"""Executes the function with each argument concurrently.
|
|
|
|
Args:
|
|
func: Function to execute that returns a Deferred
|
|
iter: An iterable that yields items that get passed as the first
|
|
argument to the function
|
|
*args: Arguments to be passed to each call to func
|
|
**kwargs: Keyword arguments to be passed to each call to func
|
|
|
|
Returns
|
|
A list containing the results of the function
|
|
"""
|
|
try:
|
|
return await make_deferred_yieldable(
|
|
defer.gatherResults(
|
|
[run_in_background(func, item, *args, **kwargs) for item in iter],
|
|
consumeErrors=True,
|
|
)
|
|
)
|
|
except defer.FirstError as dfe:
|
|
# unwrap the error from defer.gatherResults.
|
|
|
|
# The raised exception's traceback only includes func() etc if
|
|
# the 'await' happens before the exception is thrown - ie if the failure
|
|
# happens *asynchronously* - otherwise Twisted throws away the traceback as it
|
|
# could be large.
|
|
#
|
|
# We could maybe reconstruct a fake traceback from Failure.frames. Or maybe
|
|
# we could throw Twisted into the fires of Mordor.
|
|
|
|
# suppress exception chaining, because the FirstError doesn't tell us anything
|
|
# very interesting.
|
|
assert isinstance(dfe.subFailure.value, BaseException)
|
|
raise dfe.subFailure.value from None
|
|
|
|
|
|
T1 = TypeVar("T1")
|
|
T2 = TypeVar("T2")
|
|
T3 = TypeVar("T3")
|
|
|
|
|
|
@overload
|
|
def gather_results(
|
|
deferredList: Tuple[()], consumeErrors: bool = ...
|
|
) -> "defer.Deferred[Tuple[()]]":
|
|
...
|
|
|
|
|
|
@overload
|
|
def gather_results(
|
|
deferredList: Tuple["defer.Deferred[T1]"],
|
|
consumeErrors: bool = ...,
|
|
) -> "defer.Deferred[Tuple[T1]]":
|
|
...
|
|
|
|
|
|
@overload
|
|
def gather_results(
|
|
deferredList: Tuple["defer.Deferred[T1]", "defer.Deferred[T2]"],
|
|
consumeErrors: bool = ...,
|
|
) -> "defer.Deferred[Tuple[T1, T2]]":
|
|
...
|
|
|
|
|
|
@overload
|
|
def gather_results(
|
|
deferredList: Tuple[
|
|
"defer.Deferred[T1]", "defer.Deferred[T2]", "defer.Deferred[T3]"
|
|
],
|
|
consumeErrors: bool = ...,
|
|
) -> "defer.Deferred[Tuple[T1, T2, T3]]":
|
|
...
|
|
|
|
|
|
def gather_results( # type: ignore[misc]
|
|
deferredList: Tuple["defer.Deferred[T1]", ...],
|
|
consumeErrors: bool = False,
|
|
) -> "defer.Deferred[Tuple[T1, ...]]":
|
|
"""Combines a tuple of `Deferred`s into a single `Deferred`.
|
|
|
|
Wraps `defer.gatherResults` to provide type annotations that support heterogenous
|
|
lists of `Deferred`s.
|
|
"""
|
|
# The `type: ignore[misc]` above suppresses
|
|
# "Overloaded function implementation cannot produce return type of signature 1/2/3"
|
|
deferred = defer.gatherResults(deferredList, consumeErrors=consumeErrors)
|
|
return deferred.addCallback(tuple)
|
|
|
|
|
|
@attr.s(slots=True, auto_attribs=True)
|
|
class _LinearizerEntry:
|
|
# The number of things executing.
|
|
count: int
|
|
# Deferreds for the things blocked from executing.
|
|
deferreds: collections.OrderedDict
|
|
|
|
|
|
class Linearizer:
|
|
"""Limits concurrent access to resources based on a key. Useful to ensure
|
|
only a few things happen at a time on a given resource.
|
|
|
|
Example:
|
|
|
|
with await limiter.queue("test_key"):
|
|
# do some work.
|
|
|
|
"""
|
|
|
|
def __init__(
|
|
self,
|
|
name: Optional[str] = None,
|
|
max_count: int = 1,
|
|
clock: Optional[Clock] = None,
|
|
):
|
|
"""
|
|
Args:
|
|
max_count: The maximum number of concurrent accesses
|
|
"""
|
|
if name is None:
|
|
self.name: Union[str, int] = id(self)
|
|
else:
|
|
self.name = name
|
|
|
|
if not clock:
|
|
from twisted.internet import reactor
|
|
|
|
clock = Clock(cast(IReactorTime, reactor))
|
|
self._clock = clock
|
|
self.max_count = max_count
|
|
|
|
# key_to_defer is a map from the key to a _LinearizerEntry.
|
|
self.key_to_defer: Dict[Hashable, _LinearizerEntry] = {}
|
|
|
|
def is_queued(self, key: Hashable) -> bool:
|
|
"""Checks whether there is a process queued up waiting"""
|
|
entry = self.key_to_defer.get(key)
|
|
if not entry:
|
|
# No entry so nothing is waiting.
|
|
return False
|
|
|
|
# There are waiting deferreds only in the OrderedDict of deferreds is
|
|
# non-empty.
|
|
return bool(entry.deferreds)
|
|
|
|
def queue(self, key: Hashable) -> defer.Deferred:
|
|
# we avoid doing defer.inlineCallbacks here, so that cancellation works correctly.
|
|
# (https://twistedmatrix.com/trac/ticket/4632 meant that cancellations were not
|
|
# propagated inside inlineCallbacks until Twisted 18.7)
|
|
entry = self.key_to_defer.setdefault(
|
|
key, _LinearizerEntry(0, collections.OrderedDict())
|
|
)
|
|
|
|
# If the number of things executing is greater than the maximum
|
|
# then add a deferred to the list of blocked items
|
|
# When one of the things currently executing finishes it will callback
|
|
# this item so that it can continue executing.
|
|
if entry.count >= self.max_count:
|
|
res = self._await_lock(key)
|
|
else:
|
|
logger.debug(
|
|
"Acquired uncontended linearizer lock %r for key %r", self.name, key
|
|
)
|
|
entry.count += 1
|
|
res = defer.succeed(None)
|
|
|
|
# once we successfully get the lock, we need to return a context manager which
|
|
# will release the lock.
|
|
|
|
@contextmanager
|
|
def _ctx_manager(_: None) -> Iterator[None]:
|
|
try:
|
|
yield
|
|
finally:
|
|
logger.debug("Releasing linearizer lock %r for key %r", self.name, key)
|
|
|
|
# We've finished executing so check if there are any things
|
|
# blocked waiting to execute and start one of them
|
|
entry.count -= 1
|
|
|
|
if entry.deferreds:
|
|
(next_def, _) = entry.deferreds.popitem(last=False)
|
|
|
|
# we need to run the next thing in the sentinel context.
|
|
with PreserveLoggingContext():
|
|
next_def.callback(None)
|
|
elif entry.count == 0:
|
|
# We were the last thing for this key: remove it from the
|
|
# map.
|
|
del self.key_to_defer[key]
|
|
|
|
res.addCallback(_ctx_manager)
|
|
return res
|
|
|
|
def _await_lock(self, key: Hashable) -> defer.Deferred:
|
|
"""Helper for queue: adds a deferred to the queue
|
|
|
|
Assumes that we've already checked that we've reached the limit of the number
|
|
of lock-holders we allow. Creates a new deferred which is added to the list, and
|
|
adds some management around cancellations.
|
|
|
|
Returns the deferred, which will callback once we have secured the lock.
|
|
|
|
"""
|
|
entry = self.key_to_defer[key]
|
|
|
|
logger.debug("Waiting to acquire linearizer lock %r for key %r", self.name, key)
|
|
|
|
new_defer: "defer.Deferred[None]" = make_deferred_yieldable(defer.Deferred())
|
|
entry.deferreds[new_defer] = 1
|
|
|
|
def cb(_r: None) -> "defer.Deferred[None]":
|
|
logger.debug("Acquired linearizer lock %r for key %r", self.name, key)
|
|
entry.count += 1
|
|
|
|
# if the code holding the lock completes synchronously, then it
|
|
# will recursively run the next claimant on the list. That can
|
|
# relatively rapidly lead to stack exhaustion. This is essentially
|
|
# the same problem as http://twistedmatrix.com/trac/ticket/9304.
|
|
#
|
|
# In order to break the cycle, we add a cheeky sleep(0) here to
|
|
# ensure that we fall back to the reactor between each iteration.
|
|
#
|
|
# (This needs to happen while we hold the lock, and the context manager's exit
|
|
# code must be synchronous, so this is the only sensible place.)
|
|
return self._clock.sleep(0)
|
|
|
|
def eb(e: Failure) -> Failure:
|
|
logger.info("defer %r got err %r", new_defer, e)
|
|
if isinstance(e, CancelledError):
|
|
logger.debug(
|
|
"Cancelling wait for linearizer lock %r for key %r", self.name, key
|
|
)
|
|
|
|
else:
|
|
logger.warning(
|
|
"Unexpected exception waiting for linearizer lock %r for key %r",
|
|
self.name,
|
|
key,
|
|
)
|
|
|
|
# we just have to take ourselves back out of the queue.
|
|
del entry.deferreds[new_defer]
|
|
return e
|
|
|
|
new_defer.addCallbacks(cb, eb)
|
|
return new_defer
|
|
|
|
|
|
class ReadWriteLock:
|
|
"""An async read write lock.
|
|
|
|
Example:
|
|
|
|
with await read_write_lock.read("test_key"):
|
|
# do some work
|
|
"""
|
|
|
|
# IMPLEMENTATION NOTES
|
|
#
|
|
# We track the most recent queued reader and writer deferreds (which get
|
|
# resolved when they release the lock).
|
|
#
|
|
# Read: We know its safe to acquire a read lock when the latest writer has
|
|
# been resolved. The new reader is appended to the list of latest readers.
|
|
#
|
|
# Write: We know its safe to acquire the write lock when both the latest
|
|
# writers and readers have been resolved. The new writer replaces the latest
|
|
# writer.
|
|
|
|
def __init__(self) -> None:
|
|
# Latest readers queued
|
|
self.key_to_current_readers: Dict[str, Set[defer.Deferred]] = {}
|
|
|
|
# Latest writer queued
|
|
self.key_to_current_writer: Dict[str, defer.Deferred] = {}
|
|
|
|
async def read(self, key: str) -> ContextManager:
|
|
new_defer: "defer.Deferred[None]" = defer.Deferred()
|
|
|
|
curr_readers = self.key_to_current_readers.setdefault(key, set())
|
|
curr_writer = self.key_to_current_writer.get(key, None)
|
|
|
|
curr_readers.add(new_defer)
|
|
|
|
# We wait for the latest writer to finish writing. We can safely ignore
|
|
# any existing readers... as they're readers.
|
|
if curr_writer:
|
|
await make_deferred_yieldable(curr_writer)
|
|
|
|
@contextmanager
|
|
def _ctx_manager() -> Iterator[None]:
|
|
try:
|
|
yield
|
|
finally:
|
|
with PreserveLoggingContext():
|
|
new_defer.callback(None)
|
|
self.key_to_current_readers.get(key, set()).discard(new_defer)
|
|
|
|
return _ctx_manager()
|
|
|
|
async def write(self, key: str) -> ContextManager:
|
|
new_defer: "defer.Deferred[None]" = defer.Deferred()
|
|
|
|
curr_readers = self.key_to_current_readers.get(key, set())
|
|
curr_writer = self.key_to_current_writer.get(key, None)
|
|
|
|
# We wait on all latest readers and writer.
|
|
to_wait_on = list(curr_readers)
|
|
if curr_writer:
|
|
to_wait_on.append(curr_writer)
|
|
|
|
# We can clear the list of current readers since the new writer waits
|
|
# for them to finish.
|
|
curr_readers.clear()
|
|
self.key_to_current_writer[key] = new_defer
|
|
|
|
await make_deferred_yieldable(defer.gatherResults(to_wait_on))
|
|
|
|
@contextmanager
|
|
def _ctx_manager() -> Iterator[None]:
|
|
try:
|
|
yield
|
|
finally:
|
|
with PreserveLoggingContext():
|
|
new_defer.callback(None)
|
|
# `self.key_to_current_writer[key]` may be missing if there was another
|
|
# writer waiting for us and it completed entirely within the
|
|
# `new_defer.callback()` call above.
|
|
if self.key_to_current_writer.get(key) == new_defer:
|
|
self.key_to_current_writer.pop(key)
|
|
|
|
return _ctx_manager()
|
|
|
|
|
|
R = TypeVar("R")
|
|
|
|
|
|
def timeout_deferred(
|
|
deferred: "defer.Deferred[_T]", timeout: float, reactor: IReactorTime
|
|
) -> "defer.Deferred[_T]":
|
|
"""The in built twisted `Deferred.addTimeout` fails to time out deferreds
|
|
that have a canceller that throws exceptions. This method creates a new
|
|
deferred that wraps and times out the given deferred, correctly handling
|
|
the case where the given deferred's canceller throws.
|
|
|
|
(See https://twistedmatrix.com/trac/ticket/9534)
|
|
|
|
NOTE: Unlike `Deferred.addTimeout`, this function returns a new deferred.
|
|
|
|
NOTE: the TimeoutError raised by the resultant deferred is
|
|
twisted.internet.defer.TimeoutError, which is *different* to the built-in
|
|
TimeoutError, as well as various other TimeoutErrors you might have imported.
|
|
|
|
Args:
|
|
deferred: The Deferred to potentially timeout.
|
|
timeout: Timeout in seconds
|
|
reactor: The twisted reactor to use
|
|
|
|
|
|
Returns:
|
|
A new Deferred, which will errback with defer.TimeoutError on timeout.
|
|
"""
|
|
new_d: "defer.Deferred[_T]" = defer.Deferred()
|
|
|
|
timed_out = [False]
|
|
|
|
def time_it_out() -> None:
|
|
timed_out[0] = True
|
|
|
|
try:
|
|
deferred.cancel()
|
|
except Exception: # if we throw any exception it'll break time outs
|
|
logger.exception("Canceller failed during timeout")
|
|
|
|
# the cancel() call should have set off a chain of errbacks which
|
|
# will have errbacked new_d, but in case it hasn't, errback it now.
|
|
|
|
if not new_d.called:
|
|
new_d.errback(defer.TimeoutError("Timed out after %gs" % (timeout,)))
|
|
|
|
delayed_call = reactor.callLater(timeout, time_it_out)
|
|
|
|
def convert_cancelled(value: Failure) -> Failure:
|
|
# if the original deferred was cancelled, and our timeout has fired, then
|
|
# the reason it was cancelled was due to our timeout. Turn the CancelledError
|
|
# into a TimeoutError.
|
|
if timed_out[0] and value.check(CancelledError):
|
|
raise defer.TimeoutError("Timed out after %gs" % (timeout,))
|
|
return value
|
|
|
|
deferred.addErrback(convert_cancelled)
|
|
|
|
def cancel_timeout(result: _T) -> _T:
|
|
# stop the pending call to cancel the deferred if it's been fired
|
|
if delayed_call.active():
|
|
delayed_call.cancel()
|
|
return result
|
|
|
|
deferred.addBoth(cancel_timeout)
|
|
|
|
def success_cb(val: _T) -> None:
|
|
if not new_d.called:
|
|
new_d.callback(val)
|
|
|
|
def failure_cb(val: Failure) -> None:
|
|
if not new_d.called:
|
|
new_d.errback(val)
|
|
|
|
deferred.addCallbacks(success_cb, failure_cb)
|
|
|
|
return new_d
|
|
|
|
|
|
# This class can't be generic because it uses slots with attrs.
|
|
# See: https://github.com/python-attrs/attrs/issues/313
|
|
@attr.s(slots=True, frozen=True, auto_attribs=True)
|
|
class DoneAwaitable: # should be: Generic[R]
|
|
"""Simple awaitable that returns the provided value."""
|
|
|
|
value: Any # should be: R
|
|
|
|
def __await__(self) -> Any:
|
|
return self
|
|
|
|
def __iter__(self) -> "DoneAwaitable":
|
|
return self
|
|
|
|
def __next__(self) -> None:
|
|
raise StopIteration(self.value)
|
|
|
|
|
|
def maybe_awaitable(value: Union[Awaitable[R], R]) -> Awaitable[R]:
|
|
"""Convert a value to an awaitable if not already an awaitable."""
|
|
if inspect.isawaitable(value):
|
|
assert isinstance(value, Awaitable)
|
|
return value
|
|
|
|
return DoneAwaitable(value)
|
|
|
|
|
|
def stop_cancellation(deferred: "defer.Deferred[T]") -> "defer.Deferred[T]":
|
|
"""Prevent a `Deferred` from being cancelled by wrapping it in another `Deferred`.
|
|
|
|
Args:
|
|
deferred: The `Deferred` to protect against cancellation. Must not follow the
|
|
Synapse logcontext rules.
|
|
|
|
Returns:
|
|
A new `Deferred`, which will contain the result of the original `Deferred`,
|
|
but will not propagate cancellation through to the original. When cancelled,
|
|
the new `Deferred` will fail with a `CancelledError` and will not follow the
|
|
Synapse logcontext rules. `make_deferred_yieldable` should be used to wrap
|
|
the new `Deferred`.
|
|
"""
|
|
new_deferred: defer.Deferred[T] = defer.Deferred()
|
|
deferred.chainDeferred(new_deferred)
|
|
return new_deferred
|