737 lines
25 KiB
Python
737 lines
25 KiB
Python
# Copyright 2014-2016 OpenMarket Ltd
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# Copyright 2018 New Vector Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import abc
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import collections
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import inspect
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import itertools
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import logging
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from contextlib import asynccontextmanager
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from typing import (
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Any,
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AsyncIterator,
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Awaitable,
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Callable,
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Collection,
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Dict,
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Generic,
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Hashable,
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Iterable,
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List,
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Optional,
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Set,
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Tuple,
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TypeVar,
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Union,
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cast,
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overload,
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)
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import attr
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from typing_extensions import AsyncContextManager, Literal
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from twisted.internet import defer
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from twisted.internet.defer import CancelledError
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from twisted.internet.interfaces import IReactorTime
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from twisted.python.failure import Failure
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from synapse.logging.context import (
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PreserveLoggingContext,
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make_deferred_yieldable,
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run_in_background,
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)
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from synapse.util import Clock
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logger = logging.getLogger(__name__)
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_T = TypeVar("_T")
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class AbstractObservableDeferred(Generic[_T], metaclass=abc.ABCMeta):
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"""Abstract base class defining the consumer interface of ObservableDeferred"""
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__slots__ = ()
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@abc.abstractmethod
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def observe(self) -> "defer.Deferred[_T]":
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"""Add a new observer for this ObservableDeferred
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This returns a brand new deferred that is resolved when the underlying
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deferred is resolved. Interacting with the returned deferred does not
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effect the underlying deferred.
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Note that the returned Deferred doesn't follow the Synapse logcontext rules -
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you will probably want to `make_deferred_yieldable` it.
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"""
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...
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class ObservableDeferred(Generic[_T], AbstractObservableDeferred[_T]):
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"""Wraps a deferred object so that we can add observer deferreds. These
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observer deferreds do not affect the callback chain of the original
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deferred.
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If consumeErrors is true errors will be captured from the origin deferred.
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Cancelling or otherwise resolving an observer will not affect the original
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ObservableDeferred.
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NB that it does not attempt to do anything with logcontexts; in general
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you should probably make_deferred_yieldable the deferreds
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returned by `observe`, and ensure that the original deferred runs its
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callbacks in the sentinel logcontext.
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"""
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__slots__ = ["_deferred", "_observers", "_result"]
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_deferred: "defer.Deferred[_T]"
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_observers: Union[List["defer.Deferred[_T]"], Tuple[()]]
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_result: Union[None, Tuple[Literal[True], _T], Tuple[Literal[False], Failure]]
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def __init__(self, deferred: "defer.Deferred[_T]", consumeErrors: bool = False):
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object.__setattr__(self, "_deferred", deferred)
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object.__setattr__(self, "_result", None)
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object.__setattr__(self, "_observers", [])
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def callback(r: _T) -> _T:
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object.__setattr__(self, "_result", (True, r))
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# once we have set _result, no more entries will be added to _observers,
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# so it's safe to replace it with the empty tuple.
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observers = self._observers
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object.__setattr__(self, "_observers", ())
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for observer in observers:
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try:
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observer.callback(r)
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except Exception as e:
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logger.exception(
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"%r threw an exception on .callback(%r), ignoring...",
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observer,
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r,
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exc_info=e,
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)
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return r
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def errback(f: Failure) -> Optional[Failure]:
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object.__setattr__(self, "_result", (False, f))
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# once we have set _result, no more entries will be added to _observers,
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# so it's safe to replace it with the empty tuple.
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observers = self._observers
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object.__setattr__(self, "_observers", ())
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for observer in observers:
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# This is a little bit of magic to correctly propagate stack
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# traces when we `await` on one of the observer deferreds.
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f.value.__failure__ = f # type: ignore[union-attr]
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try:
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observer.errback(f)
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except Exception as e:
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logger.exception(
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"%r threw an exception on .errback(%r), ignoring...",
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observer,
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f,
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exc_info=e,
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)
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if consumeErrors:
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return None
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else:
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return f
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deferred.addCallbacks(callback, errback)
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def observe(self) -> "defer.Deferred[_T]":
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"""Observe the underlying deferred.
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This returns a brand new deferred that is resolved when the underlying
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deferred is resolved. Interacting with the returned deferred does not
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effect the underlying deferred.
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"""
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if not self._result:
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assert isinstance(self._observers, list)
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d: "defer.Deferred[_T]" = defer.Deferred()
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self._observers.append(d)
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return d
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elif self._result[0]:
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return defer.succeed(self._result[1])
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else:
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return defer.fail(self._result[1])
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def observers(self) -> "Collection[defer.Deferred[_T]]":
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return self._observers
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def has_called(self) -> bool:
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return self._result is not None
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def has_succeeded(self) -> bool:
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return self._result is not None and self._result[0] is True
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def get_result(self) -> Union[_T, Failure]:
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if self._result is None:
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raise ValueError(f"{self!r} has no result yet")
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return self._result[1]
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def __getattr__(self, name: str) -> Any:
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return getattr(self._deferred, name)
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def __setattr__(self, name: str, value: Any) -> None:
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setattr(self._deferred, name, value)
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def __repr__(self) -> str:
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return "<ObservableDeferred object at %s, result=%r, _deferred=%r>" % (
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id(self),
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self._result,
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self._deferred,
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)
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T = TypeVar("T")
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async def concurrently_execute(
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func: Callable[[T], Any], args: Iterable[T], limit: int
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) -> None:
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"""Executes the function with each argument concurrently while limiting
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the number of concurrent executions.
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Args:
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func: Function to execute, should return a deferred or coroutine.
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args: List of arguments to pass to func, each invocation of func
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gets a single argument.
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limit: Maximum number of conccurent executions.
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Returns:
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Deferred: Resolved when all function invocations have finished.
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"""
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it = iter(args)
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async def _concurrently_execute_inner(value: T) -> None:
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try:
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while True:
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await maybe_awaitable(func(value))
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value = next(it)
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except StopIteration:
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pass
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# We use `itertools.islice` to handle the case where the number of args is
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# less than the limit, avoiding needlessly spawning unnecessary background
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# tasks.
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await yieldable_gather_results(
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_concurrently_execute_inner, (value for value in itertools.islice(it, limit))
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)
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async def yieldable_gather_results(
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func: Callable[..., Awaitable[T]], iter: Iterable, *args: Any, **kwargs: Any
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) -> List[T]:
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"""Executes the function with each argument concurrently.
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Args:
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func: Function to execute that returns a Deferred
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iter: An iterable that yields items that get passed as the first
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argument to the function
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*args: Arguments to be passed to each call to func
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**kwargs: Keyword arguments to be passed to each call to func
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Returns
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A list containing the results of the function
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"""
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try:
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return await make_deferred_yieldable(
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defer.gatherResults(
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[run_in_background(func, item, *args, **kwargs) for item in iter],
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consumeErrors=True,
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)
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)
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except defer.FirstError as dfe:
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# unwrap the error from defer.gatherResults.
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# The raised exception's traceback only includes func() etc if
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# the 'await' happens before the exception is thrown - ie if the failure
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# happens *asynchronously* - otherwise Twisted throws away the traceback as it
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# could be large.
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#
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# We could maybe reconstruct a fake traceback from Failure.frames. Or maybe
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# we could throw Twisted into the fires of Mordor.
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# suppress exception chaining, because the FirstError doesn't tell us anything
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# very interesting.
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assert isinstance(dfe.subFailure.value, BaseException)
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raise dfe.subFailure.value from None
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T1 = TypeVar("T1")
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T2 = TypeVar("T2")
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T3 = TypeVar("T3")
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@overload
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def gather_results(
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deferredList: Tuple[()], consumeErrors: bool = ...
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) -> "defer.Deferred[Tuple[()]]":
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...
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@overload
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def gather_results(
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deferredList: Tuple["defer.Deferred[T1]"],
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consumeErrors: bool = ...,
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) -> "defer.Deferred[Tuple[T1]]":
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...
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@overload
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def gather_results(
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deferredList: Tuple["defer.Deferred[T1]", "defer.Deferred[T2]"],
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consumeErrors: bool = ...,
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) -> "defer.Deferred[Tuple[T1, T2]]":
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...
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@overload
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def gather_results(
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deferredList: Tuple[
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"defer.Deferred[T1]", "defer.Deferred[T2]", "defer.Deferred[T3]"
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],
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consumeErrors: bool = ...,
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) -> "defer.Deferred[Tuple[T1, T2, T3]]":
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...
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def gather_results( # type: ignore[misc]
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deferredList: Tuple["defer.Deferred[T1]", ...],
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consumeErrors: bool = False,
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) -> "defer.Deferred[Tuple[T1, ...]]":
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"""Combines a tuple of `Deferred`s into a single `Deferred`.
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Wraps `defer.gatherResults` to provide type annotations that support heterogenous
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lists of `Deferred`s.
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"""
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# The `type: ignore[misc]` above suppresses
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# "Overloaded function implementation cannot produce return type of signature 1/2/3"
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deferred = defer.gatherResults(deferredList, consumeErrors=consumeErrors)
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return deferred.addCallback(tuple)
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@attr.s(slots=True, auto_attribs=True)
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class _LinearizerEntry:
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# The number of things executing.
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count: int
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# Deferreds for the things blocked from executing.
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deferreds: collections.OrderedDict
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class Linearizer:
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"""Limits concurrent access to resources based on a key. Useful to ensure
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only a few things happen at a time on a given resource.
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Example:
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async with limiter.queue("test_key"):
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# do some work.
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"""
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def __init__(
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self,
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name: Optional[str] = None,
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max_count: int = 1,
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clock: Optional[Clock] = None,
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):
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"""
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Args:
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max_count: The maximum number of concurrent accesses
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"""
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if name is None:
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self.name: Union[str, int] = id(self)
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else:
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self.name = name
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if not clock:
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from twisted.internet import reactor
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clock = Clock(cast(IReactorTime, reactor))
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self._clock = clock
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self.max_count = max_count
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# key_to_defer is a map from the key to a _LinearizerEntry.
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self.key_to_defer: Dict[Hashable, _LinearizerEntry] = {}
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def is_queued(self, key: Hashable) -> bool:
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"""Checks whether there is a process queued up waiting"""
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entry = self.key_to_defer.get(key)
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if not entry:
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# No entry so nothing is waiting.
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return False
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# There are waiting deferreds only in the OrderedDict of deferreds is
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# non-empty.
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return bool(entry.deferreds)
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def queue(self, key: Hashable) -> AsyncContextManager[None]:
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@asynccontextmanager
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async def _ctx_manager() -> AsyncIterator[None]:
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entry = await self._acquire_lock(key)
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try:
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yield
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finally:
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self._release_lock(key, entry)
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return _ctx_manager()
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async def _acquire_lock(self, key: Hashable) -> _LinearizerEntry:
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"""Acquires a linearizer lock, waiting if necessary.
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Returns once we have secured the lock.
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"""
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entry = self.key_to_defer.setdefault(
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key, _LinearizerEntry(0, collections.OrderedDict())
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)
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if entry.count < self.max_count:
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# The number of things executing is less than the maximum.
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logger.debug(
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"Acquired uncontended linearizer lock %r for key %r", self.name, key
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)
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entry.count += 1
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return entry
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# Otherwise, the number of things executing is at the maximum and we have to
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# add a deferred to the list of blocked items.
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# When one of the things currently executing finishes it will callback
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# this item so that it can continue executing.
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logger.debug("Waiting to acquire linearizer lock %r for key %r", self.name, key)
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new_defer: "defer.Deferred[None]" = make_deferred_yieldable(defer.Deferred())
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entry.deferreds[new_defer] = 1
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try:
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await new_defer
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except Exception as e:
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logger.info("defer %r got err %r", new_defer, e)
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if isinstance(e, CancelledError):
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logger.debug(
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"Cancelling wait for linearizer lock %r for key %r",
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self.name,
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key,
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)
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else:
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logger.warning(
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"Unexpected exception waiting for linearizer lock %r for key %r",
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self.name,
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key,
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)
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# we just have to take ourselves back out of the queue.
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del entry.deferreds[new_defer]
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raise
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logger.debug("Acquired linearizer lock %r for key %r", self.name, key)
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entry.count += 1
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# if the code holding the lock completes synchronously, then it
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# will recursively run the next claimant on the list. That can
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# relatively rapidly lead to stack exhaustion. This is essentially
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# the same problem as http://twistedmatrix.com/trac/ticket/9304.
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#
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# In order to break the cycle, we add a cheeky sleep(0) here to
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# ensure that we fall back to the reactor between each iteration.
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#
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# This needs to happen while we hold the lock. We could put it on the
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# exit path, but that would slow down the uncontended case.
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try:
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await self._clock.sleep(0)
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except CancelledError:
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self._release_lock(key, entry)
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raise
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return entry
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def _release_lock(self, key: Hashable, entry: _LinearizerEntry) -> None:
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"""Releases a held linearizer lock."""
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logger.debug("Releasing linearizer lock %r for key %r", self.name, key)
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# We've finished executing so check if there are any things
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# blocked waiting to execute and start one of them
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entry.count -= 1
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if entry.deferreds:
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(next_def, _) = entry.deferreds.popitem(last=False)
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# we need to run the next thing in the sentinel context.
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with PreserveLoggingContext():
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next_def.callback(None)
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elif entry.count == 0:
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# We were the last thing for this key: remove it from the
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# map.
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del self.key_to_defer[key]
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class ReadWriteLock:
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"""An async read write lock.
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Example:
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async with read_write_lock.read("test_key"):
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# do some work
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"""
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# IMPLEMENTATION NOTES
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#
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# We track the most recent queued reader and writer deferreds (which get
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# resolved when they release the lock).
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#
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# Read: We know its safe to acquire a read lock when the latest writer has
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# been resolved. The new reader is appended to the list of latest readers.
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#
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# Write: We know its safe to acquire the write lock when both the latest
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# writers and readers have been resolved. The new writer replaces the latest
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# writer.
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def __init__(self) -> None:
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# Latest readers queued
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self.key_to_current_readers: Dict[str, Set[defer.Deferred]] = {}
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# Latest writer queued
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self.key_to_current_writer: Dict[str, defer.Deferred] = {}
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def read(self, key: str) -> AsyncContextManager:
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@asynccontextmanager
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async def _ctx_manager() -> AsyncIterator[None]:
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new_defer: "defer.Deferred[None]" = defer.Deferred()
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curr_readers = self.key_to_current_readers.setdefault(key, set())
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curr_writer = self.key_to_current_writer.get(key, None)
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curr_readers.add(new_defer)
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try:
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# We wait for the latest writer to finish writing. We can safely ignore
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# any existing readers... as they're readers.
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# May raise a `CancelledError` if the `Deferred` wrapping us is
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# cancelled. The `Deferred` we are waiting on must not be cancelled,
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# since we do not own it.
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if curr_writer:
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await make_deferred_yieldable(stop_cancellation(curr_writer))
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yield
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finally:
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with PreserveLoggingContext():
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new_defer.callback(None)
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self.key_to_current_readers.get(key, set()).discard(new_defer)
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return _ctx_manager()
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def write(self, key: str) -> AsyncContextManager:
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@asynccontextmanager
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async def _ctx_manager() -> AsyncIterator[None]:
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new_defer: "defer.Deferred[None]" = defer.Deferred()
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curr_readers = self.key_to_current_readers.get(key, set())
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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 `new_defer` waits
|
|
# for them to finish.
|
|
curr_readers.clear()
|
|
self.key_to_current_writer[key] = new_defer
|
|
|
|
to_wait_on_defer = defer.gatherResults(to_wait_on)
|
|
try:
|
|
# Wait for all current readers and the latest writer to finish.
|
|
# May raise a `CancelledError` immediately after the wait if the
|
|
# `Deferred` wrapping us is cancelled. We must only release the lock
|
|
# once we have acquired it, hence the use of `delay_cancellation`
|
|
# rather than `stop_cancellation`.
|
|
await make_deferred_yieldable(delay_cancellation(to_wait_on_defer))
|
|
yield
|
|
finally:
|
|
# Release the lock.
|
|
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`.
|
|
The new `Deferred` will not propagate cancellation through to the original.
|
|
When cancelled, the new `Deferred` will fail with a `CancelledError`.
|
|
|
|
The new `Deferred` will not follow the Synapse logcontext rules and should be
|
|
wrapped with `make_deferred_yieldable`.
|
|
"""
|
|
new_deferred: "defer.Deferred[T]" = defer.Deferred()
|
|
deferred.chainDeferred(new_deferred)
|
|
return new_deferred
|
|
|
|
|
|
def delay_cancellation(deferred: "defer.Deferred[T]") -> "defer.Deferred[T]":
|
|
"""Delay cancellation of a `Deferred` until it resolves.
|
|
|
|
Has the same effect as `stop_cancellation`, but the returned `Deferred` will not
|
|
resolve with a `CancelledError` until the original `Deferred` resolves.
|
|
|
|
Args:
|
|
deferred: The `Deferred` to protect against cancellation. May optionally follow
|
|
the Synapse logcontext rules.
|
|
|
|
Returns:
|
|
A new `Deferred`, which will contain the result of the original `Deferred`.
|
|
The new `Deferred` will not propagate cancellation through to the original.
|
|
When cancelled, the new `Deferred` will wait until the original `Deferred`
|
|
resolves before failing with a `CancelledError`.
|
|
|
|
The new `Deferred` will follow the Synapse logcontext rules if `deferred`
|
|
follows the Synapse logcontext rules. Otherwise the new `Deferred` should be
|
|
wrapped with `make_deferred_yieldable`.
|
|
"""
|
|
|
|
def handle_cancel(new_deferred: "defer.Deferred[T]") -> None:
|
|
# before the new deferred is cancelled, we `pause` it to stop the cancellation
|
|
# propagating. we then `unpause` it once the wrapped deferred completes, to
|
|
# propagate the exception.
|
|
new_deferred.pause()
|
|
new_deferred.errback(Failure(CancelledError()))
|
|
|
|
deferred.addBoth(lambda _: new_deferred.unpause())
|
|
|
|
new_deferred: "defer.Deferred[T]" = defer.Deferred(handle_cancel)
|
|
deferred.chainDeferred(new_deferred)
|
|
return new_deferred
|