563 lines
18 KiB
Python
563 lines
18 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 collections
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import inspect
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import logging
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from contextlib import contextmanager
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from typing import (
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Any,
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Awaitable,
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Callable,
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Dict,
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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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TypeVar,
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Union,
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)
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import attr
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from typing_extensions import ContextManager
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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 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, unwrapFirstError
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logger = logging.getLogger(__name__)
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class ObservableDeferred:
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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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def __init__(self, deferred: defer.Deferred, 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", set())
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def callback(r):
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object.__setattr__(self, "_result", (True, r))
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while self._observers:
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observer = self._observers.pop()
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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):
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object.__setattr__(self, "_result", (False, f))
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while self._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
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observer = self._observers.pop()
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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:
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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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d = defer.Deferred()
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def remove(r):
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self._observers.discard(d)
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return r
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d.addBoth(remove)
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self._observers.add(d)
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return d
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else:
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success, res = self._result
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return defer.succeed(res) if success else defer.fail(res)
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def observers(self) -> List[defer.Deferred]:
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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) -> Any:
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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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def concurrently_execute(
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func: Callable, args: Iterable[Any], limit: int
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) -> defer.Deferred:
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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[list]: 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():
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try:
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while True:
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await maybe_awaitable(func(next(it)))
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except StopIteration:
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pass
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return make_deferred_yieldable(
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defer.gatherResults(
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[run_in_background(_concurrently_execute_inner) for _ in range(limit)],
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consumeErrors=True,
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)
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).addErrback(unwrapFirstError)
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def yieldable_gather_results(
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func: Callable, iter: Iterable, *args: Any, **kwargs: Any
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) -> defer.Deferred:
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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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Deferred[list]: Resolved when all functions have been invoked, or errors if
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one of the function calls fails.
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"""
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return 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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).addErrback(unwrapFirstError)
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@attr.s(slots=True)
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class _LinearizerEntry:
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# The number of things executing.
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count = attr.ib(type=int)
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# Deferreds for the things blocked from executing.
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deferreds = attr.ib(type=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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with await 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 = id(self) # type: Union[str, int]
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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(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 = {} # type: 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) -> defer.Deferred:
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# we avoid doing defer.inlineCallbacks here, so that cancellation works correctly.
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# (https://twistedmatrix.com/trac/ticket/4632 meant that cancellations were not
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# propagated inside inlineCallbacks until Twisted 18.7)
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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 the number of things executing is greater than the maximum
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# then 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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if entry.count >= self.max_count:
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res = self._await_lock(key)
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else:
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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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res = defer.succeed(None)
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# once we successfully get the lock, we need to return a context manager which
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# will release the lock.
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@contextmanager
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def _ctx_manager(_):
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try:
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yield
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finally:
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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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res.addCallback(_ctx_manager)
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return res
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def _await_lock(self, key: Hashable) -> defer.Deferred:
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"""Helper for queue: adds a deferred to the queue
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Assumes that we've already checked that we've reached the limit of the number
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of lock-holders we allow. Creates a new deferred which is added to the list, and
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adds some management around cancellations.
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Returns the deferred, which will callback once we have secured the lock.
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"""
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entry = self.key_to_defer[key]
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logger.debug("Waiting to acquire linearizer lock %r for key %r", self.name, key)
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new_defer = make_deferred_yieldable(defer.Deferred())
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entry.deferreds[new_defer] = 1
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def cb(_r):
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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, and the context manager's exit
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# code must be synchronous, so this is the only sensible place.)
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return self._clock.sleep(0)
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def eb(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", self.name, 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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return e
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new_defer.addCallbacks(cb, eb)
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return new_defer
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class ReadWriteLock:
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"""An async read write lock.
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Example:
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with await 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):
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# Latest readers queued
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self.key_to_current_readers = {} # type: Dict[str, Set[defer.Deferred]]
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# Latest writer queued
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self.key_to_current_writer = {} # type: Dict[str, defer.Deferred]
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async def read(self, key: str) -> ContextManager:
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new_defer = 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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# 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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if curr_writer:
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await make_deferred_yieldable(curr_writer)
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@contextmanager
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def _ctx_manager():
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try:
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yield
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finally:
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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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async def write(self, key: str) -> ContextManager:
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new_defer = 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)
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# We wait on all latest readers and writer.
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to_wait_on = list(curr_readers)
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if curr_writer:
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to_wait_on.append(curr_writer)
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# We can clear the list of current readers since the new writer waits
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# for them to finish.
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curr_readers.clear()
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self.key_to_current_writer[key] = new_defer
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await make_deferred_yieldable(defer.gatherResults(to_wait_on))
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@contextmanager
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def _ctx_manager():
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try:
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yield
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finally:
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new_defer.callback(None)
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if self.key_to_current_writer[key] == new_defer:
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self.key_to_current_writer.pop(key)
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return _ctx_manager()
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R = TypeVar("R")
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def timeout_deferred(
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deferred: defer.Deferred,
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timeout: float,
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reactor: IReactorTime,
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) -> defer.Deferred:
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"""The in built twisted `Deferred.addTimeout` fails to time out deferreds
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that have a canceller that throws exceptions. This method creates a new
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deferred that wraps and times out the given deferred, correctly handling
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the case where the given deferred's canceller throws.
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(See https://twistedmatrix.com/trac/ticket/9534)
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NOTE: Unlike `Deferred.addTimeout`, this function returns a new deferred.
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NOTE: the TimeoutError raised by the resultant deferred is
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twisted.internet.defer.TimeoutError, which is *different* to the built-in
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TimeoutError, as well as various other TimeoutErrors you might have imported.
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Args:
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deferred: The Deferred to potentially timeout.
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timeout: Timeout in seconds
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reactor: The twisted reactor to use
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Returns:
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A new Deferred, which will errback with defer.TimeoutError on timeout.
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"""
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new_d = defer.Deferred()
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timed_out = [False]
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def time_it_out():
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timed_out[0] = True
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try:
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deferred.cancel()
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except Exception: # if we throw any exception it'll break time outs
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logger.exception("Canceller failed during timeout")
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# the cancel() call should have set off a chain of errbacks which
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# will have errbacked new_d, but in case it hasn't, errback it now.
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if not new_d.called:
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new_d.errback(defer.TimeoutError("Timed out after %gs" % (timeout,)))
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delayed_call = reactor.callLater(timeout, time_it_out)
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def convert_cancelled(value: failure.Failure):
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# if the original deferred was cancelled, and our timeout has fired, then
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# the reason it was cancelled was due to our timeout. Turn the CancelledError
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# into a TimeoutError.
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if timed_out[0] and value.check(CancelledError):
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raise defer.TimeoutError("Timed out after %gs" % (timeout,))
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return value
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deferred.addErrback(convert_cancelled)
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def cancel_timeout(result):
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# stop the pending call to cancel the deferred if it's been fired
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if delayed_call.active():
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delayed_call.cancel()
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return result
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deferred.addBoth(cancel_timeout)
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def success_cb(val):
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if not new_d.called:
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new_d.callback(val)
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def failure_cb(val):
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if not new_d.called:
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new_d.errback(val)
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deferred.addCallbacks(success_cb, failure_cb)
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return new_d
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@attr.s(slots=True, frozen=True)
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class DoneAwaitable:
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"""Simple awaitable that returns the provided value."""
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value = attr.ib()
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def __await__(self):
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return self
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def __iter__(self):
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return self
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def __next__(self):
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raise StopIteration(self.value)
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def maybe_awaitable(value: Union[Awaitable[R], R]) -> Awaitable[R]:
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"""Convert a value to an awaitable if not already an awaitable."""
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if inspect.isawaitable(value):
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assert isinstance(value, Awaitable)
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return value
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return DoneAwaitable(value)
|