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- # -*- coding: utf-8 -*-
- # 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 collections
- import logging
- from contextlib import contextmanager
- from typing import Dict, Sequence, Set, Union
- import attr
- from twisted.internet import defer
- from twisted.internet.defer import CancelledError
- from twisted.python import failure
- from synapse.logging.context import (
- PreserveLoggingContext,
- make_deferred_yieldable,
- run_in_background,
- )
- from synapse.util import Clock, unwrapFirstError
- logger = logging.getLogger(__name__)
- class ObservableDeferred(object):
- """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, consumeErrors=False):
- object.__setattr__(self, "_deferred", deferred)
- object.__setattr__(self, "_result", None)
- object.__setattr__(self, "_observers", set())
- def callback(r):
- object.__setattr__(self, "_result", (True, r))
- while self._observers:
- try:
- # TODO: Handle errors here.
- self._observers.pop().callback(r)
- except Exception:
- pass
- return r
- def errback(f):
- object.__setattr__(self, "_result", (False, f))
- while self._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
- try:
- # TODO: Handle errors here.
- self._observers.pop().errback(f)
- except Exception:
- pass
- if consumeErrors:
- return None
- else:
- return f
- deferred.addCallbacks(callback, errback)
- def observe(self) -> defer.Deferred:
- """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 underdlying deferred.
- """
- if not self._result:
- d = defer.Deferred()
- def remove(r):
- self._observers.discard(d)
- return r
- d.addBoth(remove)
- self._observers.add(d)
- return d
- else:
- success, res = self._result
- return defer.succeed(res) if success else defer.fail(res)
- def observers(self):
- return self._observers
- def has_called(self):
- return self._result is not None
- def has_succeeded(self):
- return self._result is not None and self._result[0] is True
- def get_result(self):
- return self._result[1]
- def __getattr__(self, name):
- return getattr(self._deferred, name)
- def __setattr__(self, name, value):
- setattr(self._deferred, name, value)
- def __repr__(self):
- return "<ObservableDeferred object at %s, result=%r, _deferred=%r>" % (
- id(self),
- self._result,
- self._deferred,
- )
- def concurrently_execute(func, args, limit):
- """Executes the function with each argument conncurrently while limiting
- the number of concurrent executions.
- Args:
- func (func): Function to execute, should return a deferred or coroutine.
- args (Iterable): List of arguments to pass to func, each invocation of func
- gets a single argument.
- limit (int): Maximum number of conccurent executions.
- Returns:
- deferred: Resolved when all function invocations have finished.
- """
- it = iter(args)
- async def _concurrently_execute_inner():
- try:
- while True:
- await maybe_awaitable(func(next(it)))
- except StopIteration:
- pass
- return make_deferred_yieldable(
- defer.gatherResults(
- [run_in_background(_concurrently_execute_inner) for _ in range(limit)],
- consumeErrors=True,
- )
- ).addErrback(unwrapFirstError)
- def yieldable_gather_results(func, iter, *args, **kwargs):
- """Executes the function with each argument concurrently.
- Args:
- func (func): Function to execute that returns a Deferred
- iter (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
- Returns
- Deferred[list]: Resolved when all functions have been invoked, or errors if
- one of the function calls fails.
- """
- return make_deferred_yieldable(
- defer.gatherResults(
- [run_in_background(func, item, *args, **kwargs) for item in iter],
- consumeErrors=True,
- )
- ).addErrback(unwrapFirstError)
- class Linearizer(object):
- """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 (yield limiter.queue("test_key")):
- # do some work.
- """
- def __init__(self, name=None, max_count=1, clock=None):
- """
- Args:
- max_count(int): The maximum number of concurrent accesses
- """
- if name is None:
- self.name = id(self)
- else:
- self.name = name
- if not clock:
- from twisted.internet import reactor
- clock = Clock(reactor)
- self._clock = clock
- self.max_count = max_count
- # key_to_defer is a map from the key to a 2 element list where
- # the first element is the number of things executing, and
- # the second element is an OrderedDict, where the keys are deferreds for the
- # things blocked from executing.
- self.key_to_defer = (
- {}
- ) # type: Dict[str, Sequence[Union[int, Dict[defer.Deferred, int]]]]
- def is_queued(self, key) -> 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[1])
- def queue(self, key):
- # 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, [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[0] >= self.max_count:
- res = self._await_lock(key)
- else:
- logger.debug(
- "Acquired uncontended linearizer lock %r for key %r", self.name, key
- )
- entry[0] += 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(_):
- 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[0] -= 1
- if entry[1]:
- (next_def, _) = entry[1].popitem(last=False)
- # we need to run the next thing in the sentinel context.
- with PreserveLoggingContext():
- next_def.callback(None)
- elif entry[0] == 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):
- """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 = make_deferred_yieldable(defer.Deferred())
- entry[1][new_defer] = 1
- def cb(_r):
- logger.debug("Acquired linearizer lock %r for key %r", self.name, key)
- entry[0] += 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):
- 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[1][new_defer]
- return e
- new_defer.addCallbacks(cb, eb)
- return new_defer
- class ReadWriteLock(object):
- """A deferred style read write lock.
- Example:
- with (yield 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 appeneded 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):
- # Latest readers queued
- self.key_to_current_readers = {} # type: Dict[str, Set[defer.Deferred]]
- # Latest writer queued
- self.key_to_current_writer = {} # type: Dict[str, defer.Deferred]
- @defer.inlineCallbacks
- def read(self, key):
- new_defer = 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.
- yield make_deferred_yieldable(curr_writer)
- @contextmanager
- def _ctx_manager():
- try:
- yield
- finally:
- new_defer.callback(None)
- self.key_to_current_readers.get(key, set()).discard(new_defer)
- return _ctx_manager()
- @defer.inlineCallbacks
- def write(self, key):
- new_defer = 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
- yield make_deferred_yieldable(defer.gatherResults(to_wait_on))
- @contextmanager
- def _ctx_manager():
- try:
- yield
- finally:
- new_defer.callback(None)
- if self.key_to_current_writer[key] == new_defer:
- self.key_to_current_writer.pop(key)
- return _ctx_manager()
- def _cancelled_to_timed_out_error(value, timeout):
- if isinstance(value, failure.Failure):
- value.trap(CancelledError)
- raise defer.TimeoutError(timeout, "Deferred")
- return value
- def timeout_deferred(deferred, timeout, reactor, on_timeout_cancel=None):
- """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
- Args:
- deferred (Deferred)
- timeout (float): Timeout in seconds
- reactor (twisted.interfaces.IReactorTime): The twisted reactor to use
- on_timeout_cancel (callable): A callable which is called immediately
- after the deferred times out, and not if this deferred is
- otherwise cancelled before the timeout.
- It takes an arbitrary value, which is the value of the deferred at
- that exact point in time (probably a CancelledError Failure), and
- the timeout.
- The default callable (if none is provided) will translate a
- CancelledError Failure into a defer.TimeoutError.
- Returns:
- Deferred
- """
- new_d = defer.Deferred()
- timed_out = [False]
- def time_it_out():
- timed_out[0] = True
- try:
- deferred.cancel()
- except: # noqa: E722, if we throw any exception it'll break time outs
- logger.exception("Canceller failed during timeout")
- if not new_d.called:
- new_d.errback(defer.TimeoutError(timeout, "Deferred"))
- delayed_call = reactor.callLater(timeout, time_it_out)
- def convert_cancelled(value):
- if timed_out[0]:
- to_call = on_timeout_cancel or _cancelled_to_timed_out_error
- return to_call(value, timeout)
- return value
- deferred.addBoth(convert_cancelled)
- def cancel_timeout(result):
- # 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):
- if not new_d.called:
- new_d.callback(val)
- def failure_cb(val):
- if not new_d.called:
- new_d.errback(val)
- deferred.addCallbacks(success_cb, failure_cb)
- return new_d
- @attr.s(slots=True, frozen=True)
- class DoneAwaitable(object):
- """Simple awaitable that returns the provided value.
- """
- value = attr.ib()
- def __await__(self):
- return self
- def __iter__(self):
- return self
- def __next__(self):
- raise StopIteration(self.value)
- def maybe_awaitable(value):
- """Convert a value to an awaitable if not already an awaitable.
- """
- if hasattr(value, "__await__"):
- return value
- return DoneAwaitable(value)
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