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Rename async to async_helpers because async is a keyword on Python 3.7 (#3678)

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Amber Brown 2018-08-10 23:50:21 +10:00 • committed by GitHub
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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 six.moves import range
from twisted.internet import defer
from twisted.internet.defer import CancelledError
from twisted.python import failure
from synapse.util import Clock, logcontext, unwrapFirstError
from .logcontext import (
PreserveLoggingContext,
make_deferred_yieldable,
run_in_background,
)
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:
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):
"""Observe the underlying deferred.
Can return either a deferred if the underlying deferred is still pending
(or has failed), or the actual value. Callers may need to use maybeDeferred.
"""
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 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.
args (list): List of arguments to pass to func, each invocation of func
gets a signle argument.
limit (int): Maximum number of conccurent executions.
Returns:
deferred: Resolved when all function invocations have finished.
"""
it = iter(args)
@defer.inlineCallbacks
def _concurrently_execute_inner():
try:
while True:
yield func(next(it))
except StopIteration:
pass
return logcontext.make_deferred_yieldable(defer.gatherResults([
run_in_background(_concurrently_execute_inner)
for _ in range(limit)
], 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 = {}
@defer.inlineCallbacks
def queue(self, key):
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 on of the things currently executing finishes it will callback
# this item so that it can continue executing.
if entry[0] >= self.max_count:
new_defer = defer.Deferred()
entry[1][new_defer] = 1
logger.info(
"Waiting to acquire linearizer lock %r for key %r", self.name, key,
)
try:
yield make_deferred_yieldable(new_defer)
except Exception as e:
if isinstance(e, CancelledError):
logger.info(
"Cancelling wait for linearizer lock %r for key %r",
self.name, key,
)
else:
logger.warn(
"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]
raise
logger.info("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.)
yield self._clock.sleep(0)
else:
logger.info(
"Acquired uncontended linearizer lock %r for key %r", self.name, key,
)
entry[0] += 1
@contextmanager
def _ctx_manager():
try:
yield
finally:
logger.info("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]
defer.returnValue(_ctx_manager())
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 = {}
# Latest writer queued
self.key_to_current_writer = {}
@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)
defer.returnValue(_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)
defer.returnValue(_ctx_manager())
class DeferredTimeoutError(Exception):
"""
This error is raised by default when a L{Deferred} times out.
"""
def add_timeout_to_deferred(deferred, timeout, reactor, on_timeout_cancel=None):
"""
Add a timeout to a deferred by scheduling it to be cancelled after
timeout seconds.
This is essentially a backport of deferred.addTimeout, which was introduced
in twisted 16.5.
If the deferred gets timed out, it errbacks with a DeferredTimeoutError,
unless a cancelable function was passed to its initialization or unless
a different on_timeout_cancel callable is provided.
Args:
deferred (defer.Deferred): deferred to be timed out
timeout (Number): seconds to time out after
reactor (twisted.internet.reactor): 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 DeferredTimeoutError.
"""
timed_out = [False]
def time_it_out():
timed_out[0] = True
deferred.cancel()
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 _cancelled_to_timed_out_error(value, timeout):
if isinstance(value, failure.Failure):
value.trap(CancelledError)
raise DeferredTimeoutError(timeout, "Deferred")
return value