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# -*- coding: utf-8 -*-
# Copyright 2015, 2016 OpenMarket 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.
from twisted.internet import defer, reactor
from functools import wraps
from synapse.util.logcontext import LoggingContext, PreserveLoggingContext
def debug_deferreds():
"""Cause all deferreds to wait for a reactor tick before running their
callbacks. This increases the chance of getting a stack trace out of
a defer.inlineCallback since the code waiting on the deferred will get
a chance to add an errback before the deferred runs."""
# Helper method for retrieving and restoring the current logging context
# around a callback.
def with_logging_context(fn):
context = LoggingContext.current_context()
def restore_context_callback(x):
with PreserveLoggingContext(context):
return fn(x)
return restore_context_callback
# We are going to modify the __init__ method of defer.Deferred so we
# need to get a copy of the old method so we can still call it.
old__init__ = defer.Deferred.__init__
# We need to create a deferred to bounce the callbacks through the reactor
# but we don't want to add a callback when we create that deferred so we
# we create a new type of deferred that uses the old __init__ method.
# This is safe as long as the old __init__ method doesn't invoke an
# __init__ using super.
class Bouncer(defer.Deferred):
__init__ = old__init__
# We'll add this as a callback to all Deferreds. Twisted will wait until
# the bouncer deferred resolves before calling the callbacks of the
# original deferred.
def bounce_callback(x):
bouncer = Bouncer()
reactor.callLater(0, with_logging_context(bouncer.callback), x)
return bouncer
# We'll add this as an errback to all Deferreds. Twisted will wait until
# the bouncer deferred resolves before calling the errbacks of the
# original deferred.
def bounce_errback(x):
bouncer = Bouncer()
reactor.callLater(0, with_logging_context(bouncer.errback), x)
return bouncer
@wraps(old__init__)
def new__init__(self, *args, **kargs):
old__init__(self, *args, **kargs)
self.addCallbacks(bounce_callback, bounce_errback)
defer.Deferred.__init__ = new__init__
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