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https://git.anonymousland.org/anonymousland/synapse-product.git
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f9b4bb05e0
The cache wrappers had a habit of leaking the logcontext into the reactor while
the lookup function was running, and then not restoring it correctly when the
lookup function had completed. It's all the fault of
`preserve_context_over_{fn,deferred}` which are basically a bit broken.
440 lines
14 KiB
Python
440 lines
14 KiB
Python
# Copyright 2014-2016 OpenMarket 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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""" Thread-local-alike tracking of log contexts within synapse
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This module provides objects and utilities for tracking contexts through
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synapse code, so that log lines can include a request identifier, and so that
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CPU and database activity can be accounted for against the request that caused
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them.
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See doc/log_contexts.rst for details on how this works.
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"""
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from twisted.internet import defer
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import threading
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import logging
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logger = logging.getLogger(__name__)
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try:
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import resource
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# Python doesn't ship with a definition of RUSAGE_THREAD but it's defined
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# to be 1 on linux so we hard code it.
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RUSAGE_THREAD = 1
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# If the system doesn't support RUSAGE_THREAD then this should throw an
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# exception.
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resource.getrusage(RUSAGE_THREAD)
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def get_thread_resource_usage():
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return resource.getrusage(RUSAGE_THREAD)
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except:
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# If the system doesn't support resource.getrusage(RUSAGE_THREAD) then we
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# won't track resource usage by returning None.
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def get_thread_resource_usage():
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return None
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class LoggingContext(object):
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"""Additional context for log formatting. Contexts are scoped within a
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"with" block.
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Args:
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name (str): Name for the context for debugging.
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"""
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__slots__ = [
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"previous_context", "name", "usage_start", "usage_end", "main_thread",
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"__dict__", "tag", "alive",
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]
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thread_local = threading.local()
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class Sentinel(object):
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"""Sentinel to represent the root context"""
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__slots__ = []
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def __str__(self):
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return "sentinel"
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def copy_to(self, record):
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pass
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def start(self):
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pass
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def stop(self):
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pass
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def add_database_transaction(self, duration_ms):
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pass
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def __nonzero__(self):
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return False
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sentinel = Sentinel()
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def __init__(self, name=None):
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self.previous_context = LoggingContext.current_context()
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self.name = name
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self.ru_stime = 0.
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self.ru_utime = 0.
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self.db_txn_count = 0
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self.db_txn_duration = 0.
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self.usage_start = None
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self.main_thread = threading.current_thread()
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self.tag = ""
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self.alive = True
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def __str__(self):
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return "%s@%x" % (self.name, id(self))
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@classmethod
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def current_context(cls):
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"""Get the current logging context from thread local storage"""
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return getattr(cls.thread_local, "current_context", cls.sentinel)
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@classmethod
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def set_current_context(cls, context):
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"""Set the current logging context in thread local storage
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Args:
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context(LoggingContext): The context to activate.
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Returns:
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The context that was previously active
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"""
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current = cls.current_context()
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if current is not context:
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current.stop()
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cls.thread_local.current_context = context
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context.start()
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return current
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def __enter__(self):
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"""Enters this logging context into thread local storage"""
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old_context = self.set_current_context(self)
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if self.previous_context != old_context:
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logger.warn(
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"Expected previous context %r, found %r",
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self.previous_context, old_context
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)
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self.alive = True
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return self
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def __exit__(self, type, value, traceback):
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"""Restore the logging context in thread local storage to the state it
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was before this context was entered.
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Returns:
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None to avoid suppressing any exeptions that were thrown.
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"""
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current = self.set_current_context(self.previous_context)
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if current is not self:
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if current is self.sentinel:
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logger.debug("Expected logging context %s has been lost", self)
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else:
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logger.warn(
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"Current logging context %s is not expected context %s",
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current,
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self
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)
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self.previous_context = None
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self.alive = False
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def copy_to(self, record):
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"""Copy fields from this context to the record"""
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for key, value in self.__dict__.items():
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setattr(record, key, value)
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record.ru_utime, record.ru_stime = self.get_resource_usage()
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def start(self):
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if threading.current_thread() is not self.main_thread:
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return
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if self.usage_start and self.usage_end:
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self.ru_utime += self.usage_end.ru_utime - self.usage_start.ru_utime
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self.ru_stime += self.usage_end.ru_stime - self.usage_start.ru_stime
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self.usage_start = None
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self.usage_end = None
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if not self.usage_start:
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self.usage_start = get_thread_resource_usage()
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def stop(self):
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if threading.current_thread() is not self.main_thread:
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return
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if self.usage_start:
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self.usage_end = get_thread_resource_usage()
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def get_resource_usage(self):
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ru_utime = self.ru_utime
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ru_stime = self.ru_stime
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if self.usage_start and threading.current_thread() is self.main_thread:
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current = get_thread_resource_usage()
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ru_utime += current.ru_utime - self.usage_start.ru_utime
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ru_stime += current.ru_stime - self.usage_start.ru_stime
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return ru_utime, ru_stime
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def add_database_transaction(self, duration_ms):
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self.db_txn_count += 1
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self.db_txn_duration += duration_ms / 1000.
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class LoggingContextFilter(logging.Filter):
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"""Logging filter that adds values from the current logging context to each
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record.
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Args:
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**defaults: Default values to avoid formatters complaining about
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missing fields
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"""
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def __init__(self, **defaults):
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self.defaults = defaults
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def filter(self, record):
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"""Add each fields from the logging contexts to the record.
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Returns:
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True to include the record in the log output.
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"""
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context = LoggingContext.current_context()
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for key, value in self.defaults.items():
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setattr(record, key, value)
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context.copy_to(record)
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return True
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class PreserveLoggingContext(object):
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"""Captures the current logging context and restores it when the scope is
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exited. Used to restore the context after a function using
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@defer.inlineCallbacks is resumed by a callback from the reactor."""
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__slots__ = ["current_context", "new_context", "has_parent"]
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def __init__(self, new_context=LoggingContext.sentinel):
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self.new_context = new_context
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def __enter__(self):
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"""Captures the current logging context"""
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self.current_context = LoggingContext.set_current_context(
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self.new_context
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)
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if self.current_context:
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self.has_parent = self.current_context.previous_context is not None
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if not self.current_context.alive:
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logger.debug(
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"Entering dead context: %s",
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self.current_context,
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)
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def __exit__(self, type, value, traceback):
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"""Restores the current logging context"""
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context = LoggingContext.set_current_context(self.current_context)
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if context != self.new_context:
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logger.debug(
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"Unexpected logging context: %s is not %s",
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context, self.new_context,
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)
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if self.current_context is not LoggingContext.sentinel:
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if not self.current_context.alive:
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logger.debug(
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"Restoring dead context: %s",
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self.current_context,
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)
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class _PreservingContextDeferred(defer.Deferred):
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"""A deferred that ensures that all callbacks and errbacks are called with
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the given logging context.
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"""
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def __init__(self, context):
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self._log_context = context
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defer.Deferred.__init__(self)
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def addCallbacks(self, callback, errback=None,
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callbackArgs=None, callbackKeywords=None,
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errbackArgs=None, errbackKeywords=None):
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callback = self._wrap_callback(callback)
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errback = self._wrap_callback(errback)
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return defer.Deferred.addCallbacks(
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self, callback,
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errback=errback,
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callbackArgs=callbackArgs,
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callbackKeywords=callbackKeywords,
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errbackArgs=errbackArgs,
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errbackKeywords=errbackKeywords,
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)
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def _wrap_callback(self, f):
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def g(res, *args, **kwargs):
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with PreserveLoggingContext(self._log_context):
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res = f(res, *args, **kwargs)
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return res
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return g
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def preserve_context_over_fn(fn, *args, **kwargs):
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"""Takes a function and invokes it with the given arguments, but removes
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and restores the current logging context while doing so.
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If the result is a deferred, call preserve_context_over_deferred before
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returning it.
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"""
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with PreserveLoggingContext():
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res = fn(*args, **kwargs)
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if isinstance(res, defer.Deferred):
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return preserve_context_over_deferred(res)
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else:
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return res
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def preserve_context_over_deferred(deferred, context=None):
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"""Given a deferred wrap it such that any callbacks added later to it will
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be invoked with the current context.
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Deprecated: this almost certainly doesn't do want you want, ie make
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the deferred follow the synapse logcontext rules: try
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``make_deferred_yieldable`` instead.
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"""
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if context is None:
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context = LoggingContext.current_context()
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d = _PreservingContextDeferred(context)
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deferred.chainDeferred(d)
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return d
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def preserve_fn(f):
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"""Wraps a function, to ensure that the current context is restored after
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return from the function, and that the sentinel context is set once the
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deferred returned by the funtion completes.
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Useful for wrapping functions that return a deferred which you don't yield
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on.
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"""
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def reset_context(result):
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LoggingContext.set_current_context(LoggingContext.sentinel)
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return result
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# XXX: why is this here rather than inside g? surely we want to preserve
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# the context from the time the function was called, not when it was
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# wrapped?
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current = LoggingContext.current_context()
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def g(*args, **kwargs):
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res = f(*args, **kwargs)
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if isinstance(res, defer.Deferred) and not res.called:
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# The function will have reset the context before returning, so
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# we need to restore it now.
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LoggingContext.set_current_context(current)
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# The original context will be restored when the deferred
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# completes, but there is nothing waiting for it, so it will
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# get leaked into the reactor or some other function which
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# wasn't expecting it. We therefore need to reset the context
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# here.
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#
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# (If this feels asymmetric, consider it this way: we are
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# effectively forking a new thread of execution. We are
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# probably currently within a ``with LoggingContext()`` block,
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# which is supposed to have a single entry and exit point. But
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# by spawning off another deferred, we are effectively
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# adding a new exit point.)
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res.addBoth(reset_context)
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return res
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return g
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@defer.inlineCallbacks
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def make_deferred_yieldable(deferred):
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"""Given a deferred, make it follow the Synapse logcontext rules:
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If the deferred has completed (or is not actually a Deferred), essentially
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does nothing (just returns another completed deferred with the
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result/failure).
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If the deferred has not yet completed, resets the logcontext before
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returning a deferred. Then, when the deferred completes, restores the
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current logcontext before running callbacks/errbacks.
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(This is more-or-less the opposite operation to preserve_fn.)
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"""
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with PreserveLoggingContext():
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r = yield deferred
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defer.returnValue(r)
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# modules to ignore in `logcontext_tracer`
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_to_ignore = [
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"synapse.util.logcontext",
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"synapse.http.server",
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"synapse.storage._base",
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"synapse.util.async",
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]
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def logcontext_tracer(frame, event, arg):
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"""A tracer that logs whenever a logcontext "unexpectedly" changes within
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a function. Probably inaccurate.
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Use by calling `sys.settrace(logcontext_tracer)` in the main thread.
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"""
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if event == 'call':
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name = frame.f_globals["__name__"]
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if name.startswith("synapse"):
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if name == "synapse.util.logcontext":
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if frame.f_code.co_name in ["__enter__", "__exit__"]:
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tracer = frame.f_back.f_trace
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if tracer:
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tracer.just_changed = True
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tracer = frame.f_trace
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if tracer:
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return tracer
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if not any(name.startswith(ig) for ig in _to_ignore):
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return LineTracer()
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class LineTracer(object):
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__slots__ = ["context", "just_changed"]
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def __init__(self):
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self.context = LoggingContext.current_context()
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self.just_changed = False
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def __call__(self, frame, event, arg):
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if event in 'line':
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if self.just_changed:
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self.context = LoggingContext.current_context()
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self.just_changed = False
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else:
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c = LoggingContext.current_context()
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if c != self.context:
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logger.info(
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"Context changed! %s -> %s, %s, %s",
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self.context, c,
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frame.f_code.co_filename, frame.f_lineno
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)
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self.context = c
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return self
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