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 Exception:
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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", "ru_stime", "ru_utime",
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"db_txn_count", "db_txn_duration_ms", "db_sched_duration_ms",
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"usage_start", "usage_end",
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"main_thread", "alive",
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"request", "tag",
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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 add_database_scheduled(self, sched_ms):
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pass
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def __nonzero__(self):
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return False
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__bool__ = __nonzero__ # python3
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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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# ms spent waiting for db txns, excluding scheduling time
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self.db_txn_duration_ms = 0
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# ms spent waiting for db txns to be scheduled
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self.db_sched_duration_ms = 0
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self.usage_start = None
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self.usage_end = None
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self.main_thread = threading.current_thread()
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self.request = None
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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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Returns:
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LoggingContext: the current logging context
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"""
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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.warn("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 logging fields from this context to a log record or
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another LoggingContext
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"""
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# 'request' is the only field we currently use in the logger, so that's
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# all we need to copy
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record.request = self.request
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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_ms += duration_ms
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def add_database_scheduled(self, sched_ms):
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"""Record a use of the database pool
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Args:
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sched_ms (int): number of milliseconds it took us to get a
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connection
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"""
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self.db_sched_duration_ms += sched_ms
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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.warn(
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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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def preserve_fn(f):
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"""Function decorator which wraps the function with run_in_background"""
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def g(*args, **kwargs):
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return run_in_background(f, *args, **kwargs)
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return g
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def run_in_background(f, *args, **kwargs):
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"""Calls a function, ensuring 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 function completes.
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Useful for wrapping functions that return a deferred which you don't yield
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on (for instance because you want to pass it to deferred.gatherResults()).
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Note that if you completely discard the result, you should make sure that
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`f` doesn't raise any deferred exceptions, otherwise a scary-looking
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CRITICAL error about an unhandled error will be logged without much
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indication about where it came from.
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"""
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current = LoggingContext.current_context()
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try:
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res = f(*args, **kwargs)
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except: # noqa: E722
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# the assumption here is that the caller doesn't want to be disturbed
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# by synchronous exceptions, so let's turn them into Failures.
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return defer.fail()
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if not isinstance(res, defer.Deferred):
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return res
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if res.called and not res.paused:
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# The function should have maintained the logcontext, so we can
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# optimise out the messing about
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return res
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# The function may have reset the context before returning, so
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# we need to restore it now.
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ctx = 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(_set_context_cb, ctx)
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return res
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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 run_in_background.)
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"""
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if not isinstance(deferred, defer.Deferred):
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return deferred
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if deferred.called and not deferred.paused:
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# it looks like this deferred is ready to run any callbacks we give it
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# immediately. We may as well optimise out the logcontext faffery.
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return deferred
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# ok, we can't be sure that a yield won't block, so let's reset the
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# logcontext, and add a callback to the deferred to restore it.
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prev_context = LoggingContext.set_current_context(LoggingContext.sentinel)
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deferred.addBoth(_set_context_cb, prev_context)
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return deferred
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def _set_context_cb(result, context):
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"""A callback function which just sets the logging context"""
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LoggingContext.set_current_context(context)
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return result
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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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