# Copyright 2014-2016 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. """ Thread-local-alike tracking of log contexts within synapse This module provides objects and utilities for tracking contexts through synapse code, so that log lines can include a request identifier, and so that CPU and database activity can be accounted for against the request that caused them. See doc/log_contexts.rst for details on how this works. """ import logging import threading from twisted.internet import defer logger = logging.getLogger(__name__) try: import resource # Python doesn't ship with a definition of RUSAGE_THREAD but it's defined # to be 1 on linux so we hard code it. RUSAGE_THREAD = 1 # If the system doesn't support RUSAGE_THREAD then this should throw an # exception. resource.getrusage(RUSAGE_THREAD) def get_thread_resource_usage(): return resource.getrusage(RUSAGE_THREAD) except Exception: # If the system doesn't support resource.getrusage(RUSAGE_THREAD) then we # won't track resource usage by returning None. def get_thread_resource_usage(): return None class ContextResourceUsage(object): """Object for tracking the resources used by a log context Attributes: ru_utime (float): user CPU time (in seconds) ru_stime (float): system CPU time (in seconds) db_txn_count (int): number of database transactions done db_sched_duration_sec (float): amount of time spent waiting for a database connection db_txn_duration_sec (float): amount of time spent doing database transactions (excluding scheduling time) evt_db_fetch_count (int): number of events requested from the database """ __slots__ = [ "ru_stime", "ru_utime", "db_txn_count", "db_txn_duration_sec", "db_sched_duration_sec", "evt_db_fetch_count", ] def __init__(self, copy_from=None): """Create a new ContextResourceUsage Args: copy_from (ContextResourceUsage|None): if not None, an object to copy stats from """ if copy_from is None: self.reset() else: self.ru_utime = copy_from.ru_utime self.ru_stime = copy_from.ru_stime self.db_txn_count = copy_from.db_txn_count self.db_txn_duration_sec = copy_from.db_txn_duration_sec self.db_sched_duration_sec = copy_from.db_sched_duration_sec self.evt_db_fetch_count = copy_from.evt_db_fetch_count def copy(self): return ContextResourceUsage(copy_from=self) def reset(self): self.ru_stime = 0. self.ru_utime = 0. self.db_txn_count = 0 self.db_txn_duration_sec = 0 self.db_sched_duration_sec = 0 self.evt_db_fetch_count = 0 def __repr__(self): return ("<ContextResourceUsage ru_stime='%r', ru_utime='%r', " "db_txn_count='%r', db_txn_duration_sec='%r', " "db_sched_duration_sec='%r', evt_db_fetch_count='%r'>") % ( self.ru_stime, self.ru_utime, self.db_txn_count, self.db_txn_duration_sec, self.db_sched_duration_sec, self.evt_db_fetch_count,) def __iadd__(self, other): """Add another ContextResourceUsage's stats to this one's. Args: other (ContextResourceUsage): the other resource usage object """ self.ru_utime += other.ru_utime self.ru_stime += other.ru_stime self.db_txn_count += other.db_txn_count self.db_txn_duration_sec += other.db_txn_duration_sec self.db_sched_duration_sec += other.db_sched_duration_sec self.evt_db_fetch_count += other.evt_db_fetch_count return self def __isub__(self, other): self.ru_utime -= other.ru_utime self.ru_stime -= other.ru_stime self.db_txn_count -= other.db_txn_count self.db_txn_duration_sec -= other.db_txn_duration_sec self.db_sched_duration_sec -= other.db_sched_duration_sec self.evt_db_fetch_count -= other.evt_db_fetch_count return self def __add__(self, other): res = ContextResourceUsage(copy_from=self) res += other return res def __sub__(self, other): res = ContextResourceUsage(copy_from=self) res -= other return res class LoggingContext(object): """Additional context for log formatting. Contexts are scoped within a "with" block. If a parent is given when creating a new context, then: - logging fields are copied from the parent to the new context on entry - when the new context exits, the cpu usage stats are copied from the child to the parent Args: name (str): Name for the context for debugging. parent_context (LoggingContext|None): The parent of the new context """ __slots__ = [ "previous_context", "name", "parent_context", "_resource_usage", "usage_start", "main_thread", "alive", "request", "tag", ] thread_local = threading.local() class Sentinel(object): """Sentinel to represent the root context""" __slots__ = [] def __str__(self): return "sentinel" def copy_to(self, record): pass def start(self): pass def stop(self): pass def add_database_transaction(self, duration_sec): pass def add_database_scheduled(self, sched_sec): pass def record_event_fetch(self, event_count): pass def __nonzero__(self): return False __bool__ = __nonzero__ # python3 sentinel = Sentinel() def __init__(self, name=None, parent_context=None): self.previous_context = LoggingContext.current_context() self.name = name # track the resources used by this context so far self._resource_usage = ContextResourceUsage() # If alive has the thread resource usage when the logcontext last # became active. self.usage_start = None self.main_thread = threading.current_thread() self.request = None self.tag = "" self.alive = True self.parent_context = parent_context def __str__(self): return "%s@%x" % (self.name, id(self)) @classmethod def current_context(cls): """Get the current logging context from thread local storage Returns: LoggingContext: the current logging context """ return getattr(cls.thread_local, "current_context", cls.sentinel) @classmethod def set_current_context(cls, context): """Set the current logging context in thread local storage Args: context(LoggingContext): The context to activate. Returns: The context that was previously active """ current = cls.current_context() if current is not context: current.stop() cls.thread_local.current_context = context context.start() return current def __enter__(self): """Enters this logging context into thread local storage""" old_context = self.set_current_context(self) if self.previous_context != old_context: logger.warn( "Expected previous context %r, found %r", self.previous_context, old_context ) self.alive = True if self.parent_context is not None: self.parent_context.copy_to(self) return self def __exit__(self, type, value, traceback): """Restore the logging context in thread local storage to the state it was before this context was entered. Returns: None to avoid suppressing any exceptions that were thrown. """ current = self.set_current_context(self.previous_context) if current is not self: if current is self.sentinel: logger.warn("Expected logging context %s has been lost", self) else: logger.warn( "Current logging context %s is not expected context %s", current, self ) self.previous_context = None self.alive = False # if we have a parent, pass our CPU usage stats on if self.parent_context is not None: self.parent_context._resource_usage += self._resource_usage # reset them in case we get entered again self._resource_usage.reset() def copy_to(self, record): """Copy logging fields from this context to a log record or another LoggingContext """ # 'request' is the only field we currently use in the logger, so that's # all we need to copy record.request = self.request def start(self): if threading.current_thread() is not self.main_thread: logger.warning("Started logcontext %s on different thread", self) return # If we haven't already started record the thread resource usage so # far if not self.usage_start: self.usage_start = get_thread_resource_usage() def stop(self): if threading.current_thread() is not self.main_thread: logger.warning("Stopped logcontext %s on different thread", self) return # When we stop, let's record the cpu used since we started if not self.usage_start: logger.warning( "Called stop on logcontext %s without calling start", self, ) return usage_end = get_thread_resource_usage() self._resource_usage.ru_utime += usage_end.ru_utime - self.usage_start.ru_utime self._resource_usage.ru_stime += usage_end.ru_stime - self.usage_start.ru_stime self.usage_start = None def get_resource_usage(self): """Get resources used by this logcontext so far. Returns: ContextResourceUsage: a *copy* of the object tracking resource usage so far """ # we always return a copy, for consistency res = self._resource_usage.copy() # If we are on the correct thread and we're currently running then we # can include resource usage so far. is_main_thread = threading.current_thread() is self.main_thread if self.alive and self.usage_start and is_main_thread: current = get_thread_resource_usage() res.ru_utime += current.ru_utime - self.usage_start.ru_utime res.ru_stime += current.ru_stime - self.usage_start.ru_stime return res def add_database_transaction(self, duration_sec): self._resource_usage.db_txn_count += 1 self._resource_usage.db_txn_duration_sec += duration_sec def add_database_scheduled(self, sched_sec): """Record a use of the database pool Args: sched_sec (float): number of seconds it took us to get a connection """ self._resource_usage.db_sched_duration_sec += sched_sec def record_event_fetch(self, event_count): """Record a number of events being fetched from the db Args: event_count (int): number of events being fetched """ self._resource_usage.evt_db_fetch_count += event_count class LoggingContextFilter(logging.Filter): """Logging filter that adds values from the current logging context to each record. Args: **defaults: Default values to avoid formatters complaining about missing fields """ def __init__(self, **defaults): self.defaults = defaults def filter(self, record): """Add each fields from the logging contexts to the record. Returns: True to include the record in the log output. """ context = LoggingContext.current_context() for key, value in self.defaults.items(): setattr(record, key, value) # context should never be None, but if it somehow ends up being, then # we end up in a death spiral of infinite loops, so let's check, for # robustness' sake. if context is not None: context.copy_to(record) return True class PreserveLoggingContext(object): """Captures the current logging context and restores it when the scope is exited. Used to restore the context after a function using @defer.inlineCallbacks is resumed by a callback from the reactor.""" __slots__ = ["current_context", "new_context", "has_parent"] def __init__(self, new_context=None): if new_context is None: new_context = LoggingContext.sentinel self.new_context = new_context def __enter__(self): """Captures the current logging context""" self.current_context = LoggingContext.set_current_context( self.new_context ) if self.current_context: self.has_parent = self.current_context.previous_context is not None if not self.current_context.alive: logger.debug( "Entering dead context: %s", self.current_context, ) def __exit__(self, type, value, traceback): """Restores the current logging context""" context = LoggingContext.set_current_context(self.current_context) if context != self.new_context: logger.warn( "Unexpected logging context: %s is not %s", context, self.new_context, ) if self.current_context is not LoggingContext.sentinel: if not self.current_context.alive: logger.debug( "Restoring dead context: %s", self.current_context, ) def preserve_fn(f): """Function decorator which wraps the function with run_in_background""" def g(*args, **kwargs): return run_in_background(f, *args, **kwargs) return g def run_in_background(f, *args, **kwargs): """Calls a function, ensuring that the current context is restored after return from the function, and that the sentinel context is set once the deferred returned by the function completes. Useful for wrapping functions that return a deferred which you don't yield on (for instance because you want to pass it to deferred.gatherResults()). Note that if you completely discard the result, you should make sure that `f` doesn't raise any deferred exceptions, otherwise a scary-looking CRITICAL error about an unhandled error will be logged without much indication about where it came from. """ current = LoggingContext.current_context() try: res = f(*args, **kwargs) except: # noqa: E722 # the assumption here is that the caller doesn't want to be disturbed # by synchronous exceptions, so let's turn them into Failures. return defer.fail() if not isinstance(res, defer.Deferred): return res if res.called and not res.paused: # The function should have maintained the logcontext, so we can # optimise out the messing about return res # The function may have reset the context before returning, so # we need to restore it now. ctx = LoggingContext.set_current_context(current) # The original context will be restored when the deferred # completes, but there is nothing waiting for it, so it will # get leaked into the reactor or some other function which # wasn't expecting it. We therefore need to reset the context # here. # # (If this feels asymmetric, consider it this way: we are # effectively forking a new thread of execution. We are # probably currently within a ``with LoggingContext()`` block, # which is supposed to have a single entry and exit point. But # by spawning off another deferred, we are effectively # adding a new exit point.) res.addBoth(_set_context_cb, ctx) return res def make_deferred_yieldable(deferred): """Given a deferred, make it follow the Synapse logcontext rules: If the deferred has completed (or is not actually a Deferred), essentially does nothing (just returns another completed deferred with the result/failure). If the deferred has not yet completed, resets the logcontext before returning a deferred. Then, when the deferred completes, restores the current logcontext before running callbacks/errbacks. (This is more-or-less the opposite operation to run_in_background.) """ if not isinstance(deferred, defer.Deferred): return deferred if deferred.called and not deferred.paused: # it looks like this deferred is ready to run any callbacks we give it # immediately. We may as well optimise out the logcontext faffery. return deferred # ok, we can't be sure that a yield won't block, so let's reset the # logcontext, and add a callback to the deferred to restore it. prev_context = LoggingContext.set_current_context(LoggingContext.sentinel) deferred.addBoth(_set_context_cb, prev_context) return deferred def _set_context_cb(result, context): """A callback function which just sets the logging context""" LoggingContext.set_current_context(context) return result # modules to ignore in `logcontext_tracer` _to_ignore = [ "synapse.util.logcontext", "synapse.http.server", "synapse.storage._base", "synapse.util.async_helpers", ] def logcontext_tracer(frame, event, arg): """A tracer that logs whenever a logcontext "unexpectedly" changes within a function. Probably inaccurate. Use by calling `sys.settrace(logcontext_tracer)` in the main thread. """ if event == 'call': name = frame.f_globals["__name__"] if name.startswith("synapse"): if name == "synapse.util.logcontext": if frame.f_code.co_name in ["__enter__", "__exit__"]: tracer = frame.f_back.f_trace if tracer: tracer.just_changed = True tracer = frame.f_trace if tracer: return tracer if not any(name.startswith(ig) for ig in _to_ignore): return LineTracer() class LineTracer(object): __slots__ = ["context", "just_changed"] def __init__(self): self.context = LoggingContext.current_context() self.just_changed = False def __call__(self, frame, event, arg): if event in 'line': if self.just_changed: self.context = LoggingContext.current_context() self.just_changed = False else: c = LoggingContext.current_context() if c != self.context: logger.info( "Context changed! %s -> %s, %s, %s", self.context, c, frame.f_code.co_filename, frame.f_lineno ) self.context = c return self