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Diffstat (limited to 'synapse/logging/context.py')
| -rw-r--r-- | synapse/logging/context.py | 697 |
1 files changed, 697 insertions, 0 deletions
diff --git a/synapse/logging/context.py b/synapse/logging/context.py new file mode 100644 index 0000000000..b456c31f70 --- /dev/null +++ b/synapse/logging/context.py @@ -0,0 +1,697 @@ +# 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 +import types + +from twisted.internet import defer, threads + +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 + + +# get an id for the current thread. +# +# threading.get_ident doesn't actually return an OS-level tid, and annoyingly, +# on Linux it actually returns the same value either side of a fork() call. However +# we only fork in one place, so it's not worth the hoop-jumping to get a real tid. +# +get_thread_id = threading.get_ident + + +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 = 0.0 + self.ru_utime = 0.0 + 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", + "scope", + ] + + 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, request=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 = get_thread_id() + self.request = None + self.tag = "" + self.alive = True + self.scope = None + + self.parent_context = parent_context + + if self.parent_context is not None: + self.parent_context.copy_to(self) + + if request is not None: + # the request param overrides the request from the parent context + self.request = request + + def __str__(self): + if self.request: + return str(self.request) + 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 + + 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.warning("Expected logging context %s was lost", self) + else: + logger.warning( + "Expected logging context %s but found %s", self, current + ) + 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 and hasattr( + self.parent_context, "_resource_usage" + ): + 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 + """ + + # we track the current request + record.request = self.request + + # we also track the current scope: + record.scope = self.scope + + def start(self): + if get_thread_id() != 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 get_thread_id() != 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 + + utime_delta, stime_delta = self._get_cputime() + self._resource_usage.ru_utime += utime_delta + self._resource_usage.ru_stime += stime_delta + + 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 = get_thread_id() == self.main_thread + if self.alive and self.usage_start and is_main_thread: + utime_delta, stime_delta = self._get_cputime() + res.ru_utime += utime_delta + res.ru_stime += stime_delta + + return res + + def _get_cputime(self): + """Get the cpu usage time so far + + Returns: Tuple[float, float]: seconds in user mode, seconds in system mode + """ + current = get_thread_resource_usage() + + utime_delta = current.ru_utime - self.usage_start.ru_utime + stime_delta = current.ru_stime - self.usage_start.ru_stime + + # sanity check + if utime_delta < 0: + logger.error( + "utime went backwards! %f < %f", + current.ru_utime, + self.usage_start.ru_utime, + ) + utime_delta = 0 + + if stime_delta < 0: + logger.error( + "stime went backwards! %f < %f", + current.ru_stime, + self.usage_start.ru_stime, + ) + stime_delta = 0 + + return utime_delta, stime_delta + + def add_database_transaction(self, duration_sec): + if duration_sec < 0: + raise ValueError("DB txn time can only be non-negative") + 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 + """ + if sched_sec < 0: + raise ValueError("DB scheduling time can only be non-negative") + 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: + if context is LoggingContext.sentinel: + logger.warning("Expected logging context %s was lost", self.new_context) + else: + logger.warning( + "Expected logging context %s but found %s", + self.new_context, + 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 nested_logging_context(suffix, parent_context=None): + """Creates a new logging context as a child of another. + + The nested logging context will have a 'request' made up of the parent context's + request, plus the given suffix. + + CPU/db usage stats will be added to the parent context's on exit. + + Normal usage looks like: + + with nested_logging_context(suffix): + # ... do stuff + + Args: + suffix (str): suffix to add to the parent context's 'request'. + parent_context (LoggingContext|None): parent context. Will use the current context + if None. + + Returns: + LoggingContext: new logging context. + """ + if parent_context is None: + parent_context = LoggingContext.current_context() + return LoggingContext( + parent_context=parent_context, request=parent_context.request + "-" + suffix + ) + + +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 or coroutine, which you don't + yield or await 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 isinstance(res, types.CoroutineType): + res = defer.ensureDeferred(res) + + 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 + + +def defer_to_thread(reactor, f, *args, **kwargs): + """ + Calls the function `f` using a thread from the reactor's default threadpool and + returns the result as a Deferred. + + Creates a new logcontext for `f`, which is created as a child of the current + logcontext (so its CPU usage metrics will get attributed to the current + logcontext). `f` should preserve the logcontext it is given. + + The result deferred follows the Synapse logcontext rules: you should `yield` + on it. + + Args: + reactor (twisted.internet.base.ReactorBase): The reactor in whose main thread + the Deferred will be invoked, and whose threadpool we should use for the + function. + + Normally this will be hs.get_reactor(). + + f (callable): The function to call. + + args: positional arguments to pass to f. + + kwargs: keyword arguments to pass to f. + + Returns: + Deferred: A Deferred which fires a callback with the result of `f`, or an + errback if `f` throws an exception. + """ + return defer_to_threadpool(reactor, reactor.getThreadPool(), f, *args, **kwargs) + + +def defer_to_threadpool(reactor, threadpool, f, *args, **kwargs): + """ + A wrapper for twisted.internet.threads.deferToThreadpool, which handles + logcontexts correctly. + + Calls the function `f` using a thread from the given threadpool and returns + the result as a Deferred. + + Creates a new logcontext for `f`, which is created as a child of the current + logcontext (so its CPU usage metrics will get attributed to the current + logcontext). `f` should preserve the logcontext it is given. + + The result deferred follows the Synapse logcontext rules: you should `yield` + on it. + + Args: + reactor (twisted.internet.base.ReactorBase): The reactor in whose main thread + the Deferred will be invoked. Normally this will be hs.get_reactor(). + + threadpool (twisted.python.threadpool.ThreadPool): The threadpool to use for + running `f`. Normally this will be hs.get_reactor().getThreadPool(). + + f (callable): The function to call. + + args: positional arguments to pass to f. + + kwargs: keyword arguments to pass to f. + + Returns: + Deferred: A Deferred which fires a callback with the result of `f`, or an + errback if `f` throws an exception. + """ + logcontext = LoggingContext.current_context() + + def g(): + with LoggingContext(parent_context=logcontext): + return f(*args, **kwargs) + + return make_deferred_yieldable(threads.deferToThreadPool(reactor, threadpool, g)) |