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Diffstat (limited to 'synapse/util/patch_inline_callbacks.py')
| -rw-r--r-- | synapse/util/patch_inline_callbacks.py | 224 |
1 files changed, 224 insertions, 0 deletions
diff --git a/synapse/util/patch_inline_callbacks.py b/synapse/util/patch_inline_callbacks.py new file mode 100644 index 0000000000..2605f3c65b --- /dev/null +++ b/synapse/util/patch_inline_callbacks.py @@ -0,0 +1,224 @@ +# -*- coding: utf-8 -*- +# Copyright 2018 New Vector Ltd +# +# Licensed under the Apache License, Version 2.0 (the "License"); +# you may not use this file except in compliance with the License. +# You may obtain a copy of the License at +# +# http://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, +# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +# See the License for the specific language governing permissions and +# limitations under the License. + +from __future__ import print_function + +import functools +import sys +from typing import Any, Callable, List + +from twisted.internet import defer +from twisted.internet.defer import Deferred +from twisted.python.failure import Failure + +# Tracks if we've already patched inlineCallbacks +_already_patched = False + + +def do_patch(): + """ + Patch defer.inlineCallbacks so that it checks the state of the logcontext on exit + """ + + from synapse.logging.context import current_context + + global _already_patched + + orig_inline_callbacks = defer.inlineCallbacks + if _already_patched: + return + + def new_inline_callbacks(f): + @functools.wraps(f) + def wrapped(*args, **kwargs): + start_context = current_context() + changes = [] # type: List[str] + orig = orig_inline_callbacks(_check_yield_points(f, changes)) + + try: + res = orig(*args, **kwargs) + except Exception: + if current_context() != start_context: + for err in changes: + print(err, file=sys.stderr) + + err = "%s changed context from %s to %s on exception" % ( + f, + start_context, + current_context(), + ) + print(err, file=sys.stderr) + raise Exception(err) + raise + + if not isinstance(res, Deferred) or res.called: + if current_context() != start_context: + for err in changes: + print(err, file=sys.stderr) + + err = "Completed %s changed context from %s to %s" % ( + f, + start_context, + current_context(), + ) + # print the error to stderr because otherwise all we + # see in travis-ci is the 500 error + print(err, file=sys.stderr) + raise Exception(err) + return res + + if current_context(): + err = ( + "%s returned incomplete deferred in non-sentinel context " + "%s (start was %s)" + ) % (f, current_context(), start_context) + print(err, file=sys.stderr) + raise Exception(err) + + def check_ctx(r): + if current_context() != start_context: + for err in changes: + print(err, file=sys.stderr) + err = "%s completion of %s changed context from %s to %s" % ( + "Failure" if isinstance(r, Failure) else "Success", + f, + start_context, + current_context(), + ) + print(err, file=sys.stderr) + raise Exception(err) + return r + + res.addBoth(check_ctx) + return res + + return wrapped + + defer.inlineCallbacks = new_inline_callbacks + _already_patched = True + + +def _check_yield_points(f: Callable, changes: List[str]): + """Wraps a generator that is about to be passed to defer.inlineCallbacks + checking that after every yield the log contexts are correct. + + It's perfectly valid for log contexts to change within a function, e.g. due + to new Measure blocks, so such changes are added to the given `changes` + list instead of triggering an exception. + + Args: + f: generator function to wrap + changes: A list of strings detailing how the contexts + changed within a function. + + Returns: + function + """ + + from synapse.logging.context import current_context + + @functools.wraps(f) + def check_yield_points_inner(*args, **kwargs): + gen = f(*args, **kwargs) + + last_yield_line_no = gen.gi_frame.f_lineno + result = None # type: Any + while True: + expected_context = current_context() + + try: + isFailure = isinstance(result, Failure) + if isFailure: + d = result.throwExceptionIntoGenerator(gen) + else: + d = gen.send(result) + except (StopIteration, defer._DefGen_Return) as e: + if current_context() != expected_context: + # This happens when the context is lost sometime *after* the + # final yield and returning. E.g. we forgot to yield on a + # function that returns a deferred. + # + # We don't raise here as it's perfectly valid for contexts to + # change in a function, as long as it sets the correct context + # on resolving (which is checked separately). + err = ( + "Function %r returned and changed context from %s to %s," + " in %s between %d and end of func" + % ( + f.__qualname__, + expected_context, + current_context(), + f.__code__.co_filename, + last_yield_line_no, + ) + ) + changes.append(err) + return getattr(e, "value", None) + + frame = gen.gi_frame + + if isinstance(d, defer.Deferred) and not d.called: + # This happens if we yield on a deferred that doesn't follow + # the log context rules without wrapping in a `make_deferred_yieldable`. + # We raise here as this should never happen. + if current_context(): + err = ( + "%s yielded with context %s rather than sentinel," + " yielded on line %d in %s" + % ( + frame.f_code.co_name, + current_context(), + frame.f_lineno, + frame.f_code.co_filename, + ) + ) + raise Exception(err) + + # the wrapped function yielded a Deferred: yield it back up to the parent + # inlineCallbacks(). + try: + result = yield d + except Exception: + # this will fish an earlier Failure out of the stack where possible, and + # thus is preferable to passing in an exeception to the Failure + # constructor, since it results in less stack-mangling. + result = Failure() + + if current_context() != expected_context: + + # This happens because the context is lost sometime *after* the + # previous yield and *after* the current yield. E.g. the + # deferred we waited on didn't follow the rules, or we forgot to + # yield on a function between the two yield points. + # + # We don't raise here as its perfectly valid for contexts to + # change in a function, as long as it sets the correct context + # on resolving (which is checked separately). + err = ( + "%s changed context from %s to %s, happened between lines %d and %d in %s" + % ( + frame.f_code.co_name, + expected_context, + current_context(), + last_yield_line_no, + frame.f_lineno, + frame.f_code.co_filename, + ) + ) + changes.append(err) + + last_yield_line_no = frame.f_lineno + + return check_yield_points_inner |