diff options
Diffstat (limited to 'synapse/util/logcontext.py')
| -rw-r--r-- | synapse/util/logcontext.py | 77 |
1 files changed, 66 insertions, 11 deletions
diff --git a/synapse/util/logcontext.py b/synapse/util/logcontext.py index 6c83eb213d..857afee7cb 100644 --- a/synapse/util/logcontext.py +++ b/synapse/util/logcontext.py @@ -12,6 +12,16 @@ # 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. +""" + from twisted.internet import defer import threading @@ -300,6 +310,10 @@ def preserve_context_over_fn(fn, *args, **kwargs): def preserve_context_over_deferred(deferred, context=None): """Given a deferred wrap it such that any callbacks added later to it will be invoked with the current context. + + Deprecated: this almost certainly doesn't do want you want, ie make + the deferred follow the synapse logcontext rules: try + ``make_deferred_yieldable`` instead. """ if context is None: context = LoggingContext.current_context() @@ -309,24 +323,65 @@ def preserve_context_over_deferred(deferred, context=None): def preserve_fn(f): - """Ensures that function is called with correct context and that context is - restored after return. Useful for wrapping functions that return a deferred - which you don't yield on. + """Wraps a function, to ensure that the current context is restored after + return from the function, and that the sentinel context is set once the + deferred returned by the funtion completes. + + Useful for wrapping functions that return a deferred which you don't yield + on. """ + def reset_context(result): + LoggingContext.set_current_context(LoggingContext.sentinel) + return result + + # XXX: why is this here rather than inside g? surely we want to preserve + # the context from the time the function was called, not when it was + # wrapped? current = LoggingContext.current_context() def g(*args, **kwargs): - with PreserveLoggingContext(current): - res = f(*args, **kwargs) - if isinstance(res, defer.Deferred): - return preserve_context_over_deferred( - res, context=LoggingContext.sentinel - ) - else: - return res + res = f(*args, **kwargs) + if isinstance(res, defer.Deferred) and not res.called: + # The function will have reset the context before returning, so + # we need to restore it now. + 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(reset_context) + return res return g +@defer.inlineCallbacks +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 preserve_fn.) + """ + with PreserveLoggingContext(): + r = yield deferred + defer.returnValue(r) + + # modules to ignore in `logcontext_tracer` _to_ignore = [ "synapse.util.logcontext", |