Remove preserve_context_over_{fn, deferred}

Both of these functions ae known to leak logcontexts. Replace the remaining
calls to them and kill them off.

synapse/util/async.py

@@ -17,7 +17,7 @@
 from twisted.internet import defer, reactor
 
 from .logcontext import (
-    PreserveLoggingContext, preserve_fn, preserve_context_over_deferred,
+    PreserveLoggingContext, make_deferred_yieldable, preserve_fn
 )
 from synapse.util import logcontext, unwrapFirstError
 
@@ -351,7 +351,7 @@ class ReadWriteLock(object):
 
         # We wait for the latest writer to finish writing. We can safely ignore
         # any existing readers... as they're readers.
-        yield curr_writer
+        yield make_deferred_yieldable(curr_writer)
 
         @contextmanager
         def _ctx_manager():
@@ -380,7 +380,7 @@ class ReadWriteLock(object):
         curr_readers.clear()
         self.key_to_current_writer[key] = new_defer
 
-        yield preserve_context_over_deferred(defer.gatherResults(to_wait_on))
+        yield make_deferred_yieldable(defer.gatherResults(to_wait_on))
 
         @contextmanager
         def _ctx_manager():

synapse/util/distributor.py

@@ -13,32 +13,24 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from twisted.internet import defer
-
-from synapse.util.logcontext import (
-    PreserveLoggingContext, preserve_context_over_fn
-)
-
-from synapse.util import unwrapFirstError
-
 import logging
 
+from twisted.internet import defer
+
+from synapse.util import unwrapFirstError
+from synapse.util.logcontext import PreserveLoggingContext
 
 logger = logging.getLogger(__name__)
 
 
 def user_left_room(distributor, user, room_id):
-    return preserve_context_over_fn(
-        distributor.fire,
-        "user_left_room", user=user, room_id=room_id
-    )
+    with PreserveLoggingContext():
+        distributor.fire("user_left_room", user=user, room_id=room_id)
 
 
 def user_joined_room(distributor, user, room_id):
-    return preserve_context_over_fn(
-        distributor.fire,
-        "user_joined_room", user=user, room_id=room_id
-    )
+    with PreserveLoggingContext():
+        distributor.fire("user_joined_room", user=user, room_id=room_id)
 
 
 class Distributor(object):

synapse/util/logcontext.py

@@ -291,37 +291,6 @@ class _PreservingContextDeferred(defer.Deferred):
         return g
 
 
-def preserve_context_over_fn(fn, *args, **kwargs):
-    """Takes a function and invokes it with the given arguments, but removes
-    and restores the current logging context while doing so.
-
-    If the result is a deferred, call preserve_context_over_deferred before
-    returning it.
-    """
-    with PreserveLoggingContext():
-        res = fn(*args, **kwargs)
-
-    if isinstance(res, defer.Deferred):
-        return preserve_context_over_deferred(res)
-    else:
-        return res
-
-
-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()
-    d = _PreservingContextDeferred(context)
-    deferred.chainDeferred(d)
-    return d
-
-
 def preserve_fn(f):
     """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