Remove some unused distributor signals (#8216)

Removes the `user_joined_room` and stops calling it since there are no observers.

Also cleans-up some other unused signals and related code.

synapse/util/distributor.py

@@ -16,8 +16,6 @@ import inspect
 import logging
 
 from twisted.internet import defer
-from twisted.internet.defer import Deferred, fail, succeed
-from twisted.python import failure
 
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.metrics.background_process_metrics import run_as_background_process
@@ -29,11 +27,6 @@ def user_left_room(distributor, user, room_id):
     distributor.fire("user_left_room", user=user, room_id=room_id)
 
 
-# XXX: this is no longer used. We should probably kill it.
-def user_joined_room(distributor, user, room_id):
-    distributor.fire("user_joined_room", user=user, room_id=room_id)
-
-
 class Distributor:
     """A central dispatch point for loosely-connected pieces of code to
     register, observe, and fire signals.
@@ -81,28 +74,6 @@ class Distributor:
         run_as_background_process(name, self.signals[name].fire, *args, **kwargs)
 
 
-def maybeAwaitableDeferred(f, *args, **kw):
-    """
-    Invoke a function that may or may not return a Deferred or an Awaitable.
-
-    This is a modified version of twisted.internet.defer.maybeDeferred.
-    """
-    try:
-        result = f(*args, **kw)
-    except Exception:
-        return fail(failure.Failure(captureVars=Deferred.debug))
-
-    if isinstance(result, Deferred):
-        return result
-    # Handle the additional case of an awaitable being returned.
-    elif inspect.isawaitable(result):
-        return defer.ensureDeferred(result)
-    elif isinstance(result, failure.Failure):
-        return fail(result)
-    else:
-        return succeed(result)
-
-
 class Signal:
     """A Signal is a dispatch point that stores a list of callables as
     observers of it.
@@ -132,22 +103,17 @@ class Signal:
         Returns a Deferred that will complete when all the observers have
         completed."""
 
-        def do(observer):
-            def eb(failure):
+        async def do(observer):
+            try:
+                result = observer(*args, **kwargs)
+                if inspect.isawaitable(result):
+                    result = await result
+                return result
+            except Exception as e:
                 logger.warning(
-                    "%s signal observer %s failed: %r",
-                    self.name,
-                    observer,
-                    failure,
-                    exc_info=(
-                        failure.type,
-                        failure.value,
-                        failure.getTracebackObject(),
-                    ),
+                    "%s signal observer %s failed: %r", self.name, observer, e,
                 )
 
-            return maybeAwaitableDeferred(observer, *args, **kwargs).addErrback(eb)
-
         deferreds = [run_in_background(do, o) for o in self.observers]
 
         return make_deferred_yieldable(