3 files changed, 18 insertions, 17 deletions
diff --git a/synapse/util/async_helpers.py b/synapse/util/async_helpers.py
index 804dbca443..b60a604474 100644
--- a/synapse/util/async_helpers.py
+++ b/synapse/util/async_helpers.py
@@ -86,11 +86,12 @@ class ObservableDeferred(object):
 
         deferred.addCallbacks(callback, errback)
 
-    def observe(self):
+    def observe(self) -> defer.Deferred:
         """Observe the underlying deferred.
 
-        Can return either a deferred if the underlying deferred is still pending
-        (or has failed), or the actual value. Callers may need to use maybeDeferred.
+        This returns a brand new deferred that is resolved when the underlying
+        deferred is resolved. Interacting with the returned deferred does not
+        effect the underdlying deferred.
         """
         if not self._result:
             d = defer.Deferred()
@@ -105,7 +106,7 @@ class ObservableDeferred(object):
             return d
         else:
             success, res = self._result
-            return res if success else defer.fail(res)
+            return defer.succeed(res) if success else defer.fail(res)
 
     def observers(self):
         return self._observers
@@ -138,7 +139,7 @@ def concurrently_execute(func, args, limit):
     the number of concurrent executions.
 
     Args:
-        func (func): Function to execute, should return a deferred.
+        func (func): Function to execute, should return a deferred or coroutine.
         args (list): List of arguments to pass to func, each invocation of func
             gets a signle argument.
         limit (int): Maximum number of conccurent executions.
@@ -148,11 +149,10 @@ def concurrently_execute(func, args, limit):
     """
     it = iter(args)
 
-    @defer.inlineCallbacks
-    def _concurrently_execute_inner():
+    async def _concurrently_execute_inner():
         try:
             while True:
-                yield func(next(it))
+                await maybe_awaitable(func(next(it)))
         except StopIteration:
             pass
 
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 5ac2530a6a..0e8da27f53 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -438,7 +438,7 @@ class CacheDescriptor(_CacheDescriptorBase):
                 if isinstance(cached_result_d, ObservableDeferred):
                     observer = cached_result_d.observe()
                 else:
-                    observer = cached_result_d
+                    observer = defer.succeed(cached_result_d)
 
             except KeyError:
                 ret = defer.maybeDeferred(
@@ -482,9 +482,8 @@ class CacheListDescriptor(_CacheDescriptorBase):
     Given a list of keys it looks in the cache to find any hits, then passes
     the list of missing keys to the wrapped function.
 
-    Once wrapped, the function returns either a Deferred which resolves to
-    the list of results, or (if all results were cached), just the list of
-    results.
+    Once wrapped, the function returns a Deferred which resolves to the list
+    of results.
     """
 
     def __init__(
@@ -618,7 +617,7 @@ class CacheListDescriptor(_CacheDescriptorBase):
                 )
                 return make_deferred_yieldable(d)
             else:
-                return results
+                return defer.succeed(results)
 
         obj.__dict__[self.orig.__name__] = wrapped
 
diff --git a/synapse/util/versionstring.py b/synapse/util/versionstring.py
index fa404b9d75..ab7d03af3a 100644
--- a/synapse/util/versionstring.py
+++ b/synapse/util/versionstring.py
@@ -42,6 +42,7 @@ def get_version_string(module):
     try:
         null = open(os.devnull, "w")
         cwd = os.path.dirname(os.path.abspath(module.__file__))
+
         try:
             git_branch = (
                 subprocess.check_output(
@@ -51,7 +52,8 @@ def get_version_string(module):
                 .decode("ascii")
             )
             git_branch = "b=" + git_branch
-        except subprocess.CalledProcessError:
+        except (subprocess.CalledProcessError, FileNotFoundError):
+            # FileNotFoundError can arise when git is not installed
             git_branch = ""
 
         try:
@@ -63,7 +65,7 @@ def get_version_string(module):
                 .decode("ascii")
             )
             git_tag = "t=" + git_tag
-        except subprocess.CalledProcessError:
+        except (subprocess.CalledProcessError, FileNotFoundError):
             git_tag = ""
 
         try:
@@ -74,7 +76,7 @@ def get_version_string(module):
                 .strip()
                 .decode("ascii")
             )
-        except subprocess.CalledProcessError:
+        except (subprocess.CalledProcessError, FileNotFoundError):
             git_commit = ""
 
         try:
@@ -89,7 +91,7 @@ def get_version_string(module):
             )
 
             git_dirty = "dirty" if is_dirty else ""
-        except subprocess.CalledProcessError:
+        except (subprocess.CalledProcessError, FileNotFoundError):
             git_dirty = ""
 
         if git_branch or git_tag or git_commit or git_dirty: