Use run_in_background in preference to preserve_fn

While I was going through uses of preserve_fn for other PRs, I converted places
which only use the wrapped function once to use run_in_background, to avoid
creating the function object.

1 files changed, 3 insertions, 2 deletions

diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py

index 0fc21540c6..9290d7946f 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -35,7 +35,7 @@ from ._base import FileInfo
 from synapse.api.errors import (
     SynapseError, Codes,
 )
-from synapse.util.logcontext import preserve_fn, make_deferred_yieldable
+from synapse.util.logcontext import make_deferred_yieldable, run_in_background
 from synapse.util.stringutils import random_string
 from synapse.util.caches.expiringcache import ExpiringCache
 from synapse.http.client import SpiderHttpClient
@@ -144,7 +144,8 @@ class PreviewUrlResource(Resource):
         observable = self._cache.get(url)
 
         if not observable:
-            download = preserve_fn(self._do_preview)(
+            download = run_in_background(
+                self._do_preview,
                 url, requester.user, ts,
             )
             observable = ObservableDeferred(