Run things as background processes

This fixes #3518, and ensures that we get useful logs and metrics for lots of
things that happen in the background.

(There are certainly more things that happen in the background; these are just
the common ones I've found running a single-process synapse locally).

2 files changed, 9 insertions, 1 deletions

diff --git a/synapse/util/caches/expiringcache.py b/synapse/util/caches/expiringcache.py
index 4abca91f6d..465adc54a8 100644
--- a/synapse/util/caches/expiringcache.py
+++ b/synapse/util/caches/expiringcache.py
@@ -16,6 +16,7 @@
 import logging
 from collections import OrderedDict
 
+from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.util.caches import register_cache
 
 logger = logging.getLogger(__name__)
@@ -63,7 +64,10 @@ class ExpiringCache(object):
             return
 
         def f():
-            self._prune_cache()
+            run_as_background_process(
+                "prune_cache_%s" % self._cache_name,
+                self._prune_cache,
+            )
 
         self._clock.looping_call(f, self._expiry_ms / 2)
 
diff --git a/synapse/util/distributor.py b/synapse/util/distributor.py
index 734331caaa..d91ae400eb 100644
--- a/synapse/util/distributor.py
+++ b/synapse/util/distributor.py
@@ -75,6 +75,10 @@ class Distributor(object):
             self.pre_registration[name].append(observer)
 
     def fire(self, name, *args, **kwargs):
+        """Dispatches the given signal to the registered observers.
+
+        Runs the observers as a background process. Does not return a deferred.
+        """
         if name not in self.signals:
             raise KeyError("%r does not have a signal named %s" % (self, name))