Ensure that exceptions while rendering individual metrics don't stop others from being rendered anyway - especially useful for CallbackMetric

synapse/metrics/__init__.py

@@ -13,9 +13,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import logging
+
 from .metric import CounterMetric, CallbackMetric, CacheCounterMetric
 
 
+logger = logging.getLogger(__name__)
+
+
 # We'll keep all the available metrics in a single toplevel dict, one shared
 # for the entire process. We don't currently support per-HomeServer instances
 # of metrics, because in practice any one python VM will host only one
@@ -82,6 +87,10 @@ def render_all():
     strs = []
 
     for name in sorted(all_metrics.keys()):
-        strs += all_metrics[name].render()
+        try:
+            strs += all_metrics[name].render()
+        except Exception as e:
+            strs += ["# FAILED to render %s" % name]
+            logger.exception("Failed to render %s metric", name)
 
     return "\n".join(strs)