fix: ConfigWatcher needs to register receivers using strong references (

#495)

These inner functions would otherwise get GC'd right away, since Django
only holds weak references to receivers by default.

CHANGELOG.rst

@@ -14,6 +14,12 @@ Change Log
 Unreleased
 ~~~~~~~~~~
 
+[3.1.1] - 2023-11-06
+~~~~~~~~~~~~~~~~~~~~
+Fixed
+_____
+* ConfigWatcher should now respond to model events properly now that it registers receivers with strong references. (Tested in sandbox.)
+
 [3.1.0] - 2023-10-31
 ~~~~~~~~~~~~~~~~~~~~
 

edx_arch_experiments/__init__.py

@@ -2,4 +2,4 @@
 A plugin to include applications under development by the architecture team at 2U.
 """
 
-__version__ = '3.1.0'
+__version__ = '3.1.1'

edx_arch_experiments/config_watcher/signals/receivers.py

@@ -99,15 +99,24 @@ def _register_waffle_observation(*, model, short_name, fields):
         short_name (str): A short descriptive name for an instance of the model, e.g. "flag"
         fields (list): Names of fields to report on in the Slack message
     """
-    @receiver(signals.post_save, sender=model, dispatch_uid=f"config_watcher_{short_name}_change")
+
+    # Note that weak=False is required here. Django by default only
+    # holds weak references to receiver functions. But these inner
+    # functions would then be garbage-collected, and Django would drop
+    # them. So pass weak=False to make Django hold strong references
+    # instead. (It works either way in devstack, apparently due to an
+    # interaction with settings.DEBUG causing a reference to be held:
+    # <https://stackoverflow.com/a/70651310>.)
+
+    @receiver(signals.post_save, sender=model, weak=False, dispatch_uid=f"config_watcher_{short_name}_change")
     def report_waffle_change(*args, instance, created, **kwargs):
         try:
             _report_waffle_change(short_name, instance, created, fields)
         except:  # noqa pylint: disable=bare-except
             # Log and suppress error so Waffle change can proceed
             log.exception(f"Failed to report change to waffle {short_name}")
 
-    @receiver(signals.post_delete, sender=model, dispatch_uid=f"config_watcher_{short_name}_delete")
+    @receiver(signals.post_delete, sender=model, weak=False, dispatch_uid=f"config_watcher_{short_name}_delete")
     def report_waffle_delete(*args, instance, **kwargs):
         try:
             _report_waffle_delete(short_name, instance)