fix: Cache producers so that they don't lose data (#21)

Also needed to break one test into two so that caching did not interfere.

CHANGELOG.rst

@@ -16,8 +16,16 @@ Unreleased
 
 *
 
+[0.2.0] - 2022-08-09
+~~~~~~~~~~~~~~~~~~~~
+
+Fixed
+_____
+
+* Cache producers so that they don't lose data.
+
 [0.1.0] - 2022-06-16
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~
 
 Added
 _____

edx_event_bus_kafka/__init__.py

@@ -2,4 +2,4 @@
 Kafka implementation for Open edX event bus.
 """
 
-__version__ = '0.1.1'
+__version__ = '0.2.0'

edx_event_bus_kafka/publishing/event_producer.py

@@ -114,6 +114,11 @@ def get_serializer(signal: OpenEdxPublicSignal) -> AvroSignalSerializer:
     return AvroSignalSerializer(signal)
 
 
+# Note: This caching is required, since otherwise the Producer will
+# fall out of scope and be garbage-collected, destroying the
+# outbound-message queue and threads. The use of this cache allows the
+# producers to be long-lived.
+@lru_cache
 def get_producer_for_signal(signal: OpenEdxPublicSignal, event_key_field: str) -> Optional[SerializingProducer]:
     """
     Create the producer for a signal and a key field path.

edx_event_bus_kafka/publishing/test_event_producer.py

@@ -19,6 +19,11 @@
 class TestEventProducer(TestCase):
     """Test producer."""
 
+    def setUp(self):
+        super().setUp()
+        ep.get_producer_for_signal.cache_clear()
+        ep.get_serializer.cache_clear()
+
     def test_extract_event_key(self):
         event_data = {
             'user': UserData(
@@ -56,17 +61,18 @@ def test_extract_key_schema(self):
         schema = ep.extract_key_schema(AvroSignalSerializer(signal), 'user.pii.username')
         assert schema == '{"name": "username", "type": "string"}'
 
-    def test_get_producer_for_signal(self):
+    def test_get_producer_for_signal_unconfigured(self):
+        """With missing essential settings, just warn and return None."""
         signal = openedx_events.learning.signals.SESSION_LOGIN_COMPLETED
-
-        # With missing essential settings, just warn and return None
         with warnings.catch_warnings(record=True) as caught_warnings:
             warnings.simplefilter('always')
             assert ep.get_producer_for_signal(signal, 'user.id') is None
             assert len(caught_warnings) == 1
             assert str(caught_warnings[0].message).startswith("Cannot configure event-bus-kafka: Missing setting ")
 
-        # Creation succeeds when all settings are present
+    def test_get_producer_for_signal_configured(self):
+        """Creation succeeds when all settings are present."""
+        signal = openedx_events.learning.signals.SESSION_LOGIN_COMPLETED
         with override_settings(
                 EVENT_BUS_KAFKA_SCHEMA_REGISTRY_URL='http://localhost:12345',
                 EVENT_BUS_KAFKA_SCHEMA_REGISTRY_API_KEY='some_key',