Remove references to SQLAlchemy engines which are disposed of

EngineTracer in SQLAlchemy keeps weak references to a traced engine forever which
can cause a noticeable memory leak if engines are constantly getting creating.

Author: rbagd

instrumentation/opentelemetry-instrumentation-sqlalchemy/src/opentelemetry/instrumentation/sqlalchemy/engine.py

@@ -167,13 +167,26 @@ def _pool_checkout(
         self._add_idle_to_connection_usage(-1)
         self._add_used_to_connection_usage(1)
 
+    @classmethod
+    def _dispose_of_event_listener(cls, obj):
+        try:
+            cls._remove_event_listener_params.remove(obj)
+        except ValueError:
+            pass
+
     @classmethod
     def _register_event_listener(cls, target, identifier, func, *args, **kw):
         listen(target, identifier, func, *args, **kw)
         cls._remove_event_listener_params.append(
             (weakref.ref(target), identifier, func)
         )
 
+        weakref.finalize(
+            target,
+            cls._dispose_of_event_listener,
+            (weakref.ref(target), identifier, func),
+        )
+
     @classmethod
     def remove_all_event_listeners(cls):
         for (

instrumentation/opentelemetry-instrumentation-sqlalchemy/tests/test_sqlalchemy.py

@@ -417,6 +417,10 @@ def test_no_memory_leakage_if_engine_diposed(self):
 
         from sqlalchemy import create_engine
 
+        from opentelemetry.instrumentation.sqlalchemy.engine import (
+            EngineTracer,
+        )
+
         callback = mock.Mock()
 
         def make_shortlived_engine():
@@ -432,3 +436,4 @@ def make_shortlived_engine():
 
         gc.collect()
         assert callback.call_count == 5
+        assert len(EngineTracer._remove_event_listener_params) == 0