Test ExtensibleRate memory management

test/python/test_reaction.py

@@ -2,6 +2,7 @@ from math import exp
 from pathlib import Path
 import sys
 import textwrap
+import gc
 
 import cantera as ct
 import numpy as np
@@ -1619,6 +1620,29 @@ class TestExtensible2(utilities.CanteraTest):
         with pytest.raises(ct.CanteraError, match="SyntaxError"):
             ct.Solution(yaml=self._input_template.format(module="user_ext_invalid"))
 
+    def test_memory_management(self):
+        # Make sure objects are being correctly cleaned up and not stuck in
+        # mixed Python/C++ ownership cycles
+        import user_ext
+
+        gc.collect()
+        initialRate = user_ext.SquareRate.use_count[0]
+        initialData = user_ext.SquareRateData.use_count[0]
+
+        def run():
+            gas = ct.Solution("extensible-reactions.yaml", transport_model=None)
+            assert gas.forward_rate_constants[0] > 0
+            assert user_ext.SquareRate.use_count[0] == initialRate + 1
+            assert user_ext.SquareRateData.use_count[0] == initialData + 1
+
+        run()
+
+        # The number of instances for both classes should go back to its previous value
+        # after deleting the Solution (may not be zero due to other Solution instances)
+        # held by other test classes
+        gc.collect()
+        assert user_ext.SquareRate.use_count[0] == initialRate
+        assert user_ext.SquareRateData.use_count[0] == initialData
 
 class InterfaceReactionTests(ReactionTests):
     # test suite for surface reaction expressions

test/python/user_ext.py

@@ -2,17 +2,32 @@ import cantera as ct
 
 class SquareRateData(ct.ExtensibleRateData):
     __slots__ = ("Tsquared",)
+    use_count = [0]  # used in test for memory leak
+
+    def __init__(self):
+        self.use_count[0] += 1
 
     def update(self, gas):
         self.Tsquared = gas.T**2
         return True
 
+    def __del__(self):
+        self.use_count[0] -= 1
+
 @ct.extension(name="square-rate", data=SquareRateData)
 class SquareRate(ct.ExtensibleRate):
     __slots__ = ("A",)
+    use_count = [0]  # used in test for memory leak
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.use_count[0] += 1
 
     def set_parameters(self, node, units):
         self.A = node["A"]
 
     def eval(self, data):
         return self.A * data.Tsquared
+
+    def __del__(self):
+        self.use_count[0] -= 1