Fix 1453 (#1454)

* add test and fix for cache clearing bug

* update test docstring and releasenotes

Author: j-wags

docs/releasehistory.md

@@ -15,6 +15,7 @@ Please note that all releases prior to a version 1.0.0 are considered pre-releas
 
 ### Bug fixes
 
+* #1454 Fixes a bug that causes cache operations to error under some circumstances.
 * #1435 Fixes a bug in which `Colletion.set_force_field_parameters` did not update force field parameters upon export to simulation engines.
 
 ## 0.5.1 - 2025-02-25

openff/interchange/_tests/test_issues.py

@@ -297,3 +297,28 @@ def test_issue_1234_openmm(sage, valence_handler):
 
     # energies should be different, since parameters are (wildly!) different
     assert abs(original_energy - new_energy) > 0.1
+
+
+def test_clear_caches_with_dead_weakref_proxy():
+    """Reproduce a bug where _clear_caches raises ReferenceError when dead
+    weakref proxies exist in gc.get_objects(). See
+    https://github.com/openforcefield/openff-interchange/issues/1453
+    """
+    import gc
+    import weakref
+
+    class _Dummy:
+        pass
+
+    # Create a dead weakref proxy that remains tracked by gc
+    obj = _Dummy()
+    proxy = weakref.proxy(obj)
+    container = [proxy]  # noqa: F841
+    del obj
+    gc.collect()
+
+    molecule = MoleculeWithConformer.from_smiles("C")
+    force_field = ForceField("openff-2.2.0.offxml")
+
+    # This raised ReferenceError before the fix
+    Interchange.from_smirnoff(force_field=force_field, topology=[molecule])

openff/interchange/components/interchange.py

@@ -1115,5 +1115,8 @@ def _clear_caches():
     import gc
 
     for obj in gc.get_objects():
-        if isinstance(obj, functools._lru_cache_wrapper) and obj.__module__.startswith("openff.interchange"):
-            obj.cache_clear()
+        try:
+            if isinstance(obj, functools._lru_cache_wrapper) and obj.__module__.startswith("openff.interchange"):
+                obj.cache_clear()
+        except ReferenceError:
+            continue