Test for memory leaks as described in lovasoa#198

Author: dairiki

tests/test_memory_leak.py

@@ -0,0 +1,111 @@
+import gc
+import inspect
+import sys
+import unittest
+import weakref
+from dataclasses import dataclass
+
+import marshmallow
+import marshmallow_dataclass as md
+
+
+class Referenceable:
+    pass
+
+
+class TestMemoryLeak(unittest.TestCase):
+    """Test for memory leaks as decribed in `#198`_.
+
+    .. _#198: https://github.com/lovasoa/marshmallow_dataclass/issues/198
+    """
+
+    def setUp(self):
+        gc.collect()
+        gc.disable()
+        self.frame_collected = False
+
+    def tearDown(self):
+        gc.enable()
+
+    def trackFrame(self):
+        """Create a tracked local variable in the callers frame.
+
+        We track these locals in the WeakSet self.livingLocals.
+
+        When the callers frame is freed, the locals will be GCed as well.
+        In this way we can check that the callers frame has been collected.
+        """
+        local = Referenceable()
+        weakref.finalize(local, self._set_frame_collected)
+        try:
+            frame = inspect.currentframe()
+            frame.f_back.f_locals["local_variable"] = local
+        finally:
+            del frame
+
+    def _set_frame_collected(self):
+        self.frame_collected = True
+
+    def assertFrameCollected(self):
+        """Check that all locals created by makeLocal have been GCed"""
+        if not hasattr(sys, "getrefcount"):
+            # pypy does not do reference counting
+            gc.collect(0)
+        self.assertTrue(self.frame_collected)
+
+    def test_sanity(self):
+        """Test that our scheme for detecting leaked frames works."""
+        frames = []
+
+        def f():
+            frames.append(inspect.currentframe())
+            self.trackFrame()
+
+        f()
+
+        gc.collect(0)
+        self.assertFalse(
+            self.frame_collected
+        )  # with frame leaked, f's locals are still alive
+        frames.clear()
+        self.assertFrameCollected()
+
+    def test_class_schema(self):
+        def f():
+            @dataclass
+            class Foo:
+                value: int
+
+            md.class_schema(Foo)
+
+            self.trackFrame()
+
+        f()
+        self.assertFrameCollected()
+
+    def test_md_dataclass_lazy_schema(self):
+        def f():
+            @md.dataclass
+            class Foo:
+                value: int
+
+            self.trackFrame()
+
+        f()
+        # NB: The "lazy" Foo.Schema attribute descriptor holds a reference to f's frame,
+        # which, in turn, holds a reference to class Foo, thereby creating ref cycle.
+        # So, a gc pass is required to clean that up.
+        gc.collect(0)
+        self.assertFrameCollected()
+
+    def test_md_dataclass(self):
+        def f():
+            @md.dataclass
+            class Foo:
+                value: int
+
+            self.assertIsInstance(Foo.Schema(), marshmallow.Schema)
+            self.trackFrame()
+
+        f()
+        self.assertFrameCollected()