fixed crash in finalizer of CLR types defined in Python, that survive engine shutdown

lostmsu · lostmsu · commit 9498c078585a · 2020-10-13T09:35:25.000-07:00
#1256 During engine shutdown all links from Python to .NET instances are severed. If an instance of CLR class defined in Python survives the shutdown (for example, a reference is stored in static field) and later gets finalized, it will attempt to severe link again, which is an invalid operation. The fix is to check if the link has already been severed and skip that step during finalization.
diff --git a/src/embed_tests/TestPythonDerivedType.cs b/src/embed_tests/TestPythonDerivedType.cs
@@ -0,0 +1,43 @@
+namespace Python.EmbeddingTest
+{
+    using NUnit.Framework;
+
+    using Python.Runtime;
+
+    public class TestPythonDerivedType
+    {
+        [OneTimeSetUp]
+        public void SetUp()
+        {
+            PythonEngine.Initialize();
+        }
+
+        [OneTimeTearDown]
+        public void Dispose()
+        {
+            PythonEngine.Shutdown();
+        }
+
+        // Exception in finalizer of custom encoder
+        // https://github.com/pythonnet/pythonnet/issues/1256
+        [Test]
+        public void TestFinalizer_AfterShutdown()
+        {
+            PythonEngine.Exec(@"
+import clr
+from Python.Runtime import PyObjectConversions
+from Python.Runtime.Codecs import RawProxyEncoder
+class  ListAsRawEncoder(RawProxyEncoder):
+  __namespace__ = 'Python.Runtime.Codecs'
+  def CanEncode(self, clr_type):
+    return clr_type.Name == 'IList`1' and clr_type.Namespace == 'System.Collections.Generic'
+
+list_encoder = ListAsRawEncoder()
+PyObjectConversions.RegisterEncoder(list_encoder)
+");
+            PythonEngine.Shutdown();
+            System.GC.Collect();
+            System.GC.WaitForPendingFinalizers();
+        }
+    }
+}
diff --git a/src/runtime/classderived.cs b/src/runtime/classderived.cs
@@ -857,7 +857,7 @@ public static void Finalize(IPythonDerivedType obj)
             {
                 if (0 == Runtime.Py_IsInitialized() || Runtime.IsFinalizing)
                 {
-                    self.gcHandle.Free();
+                    if (self.gcHandle.IsAllocated) self.gcHandle.Free();
                     return;
                 }
             }
@@ -872,7 +872,7 @@ public static void Finalize(IPythonDerivedType obj)
                     // If python's been terminated then just free the gchandle.
                     if (0 == Runtime.Py_IsInitialized() || Runtime.IsFinalizing)
                     {
-                        self.gcHandle.Free();
+                        if (self.gcHandle.IsAllocated) self.gcHandle.Free();
                         return;
                     }
 

Original file line number	Diff line number	Diff line change
`@@ -857,7 +857,7 @@ public static void Finalize(IPythonDerivedType obj)`
`857`	`857`	`{`
`858`	`858`	`if (0 == Runtime.Py_IsInitialized() \|\| Runtime.IsFinalizing)`
`859`	`859`	`{`
`860`		`- self.gcHandle.Free();`
	`860`	`+ if (self.gcHandle.IsAllocated) self.gcHandle.Free();`
`861`	`861`	`return;`
`862`	`862`	`}`
`863`	`863`	`}`
`@@ -872,7 +872,7 @@ public static void Finalize(IPythonDerivedType obj)`
`872`	`872`	`// If python's been terminated then just free the gchandle.`
`873`	`873`	`if (0 == Runtime.Py_IsInitialized() \|\| Runtime.IsFinalizing)`
`874`	`874`	`{`
`875`		`- self.gcHandle.Free();`
	`875`	`+ if (self.gcHandle.IsAllocated) self.gcHandle.Free();`
`876`	`876`	`return;`
`877`	`877`	`}`
`878`	`878`