filmor · Oct 6, 2026 · Oct 6, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -13,6 +13,8 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 
 ### Fixed
 
+- Fix shutdown serialization of CLR namespace modules on .NET 8 while preserving
+  namespace name tracking across runtime restarts.
 
 ## 3.2.0 - 2026-09-29
 

diff --git a/src/embed_tests/StateSerialization/ModuleSerialization.cs b/src/embed_tests/StateSerialization/ModuleSerialization.cs
@@ -0,0 +1,68 @@
+using System.Collections.Generic;
+using System.IO;
+using NUnit.Framework;
+using Python.Runtime;
+
+namespace Python.EmbeddingTest.StateSerialization;
+
+[NonParallelizable]
+public class ModuleSerialization
+{
+    [TestCase(false)]
+    [TestCase(true)]
+    public void NamespaceModuleRoundtrip(bool loadNames)
+    {
+        var formatter = RuntimeData.CreateFormatter();
+        if (formatter is NoopFormatter)
+        {
+            Assert.Inconclusive("NoopFormatter in use, cannot perform serialization test.");
+        }
+
+        using var gil = Py.GIL();
+        using var pyModule = ModuleObject.Create("System").MoveToPyObject();
+        var module = (ModuleObject)ManagedType.GetManagedObject(pyModule)!;
+        using (var int32 = module.GetAttribute("Int32", true))
+        {
+            Assert.That(int32.IsNull(), Is.False);
+        }
+
+        string[] names = null;
+        if (loadNames)
+        {
+            using var all = pyModule.GetAttr("__all__");
+            names = all.As<string[]>();
+            Assert.That(names, Does.Contain("Int32"));
+        }
+
+        for (int i = 0; i < 2; i++)
+        {
+            var context = module.Save(pyModule);
+            using var buffer = new MemoryStream();
+            formatter.Serialize(buffer, new object[] { module, context });
+            buffer.Position = 0;
+            var restored = (object[])formatter.Deserialize(buffer);
+            ExtensionType.tp_clear(pyModule);
+            module = (ModuleObject)restored[0];
+            module.Load(pyModule, (Dictionary<string, object>)restored[1]);
+
+            using (var int32 = module.GetAttribute("Int32", true))
+            {
+                Assert.That(int32.IsNull(), Is.False);
+            }
+            using (var collections = module.GetAttribute("Collections", true))
+            {
+                Assert.That(collections.IsNull(), Is.False);
+            }
+
+            using var all = pyModule.GetAttr("__all__");
+            var restoredNames = all.As<string[]>();
+            Assert.That(restoredNames, Does.Contain("Int32"));
+            Assert.That(restoredNames, Is.Unique);
+            if (names is not null)
+            {
+                Assert.That(restoredNames, Is.EquivalentTo(names));
+            }
+            names = restoredNames;
+        }
+    }
+}
diff --git a/src/runtime/Types/ModuleObject.cs b/src/runtime/Types/ModuleObject.cs
@@ -14,13 +14,15 @@ namespace Python.Runtime
     [Serializable]
     internal class ModuleObject : ExtensionType
     {
-        private readonly ConcurrentDictionary<string, PyObject> cache = new();
+        [NonSerialized]
+        private ConcurrentDictionary<string, PyObject> cache = new();
 
         internal string moduleName;
         internal PyDict dict;
         protected string _namespace;
         private readonly PyList __all__ = new ();
-        private readonly ConcurrentDictionary<string, byte> allNames = new();
+        [NonSerialized]
+        private ConcurrentDictionary<string, byte> allNames = new();
 
         // Attributes to be set on the module according to PEP302 and 451
         // by the import machinery.
@@ -378,7 +380,8 @@ public static int tp_traverse(BorrowedReference ob, IntPtr visit, IntPtr arg)
 
         protected override Dictionary<string, object?>? OnSave(BorrowedReference ob)
         {
-            var context = base.OnSave(ob);
+            var context = base.OnSave(ob) ?? new();
+            context[nameof(allNames)] = allNames.Keys.ToArray();
             System.Diagnostics.Debug.Assert(dict == GetObjectDict(ob));
             // destroy the cache(s)
             foreach (var pair in cache)
@@ -402,6 +405,9 @@ public static int tp_traverse(BorrowedReference ob, IntPtr visit, IntPtr arg)
 
         protected override void OnLoad(BorrowedReference ob, Dictionary<string, object?>? context)
         {
+            cache = new();
+            allNames = new(((string[])context![nameof(allNames)]!)
+                .Select(name => new KeyValuePair<string, byte>(name, 0)));
             base.OnLoad(ob, context);
             SetObjectDict(ob, new NewReference(dict).Steal());
         }