Clean up globals defined in Python source, make sure their __del__ is called

Src/IronPython/Runtime/PythonContext.cs

@@ -271,7 +271,7 @@ public PythonContext(ScriptDomainManager/*!*/ manager, IDictionary<string, objec
                 try {
                     HookAssemblyResolve();
                 } catch (System.Security.SecurityException) {
-                    // We may not have SecurityPermissionFlag.ControlAppDomain. 
+                    // We may not have SecurityPermissionFlag.ControlAppDomain.
                     // If so, we will not look up sys.path for module loads
                 }
             }
@@ -1238,7 +1238,7 @@ private void UnhookAssemblyResolve() {
             try {
                 AppDomain.CurrentDomain.AssemblyResolve -= _resolveHolder.AssemblyResolveEvent;
             } catch (System.Security.SecurityException) {
-                // We may not have SecurityPermissionFlag.ControlAppDomain. 
+                // We may not have SecurityPermissionFlag.ControlAppDomain.
                 // If so, we will not look up sys.path for module loads
             }
         }
@@ -1295,6 +1295,17 @@ public override void Shutdown() {
                 }
 #endif
             }
+
+            // clean up globals from modules
+            foreach (var module in SystemStateModules.Values) {
+                if (module is PythonModule pyModule) {
+                    pyModule.Cleanup(SharedContext);
+                }
+            }
+
+            // allow finalizers to run before shutdown
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
         }
 
         // TODO: ExceptionFormatter service
@@ -1569,7 +1580,7 @@ public override TService GetService<TService>(params object[] args) {
 
         /// <summary>
         /// Returns (and creates if necessary) the PythonService that is associated with this PythonContext.
-        /// 
+        ///
         /// The PythonService is used for providing remoted convenience helpers for the DLR hosting APIs.
         /// </summary>
         internal Hosting.PythonService GetPythonService(Microsoft.Scripting.Hosting.ScriptEngine engine) {
@@ -1678,7 +1689,7 @@ private Dictionary<string, Type> CreateBuiltinTable() {
 
                 if (Environment.OSVersion.Platform == PlatformID.Unix) {
                     // we make our nt package show up as a posix package
-                    // on unix platforms.  Because we build on top of the 
+                    // on unix platforms.  Because we build on top of the
                     // CLI for all file operations we should be good from
                     // there, but modules that check for the presence of
                     // names (e.g. os) will do the right thing.
@@ -2529,8 +2540,8 @@ private CallSite<Func<CallSite, object, T>> MakeConvertSite<T>(ConversionResultK
 
         /// <summary>
         /// Invokes the specified operation on the provided arguments and returns the new resulting value.
-        /// 
-        /// operation is usually a value from StandardOperators (standard CLR/DLR operator) or 
+        ///
+        /// operation is usually a value from StandardOperators (standard CLR/DLR operator) or
         /// OperatorStrings (a Python specific operator)
         /// </summary>
         internal object Operation(PythonOperationKind operation, object self, object other) {
@@ -2987,13 +2998,13 @@ internal CultureInfo NumericCulture {
         /// <summary>
         /// Sets the current command dispatcher for the Python command line.  The previous dispatcher
         /// is returned.  Null can be passed to remove the current command dispatcher.
-        /// 
+        ///
         /// The command dispatcher will be called with a delegate to be executed.  The command dispatcher
         /// should invoke the target delegate in the desired context.
-        /// 
+        ///
         /// A common use for this is to enable running all REPL commands on the UI thread while the REPL
         /// continues to run on a non-UI thread.
-        /// 
+        ///
         /// The ipy.exe REPL will call into PythonContext.DispatchCommand to dispatch each execution to
         /// the correct thread.  Other REPLs can do the same to support this functionality as well.
         /// </summary>
@@ -3094,8 +3105,8 @@ public int Compare(object x, object y) {
         /// <summary>
         /// Gets a function which can be used for comparing two values using the normal
         /// Python semantics.
-        /// 
-        /// If type is null then a generic comparison function is returned.  If type is 
+        ///
+        /// If type is null then a generic comparison function is returned.  If type is
         /// not null a comparison function is returned that's used for just that type.
         /// </summary>
         internal IComparer GetComparer(Type type) {

Src/IronPython/Runtime/PythonModule.cs

@@ -8,6 +8,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Dynamic;
+using System.Linq;
 using System.Runtime.CompilerServices;
 using System.Threading;
 
@@ -30,6 +31,7 @@ namespace IronPython.Runtime {
     public class PythonModule : IDynamicMetaObjectProvider, IPythonMembersList {
         private readonly PythonDictionary _dict;
         private Scope _scope;
+        private bool _cleanedUp = false;
 
         public PythonModule() {
             _dict = new PythonDictionary();
@@ -49,7 +51,7 @@ internal PythonModule(PythonContext context, Scope scope) {
 
         /// <summary>
         /// Creates a new PythonModule with the specified dictionary.
-        /// 
+        ///
         /// Used for creating modules for builtin modules which don't have any code associated with them.
         /// </summary>
         internal PythonModule(PythonDictionary dict) {
@@ -253,7 +255,7 @@ public DynamicMetaObject GetMember(PythonGetMemberBinder member, DynamicMetaObje
 
             private DynamicMetaObject GetMemberWorker(DynamicMetaObjectBinder binder, DynamicMetaObject codeContext) {
                 string name = GetGetMemberName(binder);
-                var tmp = Expression.Variable(typeof(object), "res");                
+                var tmp = Expression.Variable(typeof(object), "res");
 
                 return new DynamicMetaObject(
                     Expression.Block(
@@ -355,7 +357,7 @@ IList<string> IMembersList.GetMemberNames() {
         }
 
         #endregion
-        
+
         internal class DebugProxy {
             private readonly PythonModule _module;
 
@@ -375,6 +377,30 @@ public List<ObjectDebugView> Members {
             }
         }
 
-
+        /// <summary>
+        /// Cleanup globals so that they could be garbage collected.
+        /// Note that it cleans python sourced modules only,
+        /// because C# modules are more fundamental and their globals may be required when other python object's finalizer is executing.
+        /// </summary>
+        public void Cleanup(CodeContext context) {
+            if (_cleanedUp) {
+                return;
+            }
+
+            _cleanedUp = true;
+
+            if (!_dict.ContainsKey("__file__")) {
+                return; // not from Python source, skip clean up
+            }
+
+            foreach (var key in _dict.Keys.ToList()) {
+                var obj = _dict[key];
+                if (obj is PythonModule module) {
+                    module.Cleanup(context);
+                } else if (key is string name) {
+                    __delattr__(context, name);
+                }
+            }
+        }
     }
 }

Tests/test_regressions.py

@@ -17,6 +17,7 @@ def test_cp1234(): ...
 import os
 import sys
 import unittest
+from subprocess import check_output
 
 from iptest import IronPythonTestCase, is_cli, is_mono, is_netcoreapp, is_posix, run_test, skipUnlessIronPython, stdout_trapper
 
@@ -1467,4 +1468,44 @@ def get_class_class(cls):
         self.assertEqual(o.get_self_class(), o.get_class())
         self.assertEqual(o.get_class(), o.get_class_class())
 
+    @unittest.skipIf(is_mono, 'https://github.com/IronLanguages/ironpython3/issues/937')
+    def test_ipy3_gh985(self):
+        """https://github.com/IronLanguages/ironpython3/issues/985"""
+        code = """
+import sys
+
+
+class Foo:
+    def __init__(self, name):
+        self.name = name
+
+    def __del__(self):
+        sys.stdout.write(self.name + '\\n')
+
+
+def func():
+    foo = Foo('Foo 1')
+    bar = Foo('Foo 2')
+    del bar
+
+
+func()
+
+
+foo = Foo('Foo 3')
+foo = Foo('Foo 4')
+        """
+
+        test_script_name = os.path.join(self.test_dir, 'ipy3_gh985.py')
+        f = open(test_script_name, 'w')
+        try:
+            f.write(code)
+            f.close()
+
+            output = check_output([sys.executable, test_script_name]).decode(sys.stdout.encoding).strip()
+            self.assertEqual(set(output.split(os.linesep)), {'Foo 1', 'Foo 2', 'Foo 3', 'Foo 4'})
+        finally:
+            os.unlink(test_script_name)
+
+
 run_test(__name__)