gh-115490: Make the interpreter.channels and interpreter.queues Modules Handle Reloading Properly (gh-115493)

The problem manifested when the .py module got reloaded and the corresponding extension module didn't. The .py module registers types with the extension and the extension was not allowing that to happen more than once. The solution: let it happen more than once.

Lib/test/libregrtest/main.py

@@ -384,15 +384,10 @@ class Regrtest:
 
             result = self.run_test(test_name, runtests, tracer)
 
-            # Unload the newly imported test modules (best effort
-            # finalization). To work around gh-115490, don't unload
-            # test.support.interpreters and its submodules even if they
-            # weren't loaded before.
-            keep = "test.support.interpreters"
+            # Unload the newly imported test modules (best effort finalization)
             new_modules = [module for module in sys.modules
                            if module not in save_modules and
-                                module.startswith(("test.", "test_"))
-                                and not module.startswith(keep)]
+                                module.startswith(("test.", "test_"))]
             for module in new_modules:
                 sys.modules.pop(module, None)
                 # Remove the attribute of the parent module.

Lib/test/test__xxinterpchannels.py

@@ -18,6 +18,11 @@ from test.test__xxsubinterpreters import (
 channels = import_helper.import_module('_xxinterpchannels')
 
 
+# Additional tests are found in Lib/test/test_interpreters/test_channels.py.
+# New tests should be added there.
+# XXX The tests here should be moved there.  See the note under LowLevelTests.
+
+
 ##################################
 # helpers
 

Lib/test/test_interpreters/test_channels.py

@@ -1,3 +1,4 @@
+import importlib
 import threading
 from textwrap import dedent
 import unittest
@@ -11,6 +12,24 @@ from test.support.interpreters import channels
 from .utils import _run_output, TestBase
 
 
+class LowLevelTests(TestBase):
+
+    # The behaviors in the low-level module is important in as much
+    # as it is exercised by the high-level module.  Therefore the
+    # most # important testing happens in the high-level tests.
+    # These low-level tests cover corner cases that are not
+    # encountered by the high-level module, thus they
+    # mostly shouldn't matter as much.
+
+    # Additional tests are found in Lib/test/test__xxinterpchannels.py.
+    # XXX Those should be either moved to LowLevelTests or eliminated
+    # in favor of high-level tests in this file.
+
+    def test_highlevel_reloaded(self):
+        # See gh-115490 (https://github.com/python/cpython/issues/115490).
+        importlib.reload(channels)
+
+
 class TestChannels(TestBase):
 
     def test_create(self):

Lib/test/test_interpreters/test_queues.py

@@ -1,3 +1,4 @@
+import importlib
 import threading
 from textwrap import dedent
 import unittest
@@ -20,6 +21,20 @@ class TestBase(TestBase):
                 pass
 
 
+class LowLevelTests(TestBase):
+
+    # The behaviors in the low-level module is important in as much
+    # as it is exercised by the high-level module.  Therefore the
+    # most # important testing happens in the high-level tests.
+    # These low-level tests cover corner cases that are not
+    # encountered by the high-level module, thus they
+    # mostly shouldn't matter as much.
+
+    def test_highlevel_reloaded(self):
+        # See gh-115490 (https://github.com/python/cpython/issues/115490).
+        importlib.reload(queues)
+
+
 class QueueTests(TestBase):
 
     def test_create(self):

Modules/_xxinterpchannelsmodule.c

@@ -2675,12 +2675,17 @@ set_channelend_types(PyObject *mod, PyTypeObject *send, PyTypeObject *recv)
         return -1;
     }
 
-    if (state->send_channel_type != NULL
-        || state->recv_channel_type != NULL)
-    {
-        PyErr_SetString(PyExc_TypeError, "already registered");
-        return -1;
+    // Clear the old values if the .py module was reloaded.
+    if (state->send_channel_type != NULL) {
+        (void)_PyCrossInterpreterData_UnregisterClass(state->send_channel_type);
+        Py_CLEAR(state->send_channel_type);
     }
+    if (state->recv_channel_type != NULL) {
+        (void)_PyCrossInterpreterData_UnregisterClass(state->recv_channel_type);
+        Py_CLEAR(state->recv_channel_type);
+    }
+
+    // Add and register the types.
     state->send_channel_type = (PyTypeObject *)Py_NewRef(send);
     state->recv_channel_type = (PyTypeObject *)Py_NewRef(recv);
     if (ensure_xid_class(send, _channelend_shared) < 0) {

Modules/_xxinterpqueuesmodule.c

@@ -169,6 +169,9 @@ static int
 clear_module_state(module_state *state)
 {
     /* external types */
+    if (state->queue_type != NULL) {
+        (void)_PyCrossInterpreterData_UnregisterClass(state->queue_type);
+    }
     Py_CLEAR(state->queue_type);
 
     /* QueueError */
@@ -1078,15 +1081,18 @@ set_external_queue_type(PyObject *module, PyTypeObject *queue_type)
 {
     module_state *state = get_module_state(module);
 
+    // Clear the old value if the .py module was reloaded.
     if (state->queue_type != NULL) {
-        PyErr_SetString(PyExc_TypeError, "already registered");
-        return -1;
+        (void)_PyCrossInterpreterData_UnregisterClass(
+                                state->queue_type);
+        Py_CLEAR(state->queue_type);
     }
-    state->queue_type = (PyTypeObject *)Py_NewRef(queue_type);
 
+    // Add and register the new type.
     if (ensure_xid_class(queue_type, _queueobj_shared) < 0) {
         return -1;
     }
+    state->queue_type = (PyTypeObject *)Py_NewRef(queue_type);
 
     return 0;
 }
@@ -1703,10 +1709,6 @@ module_clear(PyObject *mod)
 {
     module_state *state = get_module_state(mod);
 
-    if (state->queue_type != NULL) {
-        (void)_PyCrossInterpreterData_UnregisterClass(state->queue_type);
-    }
-
     // Now we clear the module state.
     clear_module_state(state);
     return 0;