From ab2aa3ba491f5d69dd703c0150a12fcf5a1d9f3d Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Sat, 9 Sep 2023 14:23:58 -0600
Subject: [PATCH 01/19] Export _PyInterpreterState_LookUpID().

---
 Include/cpython/pystate.h        | 2 ++
 Include/internal/pycore_interp.h | 2 --
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
index 7e4c57efc7c00c..a9a2ffff16c1d4 100644
--- a/Include/cpython/pystate.h
+++ b/Include/cpython/pystate.h
@@ -236,6 +236,8 @@ PyAPI_FUNC(PyThreadState *) PyInterpreterState_ThreadHead(PyInterpreterState *);
 PyAPI_FUNC(PyThreadState *) PyThreadState_Next(PyThreadState *);
 PyAPI_FUNC(void) PyThreadState_DeleteCurrent(void);
 
+PyAPI_FUNC(PyInterpreterState *) _PyInterpreterState_LookUpID(int64_t);
+
 /* Frame evaluation API */
 
 typedef PyObject* (*_PyFrameEvalFunction)(PyThreadState *tstate, struct _PyInterpreterFrame *, int);
diff --git a/Include/internal/pycore_interp.h b/Include/internal/pycore_interp.h
index ebf02281a7a2a6..864b29ad9ca04a 100644
--- a/Include/internal/pycore_interp.h
+++ b/Include/internal/pycore_interp.h
@@ -254,8 +254,6 @@ struct _xidregitem {
     crossinterpdatafunc getdata;
 };
 
-extern PyInterpreterState* _PyInterpreterState_LookUpID(int64_t);
-
 extern int _PyInterpreterState_IDInitref(PyInterpreterState *);
 extern int _PyInterpreterState_IDIncref(PyInterpreterState *);
 extern void _PyInterpreterState_IDDecref(PyInterpreterState *);

From 4d103dd4e5bbad54d3a34b349070248da1b39438 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Sep 2023 12:36:00 -0600
Subject: [PATCH 02/19] Optionally free the pending call's data.

---
 Include/internal/pycore_ceval.h       |  6 +++++-
 Include/internal/pycore_ceval_state.h |  1 +
 Modules/signalmodule.c                |  4 ++--
 Python/ceval_gil.c                    | 31 ++++++++++++++++-----------
 4 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/Include/internal/pycore_ceval.h b/Include/internal/pycore_ceval.h
index 23d0fa399d7e6f..48861da2f19765 100644
--- a/Include/internal/pycore_ceval.h
+++ b/Include/internal/pycore_ceval.h
@@ -41,12 +41,16 @@ extern void _PyEval_InitState(PyInterpreterState *, PyThread_type_lock);
 extern void _PyEval_FiniState(struct _ceval_state *ceval);
 extern void _PyEval_SignalReceived(PyInterpreterState *interp);
 
+// bitwise flags:
+#define _Py_PENDING_MAINTHREADONLY 1
+#define _Py_PENDING_RAWFREE 2
+
 // Export for '_testinternalcapi' shared extension
 PyAPI_FUNC(int) _PyEval_AddPendingCall(
     PyInterpreterState *interp,
     _Py_pending_call_func func,
     void *arg,
-    int mainthreadonly);
+    int flags);
 
 extern void _PyEval_SignalAsyncExc(PyInterpreterState *interp);
 #ifdef HAVE_FORK
diff --git a/Include/internal/pycore_ceval_state.h b/Include/internal/pycore_ceval_state.h
index d0af5b542233e0..7befc82ea7349c 100644
--- a/Include/internal/pycore_ceval_state.h
+++ b/Include/internal/pycore_ceval_state.h
@@ -26,6 +26,7 @@ struct _pending_calls {
     struct _pending_call {
         _Py_pending_call_func func;
         void *arg;
+        int flags;
     } calls[NPENDINGCALLS];
     int first;
     int last;
diff --git a/Modules/signalmodule.c b/Modules/signalmodule.c
index 8d6556727b3a5a..673b30cff55c06 100644
--- a/Modules/signalmodule.c
+++ b/Modules/signalmodule.c
@@ -315,7 +315,7 @@ trip_signal(int sig_num)
                     _PyEval_AddPendingCall(interp,
                                            report_wakeup_send_error,
                                            (void *)(intptr_t) last_error,
-                                           1);
+                                           _Py_PENDING_MAINTHREADONLY);
                 }
             }
         }
@@ -335,7 +335,7 @@ trip_signal(int sig_num)
                     _PyEval_AddPendingCall(interp,
                                            report_wakeup_write_error,
                                            (void *)(intptr_t)errno,
-                                           1);
+                                           _Py_PENDING_MAINTHREADONLY);
                 }
             }
         }
diff --git a/Python/ceval_gil.c b/Python/ceval_gil.c
index ba16f5eb9bfe74..b45f93bd2acab8 100644
--- a/Python/ceval_gil.c
+++ b/Python/ceval_gil.c
@@ -763,7 +763,7 @@ _PyEval_SignalReceived(PyInterpreterState *interp)
 /* Push one item onto the queue while holding the lock. */
 static int
 _push_pending_call(struct _pending_calls *pending,
-                   _Py_pending_call_func func, void *arg)
+                   _Py_pending_call_func func, void *arg, int flags)
 {
     int i = pending->last;
     int j = (i + 1) % NPENDINGCALLS;
@@ -772,13 +772,14 @@ _push_pending_call(struct _pending_calls *pending,
     }
     pending->calls[i].func = func;
     pending->calls[i].arg = arg;
+    pending->calls[i].flags = flags;
     pending->last = j;
     return 0;
 }
 
 static int
 _next_pending_call(struct _pending_calls *pending,
-                   int (**func)(void *), void **arg)
+                   int (**func)(void *), void **arg, int *flags)
 {
     int i = pending->first;
     if (i == pending->last) {
@@ -788,15 +789,16 @@ _next_pending_call(struct _pending_calls *pending,
     }
     *func = pending->calls[i].func;
     *arg = pending->calls[i].arg;
+    *flags = pending->calls[i].flags;
     return i;
 }
 
 /* Pop one item off the queue while holding the lock. */
 static void
 _pop_pending_call(struct _pending_calls *pending,
-                  int (**func)(void *), void **arg)
+                  int (**func)(void *), void **arg, int *flags)
 {
-    int i = _next_pending_call(pending, func, arg);
+    int i = _next_pending_call(pending, func, arg, flags);
     if (i >= 0) {
         pending->calls[i] = (struct _pending_call){0};
         pending->first = (i + 1) % NPENDINGCALLS;
@@ -810,12 +812,12 @@ _pop_pending_call(struct _pending_calls *pending,
 
 int
 _PyEval_AddPendingCall(PyInterpreterState *interp,
-                       _Py_pending_call_func func, void *arg,
-                       int mainthreadonly)
+                       _Py_pending_call_func func, void *arg, int flags)
 {
-    assert(!mainthreadonly || _Py_IsMainInterpreter(interp));
+    assert(!(flags & _Py_PENDING_MAINTHREADONLY)
+           || _Py_IsMainInterpreter(interp));
     struct _pending_calls *pending = &interp->ceval.pending;
-    if (mainthreadonly) {
+    if (flags & _Py_PENDING_MAINTHREADONLY) {
         /* The main thread only exists in the main interpreter. */
         assert(_Py_IsMainInterpreter(interp));
         pending = &_PyRuntime.ceval.pending_mainthread;
@@ -825,7 +827,7 @@ _PyEval_AddPendingCall(PyInterpreterState *interp,
     assert(pending->lock != NULL);
 
     PyThread_acquire_lock(pending->lock, WAIT_LOCK);
-    int result = _push_pending_call(pending, func, arg);
+    int result = _push_pending_call(pending, func, arg, flags);
     PyThread_release_lock(pending->lock);
 
     /* signal main loop */
@@ -839,7 +841,7 @@ Py_AddPendingCall(_Py_pending_call_func func, void *arg)
     /* Legacy users of this API will continue to target the main thread
        (of the main interpreter). */
     PyInterpreterState *interp = _PyInterpreterState_Main();
-    return _PyEval_AddPendingCall(interp, func, arg, 1);
+    return _PyEval_AddPendingCall(interp, func, arg, _Py_PENDING_MAINTHREADONLY);
 }
 
 static int
@@ -880,17 +882,22 @@ _make_pending_calls(struct _pending_calls *pending)
     for (int i=0; i<NPENDINGCALLS; i++) {
         _Py_pending_call_func func = NULL;
         void *arg = NULL;
+        int flags = 0;
 
         /* pop one item off the queue while holding the lock */
         PyThread_acquire_lock(pending->lock, WAIT_LOCK);
-        _pop_pending_call(pending, &func, &arg);
+        _pop_pending_call(pending, &func, &arg, &flags);
         PyThread_release_lock(pending->lock);
 
         /* having released the lock, perform the callback */
         if (func == NULL) {
             break;
         }
-        if (func(arg) != 0) {
+        int res = func(arg);
+        if ((flags & _Py_PENDING_RAWFREE) && arg != NULL) {
+            PyMem_RawFree(arg);
+        }
+        if (res != 0) {
             return -1;
         }
     }

From faf77787b172c9e24e781ed8784a83c35b1803b0 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Sep 2023 12:37:44 -0600
Subject: [PATCH 03/19] Add _Py_CallInInterpreter() and
 _Py_CallInInterpreterAndRawFree().

---
 Include/internal/pycore_ceval.h | 10 ++++++++
 Python/pystate.c                | 43 ++++++++++++++++++++-------------
 2 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/Include/internal/pycore_ceval.h b/Include/internal/pycore_ceval.h
index 48861da2f19765..3bf48cd9c34ba8 100644
--- a/Include/internal/pycore_ceval.h
+++ b/Include/internal/pycore_ceval.h
@@ -52,6 +52,16 @@ PyAPI_FUNC(int) _PyEval_AddPendingCall(
     void *arg,
     int flags);
 
+typedef int (*_Py_simple_func)(void *);
+extern int _Py_CallInInterpreter(
+    PyInterpreterState *interp,
+    _Py_simple_func func,
+    void *arg);
+extern int _Py_CallInInterpreterAndRawFree(
+    PyInterpreterState *interp,
+    _Py_simple_func func,
+    void *arg);
+
 extern void _PyEval_SignalAsyncExc(PyInterpreterState *interp);
 #ifdef HAVE_FORK
 extern PyStatus _PyEval_ReInitThreads(PyThreadState *tstate);
diff --git a/Python/pystate.c b/Python/pystate.c
index fe056bf4687026..532caa816613b0 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -2492,18 +2492,36 @@ _PyCrossInterpreterData_NewObject(_PyCrossInterpreterData *data)
     return data->new_object(data);
 }
 
-static int
-_release_xidata_pending(void *data)
+int
+_Py_CallInInterpreter(PyInterpreterState *interp,
+                      _Py_simple_func func, void *arg)
 {
-    _xidata_clear((_PyCrossInterpreterData *)data);
+    if (interp == current_fast_get(interp->runtime)->interp) {
+        return func(arg);
+    }
+    // XXX Emit a warning if this fails?
+    _PyEval_AddPendingCall(interp, (_Py_pending_call_func)func, arg, 0);
+    return 0;
+}
+
+int
+_Py_CallInInterpreterAndRawFree(PyInterpreterState *interp,
+                                _Py_simple_func func, void *arg)
+{
+    if (interp == current_fast_get(interp->runtime)->interp) {
+        int res = func(arg);
+        PyMem_RawFree(arg);
+        return res;
+    }
+    // XXX Emit a warning if this fails?
+    _PyEval_AddPendingCall(interp, func, arg, _Py_PENDING_RAWFREE);
     return 0;
 }
 
 static int
-_xidata_release_and_rawfree_pending(void *data)
+_call_clear_xidata(void *data)
 {
     _xidata_clear((_PyCrossInterpreterData *)data);
-    PyMem_RawFree(data);
     return 0;
 }
 
@@ -2535,21 +2553,12 @@ _xidata_release(_PyCrossInterpreterData *data, int rawfree)
     }
 
     // "Release" the data and/or the object.
-    if (interp == current_fast_get(interp->runtime)->interp) {
-        _xidata_clear(data);
-        if (rawfree) {
-            PyMem_RawFree(data);
-        }
+    if (rawfree) {
+        return _Py_CallInInterpreterAndRawFree(interp, _call_clear_xidata, data);
     }
     else {
-        _Py_pending_call_func func = _release_xidata_pending;
-        if (rawfree) {
-            func = _xidata_release_and_rawfree_pending;
-        }
-        // XXX Emit a warning if this fails?
-        _PyEval_AddPendingCall(interp, func, data, 0);
+        return _Py_CallInInterpreter(interp, _call_clear_xidata, data);
     }
-    return 0;
 }
 
 int

From 5c5662dd9f2dd78ad80cd760c33406d98bd168d7 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Sep 2023 12:38:39 -0600
Subject: [PATCH 04/19] Add PyUnstable_Buffer_ReleaseInInterpreter() and
 PyUnstable_Buffer_ReleaseInInterpreterAndRawFree().

---
 Include/pybuffer.h |  4 ++++
 Objects/abstract.c | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/Include/pybuffer.h b/Include/pybuffer.h
index ca1c6058d9052c..ea09b9c1b31717 100644
--- a/Include/pybuffer.h
+++ b/Include/pybuffer.h
@@ -100,6 +100,10 @@ PyAPI_FUNC(int) PyBuffer_FillInfo(Py_buffer *view, PyObject *o, void *buf,
 
 /* Releases a Py_buffer obtained from getbuffer ParseTuple's "s*". */
 PyAPI_FUNC(void) PyBuffer_Release(Py_buffer *view);
+PyAPI_FUNC(int) PyUnstable_Buffer_ReleaseInInterpreter(
+        PyInterpreterState *interp, Py_buffer *view);
+PyAPI_FUNC(int) PyUnstable_Buffer_ReleaseInInterpreterAndRawFree(
+        PyInterpreterState *interp, Py_buffer *view);
 
 /* Maximum number of dimensions */
 #define PyBUF_MAX_NDIM 64
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 55d3b3ada296be..b8b4464e320362 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -806,6 +806,27 @@ PyBuffer_Release(Py_buffer *view)
     Py_DECREF(obj);
 }
 
+static int
+_buffer_release_call(void *arg)
+{
+    PyBuffer_Release((Py_buffer *)arg);
+    return 0;
+}
+
+int
+PyUnstable_Buffer_ReleaseInInterpreter(PyInterpreterState *interp,
+                                       Py_buffer *view)
+{
+    return _Py_CallInInterpreter(interp, _buffer_release_call, view);
+}
+
+int
+PyUnstable_Buffer_ReleaseInInterpreterAndRawFree(PyInterpreterState *interp,
+                                                 Py_buffer *view)
+{
+    return _Py_CallInInterpreterAndRawFree(interp, _buffer_release_call, view);
+}
+
 PyObject *
 PyObject_Format(PyObject *obj, PyObject *format_spec)
 {

From 573abef2ae87f2eaf8dc0b4faf9532f98e8694f9 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Sep 2023 15:06:49 -0600
Subject: [PATCH 05/19] Add CrossInterpreterBufferView.

---
 Modules/_xxinterpchannelsmodule.c | 70 +++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index d5be76f1f0e38e..5b82528d425b01 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -195,6 +195,68 @@ _release_xid_data(_PyCrossInterpreterData *data, int flags)
 }
 
 
+/* Cross-interpreter Buffer Views *******************************************/
+
+// XXX Release when the original interpreter is destroyed.
+
+typedef struct {
+    PyObject_HEAD
+    Py_buffer *view;
+    int64_t interp;
+} XIBufferViewObject;
+
+static void
+xibufferview_dealloc(XIBufferViewObject *self)
+{
+    PyInterpreterState *interp = _PyInterpreterState_LookUpID(self->interp);
+    /* If the interpreter is no longer alive then we have problems,
+       since other objects may be using the buffer still. */
+    assert(interp != NULL);
+
+    if (PyUnstable_Buffer_ReleaseInInterpreterAndRawFree(interp, self->view) < 0) {
+        // XXX Emit a warning?
+        PyErr_Clear();
+    }
+
+    PyTypeObject *tp = Py_TYPE(self);
+    tp->tp_free(self);
+    /* "Instances of heap-allocated types hold a reference to their type."
+     * See: https://docs.python.org/3.11/howto/isolating-extensions.html#garbage-collection-protocol
+     * See: https://docs.python.org/3.11/c-api/typeobj.html#c.PyTypeObject.tp_traverse
+    */
+    // XXX Why don't we implement Py_TPFLAGS_HAVE_GC, e.g. Py_tp_traverse,
+    // like we do for _abc._abc_data?
+    Py_DECREF(tp);
+}
+
+static int
+xibufferview_getbuf(XIBufferViewObject *self, Py_buffer *view, int flags)
+{
+    /* Only PyMemoryView_FromObject() should ever call this,
+       via _memoryview_from_xid() below. */
+    *view = *self->view;
+    view->obj = (PyObject *)self;
+    // XXX Should we leave it alone?
+    view->internal = NULL;
+    return 0;
+}
+
+static PyType_Slot XIBufferViewType_slots[] = {
+    {Py_tp_dealloc, (destructor)xibufferview_dealloc},
+    {Py_bf_getbuffer, (getbufferproc)xibufferview_getbuf},
+    // We don't bother with Py_bf_releasebuffer since we don't need it.
+    {0, NULL},
+};
+
+static PyType_Spec XIBufferViewType_spec = {
+    .name = MODULE_NAME ".CrossInterpreterBufferView",
+    .basicsize = sizeof(XIBufferViewObject),
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
+              Py_TPFLAGS_DISALLOW_INSTANTIATION | Py_TPFLAGS_IMMUTABLETYPE),
+    .slots = XIBufferViewType_slots,
+};
+
+
 /* module state *************************************************************/
 
 typedef struct {
@@ -203,6 +265,7 @@ typedef struct {
 
     /* heap types */
     PyTypeObject *ChannelIDType;
+    PyTypeObject *XIBufferViewType;
 
     /* exceptions */
     PyObject *ChannelError;
@@ -241,6 +304,7 @@ traverse_module_state(module_state *state, visitproc visit, void *arg)
 {
     /* heap types */
     Py_VISIT(state->ChannelIDType);
+    Py_VISIT(state->XIBufferViewType);
 
     /* exceptions */
     Py_VISIT(state->ChannelError);
@@ -263,6 +327,7 @@ clear_module_state(module_state *state)
         (void)_PyCrossInterpreterData_UnregisterClass(state->ChannelIDType);
     }
     Py_CLEAR(state->ChannelIDType);
+    Py_CLEAR(state->XIBufferViewType);
 
     /* exceptions */
     Py_CLEAR(state->ChannelError);
@@ -2555,6 +2620,11 @@ module_exec(PyObject *mod)
         goto error;
     }
 
+    state->XIBufferViewType = add_new_type(mod, &XIBufferViewType_spec, NULL);
+    if (state->XIBufferViewType == NULL) {
+        goto error;
+    }
+
     // Make sure chnnels drop objects owned by this interpreter
     PyInterpreterState *interp = _get_current_interp();
     PyUnstable_AtExit(interp, clear_interpreter, (void *)interp);

From be7e9279b56499887f9ae21aa5242f2274b541d7 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Sep 2023 15:08:13 -0600
Subject: [PATCH 06/19] Add _get_current_xibufferview_type().

---
 Modules/_xxinterpchannelsmodule.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index 5b82528d425b01..89f0d7110de7bd 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -340,6 +340,24 @@ clear_module_state(module_state *state)
 }
 
 
+static PyTypeObject *
+_get_current_xibufferview_type(void)
+{
+    PyObject *mod = _get_current_module();
+    if (mod == NULL) {
+        // XXX import it?
+        PyErr_SetString(PyExc_RuntimeError,
+                        MODULE_NAME " module not imported yet");
+        return NULL;
+    }
+    module_state *state = get_module_state(mod);
+    if (state == NULL) {
+        return NULL;
+    }
+    return state->XIBufferViewType;
+}
+
+
 /* channel-specific code ****************************************************/
 
 #define CHANNEL_SEND 1

From 955989db18b56c9917523e3fd00036a523e04091 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Sep 2023 15:08:45 -0600
Subject: [PATCH 07/19] Add xibufferview_from_xid().

---
 Modules/_xxinterpchannelsmodule.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index 89f0d7110de7bd..eae023e0f0c134 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -205,6 +205,22 @@ typedef struct {
     int64_t interp;
 } XIBufferViewObject;
 
+static PyObject *
+xibufferview_from_xid(PyTypeObject *cls, _PyCrossInterpreterData *data)
+{
+    assert(data->data != NULL);
+    assert(data->obj == NULL);
+    assert(data->interp >= 0);
+    XIBufferViewObject *self = PyObject_Malloc(sizeof(XIBufferViewObject));
+    if (self == NULL) {
+        return NULL;
+    }
+    PyObject_Init((PyObject *)self, cls);
+    self->view = (Py_buffer *)data->data;
+    self->interp = data->interp;
+    return (PyObject *)self;
+}
+
 static void
 xibufferview_dealloc(XIBufferViewObject *self)
 {

From 05d13f51e11f5e9091feefc828a7953ffdbaea81 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Sep 2023 15:10:07 -0600
Subject: [PATCH 08/19] Register memoryview for cross-interpreter use.

---
 Modules/_xxinterpchannelsmodule.c | 56 +++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index eae023e0f0c134..6eae9c85eb518c 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -273,6 +273,58 @@ static PyType_Spec XIBufferViewType_spec = {
 };
 
 
+/* extra XID types **********************************************************/
+
+static PyTypeObject * _get_current_xibufferview_type(void);
+
+static PyObject *
+_memoryview_from_xid(_PyCrossInterpreterData *data)
+{
+    PyTypeObject *cls = _get_current_xibufferview_type();
+    if (cls == NULL) {
+        return NULL;
+    }
+    PyObject *obj = xibufferview_from_xid(cls, data);
+    if (obj == NULL) {
+        return NULL;
+    }
+    return PyMemoryView_FromObject(obj);
+}
+
+static int
+_memoryview_shared(PyThreadState *tstate, PyObject *obj,
+                   _PyCrossInterpreterData *data)
+{
+    Py_buffer *view = PyMem_RawMalloc(sizeof(Py_buffer));
+    if (view == NULL) {
+        return -1;
+    }
+    if (PyObject_GetBuffer(obj, view, PyBUF_FULL_RO) < 0) {
+        PyMem_RawFree(view);
+        return -1;
+    }
+    _PyCrossInterpreterData_Init(data, tstate->interp, view, NULL,
+                                 _memoryview_from_xid);
+    return 0;
+}
+
+static int
+register_xid_types(void)
+{
+    PyTypeObject *cls;
+    crossinterpdatafunc func;
+
+    // builtin memoryview
+    cls = &PyMemoryView_Type;
+    func = _memoryview_shared;
+    if (_PyCrossInterpreterData_RegisterClass(cls, func)) {
+        return -1;
+    }
+
+    return 0;
+}
+
+
 /* module state *************************************************************/
 
 typedef struct {
@@ -2659,6 +2711,10 @@ module_exec(PyObject *mod)
         goto error;
     }
 
+    if (register_xid_types() < 0) {
+        goto error;
+    }
+
     // Make sure chnnels drop objects owned by this interpreter
     PyInterpreterState *interp = _get_current_interp();
     PyUnstable_AtExit(interp, clear_interpreter, (void *)interp);

From 3e4e97799e6c45a93f039a697b07c725e483a401 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 11 Sep 2023 15:10:26 -0600
Subject: [PATCH 09/19] Add _channels.send_buffer().

---
 Modules/_xxinterpchannelsmodule.c | 35 +++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index 6eae9c85eb518c..c529b9684ee6bb 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -2472,6 +2472,39 @@ PyDoc_STRVAR(channel_send_doc,
 \n\
 Add the object's data to the channel's queue.");
 
+static PyObject *
+channel_send_buffer(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    static char *kwlist[] = {"cid", "obj", NULL};
+    int64_t cid;
+    struct channel_id_converter_data cid_data = {
+        .module = self,
+    };
+    PyObject *obj;
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&O:channel_send", kwlist,
+                                     channel_id_converter, &cid_data, &obj)) {
+        return NULL;
+    }
+    cid = cid_data.cid;
+
+    PyObject *tempobj = PyMemoryView_FromObject(obj);
+    if (tempobj == NULL) {
+        return NULL;
+    }
+
+    int err = _channel_send(&_globals.channels, cid, tempobj);
+    Py_DECREF(tempobj);
+    if (handle_channel_error(err, self, cid)) {
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
+PyDoc_STRVAR(channel_send_buffer_doc,
+"channel_send_buffer(cid, obj)\n\
+\n\
+Add the object's buffer to the channel's queue.");
+
 static PyObject *
 channel_recv(PyObject *self, PyObject *args, PyObject *kwds)
 {
@@ -2660,6 +2693,8 @@ static PyMethodDef module_functions[] = {
      METH_VARARGS | METH_KEYWORDS, channel_list_interpreters_doc},
     {"send",                      _PyCFunction_CAST(channel_send),
      METH_VARARGS | METH_KEYWORDS, channel_send_doc},
+    {"send_buffer",               _PyCFunction_CAST(channel_send_buffer),
+     METH_VARARGS | METH_KEYWORDS, channel_send_buffer_doc},
     {"recv",                      _PyCFunction_CAST(channel_recv),
      METH_VARARGS | METH_KEYWORDS, channel_recv_doc},
     {"close",                     _PyCFunction_CAST(channel_close),

From 16994950ecb04f88d1881e34061f35eaff859642 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 18 Sep 2023 16:38:18 -0600
Subject: [PATCH 10/19] Use _get_current_module_state().

---
 Modules/_xxinterpchannelsmodule.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index c529b9684ee6bb..ffcc3f12787f1d 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -411,14 +411,7 @@ clear_module_state(module_state *state)
 static PyTypeObject *
 _get_current_xibufferview_type(void)
 {
-    PyObject *mod = _get_current_module();
-    if (mod == NULL) {
-        // XXX import it?
-        PyErr_SetString(PyExc_RuntimeError,
-                        MODULE_NAME " module not imported yet");
-        return NULL;
-    }
-    module_state *state = get_module_state(mod);
+    module_state *state = _get_current_module_state();
     if (state == NULL) {
         return NULL;
     }

From 0c216ff82efb431bd17241b675c567d5239a3af7 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 19 Sep 2023 11:43:37 -0600
Subject: [PATCH 11/19] Add SendChannel.send_buffer().

---
 Lib/test/support/interpreters.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index d2beba31e80283..034e046bdbe97c 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -211,6 +211,21 @@ def send_nowait(self, obj):
         # See bpo-32604 and gh-19829.
         return _channels.send(self._id, obj)
 
+    def send_buffer(self, obj, timeout=None):
+        """Send the object's buffer to the channel's receiving end.
+
+        This blocks until the object is received.
+        """
+        _channels.send_buffer(self._id, obj, timeout=timeout)
+
+    def send_buffer_nowait(self, obj):
+        """Send the object's buffer to the channel's receiving end.
+
+        If the object is immediately received then return True
+        (else False).  Otherwise this is the same as send().
+        """
+        return _channels.send_buffer(self._id, obj, blocking=False)
+
     def close(self):
         _channels.close(self._id, send=True)
 

From 0ad6f4190330e84018d7df74ef7e17b2cb90cf9e Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 2 Oct 2023 16:21:57 -0600
Subject: [PATCH 12/19] Keep some C-API functions private for now.

---
 Include/cpython/pystate.h          |  2 --
 Include/internal/pycore_interp.h   |  3 +++
 Include/internal/pycore_pybuffer.h | 21 +++++++++++++++++++++
 Include/pybuffer.h                 |  4 ----
 Makefile.pre.in                    |  1 +
 Modules/_xxinterpchannelsmodule.c  |  8 +++++++-
 Objects/abstract.c                 |  9 +++++----
 7 files changed, 37 insertions(+), 11 deletions(-)
 create mode 100644 Include/internal/pycore_pybuffer.h

diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
index a9a2ffff16c1d4..7e4c57efc7c00c 100644
--- a/Include/cpython/pystate.h
+++ b/Include/cpython/pystate.h
@@ -236,8 +236,6 @@ PyAPI_FUNC(PyThreadState *) PyInterpreterState_ThreadHead(PyInterpreterState *);
 PyAPI_FUNC(PyThreadState *) PyThreadState_Next(PyThreadState *);
 PyAPI_FUNC(void) PyThreadState_DeleteCurrent(void);
 
-PyAPI_FUNC(PyInterpreterState *) _PyInterpreterState_LookUpID(int64_t);
-
 /* Frame evaluation API */
 
 typedef PyObject* (*_PyFrameEvalFunction)(PyThreadState *tstate, struct _PyInterpreterFrame *, int);
diff --git a/Include/internal/pycore_interp.h b/Include/internal/pycore_interp.h
index 864b29ad9ca04a..10e103aceccab9 100644
--- a/Include/internal/pycore_interp.h
+++ b/Include/internal/pycore_interp.h
@@ -254,6 +254,9 @@ struct _xidregitem {
     crossinterpdatafunc getdata;
 };
 
+// Export for the _xxinterpchannels module.
+PyAPI_FUNC(PyInterpreterState *) _PyInterpreterState_LookUpID(int64_t);
+
 extern int _PyInterpreterState_IDInitref(PyInterpreterState *);
 extern int _PyInterpreterState_IDIncref(PyInterpreterState *);
 extern void _PyInterpreterState_IDDecref(PyInterpreterState *);
diff --git a/Include/internal/pycore_pybuffer.h b/Include/internal/pycore_pybuffer.h
new file mode 100644
index 00000000000000..3cbc290b2ea3ee
--- /dev/null
+++ b/Include/internal/pycore_pybuffer.h
@@ -0,0 +1,21 @@
+#ifndef Py_INTERNAL_PYBUFFER_H
+#define Py_INTERNAL_PYBUFFER_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+
+// Exported for the _xxinterpchannels module.
+PyAPI_FUNC(int) _PyBuffer_ReleaseInInterpreter(
+        PyInterpreterState *interp, Py_buffer *view);
+PyAPI_FUNC(int) _PyBuffer_ReleaseInInterpreterAndRawFree(
+        PyInterpreterState *interp, Py_buffer *view);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_PYBUFFER_H */
diff --git a/Include/pybuffer.h b/Include/pybuffer.h
index ea09b9c1b31717..ca1c6058d9052c 100644
--- a/Include/pybuffer.h
+++ b/Include/pybuffer.h
@@ -100,10 +100,6 @@ PyAPI_FUNC(int) PyBuffer_FillInfo(Py_buffer *view, PyObject *o, void *buf,
 
 /* Releases a Py_buffer obtained from getbuffer ParseTuple's "s*". */
 PyAPI_FUNC(void) PyBuffer_Release(Py_buffer *view);
-PyAPI_FUNC(int) PyUnstable_Buffer_ReleaseInInterpreter(
-        PyInterpreterState *interp, Py_buffer *view);
-PyAPI_FUNC(int) PyUnstable_Buffer_ReleaseInInterpreterAndRawFree(
-        PyInterpreterState *interp, Py_buffer *view);
 
 /* Maximum number of dimensions */
 #define PyBUF_MAX_NDIM 64
diff --git a/Makefile.pre.in b/Makefile.pre.in
index cf03c86f18b3c3..477eac0b6b49dc 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -1790,6 +1790,7 @@ PYTHON_HEADERS= \
 		$(srcdir)/Include/internal/pycore_parking_lot.h \
 		$(srcdir)/Include/internal/pycore_pathconfig.h \
 		$(srcdir)/Include/internal/pycore_pyarena.h \
+		$(srcdir)/Include/internal/pycore_pybuffer.h \
 		$(srcdir)/Include/internal/pycore_pyerrors.h \
 		$(srcdir)/Include/internal/pycore_pyhash.h \
 		$(srcdir)/Include/internal/pycore_pylifecycle.h \
diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index ffcc3f12787f1d..3a7ef2e4f61538 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -1,8 +1,14 @@
 /* interpreters module */
 /* low-level access to interpreter primitives */
 
+#ifndef Py_BUILD_CORE_BUILTIN
+#  define Py_BUILD_CORE_MODULE 1
+#endif
+
 #include "Python.h"
 #include "interpreteridobject.h"
+#include "pycore_pybuffer.h"      // _PyBuffer_ReleaseInInterpreterAndRawFree()
+#include "pycore_interp.h"        // _PyInterpreterState_LookUpID()
 
 
 /*
@@ -229,7 +235,7 @@ xibufferview_dealloc(XIBufferViewObject *self)
        since other objects may be using the buffer still. */
     assert(interp != NULL);
 
-    if (PyUnstable_Buffer_ReleaseInInterpreterAndRawFree(interp, self->view) < 0) {
+    if (_PyBuffer_ReleaseInInterpreterAndRawFree(interp, self->view) < 0) {
         // XXX Emit a warning?
         PyErr_Clear();
     }
diff --git a/Objects/abstract.c b/Objects/abstract.c
index b8b4464e320362..806ca6584bda95 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2,6 +2,7 @@
 
 #include "Python.h"
 #include "pycore_abstract.h"      // _PyIndex_Check()
+#include "pycore_pybuffer.h"
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
 #include "pycore_ceval.h"         // _Py_EnterRecursiveCallTstate()
 #include "pycore_object.h"        // _Py_CheckSlotResult()
@@ -814,15 +815,15 @@ _buffer_release_call(void *arg)
 }
 
 int
-PyUnstable_Buffer_ReleaseInInterpreter(PyInterpreterState *interp,
-                                       Py_buffer *view)
+_PyBuffer_ReleaseInInterpreter(PyInterpreterState *interp,
+                               Py_buffer *view)
 {
     return _Py_CallInInterpreter(interp, _buffer_release_call, view);
 }
 
 int
-PyUnstable_Buffer_ReleaseInInterpreterAndRawFree(PyInterpreterState *interp,
-                                                 Py_buffer *view)
+_PyBuffer_ReleaseInInterpreterAndRawFree(PyInterpreterState *interp,
+                                         Py_buffer *view)
 {
     return _Py_CallInInterpreterAndRawFree(interp, _buffer_release_call, view);
 }

From 56e3774fb9db88e618b76c17014aaf505794eed4 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 2 Oct 2023 16:43:52 -0600
Subject: [PATCH 13/19] Add a test.

---
 Lib/test/test__xxinterpchannels.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Lib/test/test__xxinterpchannels.py b/Lib/test/test__xxinterpchannels.py
index 750cd99b85e7a6..cb69f73c4348d4 100644
--- a/Lib/test/test__xxinterpchannels.py
+++ b/Lib/test/test__xxinterpchannels.py
@@ -703,6 +703,21 @@ def test_recv_sending_interp_destroyed(self):
                 channels.recv(cid2)
             del cid2
 
+    def test_send_buffer(self):
+        buf = bytearray(b'spamspamspam')
+        cid = channels.create()
+        channels.send_buffer(cid, buf)
+        obj = channels.recv(cid)
+
+        self.assertIsNot(obj, buf)
+        self.assertIsInstance(obj, memoryview)
+        self.assertEqual(obj, buf)
+
+        buf[4:8] = b'eggs'
+        self.assertEqual(obj, buf)
+        obj[4:8] = b'ham.'
+        self.assertEqual(obj, buf)
+
     def test_allowed_types(self):
         cid = channels.create()
         objects = [

From 272488a8683b3639c3704f76671e03e708d4e7ad Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 2 Oct 2023 16:48:19 -0600
Subject: [PATCH 14/19] Fix SendChannel.send_buffer_nowait().

---
 Lib/test/support/interpreters.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index 034e046bdbe97c..9a34684a1ae532 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -224,7 +224,8 @@ def send_buffer_nowait(self, obj):
         If the object is immediately received then return True
         (else False).  Otherwise this is the same as send().
         """
-        return _channels.send_buffer(self._id, obj, blocking=False)
+        return _channels.send_buffer(self._id, obj)
+        #return _channels.send_buffer(self._id, obj, blocking=False)
 
     def close(self):
         _channels.close(self._id, send=True)

From ceb3dae6ad1e1df025f891369d4220f1f9fcabe7 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 2 Oct 2023 16:48:38 -0600
Subject: [PATCH 15/19] Fix a typo.

---
 Modules/_xxinterpchannelsmodule.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index 3a7ef2e4f61538..af35374f62120b 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -2480,7 +2480,8 @@ channel_send_buffer(PyObject *self, PyObject *args, PyObject *kwds)
         .module = self,
     };
     PyObject *obj;
-    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O&O:channel_send", kwlist,
+    if (!PyArg_ParseTupleAndKeywords(args, kwds,
+                                     "O&O:channel_send_buffer", kwlist,
                                      channel_id_converter, &cid_data, &obj)) {
         return NULL;
     }

From 873eec23c996d0d23a09d6d3109430b2e996635c Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 2 Oct 2023 16:48:47 -0600
Subject: [PATCH 16/19] Add tests.

---
 Lib/test/test_interpreters.py | 43 +++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/Lib/test/test_interpreters.py b/Lib/test/test_interpreters.py
index ffdd8a12769397..ad241856b39f5e 100644
--- a/Lib/test/test_interpreters.py
+++ b/Lib/test/test_interpreters.py
@@ -1055,3 +1055,46 @@ def test_recv_nowait_default(self):
         self.assertEqual(obj4, b'spam')
         self.assertEqual(obj5, b'eggs')
         self.assertIs(obj6, default)
+
+    def test_send_buffer(self):
+        buf = bytearray(b'spamspamspam')
+        obj = None
+        rch, sch = interpreters.create_channel()
+
+        def f():
+            nonlocal obj
+            while True:
+                try:
+                    obj = rch.recv()
+                    break
+                except interpreters.ChannelEmptyError:
+                    time.sleep(0.1)
+        t = threading.Thread(target=f)
+        t.start()
+
+        sch.send_buffer(buf)
+        t.join()
+
+        self.assertIsNot(obj, buf)
+        self.assertIsInstance(obj, memoryview)
+        self.assertEqual(obj, buf)
+
+        buf[4:8] = b'eggs'
+        self.assertEqual(obj, buf)
+        obj[4:8] = b'ham.'
+        self.assertEqual(obj, buf)
+
+    def test_send_buffer_nowait(self):
+        buf = bytearray(b'spamspamspam')
+        rch, sch = interpreters.create_channel()
+        sch.send_buffer_nowait(buf)
+        obj = rch.recv()
+
+        self.assertIsNot(obj, buf)
+        self.assertIsInstance(obj, memoryview)
+        self.assertEqual(obj, buf)
+
+        buf[4:8] = b'eggs'
+        self.assertEqual(obj, buf)
+        obj[4:8] = b'ham.'
+        self.assertEqual(obj, buf)

From da9779fe12fba29d89e5ec62ab16adbd89a4c0a8 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 2 Oct 2023 17:09:50 -0600
Subject: [PATCH 17/19] Fix SendChannel.send_buffer().

---
 Lib/test/support/interpreters.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/Lib/test/support/interpreters.py b/Lib/test/support/interpreters.py
index 9a34684a1ae532..04e7dbfee9971e 100644
--- a/Lib/test/support/interpreters.py
+++ b/Lib/test/support/interpreters.py
@@ -211,12 +211,12 @@ def send_nowait(self, obj):
         # See bpo-32604 and gh-19829.
         return _channels.send(self._id, obj)
 
-    def send_buffer(self, obj, timeout=None):
+    def send_buffer(self, obj):
         """Send the object's buffer to the channel's receiving end.
 
         This blocks until the object is received.
         """
-        _channels.send_buffer(self._id, obj, timeout=timeout)
+        _channels.send_buffer(self._id, obj)
 
     def send_buffer_nowait(self, obj):
         """Send the object's buffer to the channel's receiving end.
@@ -225,7 +225,6 @@ def send_buffer_nowait(self, obj):
         (else False).  Otherwise this is the same as send().
         """
         return _channels.send_buffer(self._id, obj)
-        #return _channels.send_buffer(self._id, obj, blocking=False)
 
     def close(self):
         _channels.close(self._id, send=True)

From dea173a1c9c4b3ee118d5e8115be153322f4f9b2 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Tue, 3 Oct 2023 10:15:54 -0600
Subject: [PATCH 18/19] Clear the XID classes during module fini.

---
 Modules/_xxinterpchannelsmodule.c | 136 ++++++++++++++++++++----------
 1 file changed, 93 insertions(+), 43 deletions(-)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index af35374f62120b..01aa9f5eae64ea 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -82,6 +82,74 @@ API..  The module does not create any objects that are shared globally.
     PyMem_RawFree(VAR)
 
 
+struct xid_class_registry {
+    size_t count;
+#define MAX_XID_CLASSES 5
+    struct {
+        PyTypeObject *cls;
+    } added[MAX_XID_CLASSES];
+};
+
+static int
+register_xid_class(PyTypeObject *cls, crossinterpdatafunc shared,
+                   struct xid_class_registry *classes)
+{
+    int res = _PyCrossInterpreterData_RegisterClass(cls, shared);
+    if (res == 0) {
+        assert(classes->count < MAX_XID_CLASSES);
+        Py_INCREF(cls);
+        classes->added[classes->count].cls = cls;
+        classes->count += 1;
+    }
+    return res;
+}
+
+static void
+clear_xid_class_registry(struct xid_class_registry *classes)
+{
+    while (classes->count > 0) {
+        classes->count -= 1;
+        PyTypeObject *cls = classes->added[classes->count].cls;
+        _PyCrossInterpreterData_UnregisterClass(cls);
+        Py_DECREF(cls);
+    }
+}
+
+#define XID_IGNORE_EXC 1
+#define XID_FREE 2
+
+static int
+_release_xid_data(_PyCrossInterpreterData *data, int flags)
+{
+    int ignoreexc = flags & XID_IGNORE_EXC;
+    PyObject *exc;
+    if (ignoreexc) {
+        exc = PyErr_GetRaisedException();
+    }
+    int res;
+    if (flags & XID_FREE) {
+        res = _PyCrossInterpreterData_ReleaseAndRawFree(data);
+    }
+    else {
+        res = _PyCrossInterpreterData_Release(data);
+    }
+    if (res < 0) {
+        /* The owning interpreter is already destroyed. */
+        if (ignoreexc) {
+            // XXX Emit a warning?
+            PyErr_Clear();
+        }
+    }
+    if (flags & XID_FREE) {
+        /* Either way, we free the data. */
+    }
+    if (ignoreexc) {
+        PyErr_SetRaisedException(exc);
+    }
+    return res;
+}
+
+
 static PyInterpreterState *
 _get_current_interp(void)
 {
@@ -146,7 +214,8 @@ add_new_exception(PyObject *mod, const char *name, PyObject *base)
     add_new_exception(MOD, MODULE_NAME "." Py_STRINGIFY(NAME), BASE)
 
 static PyTypeObject *
-add_new_type(PyObject *mod, PyType_Spec *spec, crossinterpdatafunc shared)
+add_new_type(PyObject *mod, PyType_Spec *spec, crossinterpdatafunc shared,
+             struct xid_class_registry *classes)
 {
     PyTypeObject *cls = (PyTypeObject *)PyType_FromMetaclass(
                 NULL, mod, spec, NULL);
@@ -158,7 +227,7 @@ add_new_type(PyObject *mod, PyType_Spec *spec, crossinterpdatafunc shared)
         return NULL;
     }
     if (shared != NULL) {
-        if (_PyCrossInterpreterData_RegisterClass(cls, shared)) {
+        if (register_xid_class(cls, shared, classes)) {
             Py_DECREF(cls);
             return NULL;
         }
@@ -166,40 +235,6 @@ add_new_type(PyObject *mod, PyType_Spec *spec, crossinterpdatafunc shared)
     return cls;
 }
 
-#define XID_IGNORE_EXC 1
-#define XID_FREE 2
-
-static int
-_release_xid_data(_PyCrossInterpreterData *data, int flags)
-{
-    int ignoreexc = flags & XID_IGNORE_EXC;
-    PyObject *exc;
-    if (ignoreexc) {
-        exc = PyErr_GetRaisedException();
-    }
-    int res;
-    if (flags & XID_FREE) {
-        res = _PyCrossInterpreterData_ReleaseAndRawFree(data);
-    }
-    else {
-        res = _PyCrossInterpreterData_Release(data);
-    }
-    if (res < 0) {
-        /* The owning interpreter is already destroyed. */
-        if (ignoreexc) {
-            // XXX Emit a warning?
-            PyErr_Clear();
-        }
-    }
-    if (flags & XID_FREE) {
-        /* Either way, we free the data. */
-    }
-    if (ignoreexc) {
-        PyErr_SetRaisedException(exc);
-    }
-    return res;
-}
-
 
 /* Cross-interpreter Buffer Views *******************************************/
 
@@ -315,7 +350,7 @@ _memoryview_shared(PyThreadState *tstate, PyObject *obj,
 }
 
 static int
-register_xid_types(void)
+register_builtin_xid_types(struct xid_class_registry *classes)
 {
     PyTypeObject *cls;
     crossinterpdatafunc func;
@@ -323,7 +358,7 @@ register_xid_types(void)
     // builtin memoryview
     cls = &PyMemoryView_Type;
     func = _memoryview_shared;
-    if (_PyCrossInterpreterData_RegisterClass(cls, func)) {
+    if (register_xid_class(cls, func, classes)) {
         return -1;
     }
 
@@ -334,6 +369,9 @@ register_xid_types(void)
 /* module state *************************************************************/
 
 typedef struct {
+    struct xid_class_registry xid_classes;
+
+    /* Added at runtime by interpreters module. */
     PyTypeObject *send_channel_type;
     PyTypeObject *recv_channel_type;
 
@@ -2191,6 +2229,7 @@ set_channel_end_types(PyObject *mod, PyTypeObject *send, PyTypeObject *recv)
     if (state == NULL) {
         return -1;
     }
+    struct xid_class_registry *xid_classes = &state->xid_classes;
 
     if (state->send_channel_type != NULL
         || state->recv_channel_type != NULL)
@@ -2201,10 +2240,10 @@ set_channel_end_types(PyObject *mod, PyTypeObject *send, PyTypeObject *recv)
     state->send_channel_type = (PyTypeObject *)Py_NewRef(send);
     state->recv_channel_type = (PyTypeObject *)Py_NewRef(recv);
 
-    if (_PyCrossInterpreterData_RegisterClass(send, _channel_end_shared)) {
+    if (register_xid_class(send, _channel_end_shared, xid_classes)) {
         return -1;
     }
-    if (_PyCrossInterpreterData_RegisterClass(recv, _channel_end_shared)) {
+    if (register_xid_class(recv, _channel_end_shared, xid_classes)) {
         return -1;
     }
 
@@ -2722,6 +2761,7 @@ module_exec(PyObject *mod)
     if (_globals_init() != 0) {
         return -1;
     }
+    struct xid_class_registry *xid_classes = NULL;
 
     /* Add exception types */
     if (exceptions_init(mod) != 0) {
@@ -2733,20 +2773,22 @@ module_exec(PyObject *mod)
     if (state == NULL) {
         goto error;
     }
+    xid_classes = &state->xid_classes;
 
     // ChannelID
     state->ChannelIDType = add_new_type(
-            mod, &ChannelIDType_spec, _channelid_shared);
+            mod, &ChannelIDType_spec, _channelid_shared, xid_classes);
     if (state->ChannelIDType == NULL) {
         goto error;
     }
 
-    state->XIBufferViewType = add_new_type(mod, &XIBufferViewType_spec, NULL);
+    state->XIBufferViewType = add_new_type(mod, &XIBufferViewType_spec, NULL,
+                                           xid_classes);
     if (state->XIBufferViewType == NULL) {
         goto error;
     }
 
-    if (register_xid_types() < 0) {
+    if (register_builtin_xid_types(xid_classes) < 0) {
         goto error;
     }
 
@@ -2757,6 +2799,9 @@ module_exec(PyObject *mod)
     return 0;
 
 error:
+    if (xid_classes != NULL) {
+        clear_xid_class_registry(xid_classes);
+    }
     _globals_fini();
     return -1;
 }
@@ -2781,6 +2826,11 @@ module_clear(PyObject *mod)
 {
     module_state *state = get_module_state(mod);
     assert(state != NULL);
+
+    // Before clearing anything, we unregister the various XID types. */
+    clear_xid_class_registry(&state->xid_classes);
+
+    // Now we clear the module state.
     clear_module_state(state);
     return 0;
 }

From fc15f77681f819b5c195673f9ced76fa8fae7fc9 Mon Sep 17 00:00:00 2001
From: Eric Snow <ericsnowcurrently@gmail.com>
Date: Mon, 9 Oct 2023 05:55:48 -0600
Subject: [PATCH 19/19] Fix ref leaks.

---
 Modules/_xxinterpchannelsmodule.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/Modules/_xxinterpchannelsmodule.c b/Modules/_xxinterpchannelsmodule.c
index 99ae433788f3cf..a1531c5c3db34d 100644
--- a/Modules/_xxinterpchannelsmodule.c
+++ b/Modules/_xxinterpchannelsmodule.c
@@ -97,7 +97,7 @@ register_xid_class(PyTypeObject *cls, crossinterpdatafunc shared,
     int res = _PyCrossInterpreterData_RegisterClass(cls, shared);
     if (res == 0) {
         assert(classes->count < MAX_XID_CLASSES);
-        Py_INCREF(cls);
+        // The class has refs elsewhere, so we need to incref here.
         classes->added[classes->count].cls = cls;
         classes->count += 1;
     }
@@ -111,7 +111,6 @@ clear_xid_class_registry(struct xid_class_registry *classes)
         classes->count -= 1;
         PyTypeObject *cls = classes->added[classes->count].cls;
         _PyCrossInterpreterData_UnregisterClass(cls);
-        Py_DECREF(cls);
     }
 }
 
@@ -2770,17 +2769,18 @@ module_exec(PyObject *mod)
     }
     struct xid_class_registry *xid_classes = NULL;
 
+    module_state *state = get_module_state(mod);
+    if (state == NULL) {
+        goto error;
+    }
+    xid_classes = &state->xid_classes;
+
     /* Add exception types */
     if (exceptions_init(mod) != 0) {
         goto error;
     }
 
     /* Add other types */
-    module_state *state = get_module_state(mod);
-    if (state == NULL) {
-        goto error;
-    }
-    xid_classes = &state->xid_classes;
 
     // ChannelID
     state->ChannelIDType = add_new_type(
@@ -2799,7 +2799,7 @@ module_exec(PyObject *mod)
         goto error;
     }
 
-    // Make sure chnnels drop objects owned by this interpreter
+    /* Make sure chnnels drop objects owned by this interpreter. */
     PyInterpreterState *interp = _get_current_interp();
     PyUnstable_AtExit(interp, clear_interpreter, (void *)interp);
 
@@ -2847,7 +2847,13 @@ module_free(void *mod)
 {
     module_state *state = get_module_state(mod);
     assert(state != NULL);
+
+    // Before clearing anything, we unregister the various XID types. */
+    clear_xid_class_registry(&state->xid_classes);
+
+    // Now we clear the module state.
     clear_module_state(state);
+
     _globals_fini();
 }