Add CrossInterpreterBufferView.

python · ericsnowcurrently · Oct 9, 2023 · Sep 9, 2023 · Sep 11, 2023 · Sep 11, 2023
commit 573abef2ae87f2eaf8dc0b4faf9532f98e8694f9
diff --git 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);