gh-110310: Add a Per-Interpreter XID Registry for Heap Types (gh-110311)

We do the following:

* add a per-interpreter XID registry (PyInterpreterState.xidregistry)
* put heap types there (keep static types in _PyRuntimeState.xidregistry)
* clear the registries during interpreter/runtime finalization
* avoid duplicate entries in the registry (when _PyCrossInterpreterData_RegisterClass() is called more than once for a type)
* use Py_TYPE() instead of PyObject_Type() in _PyCrossInterpreterData_Lookup()

The per-interpreter registry helps preserve isolation between interpreters.  This is important when heap types are registered, which is something we haven't been doing yet but I will likely do soon.

1 files changed, 29 insertions, 15 deletions

diff --git a/Include/internal/pycore_interp.h b/Include/internal/pycore_interp.h
index 21d1ee3..523dfdc 100644
--- a/Include/internal/pycore_interp.h
+++ b/Include/internal/pycore_interp.h
@@ -39,6 +39,32 @@ struct _Py_long_state {
     int max_str_digits;
 };
 
+
+/* cross-interpreter data registry */
+
+/* For now we use a global registry of shareable classes.  An
+   alternative would be to add a tp_* slot for a class's
+   crossinterpdatafunc. It would be simpler and more efficient. */
+
+struct _xidregitem;
+
+struct _xidregitem {
+    struct _xidregitem *prev;
+    struct _xidregitem *next;
+    /* This can be a dangling pointer, but only if weakref is set. */
+    PyTypeObject *cls;
+    /* This is NULL for builtin types. */
+    PyObject *weakref;
+    size_t refcount;
+    crossinterpdatafunc getdata;
+};
+
+struct _xidregistry {
+    PyThread_type_lock mutex;
+    struct _xidregitem *head;
+};
+
+
 /* interpreter state */
 
 /* PyInterpreterState holds the global state for one of the runtime's
@@ -149,6 +175,9 @@ struct _is {
     Py_ssize_t co_extra_user_count;
     freefunc co_extra_freefuncs[MAX_CO_EXTRA_USERS];
 
+    // XXX Remove this field once we have a tp_* slot.
+    struct _xidregistry xidregistry;
+
 #ifdef HAVE_FORK
     PyObject *before_forkers;
     PyObject *after_forkers_parent;
@@ -238,21 +267,6 @@ _PyInterpreterState_SetFinalizing(PyInterpreterState *interp, PyThreadState *tst
 }
 
 
-/* cross-interpreter data registry */
-
-/* For now we use a global registry of shareable classes.  An
-   alternative would be to add a tp_* slot for a class's
-   crossinterpdatafunc. It would be simpler and more efficient. */
-
-struct _xidregitem;
-
-struct _xidregitem {
-    struct _xidregitem *prev;
-    struct _xidregitem *next;
-    PyObject *cls;  // weakref to a PyTypeObject
-    crossinterpdatafunc getdata;
-};
-
 extern PyInterpreterState* _PyInterpreterState_LookUpID(int64_t);
 
 extern int _PyInterpreterState_IDInitref(PyInterpreterState *);