Commit: d512fe441b4be668593afba9e4bfb61b361ee152
Author: Campbell Barton
Date: Wed Mar 17 15:12:13 2021 +1100
Branches: master
https://developer.blender.org/rBd512fe441b4be668593afba9e4bfb61b361ee152
Comments: document memory management for `BPyPropStore`
===================================================================
M source/blender/python/intern/bpy_props.c
===================================================================
diff --git a/source/blender/python/intern/bpy_props.c
b/source/blender/python/intern/bpy_props.c
index b6149175c91..e4e6b3ea8f2 100644
--- a/source/blender/python/intern/bpy_props.c
+++ b/source/blender/python/intern/bpy_props.c
@@ -198,15 +198,44 @@ static const EnumPropertyItem
property_subtype_array_items[] = {
* \{ */
/**
- * Slots for #PyObject slots stored in #PropertyRNA.py_data (these hold a
reference).
- * #bpy_prop_callback_free_py_data manages decrementing.
+ * Store #PyObject data for a dynamically defined property.
+ * Currently this is only used to store call-back functions.
+ * Properties that don't use custom-callbacks wont allocate this struct.
+ *
+ * Memory/Reference Management
+ * ---------------------------
+ *
+ * This struct adds/removes the user-count of each #PyObject it references,
+ * it's needed in case the function is removed from the class (unlikely but
possible),
+ * also when an annotation evaluates to a `lambda` with Python 3.10 and newer
e.g: T86332.
+ *
+ * Pointers to this struct are held in:
+ *
+ * - #PropertyRNA.py_data (owns the memory).
+ * Freed when the RNA property is freed.
+ *
+ * - #g_bpy_prop_store_list (borrows the memory)
+ * Having a global list means the users can be visited by the GC and cleared
on exit.
+ *
+ * This list can't be used for freeing as #BPyPropStore doesn't hold a
#PropertyRNA back-pointer,
+ * (while it could be supported it would only complicate things).
+ *
+ * All RNA properties are freed after Python has been shut-down.
+ * At that point Python user counts can't be touched and must have already
been dealt with.
+ *
+ * Decrementing users is handled by:
+ *
+ * - #bpy_prop_py_data_remove manages decrementing at run-time (when a
property is removed),
+ *
+ * - #BPY_rna_props_clear_all does this on exit for all dynamic properties.
*/
struct BPyPropStore {
struct BPyPropStore *next, *prev;
/**
- * Only store #PyObject types, can be cast to an an array and operated on.
- * NULL members are ignored/skipped. */
+ * Only store #PyObject types, so this member can be cast to an array and
iterated over.
+ * NULL members are skipped.
+ */
struct {
/** Wrap: `RNA_def_property_*_funcs` (depending on type). */
PyObject *get_fn;
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