Add an session-wise uuid integer to IDs.

"session-wise" here mean while editing a same .blend file. So creating
or opening a new one will reset the uuid counter. This should avoid any
overflow in practice.

Only IDs added to Main database get an uuid, runtime-only ones are not
affected.

This is intended to provide undo with a way to find IDs across several
'memory realms' (undo speedup project).

No behavior change is expected from this commit itself.

Part of T60695.

Differential Revision: https://developer.blender.org/D7007

source/blender/blenkernel/BKE_lib_id.h

@@ -67,6 +67,14 @@ void *BKE_libblock_alloc(struct Main *bmain, short type, const char *name, const
     ATTR_WARN_UNUSED_RESULT;
 void BKE_libblock_init_empty(struct ID *id) ATTR_NONNULL(1);
 
+/* *** ID's session_uuid management. *** */
+
+/* When an ID's uuid is of that value, it is unset/invalid (e.g. for runtime IDs, etc.). */
+#define MAIN_ID_SESSION_UUID_UNSET 0
+
+void BKE_lib_libblock_session_uuid_reset(void);
+void BKE_lib_libblock_session_uuid_ensure(struct ID *id);
+
 void *BKE_id_new(struct Main *bmain, const short type, const char *name);
 void *BKE_id_new_nomain(const short type, const char *name);
 

source/blender/blenkernel/BKE_main_idmap.h

@@ -40,22 +40,32 @@ struct ID;
 struct IDNameLib_Map;
 struct Main;
 
+enum {
+  MAIN_IDMAP_TYPE_NAME = 1 << 0,
+  MAIN_IDMAP_TYPE_UUID = 1 << 1,
+};
+
 struct IDNameLib_Map *BKE_main_idmap_create(struct Main *bmain,
                                             const bool create_valid_ids_set,
-                                            struct Main *old_bmain) ATTR_WARN_UNUSED_RESULT
+                                            struct Main *old_bmain,
+                                            const int idmap_types) ATTR_WARN_UNUSED_RESULT
     ATTR_NONNULL(1);
 void BKE_main_idmap_destroy(struct IDNameLib_Map *id_typemap) ATTR_NONNULL();
 struct Main *BKE_main_idmap_main_get(struct IDNameLib_Map *id_typemap) ATTR_WARN_UNUSED_RESULT
     ATTR_NONNULL();
-struct ID *BKE_main_idmap_lookup(struct IDNameLib_Map *id_typemap,
-                                 short id_type,
-                                 const char *name,
-                                 const struct Library *lib) ATTR_WARN_UNUSED_RESULT
+struct ID *BKE_main_idmap_lookup_name(struct IDNameLib_Map *id_typemap,
+                                      short id_type,
+                                      const char *name,
+                                      const struct Library *lib) ATTR_WARN_UNUSED_RESULT
     ATTR_NONNULL(1, 3);
 struct ID *BKE_main_idmap_lookup_id(struct IDNameLib_Map *id_typemap,
                                     const struct ID *id) ATTR_WARN_UNUSED_RESULT
     ATTR_NONNULL(1, 2);
 
+struct ID *BKE_main_idmap_lookup_uuid(struct IDNameLib_Map *id_typemap,
+                                      const uint session_uuid) ATTR_WARN_UNUSED_RESULT
+    ATTR_NONNULL(1);
+
 #ifdef __cplusplus
 }
 #endif

source/blender/blenkernel/intern/lib_id.c

@@ -1027,6 +1027,8 @@ void BKE_libblock_management_main_add(Main *bmain, void *idv)
   id->tag &= ~(LIB_TAG_NO_MAIN | LIB_TAG_NO_USER_REFCOUNT);
   bmain->is_memfile_undo_written = false;
   BKE_main_unlock(bmain);
+
+  BKE_lib_libblock_session_uuid_ensure(id);
 }
 
 /** Remove a data-block from given main (set it to 'NO_MAIN' status). */
@@ -1313,6 +1315,8 @@ void *BKE_libblock_alloc(Main *bmain, short type, const char *name, const int fl
       /* alphabetic insertion: is in new_id */
       BKE_main_unlock(bmain);
 
+      BKE_lib_libblock_session_uuid_ensure(id);
+
       /* TODO to be removed from here! */
       if ((flag & LIB_ID_CREATE_NO_DEG_TAG) == 0) {
         DEG_id_type_tag(bmain, type);
@@ -1456,6 +1460,33 @@ void BKE_libblock_init_empty(ID *id)
   }
 }
 
+/* ********** ID session-wise UUID management. ********** */
+static uint global_session_uuid = 0;
+
+/** Reset the session-wise uuid counter (used when reading a new file e.g.). */
+void BKE_lib_libblock_session_uuid_reset()
+{
+  global_session_uuid = 0;
+}
+
+/**
+ * Generate a session-wise uuid for the given \a id.
+ *
+ * \note "session-wise" here means while editing a given .blend file. Once a new .blend file is
+ * loaded or created, undo history is cleared/reset, and so is the uuid counter.
+ */
+void BKE_lib_libblock_session_uuid_ensure(ID *id)
+{
+  if (id->session_uuid == MAIN_ID_SESSION_UUID_UNSET) {
+    id->session_uuid = atomic_add_and_fetch_uint32(&global_session_uuid, 1);
+    /* In case overflow happens, still assign a valid ID. This way opening files many times works
+     * correctly. */
+    if (UNLIKELY(id->session_uuid == MAIN_ID_SESSION_UUID_UNSET)) {
+      id->session_uuid = atomic_add_and_fetch_uint32(&global_session_uuid, 1);
+    }
+  }
+}
+
 /**
  * Generic helper to create a new empty data-block of given type in given \a bmain database.
  *

source/blender/blenkernel/intern/main_idmap.c

@@ -26,6 +26,7 @@
 #include "DNA_ID.h"
 
 #include "BKE_idcode.h"
+#include "BKE_lib_id.h"
 #include "BKE_main.h"
 #include "BKE_main_idmap.h" /* own include */
 
@@ -65,16 +66,20 @@ struct IDNameLib_TypeMap {
  */
 struct IDNameLib_Map {
   struct IDNameLib_TypeMap type_maps[MAX_LIBARRAY];
+  struct GHash *uuid_map;
   struct Main *bmain;
   struct GSet *valid_id_pointers;
+  int idmap_types;
 };
 
 static struct IDNameLib_TypeMap *main_idmap_from_idcode(struct IDNameLib_Map *id_map,
                                                         short id_type)
 {
-  for (int i = 0; i < MAX_LIBARRAY; i++) {
-    if (id_map->type_maps[i].id_type == id_type) {
-      return &id_map->type_maps[i];
+  if (id_map->idmap_types & MAIN_IDMAP_TYPE_NAME) {
+    for (int i = 0; i < MAX_LIBARRAY; i++) {
+      if (id_map->type_maps[i].id_type == id_type) {
+        return &id_map->type_maps[i];
+      }
     }
   }
   return NULL;
@@ -94,9 +99,12 @@ static struct IDNameLib_TypeMap *main_idmap_from_idcode(struct IDNameLib_Map *id
  */
 struct IDNameLib_Map *BKE_main_idmap_create(struct Main *bmain,
                                             const bool create_valid_ids_set,
-                                            struct Main *old_bmain)
+                                            struct Main *old_bmain,
+                                            const int idmap_types)
 {
   struct IDNameLib_Map *id_map = MEM_mallocN(sizeof(*id_map), __func__);
+  id_map->bmain = bmain;
+  id_map->idmap_types = idmap_types;
 
   int index = 0;
   while (index < MAX_LIBARRAY) {
@@ -107,7 +115,22 @@ struct IDNameLib_Map *BKE_main_idmap_create(struct Main *bmain,
   }
   BLI_assert(index == MAX_LIBARRAY);
 
-  id_map->bmain = bmain;
+  if (idmap_types & MAIN_IDMAP_TYPE_UUID) {
+    ID *id;
+    id_map->uuid_map = BLI_ghash_int_new(__func__);
+    FOREACH_MAIN_ID_BEGIN (bmain, id) {
+      BLI_assert(id->session_uuid != MAIN_ID_SESSION_UUID_UNSET);
+      void **id_ptr_v;
+      const bool existing_key = BLI_ghash_ensure_p(
+          id_map->uuid_map, POINTER_FROM_UINT(id->session_uuid), &id_ptr_v);
+      BLI_assert(existing_key == false);
+      *id_ptr_v = id;
+    }
+    FOREACH_MAIN_ID_END;
+  }
+  else {
+    id_map->uuid_map = NULL;
+  }
 
   if (create_valid_ids_set) {
     id_map->valid_id_pointers = BKE_main_gset_create(bmain, NULL);
@@ -144,10 +167,10 @@ static bool idkey_cmp(const void *a, const void *b)
   return strcmp(idkey_a->name, idkey_b->name) || (idkey_a->lib != idkey_b->lib);
 }
 
-ID *BKE_main_idmap_lookup(struct IDNameLib_Map *id_map,
-                          short id_type,
-                          const char *name,
-                          const Library *lib)
+ID *BKE_main_idmap_lookup_name(struct IDNameLib_Map *id_map,
+                               short id_type,
+                               const char *name,
+                               const Library *lib)
 {
   struct IDNameLib_TypeMap *type_map = main_idmap_from_idcode(id_map, id_type);
 
@@ -188,21 +211,34 @@ ID *BKE_main_idmap_lookup_id(struct IDNameLib_Map *id_map, const ID *id)
    * when trying to get ID name).
    */
   if (id_map->valid_id_pointers == NULL || BLI_gset_haskey(id_map->valid_id_pointers, id)) {
-    return BKE_main_idmap_lookup(id_map, GS(id->name), id->name + 2, id->lib);
+    return BKE_main_idmap_lookup_name(id_map, GS(id->name), id->name + 2, id->lib);
+  }
+  return NULL;
+}
+
+ID *BKE_main_idmap_lookup_uuid(struct IDNameLib_Map *id_map, const uint session_uuid)
+{
+  if (id_map->idmap_types & MAIN_IDMAP_TYPE_UUID) {
+    return BLI_ghash_lookup(id_map->uuid_map, POINTER_FROM_UINT(session_uuid));
   }
   return NULL;
 }
 
 void BKE_main_idmap_destroy(struct IDNameLib_Map *id_map)
 {
-  struct IDNameLib_TypeMap *type_map = id_map->type_maps;
-  for (int i = 0; i < MAX_LIBARRAY; i++, type_map++) {
-    if (type_map->map) {
-      BLI_ghash_free(type_map->map, NULL, NULL);
-      type_map->map = NULL;
-      MEM_freeN(type_map->keys);
+  if (id_map->idmap_types & MAIN_IDMAP_TYPE_NAME) {
+    struct IDNameLib_TypeMap *type_map = id_map->type_maps;
+    for (int i = 0; i < MAX_LIBARRAY; i++, type_map++) {
+      if (type_map->map) {
+        BLI_ghash_free(type_map->map, NULL, NULL);
+        type_map->map = NULL;
+        MEM_freeN(type_map->keys);
+      }
     }
   }
+  if (id_map->idmap_types & MAIN_IDMAP_TYPE_UUID) {
+    BLI_ghash_free(id_map->uuid_map, NULL, NULL);
+  }
 
   if (id_map->valid_id_pointers != NULL) {
     BLI_gset_free(id_map->valid_id_pointers, NULL);

source/blender/blenloader/intern/readfile.c

@@ -8056,7 +8056,8 @@ void blo_lib_link_restore(Main *oldmain,
                           Scene *curscene,
                           ViewLayer *cur_view_layer)
 {
-  struct IDNameLib_Map *id_map = BKE_main_idmap_create(newmain, true, oldmain);
+  struct IDNameLib_Map *id_map = BKE_main_idmap_create(
+      newmain, true, oldmain, MAIN_IDMAP_TYPE_NAME);
 
   for (WorkSpace *workspace = newmain->workspaces.first; workspace;
        workspace = workspace->id.next) {
@@ -8801,6 +8802,8 @@ static ID *create_placeholder(Main *mainvar, const short idcode, const char *idn
   BLI_addtail(lb, ph_id);
   id_sort_by_name(lb, ph_id, NULL);
 
+  BKE_lib_libblock_session_uuid_ensure(ph_id);
+
   return ph_id;
 }
 
@@ -9013,6 +9016,14 @@ static BHead *read_libblock(FileData *fd,
       oldnewmap_insert(fd->libmap, bhead->old, id, bhead->code);
 
       BLI_addtail(lb, id);
+
+      if (fd->memfile == NULL) {
+        /* When actually reading a file , we do want to reset/re-generate session uuids.
+         * In unod case, we want to re-use existing ones. */
+        id->session_uuid = MAIN_ID_SESSION_UUID_UNSET;
+      }
+
+      BKE_lib_libblock_session_uuid_ensure(id);
     }
     else {
       /* unknown ID type */

source/blender/blenloader/intern/versioning_250.c

@@ -446,6 +446,8 @@ static void versions_gpencil_add_main(ListBase *lb, ID *id, const char *name)
   BKE_id_new_name_validate(lb, id, name);
   /* alphabetic insertion: is in BKE_id_new_name_validate */
 
+  BKE_lib_libblock_session_uuid_ensure(id);
+
   if (G.debug & G_DEBUG) {
     printf("Converted GPencil to ID: %s\n", id->name + 2);
   }

source/blender/makesdna/DNA_ID.h

@@ -31,6 +31,8 @@
 extern "C" {
 #endif
 
+#include "DNA_defs.h"
+
 struct FileData;
 struct GHash;
 struct GPUTexture;
@@ -243,7 +245,13 @@ typedef struct ID {
   int us;
   int icon_id;
   int recalc;
-  char _pad[4];
+
+  /**
+   * A session-wide unique identifier for a given ID, that remain the same across potential
+   * re-allocations (e.g. due to undo/redo steps).
+   */
+  unsigned int session_uuid;
+
   IDProperty *properties;
 
   /** Reference linked ID which this one overrides. */

source/blender/windowmanager/intern/wm_files.c

@@ -77,6 +77,7 @@
 #include "BKE_context.h"
 #include "BKE_global.h"
 #include "BKE_idprop.h"
+#include "BKE_lib_id.h"
 #include "BKE_lib_override.h"
 #include "BKE_main.h"
 #include "BKE_packedFile.h"
@@ -611,6 +612,9 @@ bool WM_file_read(bContext *C, const char *filepath, ReportList *reports)
 
   UI_view2d_zoom_cache_reset();
 
+  /* Reset session-wise ID UUID counter. */
+  BKE_lib_libblock_session_uuid_reset();
+
   /* first try to append data from exotic file formats... */
   /* it throws error box when file doesn't exist and returns -1 */
   /* note; it should set some error message somewhere... (ton) */
@@ -917,6 +921,9 @@ void wm_homefile_read(bContext *C,
     }
   }
 
+  /* Reset session-wise ID UUID counter. */
+  BKE_lib_libblock_session_uuid_reset();
+
   if (!use_factory_settings || (filepath_startup[0] != '\0')) {
     if (BLI_access(filepath_startup, R_OK) == 0) {
       success = BKE_blendfile_read(C,