ViewLayer: Lazy sync of scene data.

When a change happens which invalidates view layers the syncing will be postponed until the first usage.
This will improve importing or adding many objects in a single operation/script.

`BKE_view_layer_need_resync_tag` is used to tag the view layer to be out of sync. Before accessing
`BKE_view_layer_active_base_get`, `BKE_view_layer_active_object_get`, `BKE_view_layer_active_collection`
or `BKE_view_layer_object_bases` the caller should call `BKE_view_layer_synced_ensure`.

Having two functions ensures that partial syncing could be added as smaller patches in the future. Tagging a
view layer out of sync could be replaced with a partial sync. Eventually the number of full resyncs could be
reduced. After all tagging has been replaced with partial syncs the ensure_sync could be phased out.

This patch has been added to discuss the details and consequences of the current approach. For clarity
the call to BKE_view_layer_ensure_sync is placed close to the getters.
In the future this could be placed in more strategical places to reduce the number of calls or improve
performance. Finding those strategical places isn't that clear. When multiple operations are grouped
in a single script you might want to always check for resync.

Some areas found that can be improved. This list isn't complete.
These areas aren't addressed by this patch as these changes would be hard to detect to the reviewer.
The idea is to add changes to these areas as a separate patch. It might be that the initial commit would reduce
performance compared to master, but will be fixed by the additional patches.

**Object duplication**
During object duplication the syncing is temporarily disabled. With this patch this isn't useful as when disabled
the view_layer is accessed to locate bases. This can be improved by first locating the source bases, then duplicate
and sync and locate the new bases. Will be solved in a separate patch for clarity reasons ({D15886}).

**Object add**
`BKE_object_add` not only adds a new object, but also selects and activates the new base. This requires the
view_layer to be resynced. Some callers reverse the selection and activation (See `get_new_constraint_target`).
We should make the selection and activation optional. This would make it possible to add multiple objects
without having to resync per object.

**Postpone Activate Base**
Setting the basact is done in many locations. They follow a rule as after an action find the base and set
the basact. Finding the base could require a resync. The idea is to store in the view_layer the object which
base will be set in the basact during the next sync, reducing the times resyncing needs to happen.

Reviewed By: mont29

Maniphest Tasks: T73411

Differential Revision: https://developer.blender.org/D15885

17 files changed, 232 insertions, 110 deletions

diff --git a/source/blender/blenkernel/BKE_collision.h b/source/blender/blenkernel/BKE_collision.h
index b93babaaefa..291d76df4c8 100644
--- a/source/blender/blenkernel/BKE_collision.h
+++ b/source/blender/blenkernel/BKE_collision.h
@@ -17,6 +17,7 @@ struct Depsgraph;
 struct MVert;
 struct MVertTri;
 struct Object;
+struct Scene;
 
 ////////////////////////////////////////
 // used for collisions in collision.c
diff --git a/source/blender/blenkernel/BKE_layer.h b/source/blender/blenkernel/BKE_layer.h
index 486095c79d7..8cfc9ef8be9 100644
--- a/source/blender/blenkernel/BKE_layer.h
+++ b/source/blender/blenkernel/BKE_layer.h
@@ -371,8 +371,8 @@ void BKE_view_layer_visible_bases_iterator_end(BLI_Iterator *iter);
     data_.object_type = _object_type; \
     data_.view_layer = _view_layer; \
     data_.v3d = _v3d; \
-    UNUSED_VARS(_scene); \
-    data_.base_active = _view_layer->basact; \
+    BKE_view_layer_synced_ensure(_scene, _view_layer); \
+    data_.base_active = BKE_view_layer_active_base_get(_view_layer); \
     ITER_BEGIN (BKE_view_layer_bases_in_mode_iterator_begin, \
                 BKE_view_layer_bases_in_mode_iterator_next, \
                 BKE_view_layer_bases_in_mode_iterator_end, \
@@ -422,6 +422,7 @@ void BKE_view_layer_visible_bases_iterator_end(BLI_Iterator *iter);
     struct ObjectsVisibleIteratorData data_ = {NULL}; \
     data_.view_layer = _view_layer; \
     data_.v3d = _v3d; \
+    BKE_view_layer_synced_ensure(_scene, _view_layer); \
     ITER_BEGIN (BKE_view_layer_visible_bases_iterator_begin, \
                 BKE_view_layer_visible_bases_iterator_next, \
                 BKE_view_layer_visible_bases_iterator_end, \
@@ -438,8 +439,9 @@ void BKE_view_layer_visible_bases_iterator_end(BLI_Iterator *iter);
   { \
     Object *_instance; \
     Base *_base; \
-    UNUSED_VARS(scene); \
-    for (_base = (Base *)(view_layer)->object_bases.first; _base; _base = _base->next) { \
+    BKE_view_layer_synced_ensure(scene, view_layer); \
+    for (_base = (Base *)BKE_view_layer_object_bases_get(view_layer)->first; _base; \
+         _base = _base->next) { \
       _instance = _base->object;
 
 #define FOREACH_OBJECT_END \
@@ -575,6 +577,14 @@ struct Object **BKE_view_layer_array_from_objects_in_mode_unique_data(const stru
 struct Object *BKE_view_layer_active_object_get(const struct ViewLayer *view_layer);
 struct Object *BKE_view_layer_edit_object_get(const struct ViewLayer *view_layer);
 
+struct ListBase *BKE_view_layer_object_bases_get(struct ViewLayer *view_layer);
+struct Base *BKE_view_layer_active_base_get(struct ViewLayer *view_layer);
+
+struct LayerCollection *BKE_view_layer_active_collection_get(struct ViewLayer *view_layer);
+
+void BKE_view_layer_need_resync_tag(struct ViewLayer *view_layer);
+void BKE_view_layer_synced_ensure(const struct Scene *scene, struct ViewLayer *view_layer);
+
 struct ViewLayerAOV *BKE_view_layer_add_aov(struct ViewLayer *view_layer);
 void BKE_view_layer_remove_aov(struct ViewLayer *view_layer, struct ViewLayerAOV *aov);
 void BKE_view_layer_set_active_aov(struct ViewLayer *view_layer, struct ViewLayerAOV *aov);
diff --git a/source/blender/blenkernel/BKE_object.h b/source/blender/blenkernel/BKE_object.h
index c60893b6d74..60dfc0af25f 100644
--- a/source/blender/blenkernel/BKE_object.h
+++ b/source/blender/blenkernel/BKE_object.h
@@ -175,7 +175,7 @@ struct Object *BKE_object_add_only_object(struct Main *bmain,
  * \note Creates minimum required data, but without vertices etc.
  */
 struct Object *BKE_object_add(struct Main *bmain,
-                              const struct Scene *scene,
+                              struct Scene *scene,
                               struct ViewLayer *view_layer,
                               int type,
                               const char *name) ATTR_NONNULL(1, 2, 3) ATTR_RETURNS_NONNULL;
diff --git a/source/blender/blenkernel/intern/DerivedMesh.cc b/source/blender/blenkernel/intern/DerivedMesh.cc
index d7db0ad765c..0d07ea428bc 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.cc
+++ b/source/blender/blenkernel/intern/DerivedMesh.cc
@@ -1662,6 +1662,7 @@ static void object_get_datamask(const Depsgraph *depsgraph,
                                 CustomData_MeshMasks *r_mask,
                                 bool *r_need_mapping)
 {
+  Scene *scene = DEG_get_evaluated_scene(depsgraph);
   ViewLayer *view_layer = DEG_get_evaluated_view_layer(depsgraph);
 
   DEG_get_customdata_mask_for_object(depsgraph, ob, r_mask);
@@ -1676,8 +1677,11 @@ static void object_get_datamask(const Depsgraph *depsgraph,
     return;
   }
 
-  Object *actob = view_layer->basact ? DEG_get_original_object(view_layer->basact->object) :
-                                       nullptr;
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  Object *actob = BKE_view_layer_active_object_get(view_layer);
+  if (actob) {
+    actob = DEG_get_original_object(actob);
+  }
   if (DEG_get_original_object(ob) == actob) {
     bool editing = BKE_paint_select_face_test(actob);
 
diff --git a/source/blender/blenkernel/intern/blendfile_link_append.c b/source/blender/blenkernel/intern/blendfile_link_append.c
index d9ca1e74391..e3b76122ff0 100644
--- a/source/blender/blenkernel/intern/blendfile_link_append.c
+++ b/source/blender/blenkernel/intern/blendfile_link_append.c
@@ -493,6 +493,7 @@ static void loose_data_instantiate_ensure_active_collection(
 static void loose_data_instantiate_object_base_instance_init(Main *bmain,
                                                              Collection *collection,
                                                              Object *ob,
+                                                             const Scene *scene,
                                                              ViewLayer *view_layer,
                                                              const View3D *v3d,
                                                              const int flag,
@@ -506,7 +507,7 @@ static void loose_data_instantiate_object_base_instance_init(Main *bmain,
   }
 
   BKE_collection_object_add(bmain, collection, ob);
-
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Base *base = BKE_view_layer_base_find(view_layer, ob);
 
   if (v3d != NULL) {
@@ -686,8 +687,14 @@ static void loose_data_instantiate_collection_process(
       /* TODO: why is it OK to make this active here but not in other situations?
        * See other callers of #object_base_instance_init */
       const bool set_active = set_selected;
-      loose_data_instantiate_object_base_instance_init(
-          bmain, active_collection, ob, view_layer, v3d, lapp_context->params->flag, set_active);
+      loose_data_instantiate_object_base_instance_init(bmain,
+                                                       active_collection,
+                                                       ob,
+                                                       scene,
+                                                       view_layer,
+                                                       v3d,
+                                                       lapp_context->params->flag,
+                                                       set_active);
 
       /* Assign the collection. */
       ob->instance_collection = collection;
@@ -698,6 +705,7 @@ static void loose_data_instantiate_collection_process(
     else {
       /* Add collection as child of active collection. */
       BKE_collection_child_add(bmain, active_collection, collection);
+      BKE_view_layer_synced_ensure(scene, view_layer);
 
       if ((lapp_context->params->flag & FILE_AUTOSELECT) != 0) {
         LISTBASE_FOREACH (CollectionObject *, coll_ob, &collection->gobject) {
@@ -717,6 +725,7 @@ static void loose_data_instantiate_object_process(LooseDataInstantiateContext *i
 {
   BlendfileLinkAppendContext *lapp_context = instantiate_context->lapp_context;
   Main *bmain = lapp_context->params->bmain;
+  const Scene *scene = lapp_context->params->context.scene;
   ViewLayer *view_layer = lapp_context->params->context.view_layer;
   const View3D *v3d = lapp_context->params->context.v3d;
 
@@ -762,6 +771,7 @@ static void loose_data_instantiate_object_process(LooseDataInstantiateContext *i
     loose_data_instantiate_object_base_instance_init(bmain,
                                                      active_collection,
                                                      ob,
+                                                     scene,
                                                      view_layer,
                                                      v3d,
                                                      lapp_context->params->flag,
@@ -809,6 +819,7 @@ static void loose_data_instantiate_obdata_process(LooseDataInstantiateContext *i
     loose_data_instantiate_object_base_instance_init(bmain,
                                                      active_collection,
                                                      ob,
+                                                     scene,
                                                      view_layer,
                                                      v3d,
                                                      lapp_context->params->flag,
diff --git a/source/blender/blenkernel/intern/collection.c b/source/blender/blenkernel/intern/collection.c
index 95457b6f790..98b1e3d0039 100644
--- a/source/blender/blenkernel/intern/collection.c
+++ b/source/blender/blenkernel/intern/collection.c
@@ -859,15 +859,15 @@ void BKE_collection_object_cache_free(Collection *collection)
   collection_object_cache_free(collection);
 }
 
-Base *BKE_collection_or_layer_objects(const Scene *UNUSED(scene),
+Base *BKE_collection_or_layer_objects(const Scene *scene,
                                       ViewLayer *view_layer,
                                       Collection *collection)
 {
   if (collection) {
     return BKE_collection_object_cache_get(collection).first;
   }
-
-  return view_layer->object_bases.first;
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  return BKE_view_layer_object_bases_get(view_layer)->first;
 }
 
 /** \} */
@@ -1751,7 +1751,10 @@ Collection *BKE_collection_from_index(Scene *scene, const int index)
   return collection_from_index_recursive(master_collection, index, &index_current);
 }
 
-static bool collection_objects_select(ViewLayer *view_layer, Collection *collection, bool deselect)
+static bool collection_objects_select(const Scene *scene,
+                                      ViewLayer *view_layer,
+                                      Collection *collection,
+                                      bool deselect)
 {
   bool changed = false;
 
@@ -1759,6 +1762,7 @@ static bool collection_objects_select(ViewLayer *view_layer, Collection *collect
     return false;
   }
 
+  BKE_view_layer_synced_ensure(scene, view_layer);
   LISTBASE_FOREACH (CollectionObject *, cob, &collection->gobject) {
     Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
 
@@ -1779,7 +1783,7 @@ static bool collection_objects_select(ViewLayer *view_layer, Collection *collect
   }
 
   LISTBASE_FOREACH (CollectionChild *, child, &collection->children) {
-    if (collection_objects_select(view_layer, collection, deselect)) {
+    if (collection_objects_select(scene, view_layer, collection, deselect)) {
       changed = true;
     }
   }
@@ -1799,7 +1803,7 @@ bool BKE_collection_objects_select(const Scene *scene,
     return BKE_layer_collection_objects_select(scene, view_layer, layer_collection, deselect);
   }
 
-  return collection_objects_select(view_layer, collection, deselect);
+  return collection_objects_select(scene, view_layer, collection, deselect);
 }
 
 /** \} */
diff --git a/source/blender/blenkernel/intern/context.c b/source/blender/blenkernel/intern/context.c
index 1f1a49ca030..ceb84d213c3 100644
--- a/source/blender/blenkernel/intern/context.c
+++ b/source/blender/blenkernel/intern/context.c
@@ -440,6 +440,7 @@ static int ctx_data_base_collection_get(const bContext *C, const char *member, L
 
   Scene *scene = CTX_data_scene(C);
   ViewLayer *view_layer = CTX_data_view_layer(C);
+  BKE_view_layer_synced_ensure(scene, view_layer);
 
   bool ok = false;
 
@@ -1362,8 +1363,9 @@ struct Base *CTX_data_active_base(const bContext *C)
   if (ob == NULL) {
     return NULL;
   }
-
+  const Scene *scene = CTX_data_scene(C);
   ViewLayer *view_layer = CTX_data_view_layer(C);
+  BKE_view_layer_synced_ensure(scene, view_layer);
   return BKE_view_layer_base_find(view_layer, ob);
 }
 
diff --git a/source/blender/blenkernel/intern/fluid.c b/source/blender/blenkernel/intern/fluid.c
index a81274c9bd7..6e53254d162 100644
--- a/source/blender/blenkernel/intern/fluid.c
+++ b/source/blender/blenkernel/intern/fluid.c
@@ -27,6 +27,7 @@
 #include "BKE_effect.h"
 #include "BKE_fluid.h"
 #include "BKE_global.h"
+#include "BKE_layer.h"
 #include "BKE_lib_id.h"
 #include "BKE_modifier.h"
 #include "BKE_pointcache.h"
@@ -543,7 +544,9 @@ static bool BKE_fluid_modifier_init(
 }
 
 /* Forward declarations. */
-static void manta_smoke_calc_transparency(FluidDomainSettings *fds, ViewLayer *view_layer);
+static void manta_smoke_calc_transparency(FluidDomainSettings *fds,
+                                          Scene *scene,
+                                          ViewLayer *view_layer);
 static float calc_voxel_transp(
     float *result, const float *input, int res[3], int *pixel, float *t_ray, float correct);
 static void update_distances(int index,
@@ -553,12 +556,13 @@ static void update_distances(int index,
                              float surface_thickness,
                              bool use_plane_init);
 
-static int get_light(ViewLayer *view_layer, float *light)
+static int get_light(Scene *scene, ViewLayer *view_layer, float *light)
 {
   int found_light = 0;
 
   /* Try to find a lamp, preferably local. */
-  LISTBASE_FOREACH (Base *, base_tmp, &view_layer->object_bases) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base_tmp, BKE_view_layer_object_bases_get(view_layer)) {
     if (base_tmp->object->type == OB_LAMP) {
       Light *la = base_tmp->object->data;
 
@@ -3596,7 +3600,8 @@ static int manta_step(
 
   /* Compute shadow grid for gas simulations. Make sure to skip if bake job was canceled early. */
   if (fds->type == FLUID_DOMAIN_TYPE_GAS && result) {
-    manta_smoke_calc_transparency(fds, DEG_get_evaluated_view_layer(depsgraph));
+    manta_smoke_calc_transparency(
+        fds, DEG_get_evaluated_scene(depsgraph), DEG_get_evaluated_view_layer(depsgraph));
   }
 
   BLI_mutex_unlock(&object_update_lock);
@@ -4295,7 +4300,9 @@ static void bresenham_linie_3D(int x1,
   cb(result, input, res, pixel, t_ray, correct);
 }
 
-static void manta_smoke_calc_transparency(FluidDomainSettings *fds, ViewLayer *view_layer)
+static void manta_smoke_calc_transparency(FluidDomainSettings *fds,
+                                          Scene *scene,
+                                          ViewLayer *view_layer)
 {
   float bv[6] = {0};
   float light[3];
@@ -4304,7 +4311,7 @@ static void manta_smoke_calc_transparency(FluidDomainSettings *fds, ViewLayer *v
   float *shadow = manta_smoke_get_shadow(fds->fluid);
   float correct = -7.0f * fds->dx;
 
-  if (!get_light(view_layer, light)) {
+  if (!get_light(scene, view_layer, light)) {
     return;
   }
 
diff --git a/source/blender/blenkernel/intern/layer.c b/source/blender/blenkernel/intern/layer.c
index a388df7efc9..d779fc4f512 100644
--- a/source/blender/blenkernel/intern/layer.c
+++ b/source/blender/blenkernel/intern/layer.c
@@ -284,11 +284,10 @@ void BKE_view_layer_free_ex(ViewLayer *view_layer, const bool do_id_user)
   MEM_freeN(view_layer);
 }
 
-void BKE_view_layer_selected_objects_tag(const Scene *UNUSED(scene),
-                                         ViewLayer *view_layer,
-                                         const int tag)
+void BKE_view_layer_selected_objects_tag(const Scene *scene, ViewLayer *view_layer, const int tag)
 {
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     if ((base->flag & BASE_SELECTED) != 0) {
       base->object->flag |= tag;
     }
@@ -311,9 +310,10 @@ static bool find_scene_collection_in_scene_collections(ListBase *lb, const Layer
   return false;
 }
 
-Object *BKE_view_layer_camera_find(const Scene *UNUSED(scene), ViewLayer *view_layer)
+Object *BKE_view_layer_camera_find(const Scene *scene, ViewLayer *view_layer)
 {
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     if (base->object->type == OB_CAMERA) {
       return base->object;
     }
@@ -381,6 +381,8 @@ static void view_layer_bases_hash_create(ViewLayer *view_layer, const bool do_ba
 
 Base *BKE_view_layer_base_find(ViewLayer *view_layer, Object *ob)
 {
+  BLI_assert_msg((view_layer->flag & VIEW_LAYER_OUT_OF_SYNC) == 0,
+                 "View layer out of sync, invoke BKE_view_layer_synced_ensure.");
   if (!view_layer->object_bases_hash) {
     view_layer_bases_hash_create(view_layer, false);
   }
@@ -388,11 +390,10 @@ Base *BKE_view_layer_base_find(ViewLayer *view_layer, Object *ob)
   return BLI_ghash_lookup(view_layer->object_bases_hash, ob);
 }
 
-void BKE_view_layer_base_deselect_all(const Scene *UNUSED(scene), ViewLayer *view_layer)
+void BKE_view_layer_base_deselect_all(const Scene *scene, ViewLayer *view_layer)
 {
-  Base *base;
-
-  for (base = view_layer->object_bases.first; base; base = base->next) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     base->flag &= ~BASE_SELECTED;
   }
 }
@@ -504,7 +505,9 @@ void BKE_view_layer_copy_data(Scene *scene_dst,
   /* Copy layer collections and object bases. */
   /* Inline 'BLI_duplicatelist' and update the active base. */
   BLI_listbase_clear(&view_layer_dst->object_bases);
-  LISTBASE_FOREACH (Base *, base_src, &view_layer_src->object_bases) {
+  BLI_assert_msg((view_layer_src->flag & VIEW_LAYER_OUT_OF_SYNC) == 0,
+                 "View Layer Object Base out of sync, invoke BKE_view_layer_synced_ensure.");
+  LISTBASE_FOREACH (const Base *, base_src, &view_layer_src->object_bases) {
     Base *base_dst = MEM_dupallocN(base_src);
     BLI_addtail(&view_layer_dst->object_bases, base_dst);
     if (view_layer_src->basact == base_src) {
@@ -959,6 +962,19 @@ static void layer_collection_resync_unused_layers_free(ViewLayer *view_layer,
   }
 }
 
+void BKE_view_layer_need_resync_tag(struct ViewLayer *view_layer)
+{
+  view_layer->flag |= VIEW_LAYER_OUT_OF_SYNC;
+}
+
+void BKE_view_layer_synced_ensure(const Scene *scene, struct ViewLayer *view_layer)
+{
+  if (view_layer->flag & VIEW_LAYER_OUT_OF_SYNC) {
+    BKE_layer_collection_sync(scene, view_layer);
+    view_layer->flag &= ~VIEW_LAYER_OUT_OF_SYNC;
+  }
+}
+
 static void layer_collection_objects_sync(ViewLayer *view_layer,
                                           LayerCollection *layer,
                                           ListBase *r_lb_new_object_bases,
@@ -1052,8 +1068,14 @@ static void layer_collection_sync(ViewLayer *view_layer,
 
   BLI_assert(layer_resync->is_used);
 
+  uint64_t skipped_children = 0;
   LISTBASE_FOREACH (CollectionChild *, child, &layer_resync->collection->children) {
     Collection *child_collection = child->collection;
+    /* Collection relations may not have rebuild yet. */
+    if (child_collection == NULL) {
+      skipped_children++;
+      continue;
+    }
     LayerCollectionResync *child_layer_resync = layer_collection_resync_find(layer_resync,
                                                                              child_collection);
 
@@ -1158,7 +1180,7 @@ static void layer_collection_sync(ViewLayer *view_layer,
 
   /* Replace layer collection list with new one. */
   layer_resync->layer->layer_collections = new_lb_layer;
-  BLI_assert(BLI_listbase_count(&layer_resync->collection->children) ==
+  BLI_assert(BLI_listbase_count(&layer_resync->collection->children) - skipped_children ==
              BLI_listbase_count(&new_lb_layer));
 
   /* Update bases etc. for objects. */
@@ -1344,7 +1366,7 @@ void BKE_scene_collection_sync(const Scene *scene)
   }
 
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
-    BKE_layer_collection_sync(scene, view_layer);
+    BKE_view_layer_need_resync_tag(view_layer);
   }
 }
 
@@ -1422,6 +1444,7 @@ bool BKE_layer_collection_objects_select(const Scene *scene,
   bool changed = false;
 
   if (!(lc->flag & LAYER_COLLECTION_EXCLUDE)) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     LISTBASE_FOREACH (CollectionObject *, cob, &lc->collection->gobject) {
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
 
@@ -1458,6 +1481,7 @@ bool BKE_layer_collection_has_selected_objects(const Scene *scene,
   }
 
   if (!(lc->flag & LAYER_COLLECTION_EXCLUDE)) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     LISTBASE_FOREACH (CollectionObject *, cob, &lc->collection->gobject) {
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
 
@@ -1502,7 +1526,8 @@ void BKE_base_set_visible(Scene *scene, ViewLayer *view_layer, Base *base, bool
 {
   if (!extend) {
     /* Make only one base visible. */
-    LISTBASE_FOREACH (Base *, other, &view_layer->object_bases) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
+    LISTBASE_FOREACH (Base *, other, BKE_view_layer_object_bases_get(view_layer)) {
       other->flag |= BASE_HIDDEN;
     }
 
@@ -1513,7 +1538,7 @@ void BKE_base_set_visible(Scene *scene, ViewLayer *view_layer, Base *base, bool
     base->flag ^= BASE_HIDDEN;
   }
 
-  BKE_layer_collection_sync(scene, view_layer);
+  BKE_view_layer_need_resync_tag(view_layer);
 }
 
 bool BKE_base_is_visible(const View3D *v3d, const Base *base)
@@ -1592,7 +1617,7 @@ static void layer_collection_flag_unset_recursive(LayerCollection *lc, const int
   }
 }
 
-void BKE_layer_collection_isolate_global(Scene *scene,
+void BKE_layer_collection_isolate_global(Scene *UNUSED(scene),
                                          ViewLayer *view_layer,
                                          LayerCollection *lc,
                                          bool extend)
@@ -1637,7 +1662,7 @@ void BKE_layer_collection_isolate_global(Scene *scene,
     BKE_layer_collection_activate(view_layer, lc);
   }
 
-  BKE_layer_collection_sync(scene, view_layer);
+  BKE_view_layer_need_resync_tag(view_layer);
 }
 
 static void layer_collection_local_visibility_set_recursive(LayerCollection *layer_collection,
@@ -1658,7 +1683,8 @@ static void layer_collection_local_visibility_unset_recursive(LayerCollection *l
   }
 }
 
-static void layer_collection_local_sync(ViewLayer *view_layer,
+static void layer_collection_local_sync(const Scene *scene,
+                                        ViewLayer *view_layer,
                                         LayerCollection *layer_collection,
                                         const unsigned short local_collections_uuid,
                                         bool visible)
@@ -1673,6 +1699,7 @@ static void layer_collection_local_sync(ViewLayer *view_layer,
         continue;
       }
 
+      BKE_view_layer_synced_ensure(scene, view_layer);
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
       base->local_collections_bits |= local_collections_uuid;
     }
@@ -1680,14 +1707,12 @@ static void layer_collection_local_sync(ViewLayer *view_layer,
 
   LISTBASE_FOREACH (LayerCollection *, child, &layer_collection->layer_collections) {
     if ((child->flag & LAYER_COLLECTION_EXCLUDE) == 0) {
-      layer_collection_local_sync(view_layer, child, local_collections_uuid, visible);
+      layer_collection_local_sync(scene, view_layer, child, local_collections_uuid, visible);
     }
   }
 }
 
-void BKE_layer_collection_local_sync(const Scene *UNUSED(scene),
-                                     ViewLayer *view_layer,
-                                     const View3D *v3d)
+void BKE_layer_collection_local_sync(const Scene *scene, ViewLayer *view_layer, const View3D *v3d)
 {
   if (no_resync) {
     return;
@@ -1696,12 +1721,13 @@ void BKE_layer_collection_local_sync(const Scene *UNUSED(scene),
   const unsigned short local_collections_uuid = v3d->local_collections_uuid;
 
   /* Reset flags and set the bases visible by default. */
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     base->local_collections_bits &= ~local_collections_uuid;
   }
 
   LISTBASE_FOREACH (LayerCollection *, layer_collection, &view_layer->layer_collections) {
-    layer_collection_local_sync(view_layer, layer_collection, local_collections_uuid, true);
+    layer_collection_local_sync(scene, view_layer, layer_collection, local_collections_uuid, true);
   }
 }
 
@@ -1772,33 +1798,39 @@ void BKE_layer_collection_isolate_local(
   BKE_layer_collection_local_sync(scene, view_layer, v3d);
 }
 
-static void layer_collection_bases_show_recursive(ViewLayer *view_layer, LayerCollection *lc)
+static void layer_collection_bases_show_recursive(const Scene *scene,
+                                                  ViewLayer *view_layer,
+                                                  LayerCollection *lc)
 {
   if ((lc->flag & LAYER_COLLECTION_EXCLUDE) == 0) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     LISTBASE_FOREACH (CollectionObject *, cob, &lc->collection->gobject) {
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
       base->flag &= ~BASE_HIDDEN;
     }
   }
   LISTBASE_FOREACH (LayerCollection *, lc_iter, &lc->layer_collections) {
-    layer_collection_bases_show_recursive(view_layer, lc_iter);
+    layer_collection_bases_show_recursive(scene, view_layer, lc_iter);
   }
 }
 
-static void layer_collection_bases_hide_recursive(ViewLayer *view_layer, LayerCollection *lc)
+static void layer_collection_bases_hide_recursive(const Scene *scene,
+                                                  ViewLayer *view_layer,
+                                                  LayerCollection *lc)
 {
   if ((lc->flag & LAYER_COLLECTION_EXCLUDE) == 0) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     LISTBASE_FOREACH (CollectionObject *, cob, &lc->collection->gobject) {
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
       base->flag |= BASE_HIDDEN;
     }
   }
   LISTBASE_FOREACH (LayerCollection *, lc_iter, &lc->layer_collections) {
-    layer_collection_bases_hide_recursive(view_layer, lc_iter);
+    layer_collection_bases_hide_recursive(scene, view_layer, lc_iter);
   }
 }
 
-void BKE_layer_collection_set_visible(const Scene *UNUSED(scene),
+void BKE_layer_collection_set_visible(const Scene *scene,
                                       ViewLayer *view_layer,
                                       LayerCollection *lc,
                                       const bool visible,
@@ -1807,11 +1839,11 @@ void BKE_layer_collection_set_visible(const Scene *UNUSED(scene),
   if (hierarchy) {
     if (visible) {
       layer_collection_flag_unset_recursive(lc, LAYER_COLLECTION_HIDE);
-      layer_collection_bases_show_recursive(view_layer, lc);
+      layer_collection_bases_show_recursive(scene, view_layer, lc);
     }
     else {
       layer_collection_flag_set_recursive(lc, LAYER_COLLECTION_HIDE);
-      layer_collection_bases_hide_recursive(view_layer, lc);
+      layer_collection_bases_hide_recursive(scene, view_layer, lc);
     }
   }
   else {
@@ -1906,6 +1938,7 @@ bool BKE_view_layer_has_collection(const ViewLayer *view_layer, const Collection
 bool BKE_scene_has_object(Scene *scene, Object *ob)
 {
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     Base *base = BKE_view_layer_base_find(view_layer, ob);
     if (base) {
       return true;
@@ -1945,7 +1978,7 @@ static void object_bases_iterator_begin(BLI_Iterator *iter, void *data_in_v, con
   ObjectsVisibleIteratorData *data_in = data_in_v;
   ViewLayer *view_layer = data_in->view_layer;
   const View3D *v3d = data_in->v3d;
-  Base *base = view_layer->object_bases.first;
+  Base *base = BKE_view_layer_object_bases_get(view_layer)->first;
 
   /* when there are no objects */
   if (base == NULL) {
@@ -2244,18 +2277,19 @@ void BKE_base_eval_flags(Base *base)
 }
 
 static void layer_eval_view_layer(struct Depsgraph *depsgraph,
-                                  struct Scene *UNUSED(scene),
+                                  struct Scene *scene,
                                   ViewLayer *view_layer)
 {
   DEG_debug_print_eval(depsgraph, __func__, view_layer->name, view_layer);
 
   /* Create array of bases, for fast index-based lookup. */
-  const int num_object_bases = BLI_listbase_count(&view_layer->object_bases);
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  const int num_object_bases = BLI_listbase_count(BKE_view_layer_object_bases_get(view_layer));
   MEM_SAFE_FREE(view_layer->object_bases_array);
   view_layer->object_bases_array = MEM_malloc_arrayN(
       num_object_bases, sizeof(Base *), "view_layer->object_bases_array");
   int base_index = 0;
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     view_layer->object_bases_array[base_index++] = base;
   }
 }
@@ -2285,12 +2319,11 @@ static void write_layer_collections(BlendWriter *writer, ListBase *lb)
   }
 }
 
-void BKE_view_layer_blend_write(BlendWriter *writer,
-                                const Scene *UNUSED(scene),
-                                ViewLayer *view_layer)
+void BKE_view_layer_blend_write(BlendWriter *writer, const Scene *scene, ViewLayer *view_layer)
 {
+  BKE_view_layer_synced_ensure(scene, view_layer);
   BLO_write_struct(writer, ViewLayer, view_layer);
-  BLO_write_struct_list(writer, Base, &view_layer->object_bases);
+  BLO_write_struct_list(writer, Base, BKE_view_layer_object_bases_get(view_layer));
 
   if (view_layer->id_properties) {
     IDP_BlendWrite(writer, view_layer->id_properties);
diff --git a/source/blender/blenkernel/intern/layer_utils.c b/source/blender/blenkernel/intern/layer_utils.c
index f6233f215ce..23067d1a4e3 100644
--- a/source/blender/blenkernel/intern/layer_utils.c
+++ b/source/blender/blenkernel/intern/layer_utils.c
@@ -215,6 +215,27 @@ struct Object **BKE_view_layer_array_from_objects_in_mode_unique_data(const Scen
   return BKE_view_layer_array_from_objects_in_mode_params(scene, view_layer, v3d, r_len, &params);
 }
 
+ListBase *BKE_view_layer_object_bases_get(ViewLayer *view_layer)
+{
+  BLI_assert_msg((view_layer->flag & VIEW_LAYER_OUT_OF_SYNC) == 0,
+                 "Object Bases out of sync, invoke BKE_view_layer_synced_ensure.");
+  return &view_layer->object_bases;
+}
+
+Base *BKE_view_layer_active_base_get(ViewLayer *view_layer)
+{
+  BLI_assert_msg((view_layer->flag & VIEW_LAYER_OUT_OF_SYNC) == 0,
+                 "Active Base out of sync, invoke BKE_view_layer_synced_ensure.");
+  return view_layer->basact;
+}
+
+LayerCollection *BKE_view_layer_active_collection_get(ViewLayer *view_layer)
+{
+  BLI_assert_msg((view_layer->flag & VIEW_LAYER_OUT_OF_SYNC) == 0,
+                 "Active Collection out of sync, invoke BKE_view_layer_synced_ensure.");
+  return view_layer->active_collection;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
@@ -249,10 +270,11 @@ bool BKE_view_layer_filter_edit_mesh_has_edges(const Object *ob, void *UNUSED(us
   return false;
 }
 
-Object *BKE_view_layer_non_active_selected_object(const Scene *UNUSED(scene),
+Object *BKE_view_layer_non_active_selected_object(const struct Scene *scene,
                                                   struct ViewLayer *view_layer,
                                                   const struct View3D *v3d)
 {
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Object *ob_active = BKE_view_layer_active_object_get(view_layer);
   Object *ob_result = NULL;
   FOREACH_SELECTED_OBJECT_BEGIN (view_layer, v3d, ob_iter) {
@@ -280,7 +302,8 @@ Object *BKE_view_layer_non_active_selected_object(const Scene *UNUSED(scene),
 
 Object *BKE_view_layer_active_object_get(const ViewLayer *view_layer)
 {
-  return view_layer->basact ? view_layer->basact->object : NULL;
+  Base *base = BKE_view_layer_active_base_get((ViewLayer *)view_layer);
+  return base ? base->object : NULL;
 }
 
 Object *BKE_view_layer_edit_object_get(const ViewLayer *view_layer)
diff --git a/source/blender/blenkernel/intern/lib_override.cc b/source/blender/blenkernel/intern/lib_override.cc
index 0200b534ace..b05ae775be6 100644
--- a/source/blender/blenkernel/intern/lib_override.cc
+++ b/source/blender/blenkernel/intern/lib_override.cc
@@ -1269,6 +1269,8 @@ static void lib_override_library_create_post_process(Main *bmain,
     }
   }
 
+  BKE_view_layer_synced_ensure(scene, view_layer);
+
   /* We need to ensure all new overrides of objects are properly instantiated. */
   Collection *default_instantiating_collection = residual_storage;
   LISTBASE_FOREACH (Object *, ob, &bmain->objects) {
@@ -1377,7 +1379,7 @@ bool BKE_lib_override_library_create(Main *bmain,
   if (id_hierarchy_root_reference == nullptr) {
     id_hierarchy_root_reference = id_root_reference;
   }
-
+  BKE_view_layer_synced_ensure(scene, view_layer);
   const Object *old_active_object = BKE_view_layer_active_object_get(view_layer);
 
   const bool success = lib_override_library_create_do(bmain,
@@ -1716,6 +1718,7 @@ static bool lib_override_library_resync(Main *bmain,
 
   ID *id_root_reference = id_root->override_library->reference;
   ID *id;
+  BKE_view_layer_synced_ensure(scene, view_layer);
   const Object *old_active_object = BKE_view_layer_active_object_get(view_layer);
 
   if (id_root_reference->tag & LIB_TAG_MISSING) {
@@ -2696,7 +2699,8 @@ void BKE_lib_override_library_main_resync(Main *bmain,
     /* Hide the collection from viewport and render. */
     override_resync_residual_storage->flag |= COLLECTION_HIDE_VIEWPORT | COLLECTION_HIDE_RENDER;
   }
-
+  /* BKE_collection_add above could have tagged the view_layer out of sync. */
+  BKE_view_layer_synced_ensure(scene, view_layer);
   const Object *old_active_object = BKE_view_layer_active_object_get(view_layer);
 
   /* Necessary to improve performances, and prevent layers matching override sub-collections to be
diff --git a/source/blender/blenkernel/intern/mball.cc b/source/blender/blenkernel/intern/mball.cc
index 09d286b0aa0..91797f8ed2f 100644
--- a/source/blender/blenkernel/intern/mball.cc
+++ b/source/blender/blenkernel/intern/mball.cc
@@ -42,6 +42,7 @@
 #include "BKE_geometry_set.hh"
 #include "BKE_idtype.h"
 #include "BKE_lattice.h"
+#include "BKE_layer.h"
 #include "BKE_lib_id.h"
 #include "BKE_lib_query.h"
 #include "BKE_material.h"
@@ -449,7 +450,8 @@ Object *BKE_mball_basis_find(Scene *scene, Object *object)
   BLI_split_name_num(basisname, &basisnr, object->id.name + 2, '.');
 
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
-    LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
+    LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
       Object *ob = base->object;
       if ((ob->type == OB_MBALL) && !(base->flag & BASE_FROM_DUPLI)) {
         if (ob != bob) {
diff --git a/source/blender/blenkernel/intern/object.cc b/source/blender/blenkernel/intern/object.cc
index d4cf9d421d3..cbe5ea425fb 100644
--- a/source/blender/blenkernel/intern/object.cc
+++ b/source/blender/blenkernel/intern/object.cc
@@ -2271,7 +2271,7 @@ static Object *object_add_common(
 }
 
 Object *BKE_object_add(
-    Main *bmain, const Scene *scene, ViewLayer *view_layer, int type, const char *name)
+    Main *bmain, Scene *scene, ViewLayer *view_layer, int type, const char *name)
 {
   Object *ob = object_add_common(bmain, scene, view_layer, type, name);
 
@@ -2280,6 +2280,7 @@ Object *BKE_object_add(
 
   /* NOTE: There is no way to be sure that #BKE_collection_viewlayer_object_add will actually
    * manage to find a valid collection in given `view_layer` to add the new object to. */
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Base *base = BKE_view_layer_base_find(view_layer, ob);
   if (base != nullptr) {
     BKE_view_layer_base_select_and_set_active(view_layer, base);
@@ -2294,6 +2295,7 @@ Object *BKE_object_add_from(
   Object *ob = object_add_common(bmain, scene, view_layer, type, name);
   BKE_collection_object_add_from(bmain, scene, ob_src, ob);
 
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Base *base = BKE_view_layer_base_find(view_layer, ob);
   BKE_view_layer_base_select_and_set_active(view_layer, base);
 
@@ -2322,6 +2324,7 @@ Object *BKE_object_add_for_data(Main *bmain,
   LayerCollection *layer_collection = BKE_layer_collection_get_active(view_layer);
   BKE_collection_object_add(bmain, layer_collection->collection, ob);
 
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Base *base = BKE_view_layer_base_find(view_layer, ob);
   BKE_view_layer_base_select_and_set_active(view_layer, base);
 
@@ -2538,12 +2541,13 @@ Object *BKE_object_pose_armature_get(Object *ob)
 }
 
 Object *BKE_object_pose_armature_get_visible(Object *ob,
-                                             const Scene *UNUSED(scene),
+                                             const Scene *scene,
                                              ViewLayer *view_layer,
                                              View3D *v3d)
 {
   Object *ob_armature = BKE_object_pose_armature_get(ob);
   if (ob_armature) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     Base *base = BKE_view_layer_base_find(view_layer, ob_armature);
     if (base) {
       if (BASE_VISIBLE(v3d, base)) {
@@ -2557,6 +2561,7 @@ Object *BKE_object_pose_armature_get_visible(Object *ob,
 Object **BKE_object_pose_array_get_ex(
     const Scene *scene, ViewLayer *view_layer, View3D *v3d, uint *r_objects_len, bool unique)
 {
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Object *ob_active = BKE_view_layer_active_object_get(view_layer);
   Object *ob_pose = BKE_object_pose_armature_get(ob_active);
   Object **objects = nullptr;
@@ -2597,7 +2602,8 @@ Object **BKE_object_pose_array_get(const Scene *scene,
 Base **BKE_object_pose_base_array_get_ex(
     const Scene *scene, ViewLayer *view_layer, View3D *v3d, uint *r_bases_len, bool unique)
 {
-  Base *base_active = view_layer->basact;
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  Base *base_active = BKE_view_layer_active_base_get(view_layer);
   Object *ob_pose = base_active ? BKE_object_pose_armature_get(base_active->object) : nullptr;
   Base *base_pose = nullptr;
   Base **bases = nullptr;
@@ -5154,7 +5160,7 @@ static void obrel_list_add(LinkNode **links, Object *ob)
   ob->id.tag |= LIB_TAG_DOIT;
 }
 
-LinkNode *BKE_object_relational_superset(const Scene *UNUSED(scene),
+LinkNode *BKE_object_relational_superset(const Scene *scene,
                                          struct ViewLayer *view_layer,
                                          eObjectSet objectSet,
                                          eObRelationTypes includeFilter)
@@ -5162,12 +5168,13 @@ LinkNode *BKE_object_relational_superset(const Scene *UNUSED(scene),
   LinkNode *links = nullptr;
 
   /* Remove markers from all objects */
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     base->object->id.tag &= ~LIB_TAG_DOIT;
   }
 
   /* iterate over all selected and visible objects */
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     if (objectSet == OB_SET_ALL) {
       /* as we get all anyways just add it */
       Object *ob = base->object;
@@ -5203,7 +5210,7 @@ LinkNode *BKE_object_relational_superset(const Scene *UNUSED(scene),
 
         /* child relationship */
         if (includeFilter & (OB_REL_CHILDREN | OB_REL_CHILDREN_RECURSIVE)) {
-          LISTBASE_FOREACH (Base *, local_base, &view_layer->object_bases) {
+          LISTBASE_FOREACH (Base *, local_base, BKE_view_layer_object_bases_get(view_layer)) {
             if (BASE_EDITABLE(((View3D *)nullptr), local_base)) {
 
               Object *child = local_base->object;
diff --git a/source/blender/blenkernel/intern/paint.cc b/source/blender/blenkernel/intern/paint.cc
index 1a1bf285847..7ad9fd3a7c3 100644
--- a/source/blender/blenkernel/intern/paint.cc
+++ b/source/blender/blenkernel/intern/paint.cc
@@ -41,6 +41,7 @@
 #include "BKE_idtype.h"
 #include "BKE_image.h"
 #include "BKE_key.h"
+#include "BKE_layer.h"
 #include "BKE_lib_id.h"
 #include "BKE_main.h"
 #include "BKE_material.h"
@@ -447,9 +448,11 @@ Paint *BKE_paint_get_active(Scene *sce, ViewLayer *view_layer)
 {
   if (sce && view_layer) {
     ToolSettings *ts = sce->toolsettings;
+    BKE_view_layer_synced_ensure(sce, view_layer);
+    Object *actob = BKE_view_layer_active_object_get(view_layer);
 
-    if (view_layer->basact && view_layer->basact->object) {
-      switch (view_layer->basact->object->mode) {
+    if (actob) {
+      switch (actob->mode) {
         case OB_MODE_SCULPT:
           return &ts->sculpt->paint;
         case OB_MODE_VERTEX_PAINT:
@@ -490,11 +493,8 @@ Paint *BKE_paint_get_active_from_context(const bContext *C)
 
   if (sce && view_layer) {
     ToolSettings *ts = sce->toolsettings;
-    Object *obact = nullptr;
-
-    if (view_layer->basact && view_layer->basact->object) {
-      obact = view_layer->basact->object;
-    }
+    BKE_view_layer_synced_ensure(sce, view_layer);
+    Object *obact = BKE_view_layer_active_object_get(view_layer);
 
     if ((sima = CTX_wm_space_image(C)) != nullptr) {
       if (obact && obact->mode == OB_MODE_EDIT) {
@@ -524,11 +524,8 @@ ePaintMode BKE_paintmode_get_active_from_context(const bContext *C)
   SpaceImage *sima;
 
   if (sce && view_layer) {
-    Object *obact = nullptr;
-
-    if (view_layer->basact && view_layer->basact->object) {
-      obact = view_layer->basact->object;
-    }
+    BKE_view_layer_synced_ensure(sce, view_layer);
+    Object *obact = BKE_view_layer_active_object_get(view_layer);
 
     if ((sima = CTX_wm_space_image(C)) != nullptr) {
       if (obact && obact->mode == OB_MODE_EDIT) {
diff --git a/source/blender/blenkernel/intern/particle.c b/source/blender/blenkernel/intern/particle.c
index c894e507d35..bbd462d5ae1 100644
--- a/source/blender/blenkernel/intern/particle.c
+++ b/source/blender/blenkernel/intern/particle.c
@@ -53,6 +53,7 @@
 #include "BKE_idtype.h"
 #include "BKE_key.h"
 #include "BKE_lattice.h"
+#include "BKE_layer.h"
 #include "BKE_lib_id.h"
 #include "BKE_lib_query.h"
 #include "BKE_main.h"
@@ -761,13 +762,15 @@ static PTCacheEdit *psys_orig_edit_get(ParticleSystem *psys)
 
 bool psys_in_edit_mode(Depsgraph *depsgraph, const ParticleSystem *psys)
 {
-  const ViewLayer *view_layer = DEG_get_input_view_layer(depsgraph);
-  if (view_layer->basact == NULL) {
+  const Scene *scene = DEG_get_input_scene(depsgraph);
+  ViewLayer *view_layer = DEG_get_input_view_layer(depsgraph);
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  const Object *object = BKE_view_layer_active_object_get(view_layer);
+  if (object == NULL) {
     /* TODO(sergey): Needs double-check with multi-object edit. */
     return false;
   }
   const bool use_render_params = (DEG_get_mode(depsgraph) == DAG_EVAL_RENDER);
-  const Object *object = view_layer->basact->object;
   if (object->mode != OB_MODE_PARTICLE_EDIT) {
     return false;
   }
diff --git a/source/blender/blenkernel/intern/rigidbody.c b/source/blender/blenkernel/intern/rigidbody.c
index 86cccf1da69..6adb728b515 100644
--- a/source/blender/blenkernel/intern/rigidbody.c
+++ b/source/blender/blenkernel/intern/rigidbody.c
@@ -1664,7 +1664,9 @@ static void rigidbody_update_sim_ob(Depsgraph *depsgraph, Object *ob, RigidBodyO
     return;
   }
 
+  const Scene *scene = DEG_get_input_scene(depsgraph);
   ViewLayer *view_layer = DEG_get_input_view_layer(depsgraph);
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Base *base = BKE_view_layer_base_find(view_layer, ob);
   const bool is_selected = base ? (base->flag & BASE_SELECTED) != 0 : false;
 
@@ -2008,7 +2010,9 @@ static void rigidbody_free_substep_data(ListBase *substep_targets)
 }
 static void rigidbody_update_simulation_post_step(Depsgraph *depsgraph, RigidBodyWorld *rbw)
 {
+  const Scene *scene = DEG_get_input_scene(depsgraph);
   ViewLayer *view_layer = DEG_get_input_view_layer(depsgraph);
+  BKE_view_layer_synced_ensure(scene, view_layer);
 
   FOREACH_COLLECTION_OBJECT_RECURSIVE_BEGIN (rbw->group, ob) {
     Base *base = BKE_view_layer_base_find(view_layer, ob);
diff --git a/source/blender/blenkernel/intern/scene.cc b/source/blender/blenkernel/intern/scene.cc
index 96be505d214..db950492f69 100644
--- a/source/blender/blenkernel/intern/scene.cc
+++ b/source/blender/blenkernel/intern/scene.cc
@@ -803,8 +803,8 @@ static void scene_foreach_id(ID *id, LibraryForeachIDData *data)
 
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
     BKE_LIB_FOREACHID_PROCESS_IDSUPER(data, view_layer->mat_override, IDWALK_CB_USER);
-
-    LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
+    LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
       BKE_LIB_FOREACHID_PROCESS_IDSUPER(
           data, base->object, IDWALK_CB_NOP | IDWALK_CB_OVERRIDE_LIBRARY_NOT_OVERRIDABLE);
     }
@@ -2050,7 +2050,8 @@ Scene *BKE_scene_add(Main *bmain, const char *name)
 bool BKE_scene_object_find(Scene *scene, Object *ob)
 {
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
-    if (BLI_findptr(&view_layer->object_bases, ob, offsetof(Base, object))) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
+    if (BLI_findptr(BKE_view_layer_object_bases_get(view_layer), ob, offsetof(Base, object))) {
       return true;
     }
   }
@@ -2060,7 +2061,8 @@ bool BKE_scene_object_find(Scene *scene, Object *ob)
 Object *BKE_scene_object_find_by_name(const Scene *scene, const char *name)
 {
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
-    LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
+    LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
       if (STREQ(base->object->id.name + 2, name)) {
         return base->object;
       }
@@ -2081,7 +2083,8 @@ void BKE_scene_set_background(Main *bmain, Scene *scene)
 
   /* copy layers and flags from bases to objects */
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
-    LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
+    LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
       /* collection patch... */
       BKE_scene_object_base_flag_sync_from_base(base);
     }
@@ -2124,7 +2127,8 @@ int BKE_scene_base_iter_next(
       if (iter->phase == F_START) {
         ViewLayer *view_layer = (depsgraph) ? DEG_get_evaluated_view_layer(depsgraph) :
                                               BKE_view_layer_context_active_PLACEHOLDER(*scene);
-        *base = static_cast<Base *>(view_layer->object_bases.first);
+        BKE_view_layer_synced_ensure(*scene, view_layer);
+        *base = static_cast<Base *>(BKE_view_layer_object_bases_get(view_layer)->first);
         if (*base) {
           *ob = (*base)->object;
           iter->phase = F_SCENE;
@@ -2134,8 +2138,10 @@ int BKE_scene_base_iter_next(
           while ((*scene)->set) {
             (*scene) = (*scene)->set;
             ViewLayer *view_layer_set = BKE_view_layer_default_render(*scene);
-            if (view_layer_set->object_bases.first) {
-              *base = static_cast<Base *>(view_layer_set->object_bases.first);
+            BKE_view_layer_synced_ensure(*scene, view_layer_set);
+            ListBase *object_bases = BKE_view_layer_object_bases_get(view_layer_set);
+            if (object_bases->first) {
+              *base = static_cast<Base *>(object_bases->first);
               *ob = (*base)->object;
               iter->phase = F_SCENE;
               break;
@@ -2155,8 +2161,10 @@ int BKE_scene_base_iter_next(
               while ((*scene)->set) {
                 (*scene) = (*scene)->set;
                 ViewLayer *view_layer_set = BKE_view_layer_default_render(*scene);
-                if (view_layer_set->object_bases.first) {
-                  *base = static_cast<Base *>(view_layer_set->object_bases.first);
+                BKE_view_layer_synced_ensure(*scene, view_layer_set);
+                ListBase *object_bases = BKE_view_layer_object_bases_get(view_layer_set);
+                if (object_bases->first) {
+                  *base = static_cast<Base *>(object_bases->first);
                   *ob = (*base)->object;
                   break;
                 }
@@ -2505,7 +2513,9 @@ static bool check_rendered_viewport_visible(Main *bmain)
 
 /* TODO(@campbellbarton): shouldn't we be able to use 'DEG_get_view_layer' here?
  * Currently this is nullptr on load, so don't. */
-static void prepare_mesh_for_viewport_render(Main *bmain, const ViewLayer *view_layer)
+static void prepare_mesh_for_viewport_render(Main *bmain,
+                                             const Scene *scene,
+                                             ViewLayer *view_layer)
 {
   /* This is needed to prepare mesh to be used by the render
    * engine from the viewport rendering. We do loading here
@@ -2515,7 +2525,7 @@ static void prepare_mesh_for_viewport_render(Main *bmain, const ViewLayer *view_
    * This makes it so viewport render engine doesn't need to
    * call loading of the edit data for the mesh objects.
    */
-
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Object *obedit = BKE_view_layer_edit_object_get(view_layer);
   if (obedit) {
     Mesh *mesh = static_cast<Mesh *>(obedit->data);
@@ -2592,7 +2602,7 @@ static void scene_graph_update_tagged(Depsgraph *depsgraph, Main *bmain, bool on
     /* Uncomment this to check if graph was properly tagged for update. */
     // DEG_debug_graph_relations_validate(depsgraph, bmain, scene);
     /* Flush editing data if needed. */
-    prepare_mesh_for_viewport_render(bmain, view_layer);
+    prepare_mesh_for_viewport_render(bmain, scene, view_layer);
     /* Update all objects: drivers, matrices, etc. flags set
      * by depsgraph or manual, no layer check here, gets correct flushed. */
     DEG_evaluate_on_refresh(depsgraph);
@@ -2810,8 +2820,10 @@ Base *_setlooper_base_step(Scene **sce_iter, ViewLayer *view_layer, Base *base)
   if ((base == nullptr) && (view_layer != nullptr)) {
     /* First time looping, return the scenes first base. */
     /* For the first loop we should get the layer from workspace when available. */
-    if (view_layer->object_bases.first) {
-      return (Base *)view_layer->object_bases.first;
+    BKE_view_layer_synced_ensure(*sce_iter, view_layer);
+    ListBase *object_bases = BKE_view_layer_object_bases_get(view_layer);
+    if (object_bases->first) {
+      return static_cast<Base *>(object_bases->first);
     }
     /* No base on this scene layer. */
     goto next_set;
@@ -2821,7 +2833,7 @@ Base *_setlooper_base_step(Scene **sce_iter, ViewLayer *view_layer, Base *base)
     /* Reached the end, get the next base in the set. */
     while ((*sce_iter = (*sce_iter)->set)) {
       ViewLayer *view_layer_set = BKE_view_layer_default_render(*sce_iter);
-      base = (Base *)view_layer_set->object_bases.first;
+      base = (Base *)BKE_view_layer_object_bases_get(view_layer_set)->first;
 
       if (base) {
         return base;
@@ -2880,13 +2892,11 @@ bool BKE_scene_uses_cycles_experimental_features(Scene *scene)
   return RNA_enum_get(&cycles_ptr, "feature_set") == CYCLES_FEATURES_EXPERIMENTAL;
 }
 
-void BKE_scene_base_flag_to_objects(const Scene *UNUSED(scene), ViewLayer *view_layer)
+void BKE_scene_base_flag_to_objects(const Scene *scene, ViewLayer *view_layer)
 {
-  Base *base = static_cast<Base *>(view_layer->object_bases.first);
-
-  while (base) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     BKE_scene_object_base_flag_sync_from_base(base);
-    base = base->next;
   }
 }