[Bf-blender-cvs] [abbc43e4e41] master: Fix T84397: Creating and removing many objects very quickly causes a crash

[Sergey Sharybin]

Commit: abbc43e4e419c44e6d0134aec051d543a0944b3e
Author: Sergey Sharybin
Date:   Tue Jan 12 17:12:27 2021 +0100
Branches: master
https://developer.blender.org/rBabbc43e4e419c44e6d0134aec051d543a0944b3e

Fix T84397: Creating and removing many objects very quickly causes a crash

The root of the issue was caused by the dependency graph using ID pointer
to map evaluated state from old depsgraph to new one upon relations update.
This was failing when IDs were re-allocated rapidly: was possible that
Object ID's evaluated state assigned to Mesh and vice versa.

Now depsgraph uses Session UUID to identify which IDs to restore evaluated
state to. The session UUID is stored in the IDNode, so that id_orig is not
dereferenced on depsgraph update since the ID might be freed.

The root of the issue is identified by Campbell, original patch was done
by Bastien, thanks! Also thanks to Oliver and Ray and everyone else for
testing!

===================================================================

M	source/blender/depsgraph/intern/builder/deg_builder_nodes.cc
M	source/blender/depsgraph/intern/builder/deg_builder_nodes.h
M	source/blender/depsgraph/intern/node/deg_node_id.cc
M	source/blender/depsgraph/intern/node/deg_node_id.h

===================================================================

diff --git a/source/blender/depsgraph/intern/builder/deg_builder_nodes.cc b/source/blender/depsgraph/intern/builder/deg_builder_nodes.cc
index eb20dfb69a2..dcdf2f48607 100644
--- a/source/blender/depsgraph/intern/builder/deg_builder_nodes.cc
+++ b/source/blender/depsgraph/intern/builder/deg_builder_nodes.cc
@@ -83,6 +83,7 @@
 #include "BKE_key.h"
 #include "BKE_lattice.h"
 #include "BKE_layer.h"
+#include "BKE_lib_id.h"
 #include "BKE_light.h"
 #include "BKE_mask.h"
 #include "BKE_material.h"
@@ -152,12 +153,14 @@ DepsgraphNodeBuilder::~DepsgraphNodeBuilder()
 
 IDNode *DepsgraphNodeBuilder::add_id_node(ID *id)
 {
+  BLI_assert(id->session_uuid != MAIN_ID_SESSION_UUID_UNSET);
+
   IDNode *id_node = nullptr;
   ID *id_cow = nullptr;
   IDComponentsMask previously_visible_components_mask = 0;
   uint32_t previous_eval_flags = 0;
   DEGCustomDataMeshMasks previous_customdata_masks;
-  IDInfo *id_info = id_info_hash_.lookup_default(id, nullptr);
+  IDInfo *id_info = id_info_hash_.lookup_default(id->session_uuid, nullptr);
   if (id_info != nullptr) {
     id_cow = id_info->id_cow;
     previously_visible_components_mask = id_info->previously_visible_components_mask;
@@ -334,7 +337,8 @@ void DepsgraphNodeBuilder::begin_build()
     id_info->previously_visible_components_mask = id_node->visible_components_mask;
     id_info->previous_eval_flags = id_node->eval_flags;
     id_info->previous_customdata_masks = id_node->customdata_masks;
-    id_info_hash_.add_new(id_node->id_orig, id_info);
+    BLI_assert(!id_info_hash_.contains(id_node->id_orig_session_uuid));
+    id_info_hash_.add_new(id_node->id_orig_session_uuid, id_info);
     id_node->id_cow = nullptr;
   }
 
diff --git a/source/blender/depsgraph/intern/builder/deg_builder_nodes.h b/source/blender/depsgraph/intern/builder/deg_builder_nodes.h
index 6f7a8b1c6b5..174f9b129f9 100644
--- a/source/blender/depsgraph/intern/builder/deg_builder_nodes.h
+++ b/source/blender/depsgraph/intern/builder/deg_builder_nodes.h
@@ -285,8 +285,8 @@ class DepsgraphNodeBuilder : public DepsgraphBuilder {
    * very root is visible (aka not restricted.). */
   bool is_parent_collection_visible_;
 
-  /* Indexed by original ID, values are IDInfo. */
-  Map<const ID *, IDInfo *> id_info_hash_;
+  /* Indexed by original ID.session_uuid, values are IDInfo. */
+  Map<uint, IDInfo *> id_info_hash_;
 
   /* Set of IDs which were already build. Makes it easier to keep track of
    * what was already built and what was not. */
diff --git a/source/blender/depsgraph/intern/node/deg_node_id.cc b/source/blender/depsgraph/intern/node/deg_node_id.cc
index 4f2fcab5823..8e159a7ff08 100644
--- a/source/blender/depsgraph/intern/node/deg_node_id.cc
+++ b/source/blender/depsgraph/intern/node/deg_node_id.cc
@@ -80,6 +80,7 @@ void IDNode::init(const ID *id, const char *UNUSED(subdata))
   /* Store ID-pointer. */
   id_type = GS(id->name);
   id_orig = (ID *)id;
+  id_orig_session_uuid = id->session_uuid;
   eval_flags = 0;
   previous_eval_flags = 0;
   customdata_masks = DEGCustomDataMeshMasks();
diff --git a/source/blender/depsgraph/intern/node/deg_node_id.h b/source/blender/depsgraph/intern/node/deg_node_id.h
index 04a9006ac10..c4d36685bb8 100644
--- a/source/blender/depsgraph/intern/node/deg_node_id.h
+++ b/source/blender/depsgraph/intern/node/deg_node_id.h
@@ -74,12 +74,22 @@ struct IDNode : public Node {
 
   IDComponentsMask get_visible_components_mask() const;
 
-  /* ID Block referenced. */
   /* Type of the ID stored separately, so it's possible to perform check whether CoW is needed
    * without de-referencing the id_cow (which is not safe when ID is NOT covered by CoW and has
    * been deleted from the main database.) */
   ID_Type id_type;
+
+  /* ID Block referenced. */
   ID *id_orig;
+
+  /* Session-wide UUID of the id_orig.
+   * Is used on relations update to map evaluated state from old nodes to the new ones, without
+   * relying on pointers (which are not guaranteed to be unique) and without dereferencing id_orig
+   * which could be "stale" pointer. */
+  uint id_orig_session_uuid;
+
+  /* Evaluated datablock.
+   * Will be covered by the copy-on-write system if the ID Type needs it. */
   ID *id_cow;
 
   /* Hash to make it faster to look up components. */