Cycles: fix multithreading issue introduced in previous commit

The issue is that the shaders are stolen from the original Geometry by
the temporary Geometry used to accumulate data, but the main thread
still needs them for syncing the attributes.

So make a copy of the shader array to preserve the data on the original
Geometry.

2 files changed, 10 insertions, 2 deletions

diff --git a/intern/cycles/blender/blender_curves.cpp b/intern/cycles/blender/blender_curves.cpp
index b27de2081ae..9070c093492 100644
--- a/intern/cycles/blender/blender_curves.cpp
+++ b/intern/cycles/blender/blender_curves.cpp
@@ -819,8 +819,12 @@ void BlenderSync::sync_hair(Hair *hair, BL::Object &b_ob, bool motion, int motio
 
 void BlenderSync::sync_hair(BL::Depsgraph b_depsgraph, BL::Object b_ob, Hair *hair)
 {
+  /* make a copy of the shaders as the caller in the main thread still need them for syncing the
+   * attributes */
+  array<Node *> used_shaders = hair->get_used_shaders();
+
   Hair new_hair;
-  new_hair.set_used_shaders(hair->get_used_shaders());
+  new_hair.set_used_shaders(used_shaders);
 
   if (view_layer.use_hair) {
     if (b_ob.type() == BL::Object::type_HAIR) {
diff --git a/intern/cycles/blender/blender_mesh.cpp b/intern/cycles/blender/blender_mesh.cpp
index 079e087ffb6..d84433ecd27 100644
--- a/intern/cycles/blender/blender_mesh.cpp
+++ b/intern/cycles/blender/blender_mesh.cpp
@@ -1019,8 +1019,12 @@ static void sync_mesh_fluid_motion(BL::Object &b_ob, Scene *scene, Mesh *mesh)
 
 void BlenderSync::sync_mesh(BL::Depsgraph b_depsgraph, BL::Object b_ob, Mesh *mesh)
 {
+  /* make a copy of the shaders as the caller in the main thread still need them for syncing the
+   * attributes */
+  array<Node *> used_shaders = mesh->get_used_shaders();
+
   Mesh new_mesh;
-  new_mesh.set_used_shaders(mesh->get_used_shaders());
+  new_mesh.set_used_shaders(used_shaders);
 
   if (view_layer.use_surfaces) {
     /* Adaptive subdivision setup. Not for baking since that requires