intern/cycles/bvh/bvh2.h

@@ -12,6 +12,8 @@
 #include "util/vector.h"
 #include "util/thread.h"
 
+#include <atomic>
+
 CCL_NAMESPACE_BEGIN
 
 #define BVH_NODE_SIZE 4
@@ -37,6 +39,7 @@ class BVH2 : public BVH {
      are used to ensure that it the case.       */
   thread_mutex build_mutex;
   thread_condition_variable build_cv;
+  std::atomic<int> building{0};
   
   void build(Progress &progress, Stats *stats);
   void refit(Progress &progress);

intern/cycles/device/device.cpp

@@ -51,22 +51,25 @@ void Device::build_bvh(BVH *bvh, DeviceScene *dscene, Progress &progress, bool r
 {
   assert(bvh->params.bvh_layout == BVH_LAYOUT_BVH2);
   BVH2 *const bvh2 = static_cast<BVH2 *>(bvh);
-  static std::atomic<int> building{0};
   /* Top level BVH2 build must wait on all other BVH2 builds to finish
      otherwise the top level BVH2 will not have all the correct data
    */
   if(bvh2->params.top_level) {
+    /*
+      This is used to make sure all workers have reached this point.
+      device_init_update_bvh increments the counter.
+     */
+    bvh2->building--;
     thread_scoped_lock build_wait_lock(bvh2->build_mutex);
     /* Wait for other BVH2 builds to complete before proceeding */
     VLOG_INFO << std::this_thread::get_id() << ":" << bvh2 << " Waiting on other BVH2 builds.";
-    bvh2->build_cv.wait(build_wait_lock, [=]() { return (building == 0); });
+    bvh2->build_cv.wait(build_wait_lock, [=]() { return (bvh2->building == 0); });
     VLOG_INFO << std::this_thread::get_id() << ":" << bvh2 << " Done waiting on other BVH2 builds";
   }
   thread_scoped_lock build_lock(bvh2->build_mutex, std::try_to_lock);
   if (build_lock) {
     /* Has the BVH already been built? */
     if (!bvh->built) {
-      building++;
       /* Build the BVH */
       VLOG_INFO << std::this_thread::get_id() << ":" << bvh2 << " Performing BVH2 build.";
       if (refit) {
@@ -77,7 +80,6 @@ void Device::build_bvh(BVH *bvh, DeviceScene *dscene, Progress &progress, bool r
       }
       bvh->built = true;
       VLOG_INFO << std::this_thread::get_id() << ":" << bvh2 << " Done building BVH2";
-      building--;
     }
     else {
       VLOG_INFO << std::this_thread::get_id() << ":" << bvh2 << " BVH2 Already built";

intern/cycles/scene/geometry.cpp

@@ -798,7 +798,7 @@ void GeometryManager::device_data_xfer_and_bvh_update(int idx,
   }
 
   sub_dscene->device_scene_clear_modified();
-
+  device_init_update_bvh(scene);
   {
     scoped_callback_timer timer([scene, idx](double time) {
       if (scene->update_stats) {

intern/cycles/scene/geometry.h

@@ -331,6 +331,7 @@ class GeometryManager {
                                     DeviceScene *dscene,
                                     Scene *scene,
                                     Progress &progress);
+  void device_init_update_bvh(Scene *scene);
   void device_update_bvh(Device *device,
                          DeviceScene *dscene,
                          Scene *scene,

intern/cycles/scene/geometry_bvh.cpp

@@ -32,6 +32,15 @@
 
 CCL_NAMESPACE_BEGIN
 
+void GeometryManager::device_init_update_bvh(Scene *scene)
+{
+  if (scene->bvh->params.bvh_layout == BVH_LAYOUT_BVH2) {
+    /* To ensure that only 1 BVH2 scene is built a count of workers is used */
+    BVH2 *const bvh2 = static_cast<BVH2 *>(scene->bvh);
+    bvh2->building++;
+  }
+}
+
 void GeometryManager::device_update_bvh(Device *device,
                                         DeviceScene *dscene,
                                         Scene *scene,