Fix T82607: crash cancelling Cycles render during adaptive subdivision update

Now that the Blender sync mechanism deletes nodes from the scene, we need to
ensure scene update is stopped before we do this.

Also add some more early out in scene geometry update to ensure we do not
continue working on incomplete geometry data, though that was not the cause of
this crash.

intern/cycles/blender/blender_session.cpp

@@ -260,6 +260,8 @@ void BlenderSession::reset_session(BL::BlendData &b_data, BL::Depsgraph &b_depsg
 
 void BlenderSession::free_session()
 {
+  session->cancel();
+
   delete sync;
   delete session;
 }

intern/cycles/render/geometry.cpp

@@ -1275,12 +1275,17 @@ void GeometryManager::device_update(Device *device,
           true_displacement_used = true;
         }
 
-        if (progress.get_cancel())
+        if (progress.get_cancel()) {
           return;
+        }
       }
     }
   }
 
+  if (progress.get_cancel()) {
+    return;
+  }
+
   /* Tessellate meshes that are using subdivision */
   if (total_tess_needed) {
     scoped_callback_timer timer([scene](double time) {
@@ -1317,10 +1322,15 @@ void GeometryManager::device_update(Device *device,
 
         i++;
 
-        if (progress.get_cancel())
+        if (progress.get_cancel()) {
           return;
+        }
       }
     }
+
+    if (progress.get_cancel()) {
+      return;
+    }
   }
 
   /* Update images needed for true displacement. */
@@ -1350,8 +1360,9 @@ void GeometryManager::device_update(Device *device,
     });
     device_update_mesh(device, dscene, scene, true, progress);
   }
-  if (progress.get_cancel())
+  if (progress.get_cancel()) {
     return;
+  }
 
   {
     scoped_callback_timer timer([scene](double time) {
@@ -1360,8 +1371,9 @@ void GeometryManager::device_update(Device *device,
       }
     });
     device_update_attributes(device, dscene, scene, progress);
-    if (progress.get_cancel())
+    if (progress.get_cancel()) {
       return;
+    }
   }
 
   /* Update displacement. */
@@ -1391,11 +1403,16 @@ void GeometryManager::device_update(Device *device,
         }
       }
 
-      if (progress.get_cancel())
+      if (progress.get_cancel()) {
         return;
+      }
     }
   }
 
+  if (progress.get_cancel()) {
+    return;
+  }
+
   /* Device re-update after displacement. */
   if (displacement_done) {
     scoped_callback_timer timer([scene](double time) {
@@ -1407,8 +1424,9 @@ void GeometryManager::device_update(Device *device,
     device_free(device, dscene);
 
     device_update_attributes(device, dscene, scene, progress);
-    if (progress.get_cancel())
+    if (progress.get_cancel()) {
       return;
+    }
   }
 
   {
@@ -1455,8 +1473,9 @@ void GeometryManager::device_update(Device *device,
     }
   }
 
-  if (progress.get_cancel())
+  if (progress.get_cancel()) {
     return;
+  }
 
   {
     scoped_callback_timer timer([scene](double time) {
@@ -1465,8 +1484,9 @@ void GeometryManager::device_update(Device *device,
       }
     });
     device_update_bvh(device, dscene, scene, progress);
-    if (progress.get_cancel())
+    if (progress.get_cancel()) {
       return;
+    }
   }
 
   {
@@ -1477,8 +1497,9 @@ void GeometryManager::device_update(Device *device,
       }
     });
     device_update_mesh(device, dscene, scene, false, progress);
-    if (progress.get_cancel())
+    if (progress.get_cancel()) {
       return;
+    }
   }
 
   need_update = false;

intern/cycles/render/session.cpp

@@ -94,21 +94,7 @@ Session::Session(const SessionParams &params_)
 
 Session::~Session()
 {
-  if (session_thread) {
-    /* wait for session thread to end */
-    progress.set_cancel("Exiting");
-
-    gpu_need_display_buffer_update = false;
-    gpu_need_display_buffer_update_cond.notify_all();
-
-    {
-      thread_scoped_lock pause_lock(pause_mutex);
-      pause = false;
-    }
-    pause_cond.notify_all();
-
-    wait();
-  }
+  cancel();
 
   if (params.write_render_cb) {
     /* Copy to display buffer and write out image if requested */
@@ -142,6 +128,25 @@ void Session::start()
   }
 }
 
+void Session::cancel()
+{
+  if (session_thread) {
+    /* wait for session thread to end */
+    progress.set_cancel("Exiting");
+
+    gpu_need_display_buffer_update = false;
+    gpu_need_display_buffer_update_cond.notify_all();
+
+    {
+      thread_scoped_lock pause_lock(pause_mutex);
+      pause = false;
+    }
+    pause_cond.notify_all();
+
+    wait();
+  }
+}
+
 bool Session::ready_to_reset()
 {
   double dt = time_dt() - reset_time;

intern/cycles/render/session.h

@@ -146,6 +146,7 @@ class Session {
   ~Session();
 
   void start();
+  void cancel();
   bool draw(BufferParams &params, DeviceDrawParams &draw_params);
   void wait();