Fix T102292: deadlock in geometry nodes evaluation with task isolation

As described in the comment on `BLI_task_isolate`, deadlocks can happen
when isolation is used with threading primitives that separate spawning tasks
from executing them. All threads are waiting the tasks to complete but no
thread is able to continue working due to task isolation.

The fix is to not pass lazy-threading hints through task isolations. This way
isolated regions can't create new tasks in a scheduler further up the call stack.
This may lead to minor slowdowns because less threading may be used.
It's generally possible to get rid of the slowdown again by sending the
lazy-threading hint before entering the isolated region.

1 files changed, 2 insertions, 0 deletions

diff --git a/source/blender/blenlib/intern/task_scheduler.cc b/source/blender/blenlib/intern/task_scheduler.cc
index 1f7747453c1..5b056df78b4 100644
--- a/source/blender/blenlib/intern/task_scheduler.cc
+++ b/source/blender/blenlib/intern/task_scheduler.cc
@@ -8,6 +8,7 @@
 
 #include "MEM_guardedalloc.h"
 
+#include "BLI_lazy_threading.hh"
 #include "BLI_task.h"
 #include "BLI_threads.h"
 
@@ -67,6 +68,7 @@ int BLI_task_scheduler_num_threads()
 void BLI_task_isolate(void (*func)(void *userdata), void *userdata)
 {
 #ifdef WITH_TBB
+  blender::lazy_threading::ReceiverIsolation isolation;
   tbb::this_task_arena::isolate([&] { func(userdata); });
 #else
   func(userdata);