Fix T76553: Blender Freezes When Playing Back Animation

In some cases blender could freeze. When threads are blocked (waiting for other tasks completion) the scheduler can let the thread perform a different task. If this task wants a write-lock for something that was read-locked in the stack a dead lock will happen.

For task pools every task is isolated. For range tasks the inner loop will be isolated. The implementation is limited as isolation in TBB uses functors which are tricky to add to a C API. We decided to start with a simple and adapt were we need to.

During testing we came to this setup as it was reliable (we weren't able to let it freeze or crash) and didn't had noticeable performance impact.

Reviewed By: Brecht van Lommel

Differential Revision: https://developer.blender.org/D7688

1 files changed, 8 insertions, 1 deletions

diff --git a/source/blender/modifiers/intern/MOD_remesh.c b/source/blender/modifiers/intern/MOD_remesh.c
index cdb513595a1..5a262adf47c 100644
--- a/source/blender/modifiers/intern/MOD_remesh.c
+++ b/source/blender/modifiers/intern/MOD_remesh.c
@@ -25,6 +25,7 @@
 #include "BLI_utildefines.h"
 
 #include "BLI_math_base.h"
+#include "BLI_threads.h"
 
 #include "DNA_mesh_types.h"
 #include "DNA_meshdata_types.h"
@@ -177,7 +178,11 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *UNUSED(ctx)
         BLI_assert(false);
         break;
     }
-
+    /* TODO(jbakker): Dualcon crashes when run in parallel. Could be related to incorrect
+     * input data or that the library isn't thread safe. This was identified when changing the task
+     * isolations during T76553. */
+    static ThreadMutex dualcon_mutex = BLI_MUTEX_INITIALIZER;
+    BLI_mutex_lock(&dualcon_mutex);
     output = dualcon(&input,
                      dualcon_alloc_output,
                      dualcon_add_vert,
@@ -188,6 +193,8 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *UNUSED(ctx)
                      rmd->hermite_num,
                      rmd->scale,
                      rmd->depth);
+    BLI_mutex_unlock(&dualcon_mutex);
+
     result = output->mesh;
     MEM_freeN(output);
   }