Correction to early output in the parallel range implementation

The used heuristic of checking the value prior to lock is not totally safe
because assignment is not atomic and check might not give proper result.

1 files changed, 6 insertions, 8 deletions

diff --git a/source/blender/blenlib/intern/task.c b/source/blender/blenlib/intern/task.c
index f442a6219a5..08d40a158ca 100644
--- a/source/blender/blenlib/intern/task.c
+++ b/source/blender/blenlib/intern/task.c
@@ -508,16 +508,14 @@ BLI_INLINE bool parallel_range_next_iter_get(
         int * __restrict iter, int * __restrict count)
 {
 	bool result = false;
+	BLI_spin_lock(&state->lock);
 	if (state->iter < state->stop) {
-		BLI_spin_lock(&state->lock);
-		if (state->iter < state->stop) {
-			*count = min_ii(state->chunk_size, state->stop - state->iter);
-			*iter = state->iter;
-			state->iter += *count;
-			result = true;
-		}
-		BLI_spin_unlock(&state->lock);
+		*count = min_ii(state->chunk_size, state->stop - state->iter);
+		*iter = state->iter;
+		state->iter += *count;
+		result = true;
 	}
+	BLI_spin_unlock(&state->lock);
 	return result;
 }