move execution_queue in butils, cleanup

butils.py

@@ -1,5 +1,6 @@
 import bpy
 import mathutils
+import queue
 import importlib
 
 # then import dependencies for our addon
@@ -13,6 +14,19 @@ if "utils" in locals():
 else:
     from .common import utils
 
+execution_queue = queue.Queue()
+
+# This function can safely be called in another thread.
+# The function will be executed when the timer runs the next time.
+def run_in_main_thread(function):
+    execution_queue.put(function)
+
+def execute_queued_functions():
+    while not execution_queue.empty():
+        function = execution_queue.get()
+        function()
+    return 1.0
+
 def apply_all_transforms(obj):
     mb = obj.matrix_basis
     if hasattr(obj.data, "transform"):