bpo-26434: Fix multiprocessing grandchilds in a Windows service (GH-1167

)

Patch by Davin with help from Marc.

Lib/multiprocessing/forking.py

@@ -405,7 +405,8 @@ def get_preparation_data(name):
         if _logger is not None:
             d['log_level'] = _logger.getEffectiveLevel()
 
-        if not WINEXE and not WINSERVICE:
+        if not WINEXE and not WINSERVICE and \
+           not d['sys_argv'][0].lower().endswith('pythonservice.exe'):
             main_path = getattr(sys.modules['__main__'], '__file__', None)
             if not main_path and sys.argv[0] not in ('', '-c'):
                 main_path = sys.argv[0]