В примере кода

void foo()
{
  static Bar b;
  ...
}

составлено сGCC это гарантировано, чтоb будет создан и инициализирован потокобезопасным способом?

В справочной странице gcc нашел-fno-threadsafe-statics опция командной строки:

Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn't need to be thread-safe.

Does it mean, that local statics are thread-safe by default with GCC ? So no reason to put explicit guarding e.g. with pthread_mutex_lock/unlock ?

How to write portable code - how to check if compiler will add its guards ? Or is it better to turn off this feature of GCC ?