Re: Undefined ref to 'function<void ()()>::operator()() const' when called from free function defined in cc file.

["Peter Dimov" <pdimov at mmltd dot net>]

Chris Fairles wrote:

> extern function<void()> __once_proxy_object;
> extern unique_lock<mutex> __once_proxy_lock;
> extern "C" void __once_proxy();
>
> template<typename _Callable, typename... _Args>
>  void
>  call_once(once_flag& __once, _Callable __f, _Args&&... __args)
>  {
>    __once_proxy_lock.lock();
>    __once_proxy_object = bind(__f, __args...);
>
>    int __e = __gthread_once(&(__once._M_once), &__once_proxy);
>
>    if(__once_proxy_lock)
>      __once_proxy_lock.unlock();
>
>    if (__e)
>      __throw_system_error(__e);
>  }

Can you use thread locals?

extern __thread void* __once_callable;
extern __thread void (*__once_call)();
extern "C" void __once_proxy();

template<typename _Callable>
void __once_call_impl()
{
   (*(_Callable*)__once_calable)();
}

template<typename _Callable>
void call_once(once_flag& __once, _Callable __f)
{
   __once_callable = &__f;
   __once_call = &__once_call_impl<_Callable>;
   __gthread_once(&__once._M_once, &__once_proxy);
}

or something. :-)