Anthony Williams wrote:
"Peter Dimov" <pdimov@mmltd.net> writes:
There is a note in N2178 that shows how to implement call_once on top of pthread_once2_np. ;-)
I know that it's possible, just "much harder": ...
You haven't even looked at it, have you. :-/ [Note: a typical implementation of call_once is shown below: template< class F > void __call_once_helper( void * pv ) { F * pf = static_cast< F * >( pv ); (*pf)(); } template< class F > void call_once( pthread_once_t & once_control, F f ) { pthread_once2_np( &once_control, &__call_once_helper<F>, &f ); } --end note.]
Since on Windows the code for call_once is pretty much the same whether or not init_routine takes arguments, it seems pointless to go round the houses setting thread-specific data just for the benefit of writing call_once in terms of pthread_once rather than vice versa.
That is why there is pthread_once2_np in N2178. The actual call_once code is pretty much the same on POSIX as well, and it is equally pointless to use TLS there. So I tried to fix both.