Anthony Williams wrote:
On Windows we don't need two calls to call_once, as my implementation allows passing an arbitrary functor, which can therefore have state (e.g. use bind to pass parameters).
Hmm, I remember there was a sound reason why Bill Kempf ommitted parameters deliberately. Not sure about this, I will need to try to find the respective discussion thread.
Your code demonstrates how we could provide the same facility with pthreads, as an extension to call_once. Incidentally, whilst we're thinking about this, the POSIX spec says:
Indeed I have shamelessly stolen the idea from looking at Bill Kempfs call_once implementation for pthreads. He is using this there also, altough I think, superfluously.
"The behavior of pthread_once() is undefined if once_control has automatic storage duration or is not initialized by PTHREAD_ONCE_INIT."
So we need to document this restriction on the use of boost::once_flag, unless you can find a way round it. This restriction doesn't apply on Windows, at least not with my implementation.
I suspect this is because you are relying on zero initialization, right? Roland