Roland Schwarz wrote:
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.
No, there is none. He just followed pthread_once without realizing (at first) that he won't be able to use it directly on all platforms.
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.
Not superfluously. pthread_once accepts an extern "C" function. Test on a platform where extern "C" functions are incompatible with extern "C++" functions (Comeau C++) and you'll see why the second call is needed. Incidentally, that second call also enables arbitrary function objects in addition to ordinary C++ functions. :-)