#ifndef BOOST_WIN32_ONCE_HPP
#define BOOST_WIN32_ONCE_HPP

//  once_atomic.hpp
//
//  (C) Copyright 2005 John Maddock 
//
//  Distributed under the Boost Software License, Version 1.0. (See
//  accompanying file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)

#include <windows.h>

namespace boost
{
    typedef LONG volatile once_flag;

#define BOOST_ONCE_INIT 0

namespace detail{
   enum{
      uninitialized = 0,
      initialized = 1,
      initializing = 2
   };

}

   template<typename Function>
   void call_once(Function f,once_flag& flag)
   {
      bool exit = false;
      do{
         switch(::InterlockedCompareExchange(&flag, detail::initializing, detail::uninitialized))
         {
         case detail::initialized:
            // most likely situation, someone has been here before:
            exit = true;
            break;
         case detail::uninitialized:
            // we must call the proceedure:
            try{
               f();
            }
            catch(...)
            {
               // failure, reset to uninitiatized and throw:
               ::InterlockedExchange(&flag, detail::uninitialized);
               throw;
            }
            // success!
            ::InterlockedExchange(&flag, detail::initialized);
            exit = true;
            break;
         case detail::initializing:
            // race condition:
            ::Sleep(0);
            break;
         }
      }while(!exit);
   }
}

#endif