/* Once-only control (native Windows implementation).

   Copyright (C) 2005-2020 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3, or (at your option)

   any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program; if not, see <https://www.gnu.org/licenses/>.  */

/* Written by Bruno Haible <bruno@clisp.org>, 2005.

   Based on GCC's gthr-win32.h.  */

#include <config.h>

/* Specification.  */

#include "windows-once.h"

#include <stdlib.h>

void

glwthread_once (glwthread_once_t *once_control, void (*initfunction) (void))

{

  if (once_control->inited <= 0)

    {

      if (InterlockedIncrement (&once_control->started) == 0)

        {

          /* This thread is the first one to come to this once_control.  */

          InitializeCriticalSection (&once_control->lock);

          EnterCriticalSection (&once_control->lock);

          once_control->inited = 0;

          initfunction ();

          once_control->inited = 1;

          LeaveCriticalSection (&once_control->lock);

        }

      else

        {

          /* Don't let once_control->started grow and wrap around.  */

          InterlockedDecrement (&once_control->started);

          /* Some other thread has already started the initialization.

             Yield the CPU while waiting for the other thread to finish

             initializing and taking the lock.  */

          while (once_control->inited < 0)

            Sleep (0);

          if (once_control->inited <= 0)

            {

              /* Take the lock.  This blocks until the other thread has

                 finished calling the initfunction.  */

              EnterCriticalSection (&once_control->lock);

              LeaveCriticalSection (&once_control->lock);

              if (!(once_control->inited > 0))

                abort ();

            }

        }

    }

}