1  /* Once-only control (native Windows implementation).
       2     Copyright (C) 2005-2021 Free Software Foundation, Inc.
       3  
       4     This program is free software; you can redistribute it and/or modify
       5     it under the terms of the GNU General Public License as published by
       6     the Free Software Foundation; either version 3, or (at your option)
       7     any later version.
       8  
       9     This program is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      12     GNU General Public License for more details.
      13  
      14     You should have received a copy of the GNU General Public License
      15     along with this program; if not, see <https://www.gnu.org/licenses/>.  */
      16  
      17  /* Written by Bruno Haible <bruno@clisp.org>, 2005.
      18     Based on GCC's gthr-win32.h.  */
      19  
      20  #include <config.h>
      21  
      22  /* Specification.  */
      23  #include "windows-once.h"
      24  
      25  #include <stdlib.h>
      26  
      27  void
      28  glwthread_once (glwthread_once_t *once_control, void (*initfunction) (void))
      29  {
      30    if (once_control->inited <= 0)
      31      {
      32        if (InterlockedIncrement (&once_control->started) == 0)
      33          {
      34            /* This thread is the first one to come to this once_control.  */
      35            InitializeCriticalSection (&once_control->lock);
      36            EnterCriticalSection (&once_control->lock);
      37            once_control->inited = 0;
      38            initfunction ();
      39            once_control->inited = 1;
      40            LeaveCriticalSection (&once_control->lock);
      41          }
      42        else
      43          {
      44            /* Don't let once_control->started grow and wrap around.  */
      45            InterlockedDecrement (&once_control->started);
      46            /* Some other thread has already started the initialization.
      47               Yield the CPU while waiting for the other thread to finish
      48               initializing and taking the lock.  */
      49            while (once_control->inited < 0)
      50              Sleep (0);
      51            if (once_control->inited <= 0)
      52              {
      53                /* Take the lock.  This blocks until the other thread has
      54                   finished calling the initfunction.  */
      55                EnterCriticalSection (&once_control->lock);
      56                LeaveCriticalSection (&once_control->lock);
      57                if (!(once_control->inited > 0))
      58                  abort ();
      59              }
      60          }
      61      }
      62  }