gl/windows-once.c

   1 /* Once-only control (native Windows implementation).
   2    Copyright (C) 2005-2023 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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 Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser 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 }