1 /* Once-only control (native Windows implementation).
2    Copyright (C) 2005-2020 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
glwthread_once(glwthread_once_t * once_control,void (* initfunction)(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 }
63