1 /* Copyright (C) 2003, 2004, 2007 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19 #include "pthreadP.h"
20 #include <lowlevellock.h>
21
22
23 unsigned long int __fork_generation attribute_hidden;
24
25
26 static void
clear_once_control(void * arg)27 clear_once_control (void *arg)
28 {
29 pthread_once_t *once_control = (pthread_once_t *) arg;
30
31 *once_control = 0;
32 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
33 }
34
35
36 int
37 attribute_protected
__pthread_once(once_control,init_routine)38 __pthread_once (once_control, init_routine)
39 pthread_once_t *once_control;
40 void (*init_routine) (void);
41 {
42 while (1)
43 {
44 int oldval, val, newval;
45
46 val = *once_control;
47 do
48 {
49 /* Check if the initialized has already been done. */
50 if ((val & 2) != 0)
51 return 0;
52
53 oldval = val;
54 newval = (oldval & 3) | __fork_generation | 1;
55 val = atomic_compare_and_exchange_val_acq (once_control, newval,
56 oldval);
57 }
58 while (__builtin_expect (val != oldval, 0));
59
60 /* Check if another thread already runs the initializer. */
61 if ((oldval & 1) != 0)
62 {
63 /* Check whether the initializer execution was interrupted
64 by a fork. */
65 if (((oldval ^ newval) & -4) == 0)
66 {
67 /* Same generation, some other thread was faster. Wait. */
68 lll_futex_wait (once_control, newval, LLL_PRIVATE);
69 continue;
70 }
71 }
72
73 /* This thread is the first here. Do the initialization.
74 Register a cleanup handler so that in case the thread gets
75 interrupted the initialization can be restarted. */
76 pthread_cleanup_push (clear_once_control, once_control);
77
78 init_routine ();
79
80 pthread_cleanup_pop (0);
81
82
83 /* Add one to *once_control. */
84 atomic_increment (once_control);
85
86 /* Wake up all other threads. */
87 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
88 break;
89 }
90
91 return 0;
92 }
93 weak_alias (__pthread_once, pthread_once)
94 strong_alias (__pthread_once, __pthread_once_internal)
95