1 /* Copyright (C) 2003-2013 Free Software Foundation, Inc.
2 Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library 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 GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <http://www.gnu.org/licenses/>. */
17
18 #include "pthreadP.h"
19 #include <lowlevellock.h>
20
21
22 unsigned long int __fork_generation attribute_hidden;
23
24
25 static void
clear_once_control(void * arg)26 clear_once_control (void *arg)
27 {
28 pthread_once_t *once_control = (pthread_once_t *) arg;
29
30 *once_control = 0;
31 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
32 }
33
34
35 int
__pthread_once(once_control,init_routine)36 __pthread_once (once_control, init_routine)
37 pthread_once_t *once_control;
38 void (*init_routine) (void);
39 {
40 while (1)
41 {
42 int oldval, val, newval;
43
44 val = *once_control;
45 do
46 {
47 /* Check if the initialized has already been done. */
48 if ((val & 2) != 0)
49 return 0;
50
51 oldval = val;
52 newval = (oldval & 3) | __fork_generation | 1;
53 val = atomic_compare_and_exchange_val_acq (once_control, newval,
54 oldval);
55 }
56 while (__builtin_expect (val != oldval, 0));
57
58 /* Check if another thread already runs the initializer. */
59 if ((oldval & 1) != 0)
60 {
61 /* Check whether the initializer execution was interrupted
62 by a fork. */
63 if (((oldval ^ newval) & -4) == 0)
64 {
65 /* Same generation, some other thread was faster. Wait. */
66 lll_futex_wait (once_control, newval, LLL_PRIVATE);
67 continue;
68 }
69 }
70
71 /* This thread is the first here. Do the initialization.
72 Register a cleanup handler so that in case the thread gets
73 interrupted the initialization can be restarted. */
74 pthread_cleanup_push (clear_once_control, once_control);
75
76 init_routine ();
77
78 pthread_cleanup_pop (0);
79
80
81 /* Add one to *once_control. */
82 atomic_increment (once_control);
83
84 /* Wake up all other threads. */
85 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
86 break;
87 }
88
89 return 0;
90 }
91 weak_alias (__pthread_once, pthread_once)
92 strong_alias (__pthread_once, __pthread_once_internal)
93