1 /* Copyright (C) 2004, 2005 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
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 unsigned long int __fork_generation attribute_hidden;
22
23 static void
clear_once_control(void * arg)24 clear_once_control (void *arg)
25 {
26 pthread_once_t *once_control = (pthread_once_t *) arg;
27
28 *once_control = 0;
29 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
30 }
31
32 int
33 attribute_protected
__pthread_once(pthread_once_t * once_control,void (* init_routine)(void))34 __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
35 {
36 for (;;)
37 {
38 int oldval;
39 int newval;
40
41 /* Pseudo code:
42 newval = __fork_generation | 1;
43 oldval = *once_control;
44 if ((oldval & 2) == 0)
45 *once_control = newval;
46 Do this atomically.
47 */
48 do
49 {
50 newval = __fork_generation | 1;
51 oldval = *once_control;
52 if (oldval & 2)
53 break;
54 } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval);
55
56 /* Check if the initializer has already been done. */
57 if ((oldval & 2) != 0)
58 return 0;
59
60 /* Check if another thread already runs the initializer. */
61 if ((oldval & 1) == 0)
62 break;
63
64 /* Check whether the initializer execution was interrupted by a fork. */
65 if (oldval != newval)
66 break;
67
68 /* Same generation, some other thread was faster. Wait. */
69 lll_futex_wait (once_control, oldval, LLL_PRIVATE);
70 }
71
72 /* This thread is the first here. Do the initialization.
73 Register a cleanup handler so that in case the thread gets
74 interrupted the initialization can be restarted. */
75 pthread_cleanup_push (clear_once_control, once_control);
76
77 init_routine ();
78
79 pthread_cleanup_pop (0);
80
81 /* Say that the initialisation is done. */
82 *once_control = __fork_generation | 2;
83
84 /* Wake up all other threads. */
85 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
86
87 return 0;
88 }
89 weak_alias (__pthread_once, pthread_once)
90 strong_alias (__pthread_once, __pthread_once_internal)
91
92 #if defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__PIC__)
93 /* When statically linked, if pthread_create is used, this file
94 will be brought in. The exception handling code in GCC assumes
95 that if pthread_create is available, so are these. */
96 const void *include_pthread_getspecific attribute_hidden = pthread_getspecific;
97 const void *include_pthread_setspecific attribute_hidden = pthread_setspecific;
98 const void *include_pthread_key_create attribute_hidden = pthread_key_create;
99 #endif
100