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, write to the Free
16 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
17 02111-1307 USA. */
18
19 #include "pthreadP.h"
20 #include <lowlevellock.h>
21
22 unsigned long int __fork_generation attribute_hidden;
23
24 static void
clear_once_control(void * arg)25 clear_once_control (void *arg)
26 {
27 pthread_once_t *once_control = (pthread_once_t *) arg;
28
29 *once_control = 0;
30 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
31 }
32
33 int
34 attribute_protected
__pthread_once(pthread_once_t * once_control,void (* init_routine)(void))35 __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
36 {
37 for (;;)
38 {
39 int oldval;
40 int newval;
41
42 /* Pseudo code:
43 newval = __fork_generation | 1;
44 oldval = *once_control;
45 if ((oldval & 2) == 0)
46 *once_control = newval;
47 Do this atomically.
48 */
49 do
50 {
51 newval = __fork_generation | 1;
52 oldval = *once_control;
53 if (oldval & 2)
54 break;
55 } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval);
56
57 /* Check if the initializer has already been done. */
58 if ((oldval & 2) != 0)
59 return 0;
60
61 /* Check if another thread already runs the initializer. */
62 if ((oldval & 1) == 0)
63 break;
64
65 /* Check whether the initializer execution was interrupted by a fork. */
66 if (oldval != newval)
67 break;
68
69 /* Same generation, some other thread was faster. Wait. */
70 lll_futex_wait (once_control, oldval, LLL_PRIVATE);
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 /* Say that the initialisation is done. */
83 *once_control = __fork_generation | 2;
84
85 /* Wake up all other threads. */
86 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
87
88 return 0;
89 }
90 weak_alias (__pthread_once, pthread_once)
91 strong_alias (__pthread_once, __pthread_once_internal)
92
93 #if defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__PIC__)
94 /* When statically linked, if pthread_create is used, this file
95 will be brought in. The exception handling code in GCC assumes
96 that if pthread_create is available, so are these. */
97 const void *include_pthread_getspecific attribute_hidden = pthread_getspecific;
98 const void *include_pthread_setspecific attribute_hidden = pthread_setspecific;
99 const void *include_pthread_key_create attribute_hidden = pthread_key_create;
100 #endif
101