1 /* Copyright (C) 2003, 2004, 2007 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Paul Mackerras <paulus@au.ibm.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(pthread_once_t * once_control,void (* init_routine)(void))38 __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
39 {
40 for (;;)
41 {
42 int oldval;
43 int newval;
44 int tmp;
45
46 /* Pseudo code:
47 newval = __fork_generation | 1;
48 oldval = *once_control;
49 if ((oldval & 2) == 0)
50 *once_control = newval;
51 Do this atomically.
52 */
53 newval = __fork_generation | 1;
54 __asm__ __volatile__ ("1: lwarx %0,0,%3\n"
55 " andi. %1,%0,2\n"
56 " bne 2f\n"
57 " stwcx. %4,0,%3\n"
58 " bne 1b\n"
59 "2: isync"
60 : "=&r" (oldval), "=&r" (tmp), "=m" (*once_control)
61 : "r" (once_control), "r" (newval), "m" (*once_control)
62 : "cr0");
63
64 /* Check if the initializer has already been done. */
65 if ((oldval & 2) != 0)
66 return 0;
67
68 /* Check if another thread already runs the initializer. */
69 if ((oldval & 1) == 0)
70 break;
71
72 /* Check whether the initializer execution was interrupted by a fork. */
73 if (oldval != newval)
74 break;
75
76 /* Same generation, some other thread was faster. Wait. */
77 lll_futex_wait (once_control, oldval, LLL_PRIVATE);
78 }
79
80
81 /* This thread is the first here. Do the initialization.
82 Register a cleanup handler so that in case the thread gets
83 interrupted the initialization can be restarted. */
84 pthread_cleanup_push (clear_once_control, once_control);
85
86 init_routine ();
87
88 pthread_cleanup_pop (0);
89
90
91 /* Add one to *once_control to take the bottom 2 bits from 01 to 10. */
92 atomic_increment (once_control);
93
94 /* Wake up all other threads. */
95 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
96
97 return 0;
98 }
99 weak_alias (__pthread_once, pthread_once)
100 strong_alias (__pthread_once, __pthread_once_internal)
101