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