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 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
33 int
__pthread_once(once_control,init_routine)34 __pthread_once (once_control, init_routine)
35 pthread_once_t *once_control;
36 void (*init_routine) (void);
37 {
38 while (1)
39 {
40 int oldval, val, newval;
41
42 val = *once_control;
43 do
44 {
45 /* Check if the initialized has already been done. */
46 if ((val & 2) != 0)
47 return 0;
48
49 oldval = val;
50 newval = (oldval & 3) | __fork_generation | 1;
51 val = atomic_compare_and_exchange_val_acq (once_control, newval,
52 oldval);
53 }
54 while (__builtin_expect (val != oldval, 0));
55
56 /* Check if another thread already runs the initializer. */
57 if ((oldval & 1) != 0)
58 {
59 /* Check whether the initializer execution was interrupted
60 by a fork. */
61 if (((oldval ^ newval) & -4) == 0)
62 {
63 /* Same generation, some other thread was faster. Wait. */
64 lll_futex_wait (once_control, newval, LLL_PRIVATE);
65 continue;
66 }
67 }
68
69 /* This thread is the first here. Do the initialization.
70 Register a cleanup handler so that in case the thread gets
71 interrupted the initialization can be restarted. */
72 pthread_cleanup_push (clear_once_control, once_control);
73
74 init_routine ();
75
76 pthread_cleanup_pop (0);
77
78
79 /* Add one to *once_control. */
80 atomic_increment (once_control);
81
82 /* Wake up all other threads. */
83 lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
84 break;
85 }
86
87 return 0;
88 }
89 weak_alias (__pthread_once, pthread_once)
90 strong_alias (__pthread_once, __pthread_once_internal)
91