1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
/* Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include "pthreadP.h"
#include <lowlevellock.h>
unsigned long int __fork_generation attribute_hidden;
static void
clear_once_control (void *arg)
{
pthread_once_t *once_control = (pthread_once_t *) arg;
*once_control = 0;
lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
}
int
attribute_protected
__pthread_once (once_control, init_routine)
pthread_once_t *once_control;
void (*init_routine) (void);
{
while (1)
{
int oldval, val, newval;
val = *once_control;
do
{
/* Check if the initialized has already been done. */
if ((val & 2) != 0)
return 0;
oldval = val;
newval = (oldval & 3) | __fork_generation | 1;
val = atomic_compare_and_exchange_val_acq (once_control, newval,
oldval);
}
while (__builtin_expect (val != oldval, 0));
/* Check if another thread already runs the initializer. */
if ((oldval & 1) != 0)
{
/* Check whether the initializer execution was interrupted
by a fork. */
if (((oldval ^ newval) & -4) == 0)
{
/* Same generation, some other thread was faster. Wait. */
lll_futex_wait (once_control, newval, LLL_PRIVATE);
continue;
}
}
/* This thread is the first here. Do the initialization.
Register a cleanup handler so that in case the thread gets
interrupted the initialization can be restarted. */
pthread_cleanup_push (clear_once_control, once_control);
init_routine ();
pthread_cleanup_pop (0);
/* Add one to *once_control. */
atomic_increment (once_control);
/* Wake up all other threads. */
lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
break;
}
return 0;
}
weak_alias (__pthread_once, pthread_once)
strong_alias (__pthread_once, __pthread_once_internal)
|
