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1 | /* Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. | |
3 | Contributed by Jakub Jelinek <jakub@redhat.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, write to the Free | |
17 | Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA | |
18 | 02111-1307 USA. */ | |
19 | ||
20 | #include "pthreadP.h" | |
21 | #include <lowlevellock.h> | |
22 | ||
23 | ||
24 | unsigned long int __fork_generation attribute_hidden; | |
25 | ||
26 | ||
27 | static void | |
28 | clear_once_control (void *arg) | |
29 | { | |
30 | pthread_once_t *once_control = (pthread_once_t *) arg; | |
31 | ||
32 | *once_control = 0; | |
33 | lll_futex_wake (once_control, INT_MAX); | |
34 | } | |
35 | ||
36 | ||
37 | int | |
38 | __pthread_once (once_control, init_routine) | |
39 | pthread_once_t *once_control; | |
40 | void (*init_routine) (void); | |
41 | { | |
42 | while (1) | |
43 | { | |
44 | int oldval, val, newval; | |
45 | ||
46 | val = *once_control; | |
47 | do | |
48 | { | |
49 | /* Check if the initialized has already been done. */ | |
50 | if ((val & 2) != 0) | |
51 | return 0; | |
52 | ||
53 | oldval = val; | |
54 | newval = (oldval & 3) | __fork_generation | 1; | |
55 | val = atomic_compare_and_exchange_val_acq (once_control, newval, | |
56 | oldval); | |
57 | } | |
58 | while (__builtin_expect (val != oldval, 0)); | |
59 | ||
60 | /* Check if another thread already runs the initializer. */ | |
61 | if ((oldval & 1) != 0) | |
62 | { | |
63 | /* Check whether the initializer execution was interrupted | |
64 | by a fork. */ | |
65 | if (((oldval ^ newval) & -4) == 0) | |
66 | { | |
67 | /* Same generation, some other thread was faster. Wait. */ | |
68 | lll_futex_wait (once_control, newval); | |
69 | continue; | |
70 | } | |
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 | ||
83 | /* Add one to *once_control. */ | |
84 | atomic_increment (once_control); | |
85 | ||
86 | /* Wake up all other threads. */ | |
87 | lll_futex_wake (once_control, INT_MAX); | |
88 | break; | |
89 | } | |
90 | ||
91 | return 0; | |
92 | } | |
93 | weak_alias (__pthread_once, pthread_once) | |
94 | strong_alias (__pthread_once, __pthread_once_internal) |