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eb7721f2 | 1 | /* Copyright (C) 2003, 2004, 2007 Free Software Foundation, Inc. |
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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 | |
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16 | License along with the GNU C Library; if not, see |
17 | <http://www.gnu.org/licenses/>. */ | |
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18 | |
19 | #include "pthreadP.h" | |
20 | #include <lowlevellock.h> | |
21 | ||
22 | ||
23 | unsigned long int __fork_generation attribute_hidden; | |
24 | ||
25 | ||
26 | static void | |
27 | clear_once_control (void *arg) | |
28 | { | |
29 | pthread_once_t *once_control = (pthread_once_t *) arg; | |
30 | ||
31 | *once_control = 0; | |
085a4412 | 32 | lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE); |
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33 | } |
34 | ||
35 | ||
36 | int | |
37 | __pthread_once (pthread_once_t *once_control, void (*init_routine) (void)) | |
38 | { | |
39 | for (;;) | |
40 | { | |
41 | int oldval; | |
42 | int newval; | |
43 | int tmp; | |
44 | ||
45 | /* Pseudo code: | |
46 | newval = __fork_generation | 1; | |
47 | oldval = *once_control; | |
48 | if ((oldval & 2) == 0) | |
49 | *once_control = newval; | |
50 | Do this atomically. | |
51 | */ | |
52 | newval = __fork_generation | 1; | |
53 | __asm __volatile ("1: lwarx %0,0,%3\n" | |
54 | " andi. %1,%0,2\n" | |
55 | " bne 2f\n" | |
56 | " stwcx. %4,0,%3\n" | |
ca86a763 | 57 | " bne 1b\n" |
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58 | "2: isync" |
59 | : "=&r" (oldval), "=&r" (tmp), "=m" (*once_control) | |
60 | : "r" (once_control), "r" (newval), "m" (*once_control) | |
61 | : "cr0"); | |
62 | ||
63 | /* Check if the initializer has already been done. */ | |
64 | if ((oldval & 2) != 0) | |
65 | return 0; | |
66 | ||
67 | /* Check if another thread already runs the initializer. */ | |
68 | if ((oldval & 1) == 0) | |
69 | break; | |
70 | ||
71 | /* Check whether the initializer execution was interrupted by a fork. */ | |
72 | if (oldval != newval) | |
73 | break; | |
74 | ||
75 | /* Same generation, some other thread was faster. Wait. */ | |
085a4412 | 76 | lll_futex_wait (once_control, oldval, LLL_PRIVATE); |
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77 | } |
78 | ||
79 | ||
80 | /* This thread is the first here. Do the initialization. | |
81 | Register a cleanup handler so that in case the thread gets | |
82 | interrupted the initialization can be restarted. */ | |
83 | pthread_cleanup_push (clear_once_control, once_control); | |
84 | ||
85 | init_routine (); | |
86 | ||
87 | pthread_cleanup_pop (0); | |
88 | ||
89 | ||
90 | /* Add one to *once_control to take the bottom 2 bits from 01 to 10. */ | |
67254a97 | 91 | atomic_increment (once_control); |
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92 | |
93 | /* Wake up all other threads. */ | |
085a4412 | 94 | lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE); |
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95 | |
96 | return 0; | |
97 | } | |
98 | weak_alias (__pthread_once, pthread_once) | |
99 | strong_alias (__pthread_once, __pthread_once_internal) |