1 /* Copyright (C) 2010-2012 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Maxim Kuvyrkov <maxim@codesourcery.com>, 2010.
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.
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.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library. If not, see
17 <http://www.gnu.org/licenses/>. */
20 #include <lowlevellock.h>
22 unsigned long int __fork_generation attribute_hidden
;
25 clear_once_control (void *arg
)
27 pthread_once_t
*once_control
= (pthread_once_t
*) arg
;
30 lll_futex_wake (once_control
, INT_MAX
, LLL_PRIVATE
);
34 __pthread_once (pthread_once_t
*once_control
, void (*init_routine
) (void))
42 newval = __fork_generation | 1;
43 oldval = *once_control;
44 if ((oldval & 2) == 0)
45 *once_control = newval;
50 newval
= __fork_generation
| 1;
51 oldval
= *once_control
;
54 } while (atomic_compare_and_exchange_val_acq (once_control
, newval
, oldval
) != oldval
);
56 /* Check if the initializer has already been done. */
57 if ((oldval
& 2) != 0)
60 /* Check if another thread already runs the initializer. */
61 if ((oldval
& 1) == 0)
64 /* Check whether the initializer execution was interrupted by a fork. */
68 /* Same generation, some other thread was faster. Wait. */
69 lll_futex_wait (once_control
, oldval
, LLL_PRIVATE
);
72 /* This thread is the first here. Do the initialization.
73 Register a cleanup handler so that in case the thread gets
74 interrupted the initialization can be restarted. */
75 pthread_cleanup_push (clear_once_control
, once_control
);
79 pthread_cleanup_pop (0);
81 /* Say that the initialisation is done. */
82 *once_control
= __fork_generation
| 2;
84 /* Wake up all other threads. */
85 lll_futex_wake (once_control
, INT_MAX
, LLL_PRIVATE
);
89 weak_alias (__pthread_once
, pthread_once
)
90 hidden_def (__pthread_once
)