projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 568035b7 | 1 | /* Copyright (C) 2010-2013 Free Software Foundation, Inc. |
| 40111cb9 MK |
2 | This file is part of the GNU C Library. |
| 3 | Contributed by Maxim Kuvyrkov <maxim@codesourcery.com>, 2010. | |
| 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 | |
| ab84e3ff PE |
16 | License along with the GNU C Library. If not, see |
| 17 | <http://www.gnu.org/licenses/>. */ | |
| 40111cb9 MK |
18 | |
| 19 | #include "pthreadP.h" | |
| 20 | #include <lowlevellock.h> | |
| 21 | ||
| 22 | unsigned long int __fork_generation attribute_hidden; | |
| 23 | ||
| 24 | static void | |
| 25 | clear_once_control (void *arg) | |
| 26 | { | |
| 27 | pthread_once_t *once_control = (pthread_once_t *) arg; | |
| 28 | ||
| 29 | *once_control = 0; | |
| 30 | lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE); | |
| 31 | } | |
| 32 | ||
| 33 | int | |
| 34 | __pthread_once (pthread_once_t *once_control, void (*init_routine) (void)) | |
| 35 | { | |
| 36 | for (;;) | |
| 37 | { | |
| 38 | int oldval; | |
| 39 | int newval; | |
| 40 | ||
| 41 | /* Pseudo code: | |
| 42 | newval = __fork_generation | 1; | |
| 43 | oldval = *once_control; | |
| 44 | if ((oldval & 2) == 0) | |
| 45 | *once_control = newval; | |
| 46 | Do this atomically. | |
| 47 | */ | |
| 48 | do | |
| 49 | { | |
| 50 | newval = __fork_generation | 1; | |
| 51 | oldval = *once_control; | |
| 52 | if (oldval & 2) | |
| 53 | break; | |
| 54 | } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval); | |
| 55 | ||
| 56 | /* Check if the initializer has already been done. */ | |
| 57 | if ((oldval & 2) != 0) | |
| 58 | return 0; | |
| 59 | ||
| 60 | /* Check if another thread already runs the initializer. */ | |
| 61 | if ((oldval & 1) == 0) | |
| 62 | break; | |
| 63 | ||
| 64 | /* Check whether the initializer execution was interrupted by a fork. */ | |
| 65 | if (oldval != newval) | |
| 66 | break; | |
| 67 | ||
| 68 | /* Same generation, some other thread was faster. Wait. */ | |
| 69 | lll_futex_wait (once_control, oldval, LLL_PRIVATE); | |
| 70 | } | |
| 71 | ||
| 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); | |
| 76 | ||
| 77 | init_routine (); | |
| 78 | ||
| 79 | pthread_cleanup_pop (0); | |
| 80 | ||
| 81 | /* Say that the initialisation is done. */ | |
| 82 | *once_control = __fork_generation | 2; | |
| 83 | ||
| 84 | /* Wake up all other threads. */ | |
| 85 | lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE); | |
| 86 | ||
| 87 | return 0; | |
| 88 | } | |
| 89 | weak_alias (__pthread_once, pthread_once) | |
| 7fce2e26 | 90 | hidden_def (__pthread_once) |