| /* Copyright (C) 2004-2014 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| |
| 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 |
| __pthread_once (pthread_once_t *once_control, void (*init_routine) (void)) |
| { |
| for (;;) |
| { |
| int oldval; |
| int newval; |
| |
| /* Pseudo code: |
| newval = __fork_generation | 1; |
| oldval = *once_control; |
| if ((oldval & 2) == 0) |
| *once_control = newval; |
| Do this atomically. |
| */ |
| do |
| { |
| newval = __fork_generation | 1; |
| oldval = *once_control; |
| if (oldval & 2) |
| break; |
| } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval); |
| |
| /* Check if the initializer has already been done. */ |
| if ((oldval & 2) != 0) |
| return 0; |
| |
| /* Check if another thread already runs the initializer. */ |
| if ((oldval & 1) == 0) |
| break; |
| |
| /* Check whether the initializer execution was interrupted by a fork. */ |
| if (oldval != newval) |
| break; |
| |
| /* Same generation, some other thread was faster. Wait. */ |
| lll_futex_wait (once_control, oldval, LLL_PRIVATE); |
| } |
| |
| /* 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); |
| |
| /* Say that the initialisation is done. */ |
| *once_control = __fork_generation | 2; |
| |
| /* Wake up all other threads. */ |
| lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE); |
| |
| return 0; |
| } |
| weak_alias (__pthread_once, pthread_once) |
| hidden_def (__pthread_once) |
