| /* Copyright (C) 2003-2014 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003. |
| |
| 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; |
| |
| __asm __volatile (__lll_rel_instr); |
| *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; |
| int tmp; |
| |
| /* Pseudo code: |
| newval = __fork_generation | 1; |
| oldval = *once_control; |
| if ((oldval & 2) == 0) |
| *once_control = newval; |
| Do this atomically with an acquire barrier. |
| */ |
| newval = __fork_generation | 1; |
| __asm __volatile ("1: lwarx %0,0,%3" MUTEX_HINT_ACQ "\n" |
| " andi. %1,%0,2\n" |
| " bne 2f\n" |
| " stwcx. %4,0,%3\n" |
| " bne 1b\n" |
| "2: " __lll_acq_instr |
| : "=&r" (oldval), "=&r" (tmp), "=m" (*once_control) |
| : "r" (once_control), "r" (newval), "m" (*once_control) |
| : "cr0"); |
| |
| /* 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); |
| |
| |
| /* Add one to *once_control to take the bottom 2 bits from 01 to 10. |
| A release barrier is needed to ensure memory written by init_routine |
| is seen in other threads before *once_control changes. */ |
| int tmp; |
| __asm __volatile (__lll_rel_instr "\n" |
| "1: lwarx %0,0,%2" MUTEX_HINT_REL "\n" |
| " addi %0,%0,1\n" |
| " stwcx. %0,0,%2\n" |
| " bne- 1b" |
| : "=&b" (tmp), "=m" (*once_control) |
| : "r" (once_control), "m" (*once_control) |
| : "cr0"); |
| |
| /* 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) |
