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/* Copyright (C) 2003, 2004, 2007 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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#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;
int tmp;
/* Pseudo code:
newval = __fork_generation | 1;
oldval = *once_control;
if ((oldval & 2) == 0)
*once_control = newval;
Do this atomically.
*/
newval = __fork_generation | 1;
__asm __volatile ("1: lwarx %0,0,%3\n"
" andi. %1,%0,2\n"
" bne 2f\n"
" stwcx. %4,0,%3\n"
" bne 1b\n"
"2: isync"
: "=&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. */
atomic_increment (once_control);
/* Wake up all other threads. */
lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
return 0;
}
weak_alias (__pthread_once, pthread_once)
strong_alias (__pthread_once, __pthread_once_internal)
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