mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-12 06:10:10 +00:00
92 lines
2.7 KiB
C
92 lines
2.7 KiB
C
/* Copyright (C) 2010 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
Contributed by Maxim Kuvyrkov <maxim@codesourcery.com>, 2010.
|
|
|
|
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;
|
|
|
|
/* 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)
|
|
strong_alias (__pthread_once, __pthread_once_internal)
|