libpthread/nptl/sysdeps/unix/sysv/linux/aarch64/pthread_once.c

   1 /* Copyright (C) 2003-2013 Free Software Foundation, Inc.
   2    Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include "pthreadP.h"
  19 #include <lowlevellock.h>
  20
  21 unsigned long int __fork_generation attribute_hidden;
  22
  23 static void
  24 clear_once_control (void *arg)
  25 {
  26   pthread_once_t *once_control = (pthread_once_t *) arg;
  27
  28   *once_control = 0;
  29   lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  30 }
  31
  32
  33 int
  34 __pthread_once (once_control, init_routine)
  35      pthread_once_t *once_control;
  36      void (*init_routine) (void);
  37 {
  38   while (1)
  39     {
  40       int oldval, val, newval;
  41
  42       val = *once_control;
  43       do
  44         {
  45           /* Check if the initialized has already been done.  */
  46           if ((val & 2) != 0)
  47             return 0;
  48
  49           oldval = val;
  50           newval = (oldval & 3) | __fork_generation | 1;
  51           val = atomic_compare_and_exchange_val_acq (once_control, newval,
  52                                                      oldval);
  53         }
  54       while (__builtin_expect (val != oldval, 0));
  55
  56       /* Check if another thread already runs the initializer.  */
  57       if ((oldval & 1) != 0)
  58         {
  59           /* Check whether the initializer execution was interrupted
  60              by a fork.  */
  61           if (((oldval ^ newval) & -4) == 0)
  62             {
  63               /* Same generation, some other thread was faster. Wait.  */
  64               lll_futex_wait (once_control, newval, LLL_PRIVATE);
  65               continue;
  66             }
  67         }
  68
  69       /* This thread is the first here.  Do the initialization.
  70          Register a cleanup handler so that in case the thread gets
  71          interrupted the initialization can be restarted.  */
  72       pthread_cleanup_push (clear_once_control, once_control);
  73
  74       init_routine ();
  75
  76       pthread_cleanup_pop (0);
  77
  78
  79       /* Add one to *once_control.  */
  80       atomic_increment (once_control);
  81
  82       /* Wake up all other threads.  */
  83       lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  84       break;
  85     }
  86
  87   return 0;
  88 }
  89 weak_alias (__pthread_once, pthread_once)
  90 strong_alias (__pthread_once, __pthread_once_internal)