libpthread/nptl/sysdeps/unix/sysv/linux/or1k/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
  22 unsigned long int __fork_generation attribute_hidden;
  23
  24
  25 static void
  26 clear_once_control (void *arg)
  27 {
  28   pthread_once_t *once_control = (pthread_once_t *) arg;
  29
  30   *once_control = 0;
  31   lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  32 }
  33
  34
  35 int
  36 __pthread_once (once_control, init_routine)
  37      pthread_once_t *once_control;
  38      void (*init_routine) (void);
  39 {
  40   while (1)
  41     {
  42       int oldval, val, newval;
  43
  44       val = *once_control;
  45       do
  46         {
  47           /* Check if the initialized has already been done.  */
  48           if ((val & 2) != 0)
  49             return 0;
  50
  51           oldval = val;
  52           newval = (oldval & 3) | __fork_generation | 1;
  53           val = atomic_compare_and_exchange_val_acq (once_control, newval,
  54                                                      oldval);
  55         }
  56       while (__builtin_expect (val != oldval, 0));
  57
  58       /* Check if another thread already runs the initializer.  */
  59       if ((oldval & 1) != 0)
  60         {
  61           /* Check whether the initializer execution was interrupted
  62              by a fork.  */
  63           if (((oldval ^ newval) & -4) == 0)
  64             {
  65               /* Same generation, some other thread was faster. Wait.  */
  66               lll_futex_wait (once_control, newval, LLL_PRIVATE);
  67               continue;
  68             }
  69         }
  70
  71       /* This thread is the first here.  Do the initialization.
  72          Register a cleanup handler so that in case the thread gets
  73          interrupted the initialization can be restarted.  */
  74       pthread_cleanup_push (clear_once_control, once_control);
  75
  76       init_routine ();
  77
  78       pthread_cleanup_pop (0);
  79
  80
  81       /* Add one to *once_control.  */
  82       atomic_increment (once_control);
  83
  84       /* Wake up all other threads.  */
  85       lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  86       break;
  87     }
  88
  89   return 0;
  90 }
  91 weak_alias (__pthread_once, pthread_once)
  92 strong_alias (__pthread_once, __pthread_once_internal)