sysdeps/unix/sysv/linux/mips/nptl/pthread_once.c

   1 /* Copyright (C) 2003-2012 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library.  If not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include "pthreadP.h"
  20 #include <lowlevellock.h>
  21
  22
  23 unsigned long int __fork_generation attribute_hidden;
  24
  25
  26 static void
  27 clear_once_control (void *arg)
  28 {
  29   pthread_once_t *once_control = (pthread_once_t *) arg;
  30
  31   *once_control = 0;
  32   lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  33 }
  34
  35
  36 int
  37 __pthread_once (once_control, init_routine)
  38      pthread_once_t *once_control;
  39      void (*init_routine) (void);
  40 {
  41   while (1)
  42     {
  43       int oldval, val, newval;
  44
  45       val = *once_control;
  46       do
  47         {
  48           /* Check if the initialized has already been done.  */
  49           if ((val & 2) != 0)
  50             return 0;
  51
  52           oldval = val;
  53           newval = (oldval & 3) | __fork_generation | 1;
  54           val = atomic_compare_and_exchange_val_acq (once_control, newval,
  55                                                      oldval);
  56         }
  57       while (__builtin_expect (val != oldval, 0));
  58
  59       /* Check if another thread already runs the initializer.  */
  60       if ((oldval & 1) != 0)
  61         {
  62           /* Check whether the initializer execution was interrupted
  63              by a fork.  */
  64           if (((oldval ^ newval) & -4) == 0)
  65             {
  66               /* Same generation, some other thread was faster. Wait.  */
  67               lll_futex_wait (once_control, newval, LLL_PRIVATE);
  68               continue;
  69             }
  70         }
  71
  72       /* This thread is the first here.  Do the initialization.
  73          Register a cleanup handler so that in case the thread gets
  74          interrupted the initialization can be restarted.  */
  75       pthread_cleanup_push (clear_once_control, once_control);
  76
  77       init_routine ();
  78
  79       pthread_cleanup_pop (0);
  80
  81
  82       /* Add one to *once_control.  */
  83       atomic_increment (once_control);
  84
  85       /* Wake up all other threads.  */
  86       lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  87       break;
  88     }
  89
  90   return 0;
  91 }
  92 weak_alias (__pthread_once, pthread_once)
  93 hidden_def (__pthread_once)