ports/sysdeps/unix/sysv/linux/tile/nptl/pthread_once.c

   1 /* Copyright (C) 2011-2012 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
   4    Based on work contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library.  If not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <nptl/pthreadP.h>
  21 #include <lowlevellock.h>
  22
  23
  24 unsigned long int __fork_generation attribute_hidden;
  25
  26
  27 static void
  28 clear_once_control (void *arg)
  29 {
  30   pthread_once_t *once_control = (pthread_once_t *) arg;
  31
  32   *once_control = 0;
  33   lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  34 }
  35
  36
  37 int
  38 __pthread_once (once_control, init_routine)
  39      pthread_once_t *once_control;
  40      void (*init_routine) (void);
  41 {
  42   while (1)
  43     {
  44       int oldval, val, newval;
  45
  46       val = *once_control;
  47       do
  48         {
  49           /* Check if the initialized has already been done.  */
  50           if ((val & 2) != 0)
  51             return 0;
  52
  53           oldval = val;
  54           newval = (oldval & 3) | __fork_generation | 1;
  55           val = atomic_compare_and_exchange_val_acq (once_control, newval,
  56                                                      oldval);
  57         }
  58       while (__builtin_expect (val != oldval, 0));
  59
  60       /* Check if another thread already runs the initializer.  */
  61       if ((oldval & 1) != 0)
  62         {
  63           /* Check whether the initializer execution was interrupted
  64              by a fork.  */
  65           if (((oldval ^ newval) & -4) == 0)
  66             {
  67               /* Same generation, some other thread was faster. Wait.  */
  68               lll_futex_wait (once_control, newval, LLL_PRIVATE);
  69               continue;
  70             }
  71         }
  72
  73       /* This thread is the first here.  Do the initialization.
  74          Register a cleanup handler so that in case the thread gets
  75          interrupted the initialization can be restarted.  */
  76       pthread_cleanup_push (clear_once_control, once_control);
  77
  78       init_routine ();
  79
  80       pthread_cleanup_pop (0);
  81
  82
  83       /* Add one to *once_control.  */
  84       atomic_increment (once_control);
  85
  86       /* Wake up all other threads.  */
  87       lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  88       break;
  89     }
  90
  91   return 0;
  92 }
  93 weak_alias (__pthread_once, pthread_once)
  94 hidden_def (__pthread_once)