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

   1 /* Copyright (C) 2003, 2004, 2007 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Paul Mackerras <paulus@au.ibm.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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include "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 (pthread_once_t *once_control, void (*init_routine) (void))
  39 {
  40   for (;;)
  41     {
  42       int oldval;
  43       int newval;
  44       int tmp;
  45
  46       /* Pseudo code:
  47          newval = __fork_generation | 1;
  48          oldval = *once_control;
  49          if ((oldval & 2) == 0)
  50            *once_control = newval;
  51          Do this atomically.
  52       */
  53       newval = __fork_generation | 1;
  54       __asm __volatile ("1:     lwarx   %0,0,%3\n"
  55                         "       andi.   %1,%0,2\n"
  56                         "       bne     2f\n"
  57                         "       stwcx.  %4,0,%3\n"
  58                         "       bne     1b\n"
  59                         "2:     isync"
  60                         : "=&r" (oldval), "=&r" (tmp), "=m" (*once_control)
  61                         : "r" (once_control), "r" (newval), "m" (*once_control)
  62                         : "cr0");
  63
  64       /* Check if the initializer has already been done.  */
  65       if ((oldval & 2) != 0)
  66         return 0;
  67
  68       /* Check if another thread already runs the initializer.  */
  69       if ((oldval & 1) == 0)
  70         break;
  71
  72       /* Check whether the initializer execution was interrupted by a fork.  */
  73       if (oldval != newval)
  74         break;
  75
  76       /* Same generation, some other thread was faster. Wait.  */
  77       lll_futex_wait (once_control, oldval, LLL_PRIVATE);
  78     }
  79
  80
  81   /* This thread is the first here.  Do the initialization.
  82      Register a cleanup handler so that in case the thread gets
  83      interrupted the initialization can be restarted.  */
  84   pthread_cleanup_push (clear_once_control, once_control);
  85
  86   init_routine ();
  87
  88   pthread_cleanup_pop (0);
  89
  90
  91   /* Add one to *once_control to take the bottom 2 bits from 01 to 10.  */
  92   atomic_increment (once_control);
  93
  94   /* Wake up all other threads.  */
  95   lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  96
  97   return 0;
  98 }
  99 weak_alias (__pthread_once, pthread_once)
 100 strong_alias (__pthread_once, __pthread_once_internal)