nptl/sysdeps/unix/sysv/linux/s390/pthread_once.c

   1 /* Copyright (C) 2003, 2007 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Martin Schwidefsky <schwidefsky@de.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 (once_control, init_routine)
  39      pthread_once_t *once_control;
  40      void (*init_routine) (void);
  41 {
  42   while (1)
  43     {
  44       int oldval;
  45       int newval;
  46
  47       /* Pseudo code:
  48            oldval = *once_control;
  49            if ((oldval & 2) == 0)
  50             {
  51               newval = (oldval & 3) | __fork_generation | 1;
  52               *once_control = newval;
  53             }
  54          Do this atomically.  */
  55       __asm __volatile ("   l    %1,%0\n"
  56                         "0: lhi  %2,2\n"
  57                         "   tml  %1,2\n"
  58                         "   jnz  1f\n"
  59                         "   nr   %2,%1\n"
  60                         "   ahi  %2,1\n"
  61                         "   o    %2,%3\n"
  62                         "   cs   %1,%2,%0\n"
  63                         "   jl   0b\n"
  64                         "1:"
  65                         : "=Q" (*once_control), "=&d" (oldval), "=&d" (newval)
  66                         : "m" (__fork_generation), "m" (*once_control)
  67                         : "cc" );
  68       /* Check if the initialized has already been done.  */
  69       if ((oldval & 2) != 0)
  70           break;
  71       /* Check if another thread already runs the initializer.  */
  72       if ((oldval & 1) != 0)
  73         {
  74           /* Check whether the initializer execution was interrupted
  75              by a fork.  */
  76           if (((oldval ^ newval) & -4) == 0)
  77             {
  78               /* Same generation, some other thread was faster. Wait.  */
  79               lll_futex_wait (once_control, newval, LLL_PRIVATE);
  80               continue;
  81             }
  82         }
  83
  84       /* This thread is the first here.  Do the initialization.
  85          Register a cleanup handler so that in case the thread gets
  86          interrupted the initialization can be restarted.  */
  87       pthread_cleanup_push (clear_once_control, once_control);
  88
  89       init_routine ();
  90
  91       pthread_cleanup_pop (0);
  92
  93
  94       /* Add one to *once_control.  */
  95       __asm __volatile ("   l    %1,%0\n"
  96                         "0: lr   %2,%1\n"
  97                         "   ahi  %2,1\n"
  98                         "   cs   %1,%2,%0\n"
  99                         "   jl   0b\n"
 100                         : "=Q" (*once_control), "=&d" (oldval), "=&d" (newval)
 101                         : "m" (*once_control) : "cc" );
 102
 103       /* Wake up all other threads.  */
 104       lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
 105       break;
 106     }
 107
 108   return 0;
 109 }
 110 weak_alias (__pthread_once, pthread_once)
 111 strong_alias (__pthread_once, __pthread_once_internal)