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

   1 /* Copyright (C) 2003-2014 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, 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;
  44       int newval;
  45
  46       /* Pseudo code:
  47            oldval = *once_control;
  48            if ((oldval & 2) == 0)
  49             {
  50               newval = (oldval & 3) | __fork_generation | 1;
  51               *once_control = newval;
  52             }
  53          Do this atomically.  */
  54       __asm __volatile ("   l    %1,%0\n"
  55                         "0: lhi  %2,2\n"
  56                         "   tml  %1,2\n"
  57                         "   jnz  1f\n"
  58                         "   nr   %2,%1\n"
  59                         "   ahi  %2,1\n"
  60                         "   o    %2,%3\n"
  61                         "   cs   %1,%2,%0\n"
  62                         "   jl   0b\n"
  63                         "1:"
  64                         : "=Q" (*once_control), "=&d" (oldval), "=&d" (newval)
  65                         : "m" (__fork_generation), "m" (*once_control)
  66                         : "cc" );
  67       /* Check if the initialized has already been done.  */
  68       if ((oldval & 2) != 0)
  69           break;
  70       /* Check if another thread already runs the initializer.  */
  71       if ((oldval & 1) != 0)
  72         {
  73           /* Check whether the initializer execution was interrupted
  74              by a fork.  */
  75           if (((oldval ^ newval) & -4) == 0)
  76             {
  77               /* Same generation, some other thread was faster. Wait.  */
  78               lll_futex_wait (once_control, newval, LLL_PRIVATE);
  79               continue;
  80             }
  81         }
  82
  83       /* This thread is the first here.  Do the initialization.
  84          Register a cleanup handler so that in case the thread gets
  85          interrupted the initialization can be restarted.  */
  86       pthread_cleanup_push (clear_once_control, once_control);
  87
  88       init_routine ();
  89
  90       pthread_cleanup_pop (0);
  91
  92
  93       /* Add one to *once_control.  */
  94       __asm __volatile ("   l    %1,%0\n"
  95                         "0: lr   %2,%1\n"
  96                         "   ahi  %2,1\n"
  97                         "   cs   %1,%2,%0\n"
  98                         "   jl   0b\n"
  99                         : "=Q" (*once_control), "=&d" (oldval), "=&d" (newval)
 100                         : "m" (*once_control) : "cc" );
 101
 102       /* Wake up all other threads.  */
 103       lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
 104       break;
 105     }
 106
 107   return 0;
 108 }
 109 weak_alias (__pthread_once, pthread_once)
 110 hidden_def (__pthread_once)