/* Copyright (C) 2003-2014 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include "pthreadP.h"
#include <lowlevellock.h>


unsigned long int __fork_generation attribute_hidden;


static void
clear_once_control (void *arg)
{
  pthread_once_t *once_control = (pthread_once_t *) arg;

  __asm __volatile (__lll_rel_instr);
  *once_control = 0;
  lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
}


int
__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
{
  for (;;)
    {
      int oldval;
      int newval;
      int tmp;

      /* Pseudo code:
	 newval = __fork_generation | 1;
	 oldval = *once_control;
	 if ((oldval & 2) == 0)
	   *once_control = newval;
	 Do this atomically with an acquire barrier.
      */
      newval = __fork_generation | 1;
      __asm __volatile ("1:	lwarx	%0,0,%3" MUTEX_HINT_ACQ "\n"
			"	andi.	%1,%0,2\n"
			"	bne	2f\n"
			"	stwcx.	%4,0,%3\n"
			"	bne	1b\n"
			"2:	" __lll_acq_instr
			: "=&r" (oldval), "=&r" (tmp), "=m" (*once_control)
			: "r" (once_control), "r" (newval), "m" (*once_control)
			: "cr0");

      /* Check if the initializer has already been done.  */
      if ((oldval & 2) != 0)
	return 0;

      /* Check if another thread already runs the initializer.	*/
      if ((oldval & 1) == 0)
	break;

      /* Check whether the initializer execution was interrupted by a fork.  */
      if (oldval != newval)
	break;

      /* Same generation, some other thread was faster. Wait.  */
      lll_futex_wait (once_control, oldval, LLL_PRIVATE);
    }


  /* This thread is the first here.  Do the initialization.
     Register a cleanup handler so that in case the thread gets
     interrupted the initialization can be restarted.  */
  pthread_cleanup_push (clear_once_control, once_control);

  init_routine ();

  pthread_cleanup_pop (0);


  /* Add one to *once_control to take the bottom 2 bits from 01 to 10.
     A release barrier is needed to ensure memory written by init_routine
     is seen in other threads before *once_control changes.  */
  int tmp;
  __asm __volatile (__lll_rel_instr "\n"
		    "1:	lwarx	%0,0,%2" MUTEX_HINT_REL "\n"
		    "	addi	%0,%0,1\n"
		    "	stwcx.	%0,0,%2\n"
		    "	bne-	1b"
		    : "=&b" (tmp), "=m" (*once_control)
		    : "r" (once_control), "m" (*once_control)
		    : "cr0");

  /* Wake up all other threads.  */
  lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);

  return 0;
}
weak_alias (__pthread_once, pthread_once)
hidden_def (__pthread_once)