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/* POSIX spinlock implementation.  x86 version.

   Copyright (C) 2000 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Library General Public License as

   published by the Free Software Foundation; either version 2 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

   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public

   License along with the GNU C Library; see the file COPYING.LIB.  If not,

   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,

   Boston, MA 02111-1307, USA.  */

#include <errno.h>

#include <pthread.h>

#include "internals.h"

/* This implementation is similar to the one used in the Linux kernel.

   But the kernel is byte instructions for the memory access.  This is

   faster but unusable here.  The problem is that only 128

   threads/processes could use the spinlock at the same time.  If (by

   a design error in the program) a thread/process would hold the

   spinlock for a time long enough to accumulate 128 waiting

   processes, the next one will find a positive value in the spinlock

   and assume it is unlocked.  We cannot accept that.  */

int

__pthread_spin_lock (pthread_spinlock_t *lock)

{

  asm volatile

    ("\n"

     "1:\n\t"

     "lock; decl %0\n\t"

     "js 2f\n\t"

     ".section .text.spinlock,\"ax\"\n"

     "2:\n\t"

     "cmpl $0,%0\n\t"

     "rep; nop\n\t"

     "jle 2b\n\t"

     "jmp 1b\n\t"

     ".previous"

     : "=m" (*lock));

  return 0;

}

weak_alias (__pthread_spin_lock, pthread_spin_lock)

int

__pthread_spin_trylock (pthread_spinlock_t *lock)

{

  int oldval;

  asm volatile

    ("xchgl %0,%1"

     : "=r" (oldval), "=m" (*lock)

     : "0" (0));

  return oldval > 0 ? 0 : EBUSY;

}

weak_alias (__pthread_spin_trylock, pthread_spin_trylock)

int

__pthread_spin_unlock (pthread_spinlock_t *lock)

{

  asm volatile

    ("movl $1,%0"

     : "=m" (*lock));

  return 0;

}

weak_alias (__pthread_spin_unlock, pthread_spin_unlock)

int

__pthread_spin_init (pthread_spinlock_t *lock, int pshared)

{

  /* We can ignore the `pshared' parameter.  Since we are busy-waiting

     all processes which can access the memory location `lock' points

     to can use the spinlock.  */

  *lock = 1;

  return 0;

}

weak_alias (__pthread_spin_init, pthread_spin_init)

int

__pthread_spin_destroy (pthread_spinlock_t *lock)

{

  /* Nothing to do.  */

  return 0;

}

weak_alias (__pthread_spin_destroy, pthread_spin_destroy)