linuxthreads/sysdeps/i386/pspinlock.c

   1 /* POSIX spinlock implementation.  x86 version.
   2    Copyright (C) 2000, 2002 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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 License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    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; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <errno.h>
  21 #include <pthread.h>
  22 #include "internals.h"
  23 #include "kernel-features.h"
  24
  25
  26 /* This implementation is similar to the one used in the Linux kernel.
  27    But the kernel is byte instructions for the memory access.  This is
  28    faster but unusable here.  The problem is that only 128
  29    threads/processes could use the spinlock at the same time.  If (by
  30    a design error in the program) a thread/process would hold the
  31    spinlock for a time long enough to accumulate 128 waiting
  32    processes, the next one will find a positive value in the spinlock
  33    and assume it is unlocked.  We cannot accept that.  */
  34
  35 int
  36 __pthread_spin_lock (pthread_spinlock_t *lock)
  37 {
  38   asm volatile
  39     ("\n"
  40      "1:\n\t"
  41      "lock; decl %0\n\t"
  42      "js 2f\n\t"
  43      ".section .text.spinlock,\"ax\"\n"
  44      "2:\n\t"
  45      "cmpl $0,%0\n\t"
  46      "rep; nop\n\t"
  47      "jle 2b\n\t"
  48      "jmp 1b\n\t"
  49      ".previous"
  50      : "=m" (*lock));
  51   return 0;
  52 }
  53 weak_alias (__pthread_spin_lock, pthread_spin_lock)
  54
  55
  56 int
  57 __pthread_spin_trylock (pthread_spinlock_t *lock)
  58 {
  59   int oldval;
  60
  61   asm volatile
  62     ("xchgl %0,%1"
  63      : "=r" (oldval), "=m" (*lock)
  64      : "0" (0));
  65   return oldval > 0 ? 0 : EBUSY;
  66 }
  67 weak_alias (__pthread_spin_trylock, pthread_spin_trylock)
  68
  69
  70 int
  71 __pthread_spin_unlock (pthread_spinlock_t *lock)
  72 {
  73   asm volatile
  74     ("movl $1,%0"
  75      : "=m" (*lock));
  76   return 0;
  77 }
  78 weak_alias (__pthread_spin_unlock, pthread_spin_unlock)
  79
  80
  81 int
  82 __pthread_spin_init (pthread_spinlock_t *lock, int pshared)
  83 {
  84   /* We can ignore the `pshared' parameter.  Since we are busy-waiting
  85      all processes which can access the memory location `lock' points
  86      to can use the spinlock.  */
  87   *lock = 1;
  88   return 0;
  89 }
  90 weak_alias (__pthread_spin_init, pthread_spin_init)
  91
  92
  93 int
  94 __pthread_spin_destroy (pthread_spinlock_t *lock)
  95 {
  96   /* Nothing to do.  */
  97   return 0;
  98 }
  99 weak_alias (__pthread_spin_destroy, pthread_spin_destroy)
 100
 101 #ifndef __ASSUME_SET_THREAD_AREA_SYSCALL
 102 int __have_no_set_thread_area;
 103 #endif