linuxthreads/sysdeps/x86_64/pspinlock.c

   1 /* POSIX spinlock implementation.  x86-64 version.
   2    Copyright (C) 2001 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
   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 <errno.h>
  21 #include <pthread.h>
  22 #include "internals.h"
  23
  24 /* This implementation is similar to the one used in the Linux kernel.
  25    But the kernel is byte instructions for the memory access.  This is
  26    faster but unusable here.  The problem is that only 128
  27    threads/processes could use the spinlock at the same time.  If (by
  28    a design error in the program) a thread/process would hold the
  29    spinlock for a time long enough to accumulate 128 waiting
  30    processes, the next one will find a positive value in the spinlock
  31    and assume it is unlocked.  We cannot accept that.  */
  32
  33 int
  34 __pthread_spin_lock (pthread_spinlock_t *lock)
  35 {
  36   asm volatile
  37     ("\n"
  38      "1:\n\t"
  39      "lock; decl %0\n\t"
  40      "js 2f\n\t"
  41      ".section .text.spinlock,\"ax\"\n"
  42      "2:\n\t"
  43      "cmpl $0,%0\n\t"
  44      "rep; nop\n\t"
  45      "jle 2b\n\t"
  46      "jmp 1b\n\t"
  47      ".previous"
  48      : "=m" (*lock));
  49   return 0;
  50 }
  51 weak_alias (__pthread_spin_lock, pthread_spin_lock)
  52
  53
  54 int
  55 __pthread_spin_trylock (pthread_spinlock_t *lock)
  56 {
  57   int oldval;
  58
  59   asm volatile
  60     ("xchgl %0,%1"
  61      : "=r" (oldval), "=m" (*lock)
  62      : "0" (0));
  63   return oldval > 0 ? 0 : EBUSY;
  64 }
  65 weak_alias (__pthread_spin_trylock, pthread_spin_trylock)
  66
  67
  68 int
  69 __pthread_spin_unlock (pthread_spinlock_t *lock)
  70 {
  71   asm volatile
  72     ("movl $1,%0"
  73      : "=m" (*lock));
  74   return 0;
  75 }
  76 weak_alias (__pthread_spin_unlock, pthread_spin_unlock)
  77
  78
  79 int
  80 __pthread_spin_init (pthread_spinlock_t *lock, int pshared)
  81 {
  82   /* We can ignore the `pshared' parameter.  Since we are busy-waiting
  83      all processes which can access the memory location `lock' points
  84      to can use the spinlock.  */
  85   *lock = 1;
  86   return 0;
  87 }
  88 weak_alias (__pthread_spin_init, pthread_spin_init)
  89
  90
  91 int
  92 __pthread_spin_destroy (pthread_spinlock_t *lock)
  93 {
  94   /* Nothing to do.  */
  95   return 0;
  96 }
  97 weak_alias (__pthread_spin_destroy, pthread_spin_destroy)