pt-machine.h

linux 下的线程库源码

/* Machine-dependent pthreads configuration and inline functions.
   i386 version.
Copyright (C) 1996 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Richard Henderson <[e-mail]>.

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., 675 Mass Ave,
Cambridge, MA 02139, USA.  */


/* Spinlock implementation; required.  */
static inline int testandset(int *spinlock)
{
  int ret;

  __asm__ __volatile__("xchgl %0, %1"
	: "=r"(ret), "=m"(*spinlock)
	: "0"(1), "m"(*spinlock));

  return ret;
}


/* Get some notion of the current stack.  Need not be exactly the top
   of the stack, just something somewhere in the current frame.  */
#define CURRENT_STACK_FRAME  stack_pointer
register char * stack_pointer __asm__("%esp");

/* Compare-and-swap for semaphores.
   Available on the 486 and above, but not on the 386.
   We test dynamically whether it's available or not. */

#define HAS_COMPARE_AND_SWAP
#define TEST_FOR_COMPARE_AND_SWAP

static inline int compare_and_swap(long * p, long oldval, long newval)
{
  char ret;
  long readval;

  __asm__ __volatile__ ("lock; cmpxchg %3, %1; sete %0"
                       : "=q" (ret), "=m" (*p), "=a" (readval)
                       : "r" (newval), "m" (*p), "a" (oldval));
  return ret;
}

static inline int get_eflags()
{
  int res;
  __asm__ __volatile__ ("pushfl; popl %0" : "=r" (res) : );
  return res;
}

static inline void set_eflags(int newflags)
{
  __asm__ __volatile__ ("pushl %0; popfl" : : "r" (newflags) : "cc");
}

static inline int compare_and_swap_is_available(void)
{
  int oldflags = get_eflags();
  int changed;
  /* Flip AC bit in EFLAGS */
  set_eflags(oldflags ^ 0x40000);
  /* See if bit changed */
  changed = (get_eflags() ^ oldflags) & 0x40000;
  /* Restore EFLAGS */
  set_eflags(oldflags);
  /* If the AC flag did not change, it's a 386 and it lacks cmpxchg.
     Otherwise, it's a 486 or above and it has cmpxchg. */
  return (changed != 0);
}