spinlock.c

用c++包装好的线程库,直接拿来使用,提高效率.

//
// struct spinlock
//
// this structure is a primitive semaphore.  It simple controls
// the situation of a single integer... with an on/off value.

#include "threads/spinlock.h"

extern "C" {

#       include <sched.h>

};

namespace cpp_threads {

  // Initializer, just to make sure.
  spinlock::spinlock()
  {
    s_spinlock = 0;
  }

  spinlock::~spinlock()
  {
  }

  //
  // testandset
  //
  // test if the spinlock is clear, and set it in one atomic
  // instruction.  Ensuring it is owned by only one process.
  int spinlock::testandset()
  {
    register int ret=1;

#if defined(__i386__)

#ifdef __SMP__
#define LOCK "lock ; "
#else
#define LOCK
#endif

    __asm__ __volatile__(LOCK 
    			 "xchgl %0, %1"
    			 : "=r"(ret), "=m"(s_spinlock)
    			 : "0"(1), "m"(s_spinlock));
#else
#  if defined( __SPARC__ )
        __asm__ __volatile__("swap [%2], %0"
                             : "=&r" (ret)
                             : "0" (1), "r" (&s_spinlock));
#  else
#   if defined( __PPC__ )
        __asm__ __volatile__ ("1:      lwarx   %0,0,%2 \n"
			      "        stwcx.  %3,0,%2 \n"
			      "        bne-    1b"
			      : "=&r" (ret), "=m" (s_spinlock)
			      : "r" (&s_spinlock), "r" (1), "m" (s_spinlock)
			      : "cc", "memory");
#   else
#    if defined( __alpha__ )
	long dummy;
        __asm__ __volatile__(
			     "1:     ldl_l %0,%4\n"
			     "       bis $31,%3,%1\n"
			     "       stl_c %1,%2\n"
			     "       beq %1,2f\n"
#ifdef __SMP__
			     "       mb\n"
#endif
			     ".subsection 2\n"
			     "2:     br 1b\n"
			     ".previous"
			     : "=&r" (ret), "=&r" (dummy), "=m" (s_spinlock)
			     : "rI" (1), "m" (s_spinlock) : "memory");
#    else
#      warning "FIXME: This CPU needs inlined assembly"
	register __volatile__ int& refp = s_spinlock;
	if( refp++ == 0 )
	  ret  = 0;
	else
	  refp--;
#    endif
#   endif
#  endif

#endif

    return ret;
  }

  //
  // acquire
  //
  // continue to try and set the spinlock, until successfull.  Yielding
  // to other processes in the scheduling while waiting.
  void spinlock::acquire()
  {
    do {
      sched_yield();
    } while (testandset());
  }

  //
  // release
  //
  // release the spinlock, by setting it to 0.
  void spinlock::release()
  {
    s_spinlock = 0;
  }

}; // namespace