spinlock.c

来自「多线程库」· C语言 代码 · 共 55 行

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

#include <thread_spinlock.h>

extern "C" {

#       include <sched.h>

};

//
// 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()
{
  int ret;

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

  return ret;
}

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

//
// release
//
// release the spinlock, by setting it to 0.
void spinlock::release()
{
#ifndef RELEASE
  s_spinlock = 0;
#else
  RELEASE(&s_spinlock);
#endif
}