xv6/spinlock.c

#include "types.h"
#include "defs.h"
#include "x86.h"
#include "mmu.h"
#include "param.h"
#include "proc.h"
#include "spinlock.h"

// Can't call cprintf from inside these routines,
// because cprintf uses them itself.
#define cprintf dont_use_cprintf

extern int bootstrap;

int
getcallerpc(void *v)
{
	return ((int*)v)[-1];
}

void
acquire(struct spinlock * lock)
{
	if(cpus[cpu()].nlock++ == 0)
		cli();
	while(cmpxchg(0, 1, &lock->locked) == 1)
		;
	cpuid(0, 0, 0, 0, 0);	// memory barrier
	lock->locker_pc = getcallerpc(&lock);
}

void
release(struct spinlock * lock)
{
	cpuid(0, 0, 0, 0, 0);	// memory barrier
	lock->locked = 0;
	if(--cpus[cpu()].nlock == 0 && !bootstrap)
		sti();
}