1 #include <u.h>
2 #include <unistd.h>
3 #include <sys/time.h>
4 #include <sched.h>
5 #include <libc.h>
6 
7 int _ntas;
8 static int
9 _xtas(void *v)
10 {
11 	int x;
12 
13 	_ntas++;
14 	x = _tas(v);
15 	if(x != 0 && x != 0xcafebabe){
16 		print("bad tas value %d\n", x);
17 		abort();
18 	}
19 	return x;
20 }
21 
22 int
23 canlock(Lock *l)
24 {
25 	return !_xtas(&l->val);
26 }
27 
28 void
29 unlock(Lock *l)
30 {
31 	l->val = 0;
32 }
33 
34 void
35 lock(Lock *lk)
36 {
37 	int i;
38 
39 	/* once fast */
40 	if(!_xtas(&lk->val))
41 		return;
42 	/* a thousand times pretty fast */
43 	for(i=0; i<1000; i++){
44 		if(!_xtas(&lk->val))
45 			return;
46 		sched_yield();
47 	}
48 	/* now nice and slow */
49 	for(i=0; i<1000; i++){
50 		if(!_xtas(&lk->val))
51 			return;
52 		usleep(100*1000);
53 	}
54 	/* take your time */
55 	while(_xtas(&lk->val))
56 		usleep(1000*1000);
57 }