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