1 #include <unistd.h>
2 #include <sched.h>
3 #include <lib9.h>
4 
5 int _ntas;
6 static int
7 _xtas(void *v)
8 {
9 	int x;
10 
11 	_ntas++;
12 	x = _tas(v);
13 	return x;
14 }
15 
16 int
17 canlock(Lock *l)
18 {
19 	return !_xtas(&l->val);
20 }
21 
22 void
23 unlock(Lock *l)
24 {
25 	l->val = 0;
26 }
27 
28 void
29 lock(Lock *lk)
30 {
31 	int i;
32 
33 	/* once fast */
34 	if(!_xtas(&lk->val))
35 		return;
36 	/* a thousand times pretty fast */
37 	for(i=0; i<1000; i++){
38 		if(!_xtas(&lk->val))
39 			return;
40 		sched_yield();
41 	}
42 	/* now nice and slow */
43 	for(i=0; i<1000; i++){
44 		if(!_xtas(&lk->val))
45 			return;
46 		usleep(100*1000);
47 	}
48 	/* take your time */
49 	while(_xtas(&lk->val))
50 		usleep(1000*1000);
51 }