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 	return x;
16 }
17 
18 int
19 canlock(Lock *l)
20 {
21 	return !_xtas(&l->val);
22 }
23 
24 void
25 unlock(Lock *l)
26 {
27 	l->val = 0;
28 }
29 
30 void
31 lock(Lock *lk)
32 {
33 	int i;
34 
35 	/* once fast */
36 	if(!_xtas(&lk->val))
37 		return;
38 	/* a thousand times pretty fast */
39 	for(i=0; i<1000; i++){
40 		if(!_xtas(&lk->val))
41 			return;
42 		sched_yield();
43 	}
44 	/* now nice and slow */
45 	for(i=0; i<1000; i++){
46 		if(!_xtas(&lk->val))
47 			return;
48 		usleep(100*1000);
49 	}
50 	/* take your time */
51 	while(_xtas(&lk->val))
52 		usleep(1000*1000);
53 }