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#include "dat.h"
#include "fns.h"
#include "error.h"
void
lock(Lock *l)
{
int i;
if(_tas(&l->val) == 0)
return;
for(i=0; i<100; i++){
if(_tas(&l->val) == 0)
return;
osyield();
}
for(i=1;; i++){
if(_tas(&l->val) == 0)
return;
osmillisleep(i*10);
if(i > 100){
osyield();
i = 1;
}
}
}
int
canlock(Lock *l)
{
return _tas(&l->val) == 0;
}
void
unlock(Lock *l)
{
coherence();
l->val = 0;
}
void
qlock(QLock *q)
{
Proc *p;
lock(&q->use);
if(!q->locked) {
q->locked = 1;
unlock(&q->use);
return;
}
p = q->tail;
if(p == 0)
q->head = up;
else
p->qnext = up;
q->tail = up;
up->qnext = 0;
unlock(&q->use);
osblock();
}
int
canqlock(QLock *q)
{
if(!canlock(&q->use))
return 0;
if(q->locked){
unlock(&q->use);
return 0;
}
q->locked = 1;
unlock(&q->use);
return 1;
}
void
qunlock(QLock *q)
{
Proc *p;
lock(&q->use);
p = q->head;
if(p) {
q->head = p->qnext;
if(q->head == 0)
q->tail = 0;
unlock(&q->use);
osready(p);
return;
}
q->locked = 0;
unlock(&q->use);
}
void
rlock(RWlock *l)
{
qlock(&l->x); /* wait here for writers and exclusion */
lock(&l->l);
l->readers++;
canqlock(&l->k); /* block writers if we are the first reader */
unlock(&l->l);
qunlock(&l->x);
}
/* same as rlock but punts if there are any writers waiting */
int
canrlock(RWlock *l)
{
if (!canqlock(&l->x))
return 0;
lock(&l->l);
l->readers++;
canqlock(&l->k); /* block writers if we are the first reader */
unlock(&l->l);
qunlock(&l->x);
return 1;
}
void
runlock(RWlock *l)
{
lock(&l->l);
if(--l->readers == 0) /* last reader out allows writers */
qunlock(&l->k);
unlock(&l->l);
}
void
wlock(RWlock *l)
{
qlock(&l->x); /* wait here for writers and exclusion */
qlock(&l->k); /* wait here for last reader */
}
void
wunlock(RWlock *l)
{
qunlock(&l->k);
qunlock(&l->x);
}
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