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#define _LOCK_EXTENSION
#define _QLOCK_EXTENSION
#define _RESEARCH_SOURCE
#include <u.h>
#include <lock.h>
#include <qlock.h>
#include <stdlib.h>
#include "sys9.h"
#define rendezvous _RENDEZVOUS
#define _rendezvousp rendezvous
#define _tas tas
#define nelem(x) (sizeof(x)/sizeof((x)[0]))
static struct {
QLp *p;
QLp x[1024];
} ql = {
ql.x
};
enum
{
Queuing,
};
/* find a free shared memory location to queue ourselves in */
static QLp*
getqlp(void)
{
QLp *p, *op;
op = ql.p;
for(p = op+1; ; p++){
if(p == &ql.x[nelem(ql.x)])
p = ql.x;
if(p == op)
abort();
if(_tas(&(p->inuse)) == 0){
ql.p = p;
break;
}
}
p->next = nil;
return p;
}
void
qlock(QLock *q)
{
QLp *p, *mp;
lock(&q->lock);
if(!q->locked){
q->locked = 1;
unlock(&q->lock);
return;
}
/* chain into waiting list */
mp = getqlp();
p = q->tail;
if(p == nil)
q->head = mp;
else
p->next = mp;
q->tail = mp;
mp->state = Queuing;
unlock(&q->lock);
/* wait */
while((*_rendezvousp)(mp, (void*)1) == (void*)~0)
;
mp->inuse = 0;
}
void
qunlock(QLock *q)
{
QLp *p;
lock(&q->lock);
p = q->head;
if(p != nil){
/* wakeup head waiting process */
q->head = p->next;
if(q->head == nil)
q->tail = nil;
unlock(&q->lock);
while((*_rendezvousp)(p, (void*)0x12345) == (void*)~0)
;
return;
}
q->locked = 0;
unlock(&q->lock);
}
int
canqlock(QLock *q)
{
if(!canlock(&q->lock))
return 0;
if(!q->locked){
q->locked = 1;
unlock(&q->lock);
return 1;
}
unlock(&q->lock);
return 0;
}
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