#include "u.h"
#include "../port/lib.h"
#include "mem.h"
#include "dat.h"
#include "fns.h"

struct {
	ulong rlock;
	ulong rlockq;
	ulong wlock;
	ulong wlockq;
	ulong qlock;
	ulong qlockq;
} rwstats;

void
qlock(QLock *q)
{
	Proc *p, *mp;

	lock(&q->use);
rwstats.qlock++;
	if(!q->locked) {
		q->locked = 1;
		unlock(&q->use);
		return;
	}
rwstats.qlockq++;
	p = q->tail;
	mp = up;
	if(p == 0)
		q->head = mp;
	else
		p->qnext = mp;
	q->tail = mp;
	mp->qnext = 0;
	mp->state = Queueing;
	unlock(&q->use);
	sched();
}

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);
		ready(p);
		return;
	}
	q->locked = 0;
	unlock(&q->use);
}

void
rlock(RWlock *q)
{
	Proc *p, *mp;

	lock(&q->use);
rwstats.rlock++;
	if(q->writer == 0 && q->head == nil){
		/* no writer, go for it */
		q->readers++;
		unlock(&q->use);
		return;
	}

rwstats.rlockq++;
	p = q->tail;
	mp = up;
	if(p == 0)
		q->head = mp;
	else
		p->qnext = mp;
	q->tail = mp;
	mp->qnext = 0;
	mp->state = QueueingR;
	unlock(&q->use);
	sched();
}

void
runlock(RWlock *q)
{
	Proc *p;

	lock(&q->use);
	p = q->head;
	if(--(q->readers) > 0 || p == nil){
		unlock(&q->use);
		return;
	}

	/* start waiting writer */
	if(p->state != QueueingW)
		panic("runlock");
	q->head = p->qnext;
	if(q->head == 0)
		q->tail = 0;
	q->writer = 1;
	unlock(&q->use);
	ready(p);
}

void
wlock(RWlock *q)
{
	Proc *p, *mp;

	lock(&q->use);
rwstats.wlock++;
	if(q->readers == 0 && q->writer == 0){
		/* noone waiting, go for it */
		q->writer = 1;
		unlock(&q->use);
		return;
	}

	/* wait */
rwstats.wlockq++;
	p = q->tail;
	mp = up;
	if(p == nil)
		q->head = mp;
	else
		p->qnext = mp;
	q->tail = mp;
	mp->qnext = 0;
	mp->state = QueueingW;
	unlock(&q->use);
	sched();
}

void
wunlock(RWlock *q)
{
	Proc *p;

	lock(&q->use);
	p = q->head;
	if(p == nil){
		q->writer = 0;
		unlock(&q->use);
		return;
	}
	if(p->state == QueueingW){
		/* start waiting writer */
		q->head = p->qnext;
		if(q->head == nil)
			q->tail = nil;
		unlock(&q->use);
		ready(p);
		return;
	}

	if(p->state != QueueingR)
		panic("wunlock");

	/* waken waiting readers */
	while(q->head != nil && q->head->state == QueueingR){
		p = q->head;
		q->head = p->qnext;
		q->readers++;
		ready(p);
	}
	if(q->head == nil)
		q->tail = nil;
	q->writer = 0;
	unlock(&q->use);
}