#include <u.h>#include <libc.h> static struct {	QLp	*p;	QLp	x[1024];} ql = {	ql.x}; enum{	Queuing,	QueuingR,	QueuingW,}; static ulong	(*_rendezvousp)(ulong, ulong) = rendezvous; /* this gets called by the thread library ONLY to get us to use its rendezvous */void_qlockinit(ulong (*r)(ulong, ulong)){	_rendezvousp = r;} /* 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;			p->next = nil;			break;		}	}	return p;} voidqlock(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)((ulong)mp, 1) == ~0)		;	mp->inuse = 0;} voidqunlock(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)((ulong)p, 0x12345) == ~0)			;		return;	}	q->locked = 0;	unlock(&q->lock);} intcanqlock(QLock *q){	lock(&q->lock);	if(!q->locked){		q->locked = 1;		unlock(&q->lock);		return 1;	}	unlock(&q->lock);	return 0;} voidrlock(RWLock *q){	QLp *p, *mp; 	lock(&q->lock);	if(q->writer == 0 && q->head == nil){		/* no writer, go for it */		q->readers++;		unlock(&q->lock);		return;	} 	mp = getqlp();	p = q->tail;	if(p == 0)		q->head = mp;	else		p->next = mp;	q->tail = mp;	mp->next = nil;	mp->state = QueuingR;	unlock(&q->lock); 	/* wait in kernel */	while((*_rendezvousp)((ulong)mp, 1) == ~0)		;	mp->inuse = 0;} intcanrlock(RWLock *q){	lock(&q->lock);	if (q->writer == 0 && q->head == nil) {		/* no writer; go for it */		q->readers++;		unlock(&q->lock);		return 1;	}	unlock(&q->lock);	return 0;} voidrunlock(RWLock *q){	QLp *p; 	lock(&q->lock);	if(q->readers <= 0)		abort();	p = q->head;	if(--(q->readers) > 0 || p == nil){		unlock(&q->lock);		return;	} 	/* start waiting writer */	if(p->state != QueuingW)		abort();	q->head = p->next;	if(q->head == 0)		q->tail = 0;	q->writer = 1;	unlock(&q->lock); 	/* wakeup waiter */	while((*_rendezvousp)((ulong)p, 0) == ~0)		;} voidwlock(RWLock *q){	QLp *p, *mp; 	lock(&q->lock);	if(q->readers == 0 && q->writer == 0){		/* noone waiting, go for it */		q->writer = 1;		unlock(&q->lock);		return;	} 	/* wait */	p = q->tail;	mp = getqlp();	if(p == nil)		q->head = mp;	else		p->next = mp;	q->tail = mp;	mp->next = nil;	mp->state = QueuingW;	unlock(&q->lock); 	/* wait in kernel */	while((*_rendezvousp)((ulong)mp, 1) == ~0)		;	mp->inuse = 0;} intcanwlock(RWLock *q){	lock(&q->lock);	if (q->readers == 0 && q->writer == 0) {		/* no one waiting; go for it */		q->writer = 1;		unlock(&q->lock);		return 1;	}	unlock(&q->lock);	return 0;} voidwunlock(RWLock *q){	QLp *p; 	lock(&q->lock);	if(q->writer == 0)		abort();	p = q->head;	if(p == nil){		q->writer = 0;		unlock(&q->lock);		return;	}	if(p->state == QueuingW){		/* start waiting writer */		q->head = p->next;		if(q->head == nil)			q->tail = nil;		unlock(&q->lock);		while((*_rendezvousp)((ulong)p, 0) == ~0)			;		return;	} 	if(p->state != QueuingR)		abort(); 	/* wake waiting readers */	while(q->head != nil && q->head->state == QueuingR){		p = q->head;		q->head = p->next;		q->readers++;		while((*_rendezvousp)((ulong)p, 0) == ~0)			;	}	if(q->head == nil)		q->tail = nil;	q->writer = 0;	unlock(&q->lock);}