Subversion Repositories planix.SVN

#include "u.h"
#include "lib.h"
#include "dat.h"
#include "fns.h"

static void
queue(Proc **first, Proc **last)
{
        Proc *t;

        t = *last;
        if(t == 0)
                *first = up;
        else
                t->qnext = up;
        *last = up;
        up->qnext = 0;
}

static Proc*
dequeue(Proc **first, Proc **last)
{
        Proc *t;

        t = *first;
        if(t == 0)
                return 0;
        *first = t->qnext;
        if(*first == 0)
                *last = 0;
        return t;
}

void
qlock(QLock *q)
{
        lock(&q->lk);

        if(q->hold == 0) {
                q->hold = up;
                unlock(&q->lk);
                return;
        }

        /*
         * Can't assert this because of RWLock
        assert(q->hold != up);
         */             

        queue((Proc**)&q->first, (Proc**)&q->last);
        unlock(&q->lk);
        procsleep();
}

int
canqlock(QLock *q)
{
        lock(&q->lk);
        if(q->hold == 0) {
                q->hold = up;
                unlock(&q->lk);
                return 1;
        }
        unlock(&q->lk);
        return 0;
}

void
qunlock(QLock *q)
{
        Proc *p;

        lock(&q->lk);
        /* 
         * Can't assert this because of RWlock
        assert(q->hold == CT);
         */
        p = dequeue((Proc**)&q->first, (Proc**)&q->last);
        if(p) {
                q->hold = p;
                unlock(&q->lk);
                procwakeup(p);
        } else {
                q->hold = 0;
                unlock(&q->lk);
        }
}

int
holdqlock(QLock *q)
{
        return q->hold == up;
}