queue.go

package mongogo


type queue struct {
    elems []interface{}
    nelems, popi, pushi int
}

func (q *queue) Len() int {
    return q.nelems
}

func (q *queue) Push(elem interface{}) {
    //debugf("Pushing(pushi=%d popi=%d cap=%d): %#v\n",
    //       q.pushi, q.popi, len(q.elems), elem)
    if q.nelems == len(q.elems) {
        q.expand()
    }
    q.elems[q.pushi] = elem
    q.nelems++
    q.pushi = (q.pushi + 1) % len(q.elems)
    //debugf(" Pushed(pushi=%d popi=%d cap=%d): %#v\n",
    //       q.pushi, q.popi, len(q.elems), elem)
}

func (q *queue) Pop() (elem interface{}) {
    //debugf("Popping(pushi=%d popi=%d cap=%d)\n",
    //       q.pushi, q.popi, len(q.elems))
    if q.nelems == 0 {
        return nil
    }
    elem = q.elems[q.popi]
    q.elems[q.popi] = nil // Help GC.
    q.nelems--
    q.popi = (q.popi + 1) % len(q.elems)
    //debugf(" Popped(pushi=%d popi=%d cap=%d): %#v\n",
    //       q.pushi, q.popi, len(q.elems), elem)
    return elem
}

func (q *queue) expand() {
    curcap := len(q.elems)
    var newcap int
    if curcap == 0 {
        newcap = 8
    } else if curcap < 1024 {
        newcap = curcap * 2
    } else {
        newcap = curcap + (curcap / 4)
    }
    elems := make([]interface{}, newcap)

    if q.popi == 0 {
        copy(elems, q.elems)
        q.pushi = curcap
    } else {
        newpopi := newcap - (curcap - q.popi)
        copy(elems, q.elems[:q.popi])
        copy(elems[newpopi:], q.elems[q.popi:])
        q.popi = newpopi
    }
    q.elems = elems
}