Function zslDefrag

app/redis-6.2.6/src/defrag.c:204–237

Defrag helper for sorted set. * Update the robj pointer, defrag the skiplist struct and return the new score * reference. We may not access oldele pointer (not even the pointer stored in * the skiplist), as it was already freed. Newele may be null, in which case we * only need to defrag the skiplist, but not update the obj pointer. * When return value is non-NULL, it is the score reference th

 * When return value is non-NULL, it is the score reference that must be updated
 * in the dict record. */
double *zslDefrag(zskiplist *zsl, double score, sds oldele, sds newele) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x, *newx;
    int i;
    sds ele = newele? newele: oldele;

    /* find the skiplist node referring to the object that was moved,
     * and all pointers that need to be updated if we'll end up moving the skiplist node. */
    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        while (x->level[i].forward &&
            x->level[i].forward->ele != oldele && /* make sure not to access the
                                                     ->obj pointer if it matches
                                                     oldele */
            (x->level[i].forward->score < score ||
                (x->level[i].forward->score == score &&
                sdscmp(x->level[i].forward->ele,ele) < 0)))
            x = x->level[i].forward;
        update[i] = x;
    }

    /* update the robj pointer inside the skip list record. */
    x = x->level[0].forward;
    serverAssert(x && score == x->score && x->ele==oldele);
    if (newele)
        x->ele = newele;

    /* try to defrag the skiplist record itself */
    newx = activeDefragAlloc(x);
    if (newx) {
        zslUpdateNode(zsl, x, newx, update);
        return &newx->score;
    }
    return NULL;
}

/* Defrag helper for sorted set.
 * Defrag a single dict entry key name, and corresponding skiplist struct */