Function popGenericCommand

src/t_list.cpp:458–502

Implements the generic list pop operation for LPOP/RPOP. * The where argument specifies which end of the list is operated on. An * optional count may be provided as the third argument of the client's * command. */

 * optional count may be provided as the third argument of the client's
 * command. */
void popGenericCommand(client *c, int where) {
    long count = 0;
    robj *value;

    if (c->argc > 3) {
        addReplyErrorFormat(c,"wrong number of arguments for '%s' command",
                            c->cmd->name);
        return;
    } else if (c->argc == 3) {
        /* Parse the optional count argument. */
        if (getPositiveLongFromObjectOrReply(c,c->argv[2],&count,NULL) != C_OK) 
            return;
        if (count == 0) {
            /* Fast exit path. */
            addReplyNullArray(c);
            return;
        }
    }

    robj *o = lookupKeyWriteOrReply(c, c->argv[1], shared.null[c->resp]);
    if (o == NULL || checkType(c, o, OBJ_LIST))
        return;

    if (!count) {
        /* Pop a single element. This is POP's original behavior that replies
         * with a bulk string. */
        value = listTypePop(o,where);
        serverAssert(value != NULL);
        addReplyBulk(c,value);
        decrRefCount(value);
        listElementsRemoved(c,c->argv[1],where,o,1);
    } else {
        /* Pop a range of elements. An addition to the original POP command,
         *  which replies with a multi-bulk. */
        long llen = listTypeLength(o);
        long rangelen = (count > llen) ? llen : count;
        long rangestart = (where == LIST_HEAD) ? 0 : -rangelen;
        long rangeend = (where == LIST_HEAD) ? rangelen - 1 : -1;
        int reverse = (where == LIST_HEAD) ? 0 : 1;

        addListRangeReply(c,o,rangestart,rangeend,reverse);
        quicklistDelRange((quicklist*)ptrFromObj(o),rangestart,rangelen);
        listElementsRemoved(c,c->argv[1],where,o,rangelen);
    }
}

/* LPOP <key> [count] */
void lpopCommand(client *c) {