void  waitFinished (QModbusReply *reply)
{
    // ...
    
    QModbusRequest modbusRequest(QModbusRequest::MaskWriteRegister, request);
    auto reply = client->sendRawRequest(modbusRequest, macAddr);
    if (!reply) {
        return false;
    }
    if (!reply->isFinished()) {
        QEventLoop loop;
        connect(this, &Engine::sigCancel, &loop, &QEventLoop::quit);
        connect(reply, &QModbusReply::finished, &loop, &QEventLoop::quit);
        loop.exec();
    }
    reply->deleteLater();
    if (cancel_task) {
        LOG_WARN("Task canceled");
        return false;
    }
    
    // do other things...
} 

bool QModbusRtuSerialClientPrivate::canMatchRequestAndResponse(const QModbusResponse& response,
                                                               int sendingServer) const {
    if (m_queue.isEmpty())
        return false;
    const auto& current = m_queue.first();    if (current.reply.isNull())
        return false;  // reply deleted
    if (current.reply->serverAddress() != sendingServer)
        return false;  // server mismatch
    if (current.requestPdu.functionCode() != response.functionCode())
        return false;  // request for different function code
    return true;
}

void QModbusRtuSerialClientPrivate::onReadyRead() {
    // ...
    const QModbusResponse response = adu.pdu();
    if (!canMatchRequestAndResponse(response, adu.serverAddress())) {
        qCWarning(QT_MODBUS) << "(RTU client) Cannot match response with open request, "
                                "ignoring";
        m_queue.first().reply->addIntermediateError(QModbusClient::ResponseRequestMismatch);
        return;
    }
    // ...
}