void DataReader::read_one(){
// could block here when pre-buffer enough Datum
Datum *datum = pair->free.pop();
datum->Clear();
DataParameter data_param = param.data_param();
if (data_param.shuffle()) cur_idx = Dragon::get_random_value() % indices.size();
else cur_idx = (cur_idx + 1) % indices.size();
IplImage *img = cvLoadImage((data_param.source() + "/" + indices[cur_idx].data()).c_str());
DataTransformer<float>::transform(img, datum);
cvReleaseImage(&img);
datum->set_label(indices[cur_idx].label());
pair->full.push(datum);
}
