batch scoring in cpp

まず、ResNet のシンボルファイルとパラメータファイルを使って issue にある 2 つの経路を再現し、次に各方法で使用される C++ NDArray::Load、Symbol::SimpleBind、および executor のセットアップ呼び出しを追跡します。結果として得られる引数マップとバッチ処理を比較し、segmentation fault の原因を特定し、どの batch-scoring アプローチが有効でその理由は何かを文書化できたことを完了の定義とします。

I am trying to load a pre-built model and do batch scoring, I tried the following two ways, the first one can produce some results, and the second one compiles successfully but runs with segmentation fault. Could you please let me know which way I should follow, and why the second way doesn't work? Thanks!
method 1:

/* Image size and channels */
int width = 224;
int height = 224;
int channels = 3;
int batch_size = 5;

Context ctx_dev(DeviceType::kCPU, 0);
map<string, NDArray> args_map;
map<string, NDArray> aux_map;
map<string, NDArray> parameters;

NDArray::Load("../Resnet/resnet-152-0000.params", 0, &parameters);

for (const auto &k : parameters) {
  if (k.first.substr(0, 4) == "aux:") {
    auto name = k.first.substr(4, k.first.size() - 4);
    aux_map[name] = k.second.Copy(ctx_dev);
  }
  if (k.first.substr(0, 4) == "arg:") {
    auto name = k.first.substr(4, k.first.size() - 4);
    args_map[name] = k.second.Copy(ctx_dev);
  }
}

auto net = Symbol::Load("../Resnet/resnet-152-symbol.json");

auto data_iter = MXDataIter("ImageRecordIter")
.SetParam("path_imglist","../caltech_256/caltech-256-60-train.lst")
.SetParam("path_imgrec","../caltech_256/caltech-256-60-train.rec")
.SetParam("data_shape", Shape(3, 224, 224))
.SetParam("batch_size", batch_size)
.SetParam("shuffle", 1)
.CreateDataIter();

while(data_iter.Next()){
auto batch = data_iter.GetData();
args_map["data"] = batch;
auto *exec = net.SimpleBind(ctx_dev, args_map);
exec->Forward(false);
auto outputs = exec->outputs[0].Copy(Context(kCPU, 0));
NDArray::WaitAll();
for (int i = 0; i <2; i++) {
cout << outputs.At(0, i) <<",";
}
cout << endl;
}
MXNotifyShutdown();

method 2:

int width = 224;
int height = 224;
int channels = 3;
int batch_size = 5;

Context ctx_dev(DeviceType::kCPU, 0);

map<string, NDArray> args_map;
map<string, NDArray> aux_map;

args_map["data"] = NDArray(Shape(batch_size, channels, width, height), ctx_dev);
args_map["label"] = NDArray(Shape(batch_size), ctx_dev);

auto net = Symbol::Load("../Resnet/resnet-152-symbol.json");

auto *exec = net.SimpleBind(ctx_dev, args_map);

NDArray::Load("../Resnet/resnet-152-0000.params", 0, &args_map);

auto data_iter = MXDataIter("ImageRecordIter")
  .SetParam("path_imglist","../caltech_256/caltech-256-60-train.lst")
  .SetParam("path_imgrec","../caltech_256/caltech-256-60-train.rec")
  .SetParam("data_shape", Shape(3, 224, 224))
  .SetParam("batch_size", batch_size)
  .SetParam("shuffle", 1)
  .CreateDataIter();

while(data_iter.Next()){
auto batch = data_iter.GetDataBatch();
batch.data.CopyTo(&args_map["data"]);
batch.label.CopyTo(&args_map["label"]);
exec->Forward(false);
NDArray::WaitAll();
}

delete exec;
MXNotifyShutdown();