Android Java Dnn.forward multiple output layers -> segmentation fault

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Hello all,

I want to run a yolov3-tiny darknet model on an android device using opencv. that yolo model has 2 output layers named "yolo_16" and "yolo_23". When i try to run the model with either one of these layers as output the code works as expected:

net.forward(outputs, "yolo_16")

but when i try to get both layers in one call like in these examples

• https://answers.opencv.org/question/2...
• https://github.com/opencv/opencv/issu...

i get a segmentation fault error like this:

Fatal signal 11 (SIGSEGV), code 1, fault addr 0x0 in tid 5691 (Thread-8)

the opencv version is 3.4.3 installed according to these instructions on android studio.

a reduced version of the code that i use is here:

public class MainActivity extends AppCompatActivity implements CvCameraViewListener2 {

    private Mat                  mRgba;
    private Net                  net;
    private List<String>         ln;
    private CameraBridgeViewBase mOpenCvCameraView;

    private BaseLoaderCallback  mLoaderCallback = new BaseLoaderCallback(this) {
        @Override public void onManagerConnected(int status) {
            if (status == LoaderCallbackInterface.SUCCESS) { mOpenCvCameraView.enableView(); }
            else { super.onManagerConnected(status); }
        }
    };

    @Override public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.CAMERA}, 200);
            return;
        }

        mOpenCvCameraView = (CameraBridgeViewBase) findViewById(R.id.color_blob_detection_activity_surface_view);
        mOpenCvCameraView.setMaxFrameSize(720, 720);
        mOpenCvCameraView.setVisibility(SurfaceView.VISIBLE);
        mOpenCvCameraView.setCvCameraViewListener(this);
    }

    public void onCameraViewStarted(int width, int height) {
        mRgba = new Mat(height, width, CvType.CV_8UC4);
        net = Dnn.readNetFromDarknet(getFile("yolov3-tiny.cfg", this), getFile("yolov3-tiny.weights", this));
        ln = getOutputNames(net);

    }
    public void onCameraViewStopped() {
        mRgba.release();
    }

    public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
        mRgba = inputFrame.rgba();

        Imgproc.cvtColor(mRgba, mRgba, Imgproc.COLOR_RGBA2RGB);
        Mat inputBlob = Dnn.blobFromImage(mRgba, 1.0, new Size(416,416), new Scalar(0), false, false);

        net.setInput(inputBlob);
        List<Mat> output = new ArrayList<Mat>();

        net.forward(output, ln);

        inputBlob.release();
        return mRgba;
    }

    @Override public void onPause() {
        super.onPause();
        if (mOpenCvCameraView != null) { mOpenCvCameraView.disableView(); }
    }

    @Override public void onResume() {
        super.onResume();
        if (!OpenCVLoader.initDebug()) { OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_0_0, this, mLoaderCallback); }
        else { mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS); }
    }

    public void onDestroy() {
        super.onDestroy();
        if (mOpenCvCameraView != null) { mOpenCvCameraView.disableView(); }
    }



    private static MatOfByte getFile(String file, Context context) {
        AssetManager assetManager = context.getAssets();
        BufferedInputStream inputStream = null;
        try {
            // Read data from assets.
            inputStream = new BufferedInputStream(assetManager.open(file));
            byte[] data = new byte[inputStream.available()];
            inputStream.read(data);
            inputStream.close();

            return new MatOfByte(data);
        } catch (IOException ex) { }
        return new MatOfByte();
    }

    private static List<String> getOutputNames(Net net) {
        List<String> names = new ArrayList<>();

        List<Integer> outLayers = net.getUnconnectedOutLayers().toList();
        List<String> layersNames = net.getLayerNames();

        outLayers.forEach((item) -> names.add(layersNames.get(item - 1)));
        return names;
    }

and the full error is here:

Fatal signal 11 (SIGSEGV), code 1, fault addr 0x0 in tid 5691 (Thread-8)

*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Build fingerprint: 'HUAWEI/ANE-LX1/HWANE:8.0.0/HUAWEIANE-LX1/178(C432):user/release-keys'
Revision: '0'
ABI: 'arm64'
pid: 5634, tid: 5691, name: Thread-8  >>> com.example.opencv_yolo <<<
signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0
Cause: null pointer dereference
    x0   0000000000000000  x1   0000000000000000  x2   0000000000000000  x3   0000000000000000
    x4   000000742cf09380  x5   0000000000000000  x6   000000743b66b3c0  x7   0000000000000000
    x8   34b0d45095ce85c8  x9   34b0d45095ce85c8  x10  000000000000006b ...