opencv_dnn produce errors when a thirdparty also links against protobuf

[agilmor]

System information (version)

• OpenCV => 3.1 (and probably 3.0)
• Operating System / Platform => Debian Jessie (and others)
• Compiler => Gcc 4.9 (and probably others)

Detailed description

When using OpenCV DNN with Caffe, both linking against Protobuf the following error apears:

[libprotobuf ERROR google/protobuf/descriptor_database.cc:57] File already exists in database: caffe.proto
[libprotobuf FATAL google/protobuf/descriptor.cc:1272] CHECK failed: generated_database_->Add(encoded_file_descriptor, size): 
terminate called after throwing an instance of 'google::protobuf::FatalException'

And then a std::terminate is thrown by protobuf.

Some people reported that its a problem with dynamic linking against Protobuf, but in my experience it also happen using static linking.

I'm not sure if the problem is in OpenCV, in Protobuf, or in Caffe.
But the current workaround is disable OpenCV DNN.
Is the problem really there, in opencv_dnn? Can we solve it?

Steps to reproduce

Build OpenCV with DNN.
Build Caffe with pycaffe or matcaffe.
In caffe, just run something like:

$ matlab -nodesktop -r "addpath ./matlab/; caffe.set_mode_cpu();"

And you will get the std::terminate.

Similar commands with pycaffe also reproduce this error.

Thanks!

PS: This comes from opencv/opencv#7425

[mshabunin]

Can you please check whether the problem persists with the latest OpenCV version? Can you provide reproducing example in Python or C++?

[arrybn]

@agilmor, there are modules in contrib, which try to use system protobuf and load caffe.proto: dnn_modern and cnn_3dobj. But dnn module builds its own version of protobuf, so there shouldn't be any conflicts with system protobuf. Try to disable dnn_modern and cnn_3dobj modules in your build (-DBUILD_opencv_cnn_3dobj=OFF -DBUILD_opencv_dnn_modern=OFF as options for cmake) and please let me know about results

[dkurt]

@agilmor , also the latest Caffe changes might help, BVLC/caffe#5624.

[basvandijk]

In NixOS we also run into the same File already exists in database: caffe.proto error. We currently disable the dnn_modern and cnn_3dob modules to work around this issue.

@dkurt I tried building with the latest caffe which includes the cmake: rename libproto.a -> libcaffeproto.a patch but that didn't help unfortunately.

[dkurt]

@basvandijk, we're going to avoid protobuf dependency by own parser, #1291 + opencv/opencv#9106. You may try it if you want to use DNN module.

[alalek]

Migrate here: opencv/opencv#7425