There is a known issue with protobuf in loading dynamically linked libraries that all link to protobuf: https://code.google.com/p/protobuf/issues/detail?id=128. @longjon may be able to comment from his experience on this. A possible workaround is to combine your separate library-classifier combinations into a single library-classifiers arrangement with different calls for each model -- but in my own work I've only worked with a single libcaffe.so linked library that may execute different models depending on the calling code.

Well, the point is, that it works fine until I've updated the caffe version yesterday and checked out the latest master (because of the modification of the net-constructor!). Even with the same protobuf version our implementation works with an older version of caffe on other 14.04 ubuntu systems we have. But this is a caffe version, we checked out by means of a snapshot (zip-file) more than half a year ago, so unfortunately we don't have any version number! But I already used a newer version, that also works in our framework with dynamic loading. Unfortunately I removed this trunk (before I checked out the current version) and thus I don't know its exact version.

We found out, that in the new caffe version, the CMakeList files and structure changed for building the protobuf files and part, respectively (in comparison to our old caffe snapshot!). So it seems, that these changes cause our trouble. I would like to test the last 2-3 caffe master versions. Is there a way to check out these older versions?

One more issue: Handling different classifiers in different libraries is a perfect way to allow for a flexible system structure, which is essential for a modular system concept. But even in this dynamic framework we only load "libcaffe.so" once which is a part of the main application. This is the usual way to handle shared objects.

Is there a way to check out these older versions?

You can check out any version of the project since it is versioned through git. You can also look at our releases and pick a favorite.

CMakeList files and structure changed

#1667 overhauled the CMake build.

One more issue: Handling different classifiers in different libraries is a perfect way to allow for a flexible system structure, which is essential for a modular system concept. But even in this dynamic framework we only load "libcaffe.so" once which is a part of the main application. This is the usual way to handle shared objects.

Right, that's sensible and fine -- what I was trying to say and why I linked the protobuf issue is that multiple libraries linked to protobuf (like Caffe classifiers) can conflict if they have a shared message. The protobuf issue suggests statically linking your classifier modules to libprotobuf. Earlier the whole Caffe project was static linked but we've switched to dynamic linking.

You may want to try the Makefile/Makefile.config build; at present the CMake build is still community-supported, so I can't offer specific help with that.

The error you're getting does suggest that libcaffe is being loaded twice. You may want to check this with LD_DEBUG.

If you can produce a minimal non-working example using the Makefile build, I may be able to look into the issue.

Thanks for you fast replies. We solved our problem, which was caused by linking the "libproto.a" to our dynamic libraries. This causes the above error and is not necessary anymore with the new caffe version. Now everything is fine and works. :-)

Thank you for your great support & best regards, Tom

Yep, linking caffe against libprotobuf.a instead of libprotobuf.so could solve this issue.

@tianzhi0549 Can you show in details how to link caffe against libprotobuf.a instead of libprotobuf.so. Thank you so much.

@denny1108 I changed caffe's Makefile. Specifically, I added -Wl,-Bstatic -lprotobuf -Wl,-Bdynamic to LDFLAGS and removed protobuf from LIBRARIES.

I have uploaded my Makefile to gist(https://gist.github.com/tianzhi0549/773c8dbc383c0cb80e7b). You could check it out to see what changes I made (Line 172 and 369).

@tianzhi0549 Changing the Makefile gives:

LD -o .build_debug/lib/libcaffe.so
/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/libprotobuf.a(common.o): relocation R_X86_64_32S against `_ZTVN6google8protobuf7ClosureE' can not be used when making a shared object; recompile with -fPIC
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/libprotobuf.a: error adding symbols: Bad value
collect2: error: ld returned 1 exit status

ANy ideas on how to solve this?