如何在Mac上的JNI构建中包括外部框架/库

Question

I have an API I am building that calls native operations through C/C++. I have created a JNI project and built the jnilib using the following arguments:

g++ -dynamiclib -rpath @loader_path -F /Users/nstuart/Downloads/myo-sdk -framework myo -framework JavaVM -o libmyo.jnilib *.o

I'm trying to have my API be self-contained, so all the libraries are in my /src/main/resources and I just copy them to a temp directory before setting the java.library.path and loading my JNI library from there. I've gotten this to work on Windows, as I just need my JNI DLL, and another DLL that I can copy over too.

When I try this on Mac, I run into issues:

Exception in thread "main" java.lang.UnsatisfiedLinkError: /private/var/folders/sf/3_7c7p452dq9jt_39yx76cn55rd8xh/T/libmyo.jnilib: dlopen(/private/var/folders/sf/3_7c7p452dq9jt_39yx76cn55rd8xh/T/libmyo.jnilib, 1): Library not loaded: @rpath/myo.framework/Versions/A/myo
  Referenced from: /private/var/folders/sf/3_7c7p452dq9jt_39yx76cn55rd8xh/T/libmyo.jnilib
  Reason: image not found

I assume this is because I have my @rpath set up incorrectly, and I'm wondering the "correct" way to set it up. From the perspective of java, where is @rpath ? If it's relative, or at the loader_path location, where is that? I would prefer to be able to set this at run time such that I can copy over my library files, then point to where they are for the program.

In Java, how do I determine: @rpath ? loader_path ? Where dependent frameworks are being loaded from?

Answer 1

The way @rpath works is each executable or library replaces @rpath in the framework's install name with a list of directories to search for the framework when linking to it. The error you're seeing is libmyo.jnilib being unable to find myo.framework since its runpath is set to @loader_path , meaning it will look for myo.framework in /private/var/folders/sf/3_7c7p452dq9jt_39yx76cn55rd8xh/T/ .

From what I can tell, you have myo.framework in /Users/nstuart/Downloads/myo-sdk . You can fix the issue by adjusting your runpath, or moving myo.framework to your output directory.

Reference: Myo SDK Reference subsection "Terminal"

Answer 2

I got that working for the JavaCPP Presets . On the third-party libraries we link with, we need to use install_name_tool to change whatever the build process put there to @rpath (which is lib in the case of OpenCV), as demonstrated by these lines in the cppbuild.sh script for OpenCV:

VER=${OPENCV_VERSION:0:3}
BADPATH=lib
LIBS="../lib/libtbb.dylib ../lib/libopencv_*.$VER.dylib"
for f in $LIBS; do install_name_tool $f -id @rpath/`basename $f` \
    -add_rpath /usr/local/lib/ -add_rpath /opt/local/lib/ -add_rpath @loader_path/. \
    -change libtbb.dylib @rpath/libtbb.dylib \
    -change $BADPATH/libopencv_core.$VER.dylib @rpath/libopencv_core.$VER.dylib \
    -change $BADPATH/libopencv_calib3d.$VER.dylib @rpath/libopencv_calib3d.$VER.dylib \
    -change $BADPATH/libopencv_features2d.$VER.dylib @rpath/libopencv_features2d.$VER.dylib \
    -change $BADPATH/libopencv_flann.$VER.dylib @rpath/libopencv_flann.$VER.dylib \
    -change $BADPATH/libopencv_gpu.$VER.dylib @rpath/libopencv_gpu.$VER.dylib \
    -change $BADPATH/libopencv_highgui.$VER.dylib @rpath/libopencv_highgui.$VER.dylib \
    -change $BADPATH/libopencv_imgproc.$VER.dylib @rpath/libopencv_imgproc.$VER.dylib \
    -change $BADPATH/libopencv_legacy.$VER.dylib @rpath/libopencv_legacy.$VER.dylib \
    -change $BADPATH/libopencv_ml.$VER.dylib @rpath/libopencv_ml.$VER.dylib \
    -change $BADPATH/libopencv_nonfree.$VER.dylib @rpath/libopencv_nonfree.$VER.dylib \
    -change $BADPATH/libopencv_objdetect.$VER.dylib @rpath/libopencv_objdetect.$VER.dylib \
    -change $BADPATH/libopencv_photo.$VER.dylib @rpath/libopencv_photo.$VER.dylib \
    -change $BADPATH/libopencv_video.$VER.dylib @rpath/libopencv_video.$VER.dylib; done
;;

To find what we have as BADPATH for myo, we can use the otool -L command. Once the framework library file is fixed, you would need to rebuild your libmyo.jnilib file.