bytedeco/javacpp

The missing bridge between Java and native C++

Samuel Audet

@saudet

That was 1.3

Srdjan Prodanovic

@prodanovic

Yes, the binaries. Thanks!

Samuel Audet

@saudet

It's always possible to rebuild from source on older versions of CUDA though

Srdjan Prodanovic

@prodanovic

I was doing that 3 years ago, and frankly its much easier for me to upgrade CUDA :)

Kim Eik

@netbrain

how should i debug symbol lookup errors like the following?

symbol lookup error: /home/netbrain/.javacpp/cache/imbs-mt-linux-x86_64.jar/org/bytedeco/imbs/linux-x86_64/libjniimbs.so: undefined symbol: _ZN24BackgroundSubtractorIMBSC1Ev

Samuel Audet

@saudet

$ c++filt _ZN24BackgroundSubtractorIMBSC1Ev
BackgroundSubtractorIMBS::BackgroundSubtractorIMBS()

Looks like that class is missing the default constructor's definition. If it's actually missing, we can Info.skip() it or in this case might be easier to use Info.purify() if we're not supposed to be able to allocate it directly anyway.

Kim Eik

@netbrain

well thing is,, seems to be there..

Samuel Audet

@saudet

If you're not linking with it though it won't be able to find it.

Kim Eik

@netbrain

$ readelf -Ws org/bytedeco/imbs/linux-x86_64/libjniimbs.so | grep _ZN24BackgroundSubtractorIMBSC1Ev
    10: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND _ZN24BackgroundSubtractorIMBSC1Ev

Samuel Audet

@saudet

You'll need to link it with the library that has that symbol, but with a number instead of "UND".

If you don't have that library, you'll need to figure out how you're supposed to build that library so that it ends up somewhere.

Kim Eik

@netbrain

I believe this is whats being linked from the java application

Samuel Audet

@saudet

No, Java can't do that, your C++ compiler needs to do that.

Kim Eik

@netbrain

ok, so where is the fault, in cppbuild.sh?

Samuel Audet

@saudet

Well, where is that library anyway?

Kim Eik

@netbrain

its the preset that im building

Samuel Audet

@saudet

If it's nowhere to be found, yes, you'd want to build it as part of cppbuild.sh

You may want to read this if you haven't already:
https://github.com/bytedeco/javacpp-presets/wiki/Create-New-Presets

Kim Eik

@netbrain

Im confused, what does UND mean in this context?

undefined?

Kim Eik

@netbrain

ok, think im on to something

ok.. now i understand..

so the so file produced by javacpp doesnt actually contain the library so aswell, only the generated code from javacpp to serve as the jni binding

would that be a fair statement?

Kim Eik

@netbrain

no.. guess im wrong.

Kim Eik

@netbrain

Wohoo, victory.

so, was basically missing to move the compiled library into the lib folder under cppbuild.

now, i get to do the same thing all over again in windows :)

Samuel Audet

@saudet

@netbrain BTW, we can use AppVeyor and Travis CI for that cross-platform builds on forks by modifying the .appveyor.yml and .travis.yml files

Kim Eik

@netbrain

Wasnt the end of th story after all :( seems to be something wrong with load order. if i try to use the library it gets unsatisfied link error on opencv_stitching. If i add opencv_stitching to the inherit clause then it get's a bit further. but now it complains it is missing cudafeatures2d. So what should i do in this situation keep adding to the inherit clause? or is the issue elsewhere?

i mean, all the required libraries are present, its just that it does not load them implicitly in the correct order. So im guessing i need to define how these libraries should be loaded?

and my gut feeling is telling me that the inherit clause should only be used for resolving compile time issues. not runtime..

Samuel Audet

@saudet

It's also used at runtime, although there is "preload" for that too, so yes just put everything there.

Kim Eik

@netbrain

would you prefer preload over inherit?

Kim Eik

@netbrain

is this really the way to go? i'm getting a foul taste from this..

@Properties(
        inherit = {
                opencv_core.class,
                opencv_highgui.class,
                opencv_imgproc.class,
                opencv_features2d.class,
                opencv_stitching.class,
                opencv_aruco.class,
                opencv_bgsegm.class,
                opencv_bioinspired.class,
                opencv_face.class,
                opencv_img_hash.class,
                opencv_quality.class,
                opencv_saliency.class,
        },
....

I find it weird that i have to add dependency on stuff that the library itself (afaik) doesnt depend on

Samuel Audet

@saudet

yes, we just need to add the ones it depends on, and those will inherit others transitively

Kim Eik

@netbrain

Caused by: java.lang.UnsatisfiedLinkError: C:\dev\javacpp\target\test-classes\org\bytedeco\javacpp\windows-x86_64\jniPointerTest.dll: Can't load IA 32-bit .dll on a AMD 64-bit platform

anyone ever seen this before on a windows system?

Samuel Audet

@saudet

It just means you'll need to use the compiler for x64 (amd64)

Kim Eik

@netbrain

is there an environment variable for that? i followed the guide on https://github.com/bytedeco/javacpp-presets/wiki/Building-on-Windows#installation-recipe-for-visual-studiuo-2015-and-windows-10

tried setting TARGET_ARCH and explicitly setting -Djavacpp.platform

Kim Eik

@netbrain

Target: x86_64-w64-mingw32

Kim Eik

@netbrain

ah, ok. seems to be visual studio with is confiugured for 32bit.

Samuel Audet

@saudet

vcvarsall.bat amd64, if you're using that

Kim Eik

@netbrain

yeah, testing that now. so would it be possible to use dockcross to compile javacpp and javacpp-presets or is there anything they require native toolchains?

Compiling C:\dev\javacpp\target\test-classes\org\bytedeco\javacpp\windows-x86_64-ext1\jniBuilderTest.dll
cl /IC:\jdk-13\include /IC:\jdk-13\include\win32 C:\dev\javacpp\target\test-classes\org\bytedeco\javacpp\jniBuilderTest.cpp C:\dev\javacpp\jnijavacpp.cpp /Oi /O2 /EHsc /Gy /GL /MD /LD /W3 /link /OUT:jniBuilderTest.dll psapi.lib
Deleting C:\dev\javacpp\target\test-classes\org\bytedeco\javacpp\jniBuilderTest.cpp
Deleting C:\dev\javacpp\jnijavacpp.cpp
Loader
Note: UnsatisfiedLinkError should get thrown here and printed below.
java.lang.UnsatisfiedLinkError: LoadLibrary() failed with 0x7e
Builder

test was successful though

ah haha, that was expected..

didnt read the line above. lol

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