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Undefined reference to opencv method at runtime when using openCV from a dynamic library

I'm developing a Java application for face recognition based on OpenCV (Image processing) and dlib (face's landmark detection). For that purpose, I built and installed manually both libraries.
> git clone https://github.com/opencv/opencv.git
> cd opencv
> git checkout 3.4 && git reset --hard && git clean -qfdx
> mkdir release
> cd release
> cmake -D BUILD_SHARED_LIBS=OFF -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local ..
> make -j8
> make install
> cd ..
> git clone https://github.com/davisking/dlib.git
> cd dlib
> mkdir build
> cd build
> cmake --config Release -DBUILD_SHARED_LIBS=1 ..
> make -j 8
> make install
I haven't seen a way to create a Java binding for dlib. So, my approach is to create a dynamic library in C that performs some operation mixing dlib and opencv.
On my Java application, I created a Java class (ShapePredictor) with the corresponding native methods
public final class ShapePredictor {
static {
System.loadLibrary("dlibsp");
}
public final long nativeObj;
ShapePredictor(String file) {
nativeObj = n_shape_predictor(file);
}
public long predict(Mat img, int rowStart, int rowEnd, int colStart, int colEnd) {
long nativeLandmarks = n_predict(nativeObj, img.nativeObj, colStart, colEnd, rowStart, rowEnd);
return landmarks;
}
#Override
protected void finalize() throws Throwable {
n_delete(nativeObj);
super.finalize();
}
static native long n_predict(long nativeObj, long img, int rowStart, int rowEnd, int colStart, int colEnd);
static native long n_shape_predictor(String filePath);
// native support for java finalize()
static native void n_delete(long nativeObj);
}
With that, I created the headers file (dlibsp/shape_predictor_java.h)
javah -jni -cp target/face_recognition.jar -o build/include/dlibsp/shape_predictor_java.h es.bsc.compss.apps.utils.aligners.face.DlibAligner.ShapePredictor
and written a cpp file (shape_predictor_java.cpp) implementing such methods.
#include <dlib/image_processing/shape_predictor.h>
#include <dlib/image_processing.h>
#include <dlib/opencv/cv_image.h>
#include <dlib/opencv.h>
#include <dlibsp/shape_predictor_java.h>
#include <opencv2/opencv.hpp>
#include <opencv2/objdetect/objdetect.hpp>
jlong Java_es_bsc_compss_apps_utils_aligners_face_DlibAligner_00024ShapePredictor_n_1shape_1predictor( JNIEnv *env, jclass obj, jstring path)
{
const char *str = (env)->GetStringUTFChars(path, 0);
dlib::shape_predictor *sp = new dlib::shape_predictor();
dlib::deserialize(str) >> *sp;
(env)->ReleaseStringUTFChars(path, str);
return (jlong)sp;
}
jlong Java_es_bsc_compss_apps_utils_aligners_face_DlibAligner_00024ShapePredictor_n_1predict(JNIEnv *env, jclass obj, jlong me, jlong mat_ptr, jint x_start, jint x_end, jint y_start, jint y_end)
{
dlib::shape_predictor *sp_ptr = (dlib::shape_predictor *)me;
dlib::shape_predictor sp = *sp_ptr;
cv::Mat *img = (cv::Mat *)mat_ptr;
cv::Mat img_cv = *(img);
cv::Mat gray;
cv::cvtColor(img_cv, gray, cv::COLOR_BGR2GRAY);
return (jlong) new cv::Mat(gray);
}
void Java_es_bsc_compss_apps_utils_aligners_face_DlibAligner_00024ShapePredictor_n_1delete(JNIEnv *env, jclass obj, jlong self)
{
delete (dlib::shape_predictor *)self;
}
I compile the file to create a .o object and then create a .so library with the following commands:
cc -c -std=c++0x -fPIC -fpermissive shape_predictor_java.cpp -o shape_predictor_java.o -I/usr/lib/jvm/java-8-openjdk-amd64/include -I/usr/lib/jvm/java-8-openjdk-amd64//include/linux -I/usr/local/include -Ibuild/include
cc -shared -Wl,-soname,libdlibsp.so -o libdlibsp.so shape_predictor_java.o -Wl,-rpath,/usr/local/lib:/usr/local/share/OpenCV/java -L/usr/local/lib -ldlib -L/usr/local/share/OpenCV/java -lopencv_java349
Finally I copied both the include and the dynamic library file onto the /usr/local/lib folder.
When running the Java application, my library seems to load properly. The shape_predictor object is properly created and when the predict method is invoked, then an error arises
java: symbol lookup error: /usr/local/lib/libdlibsp.so: undefined symbol: _ZN2cv8cvtColorERKNS_11_InputArrayERKNS_12_OutputArrayEii
I ran nm on /usr/local/share/OpenCV/java/libopencv_java349.so and the symbol is there. I also executed an ldd on my library, and, for some reason,libopencv_java349 is not listed as a dependency. Thus, it looks like there is some kind of linking problem.
ldd /usr/local/lib/libdlibsp.so
linux-vdso.so.1 => (0x00007ffed6100000)
libdlib.so.19.19.99 => /usr/local/lib/libdlib.so.19.19.99 (0x00007f3c048ea000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f3c046d4000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3c0430a000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f3c040ed000)
libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f3c03d6b000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f3c03a62000)
/lib64/ld-linux-x86-64.so.2 (0x00007f3c05045000)
I tried adding /usr/local/share/OpenCV/java/libopencv_java349.so on the LD_LIBRARY_PATH and added the -Wl,-rpath flag on the linker step to try to force the library to be loaded.

Android NDK - Gradle Build Error

I've successfully compiled the SoundTouch library and copied the resulting files into my project's libs folder.
within each one of this folders there is a libsoundtouch.so file.
in my project's jni folder I have the following files:
Android.mk
Application.mk
soundtouch-jni.cpp
my Android.mk looks like this:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
# *** Remember: Change -O0 into -O2 in add-applications.mk ***
LOCAL_MODULE := soundtouch
LOCAL_SRC_FILES := soundtouch-jni.cpp ../../SoundTouch/AAFilter.cpp ../../SoundTouch/FIFOSampleBuffer.cpp \
../../SoundTouch/FIRFilter.cpp ../../SoundTouch/cpu_detect_x86.cpp \
../../SoundTouch/sse_optimized.cpp ../../SoundStretch/WavFile.cpp \
../../SoundTouch/RateTransposer.cpp ../../SoundTouch/SoundTouch.cpp \
../../SoundTouch/InterpolateCubic.cpp ../../SoundTouch/InterpolateLinear.cpp \
../../SoundTouch/InterpolateShannon.cpp ../../SoundTouch/TDStretch.cpp \
../../SoundTouch/BPMDetect.cpp ../../SoundTouch/PeakFinder.cpp
# for native audio
LOCAL_SHARED_LIBRARIES += -lgcc
# --whole-archive -lgcc
# for logging
LOCAL_LDLIBS += -llog
# for native asset manager
#LOCAL_LDLIBS += -landroid
# Custom Flags:
# -fvisibility=hidden : don't export all symbols
LOCAL_CFLAGS += -fvisibility=hidden -I ../../../include -fdata-sections -ffunction-sections
# OpenMP mode : enable these flags to enable using OpenMP for parallel computation
#LOCAL_CFLAGS += -fopenmp
#LOCAL_LDFLAGS += -fopenmp
# Use ARM instruction set instead of Thumb for improved calculation performance in ARM CPUs
LOCAL_ARM_MODE := arm
include $(BUILD_SHARED_LIBRARY)
and this is my module build.gradle file:
apply plugin: 'com.android.application'
android {
signingConfigs {
dev_key {
keyAlias '#########'
keyPassword '########'
storeFile file('/Users/daniele/Desktop/Chords/########')
storePassword '#######'
}
}
compileSdkVersion 26
buildToolsVersion "26.0.1"
defaultConfig {
applicationId "com.dancam.chords"
minSdkVersion 21
targetSdkVersion 26
versionCode 16
versionName "2.1"
signingConfig ##########
multiDexEnabled true
}
buildTypes {
release {
shrinkResources true
minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
productFlavors {
}
dataBinding {
enabled = true
}
}
dependencies {
compile fileTree(include: ['*.jar'], dir: 'libs')
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
exclude group: 'com.android.support', module: 'support-annotations'
})
I import a native function:
public final class SoundTouch {
public native final static String getVersionString();
// Load the native library upon startup
static
{
System.loadLibrary("soundtouch");
}
}
This is my soundtouch-jni.cpp file:
#include <jni.h>
#include <android/log.h>
#include <stdexcept>
#include <string>
using namespace std;
#include "../../../include/SoundTouch.h"
#include "../source/SoundStretch/WavFile.h"
#define LOGV(...) __android_log_print((int)ANDROID_LOG_INFO, "SOUNDTOUCH", __VA_ARGS__)
//#define LOGV(...)
// String for keeping possible c++ exception error messages. Notice that this isn't
// thread-safe but it's expected that exceptions are special situations that won't
// occur in several threads in parallel.
static string _errMsg = "";
#define DLL_PUBLIC __attribute__ ((visibility ("default")))
#define BUFF_SIZE 4096
using namespace soundtouch;
// Set error message to return
static void _setErrmsg(const char *msg)
{
_errMsg = msg;
}
#ifdef _OPENMP
#include <pthread.h>
extern pthread_key_t gomp_tls_key;
static void * _p_gomp_tls = NULL;
/// Function to initialize threading for OpenMP.
///
/// This is a workaround for bug in Android NDK v10 regarding OpenMP: OpenMP works only if
/// called from the Android App main thread because in the main thread the gomp_tls storage is
/// properly set, however, Android does not properly initialize gomp_tls storage for other threads.
/// Thus if OpenMP routines are invoked from some other thread than the main thread,
/// the OpenMP routine will crash the application due to NULL pointer access on uninitialized storage.
///
/// This workaround stores the gomp_tls storage from main thread, and copies to other threads.
/// In order this to work, the Application main thread needws to call at least "getVersionString"
/// routine.
static int _init_threading(bool warn)
{
void *ptr = pthread_getspecific(gomp_tls_key);
LOGV("JNI thread-specific TLS storage %ld", (long)ptr);
if (ptr == NULL)
{
LOGV("JNI set missing TLS storage to %ld", (long)_p_gomp_tls);
pthread_setspecific(gomp_tls_key, _p_gomp_tls);
}
else
{
LOGV("JNI store this TLS storage");
_p_gomp_tls = ptr;
}
// Where critical, show warning if storage still not properly initialized
if ((warn) && (_p_gomp_tls == NULL))
{
_setErrmsg("Error - OpenMP threading not properly initialized: Call SoundTouch.getVersionString() from the App main thread!");
return -1;
}
return 0;
}
#else
static int _init_threading(bool warn)
{
// do nothing if not OpenMP build
return 0;
}
#endif
// Processes the sound file
static void _processFile(SoundTouch *pSoundTouch, const char *inFileName, const char *outFileName)
{
int nSamples;
int nChannels;
int buffSizeSamples;
SAMPLETYPE sampleBuffer[BUFF_SIZE];
// open input file
WavInFile inFile(inFileName);
int sampleRate = inFile.getSampleRate();
int bits = inFile.getNumBits();
nChannels = inFile.getNumChannels();
// create output file
WavOutFile outFile(outFileName, sampleRate, bits, nChannels);
pSoundTouch->setSampleRate(sampleRate);
pSoundTouch->setChannels(nChannels);
assert(nChannels > 0);
buffSizeSamples = BUFF_SIZE / nChannels;
// Process samples read from the input file
while (inFile.eof() == 0)
{
int num;
// Read a chunk of samples from the input file
num = inFile.read(sampleBuffer, BUFF_SIZE);
nSamples = num / nChannels;
// Feed the samples into SoundTouch processor
pSoundTouch->putSamples(sampleBuffer, nSamples);
// Read ready samples from SoundTouch processor & write them output file.
// NOTES:
// - 'receiveSamples' doesn't necessarily return any samples at all
// during some rounds!
// - On the other hand, during some round 'receiveSamples' may have more
// ready samples than would fit into 'sampleBuffer', and for this reason
// the 'receiveSamples' call is iterated for as many times as it
// outputs samples.
do
{
nSamples = pSoundTouch->receiveSamples(sampleBuffer, buffSizeSamples);
outFile.write(sampleBuffer, nSamples * nChannels);
} while (nSamples != 0);
}
// Now the input file is processed, yet 'flush' few last samples that are
// hiding in the SoundTouch's internal processing pipeline.
pSoundTouch->flush();
do
{
nSamples = pSoundTouch->receiveSamples(sampleBuffer, buffSizeSamples);
outFile.write(sampleBuffer, nSamples * nChannels);
} while (nSamples != 0);
}
extern "C" DLL_PUBLIC jstring Java_net_surina_soundtouch_SoundTouch_getVersionString(JNIEnv *env, jobject thiz)
{
const char *verStr;
LOGV("JNI call SoundTouch.getVersionString");
// Call example SoundTouch routine
verStr = SoundTouch::getVersionString();
/// gomp_tls storage bug workaround - see comments in _init_threading() function!
_init_threading(false);
int threads = 0;
#pragma omp parallel
{
#pragma omp atomic
threads ++;
}
LOGV("JNI thread count %d", threads);
// return version as string
return env->NewStringUTF(verStr);
}
extern "C" DLL_PUBLIC jlong Java_net_surina_soundtouch_SoundTouch_newInstance(JNIEnv *env, jobject thiz)
{
return (jlong)(new SoundTouch());
}
extern "C" DLL_PUBLIC void Java_net_surina_soundtouch_SoundTouch_deleteInstance(JNIEnv *env, jobject thiz, jlong handle)
{
SoundTouch *ptr = (SoundTouch*)handle;
delete ptr;
}
extern "C" DLL_PUBLIC void Java_net_surina_soundtouch_SoundTouch_setTempo(JNIEnv *env, jobject thiz, jlong handle, jfloat tempo)
{
SoundTouch *ptr = (SoundTouch*)handle;
ptr->setTempo(tempo);
}
extern "C" DLL_PUBLIC void Java_net_surina_soundtouch_SoundTouch_setPitchSemiTones(JNIEnv *env, jobject thiz, jlong handle, jfloat pitch)
{
SoundTouch *ptr = (SoundTouch*)handle;
ptr->setPitchSemiTones(pitch);
}
extern "C" DLL_PUBLIC void Java_net_surina_soundtouch_SoundTouch_setSpeed(JNIEnv *env, jobject thiz, jlong handle, jfloat speed)
{
SoundTouch *ptr = (SoundTouch*)handle;
ptr->setRate(speed);
}
extern "C" DLL_PUBLIC jstring Java_net_surina_soundtouch_SoundTouch_getErrorString(JNIEnv *env, jobject thiz)
{
jstring result = env->NewStringUTF(_errMsg.c_str());
_errMsg.clear();
return result;
}
extern "C" DLL_PUBLIC int Java_net_surina_soundtouch_SoundTouch_processFile(JNIEnv *env, jobject thiz, jlong handle, jstring jinputFile, jstring joutputFile)
{
SoundTouch *ptr = (SoundTouch*)handle;
const char *inputFile = env->GetStringUTFChars(jinputFile, 0);
const char *outputFile = env->GetStringUTFChars(joutputFile, 0);
LOGV("JNI process file %s", inputFile);
/// gomp_tls storage bug workaround - see comments in _init_threading() function!
if (_init_threading(true)) return -1;
try
{
_processFile(ptr, inputFile, outputFile);
}
catch (const runtime_error &e)
{
const char *err = e.what();
// An exception occurred during processing, return the error message
LOGV("JNI exception in SoundTouch::processFile: %s", err);
_setErrmsg(err);
return -1;
}
env->ReleaseStringUTFChars(jinputFile, inputFile);
env->ReleaseStringUTFChars(joutputFile, outputFile);
return 0;
}
EDIT:
After doing what Alex Cohn suggested, I ended up with the following errors:
Build command failed.
Error while executing process /Users/daniele/Library/Android/sdk/ndk-bundle/ndk-build with arguments {NDK_PROJECT_PATH=null APP_BUILD_SCRIPT=/Users/daniele/Developer/AndroidProjects/Chords2/app/jni/Android.mk NDK_APPLICATION_MK=/Users/daniele/Developer/AndroidProjects/Chords2/app/jni/Application.mk APP_ABI=armeabi-v7a NDK_ALL_ABIS=armeabi-v7a NDK_DEBUG=0 APP_PLATFORM=android-21 NDK_OUT=/Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/release/obj NDK_LIBS_OUT=/Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/release/lib APP_SHORT_COMMANDS=false LOCAL_SHORT_COMMANDS=false -B -n}
rm -f /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/release/lib/armeabi-v7a/*
rm -f /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/release/lib/armeabi-v7a/gdbserver
rm -f /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/release/lib/armeabi-v7a/gdb.setup
mkdir -p /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/release/obj/local/armeabi-v7a/objs/soundtouch
echo [armeabi-v7a] "Compile++ arm ": "soundtouch <= soundtouch-jni.cpp"
/Users/daniele/Library/Android/sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang++ -MMD -MP -MF /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/release/obj/local/armeabi-v7a/objs/soundtouch/soundtouch-jni.o.d -gcc-toolchain /Users/daniele/Library/Android/sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/darwin-x86_64 -fpic -ffunction-sections -funwind-tables -fstack-protector-strong -Wno-invalid-command-line-argument -Wno-unused-command-line-argument -no-canonical-prefixes -fno-integrated-as -g -target armv7-none-linux-androideabi -march=armv7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -fno-exceptions -fno-rtti -marm -O2 -DNDEBUG -I/Users/daniele/Library/Android/sdk/ndk-bundle/sources/cxx-stl/stlport/stlport -I/Users/daniele/Library/Android/sdk/ndk-bundle/sources/cxx-stl//gabi++/include -I/Users/daniele/Developer/AndroidProjects/Chords2/app/jni -DANDROID -fvisibility=hidden -I ../../../include -fdata-sections -ffunction-sections -Wa,--noexecstack -Wformat -Werror=format-security -frtti -fexceptions -isystem /Users/daniele/Library/Android/sdk/ndk-mbundake: *** No rule to make target `/Users/daniele/Delveeloper/platforms/android-/AndroidProjects/Chords2/app/jni/../../SoundTouch/AAFilter.cpp', needed by `/Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermedi2ates/ndkBuild/1/arch-arm/usr/include -c release/obj/local/armeabi-v7a/objs/soun /Users/dtdaniele/Douch/__/__/SoeveloundTouch/AAFpilter.o'. Stop.
er/AndroidProjects/Chords2/app/jni/soundtouch-jni.cpp -o /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/release/obj/local/armeabi-v7a/objs/soundtouch/soundtouch-jni.o
Build command failed.
Error while executing process /Users/daniele/Library/Android/sdk/ndk-bundle/ndk-build with arguments {NDK_PROJECT_PATH=null APP_BUILD_SCRIPT=/Users/daniele/Developer/AndroidProjects/Chords2/app/jni/Android.mk NDK_APPLICATION_MK=/Users/daniele/Developer/AndroidProjects/Chords2/app/jni/Application.mk APP_ABI=armeabi-v7a NDK_ALL_ABIS=armeabi-v7a NDK_DEBUG=1 APP_PLATFORM=android-21 NDK_OUT=/Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/obj NDK_LIBS_OUT=/Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib APP_SHORT_COMMANDS=false LOCAL_SHORT_COMMANDS=false -B -n}
rm -f /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a/*
rm -f /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a/gdbserver
rm -f /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a/gdb.setup
mkdir -p /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a
echo [armeabi-v7a] "Gdbserver ": "[arm-linux-androideabi] /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a/gdbserver"
install -p /Users/daniele/Library/Android/sdk/ndk-bundle/prebuilt/android-arm/gdbserver/gdbserver /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a/gdbserver
echo [armeabi-v7a] "Gdbsetup ": "/Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a/gdb.setup"
echo "set solib-search-path /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/obj/local/armeabi-v7a" > /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a/gdb.setup
echo "directory /Users/daniele/Library/Android/sdk/ndk-bundle/platforms/android-21/arch-arm/usr/include /Users/daniele/Library/Android/sdk/ndk-bundle/sources/cxx-stl/stlport/stlport /Users/daniele/Library/Android/sdk/ndk-bundle/sources/cxx-stl//gabi++/include /Users/daniele/Developer/AndroidProjects/Chords2/app/jni" >> /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/lib/armeabi-v7a/gdb.setup
mkdir -p /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/obj/local/armeabi-v7a/objs/soundtouch
echo [armeabi-v7a] "Compile++ arm ": "soundtouch <= soundtouch-jni.cpp"
/Users/daniele/Library/Android/sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang++ -MMD -MP -MF /Users/daniele/Developer/Androidmake: *** No rule to make target `/Users/daniele/Developer/AndroidProjects/Chords2/app/jniPro/../../SojeundTouch/AAFilter.cpp'c, ts/nCheeded by `o/Usrdsers/daniele/Develo2/apper/AndroidpProjects/Chords2/app/build/intermediates/ndkBuild//bdebug/obj/local/uiarmeabi-v7a/objs/soundtouch/__/__/SoundldTouch/AAFilter.o'. Stop.
/intermediates/ndkBuild/debug/obj/local/armeabi-v7a/objs/soundtouch/soundtouch-jni.o.d -gcc-toolchain /Users/daniele/Library/Android/sdk/ndk-bundle/toolchains/arm-linux-androideabi-4.9/prebuilt/darwin-x86_64 -fpic -ffunction-sections -funwind-tables -fstack-protector-strong -Wno-invalid-command-line-argument -Wno-unused-command-line-argument -no-canonical-prefixes -fno-integrated-as -g -target armv7-none-linux-androideabi -march=armv7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -fno-exceptions -fno-rtti -marm -O2 -DNDEBUG -I/Users/daniele/Library/Android/sdk/ndk-bundle/sources/cxx-stl/stlport/stlport -I/Users/daniele/Library/Android/sdk/ndk-bundle/sources/cxx-stl//gabi++/include -I/Users/daniele/Developer/AndroidProjects/Chords2/app/jni -DANDROID -fvisibility=hidden -I ../../../include -fdata-sections -ffunction-sections -Wa,--noexecstack -Wformat -Werror=format-security -frtti -fexceptions -isystem /Users/daniele/Library/Android/sdk/ndk-bundle/platforms/android-21/arch-arm/usr/include -c /Users/daniele/Developer/AndroidProjects/Chords2/app/jni/soundtouch-jni.cpp -o /Users/daniele/Developer/AndroidProjects/Chords2/app/build/intermediates/ndkBuild/debug/obj/local/armeabi-v7a/objs/soundtouch/soundtouch-jni.o
Please notice: I compiled the Soundtouch Library using ndk-build on Ubuntu Linux, then copied it over to macOS where I normally work
Any clue on how to fix this?

I see you have problems building libsoundtouch.so in Android Studio. This happens, e.g. when the build scripts of a third-part library require special environment. E.g. the only supported way to build webrtc for Android is on 64-bit Linux.
In this case, you can use the prebuilt libraries. Put them in a jniLibs folder under your project (jniLibs/armeabi-v7a/libsoundtouch.so etc.), or set a custom folder for jniLibs in build.gradle (in android {} block):
sourceSets.main.jniLibs.srcDir 'libs'
You should not use externalNativeBuild.ndkBuild.path together with this.

You should setup your gradle project to build the C++ library.
Please add to your build.gradle the following line (inside the android {} block):
externalNativeBuild.ndkBuild.path = 'jni/Android.mk'
(assuming paths ~/AndroidStudioProjects/Chords2/app/build.gradle and ~/AndroidStudioProjects/Chords2/app/jni/Android.mk).
To reduce compilation time and APK size, you can filter out the ABIs that you don't use, at least while debugging:
ndk { abiFilters 'armeabi-v7a' }
This line goes inside the defaultConfig {} block.
At any rate, after the APK is ready, you can use Build/Analyze APK from Android Studio's menu and check that all .so files are packed into it.

How to call C# function from java [duplicate]

This question already has answers here:
Calling C# method within a Java program
(2 answers)
Closed 7 years ago.
I need to call C# function from java and to this I have created the following.
I have a create a java header file Authenticator.h , here is the code:
#include <jni.h>
/* Header for class Authenticator */
#ifndef _Included_Authenticator
#define _Included_Authenticator
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: Authenticator
* Method: authenticate
* Signature: (Ljava/lang/String;Ljava/lang/String;)Z
*/
JNIEXPORT jboolean JNICALL Java_Authenticator_authenticate
(JNIEnv *, jobject, jstring, jstring);
#ifdef __cplusplus
}
#endif
#endif
I have then create a C# function that Authenticate
namespace SharpAuthenticator
{
public class Authenticator
{
public bool Authenticate(String username,String password)
{
return username == "user" && password == "login";
}
}
}
Then I am trying to call the C# function from C++(project to create a dll) using the code below;
String^ toString(const char *str)
{
int len = (int)strlen(str);
array<unsigned char>^ a = gcnew array<unsigned char>(len);
int i = 0;
while (i < len)
{
a[i] = str[i];
i++;
}
return Encoding::UTF8->GetString(a);
}
bool authenticate(const char *username, const char *password)
{
SharpAuthenticator::Authenticator::Authenticate(toString(username), toString(password));
}
JNIEXPORT jboolean JNICALL Java_Authenticator_authenticate
(JNIEnv *env, jobject c, jstring name, jstring pass)
{
jboolean result;
jboolean isCopyUsername;
const char * username = env->GetStringUTFChars(name, &isCopyUsername);
jboolean isCopypassword;
const char * password = env->GetStringUTFChars(pass, &isCopypassword);
result = authenticate(username, password);
env->ReleaseStringUTFChars(name, username);
env->ReleaseStringUTFChars(pass, password);
return result;
}
And finnally create a dll that i need to call from java. The dll is created and I load it well in java but I get this error log in java. What could I be Missing.
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (0xe0434352), pid=9708, tid=7756
#
# JRE version: 7.0-b147
# Java VM: Java HotSpot(TM) Client VM (21.0-b17 mixed mode, sharing windows-x86 )
# Problematic frame:
# C [KERNELBASE.dll+0x812f]
#
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows

First of all lets create a C# file like this:
using System;
public class Test{
public Test(){}
public String ping(){
return "C# is here.";
}
}
Then compile this with command below:
csc.exe /target:module Test.cs
You can find csc.exe in install path of .NET framework. After that create java file:
public class Test{
public native String ping();
public static void main(String[] args){
System.load("/path/to/dll");
System.out.println("Java is running.");
Test t = new Test();
System.out.println("Trying to catch C# " + r.ping());
}
}
javac Test.java This generates a Test.class.
javah -jni Test This generates a Test.h file which will be included in
C++ code.
After that we need to create our C++ file:
#include "stdafx.h"
#include "JAVA/Test.h"
#include "MCPP/Test.h"
#pragma once
#using <mscorlib.dll>
#using "Test.netmodule"
JNIEXPORT jstring JNICALL Java_Test_ping(JNIEnv *env, jobject obj){
Test^ t = gcnew Test();
String^ ping = t->ping();
char* str = static_cast<char*>((System::Runtime::InteropServices::Marshal::StringToHGlobalAnsi(ping)).ToPointer());
char cap[128];
strcpy_s(cap, str);
return env->NewStringUTF(cap);
}
Finally:
c:\>java Test
I hope this helps you. A basic example to use function C# in Java.
Sources:
https://www.quora.com/How-common-is-the-problem-of-calling-C-methods-from-Java-Do-many-developers-come-across-such-necessity

Loading dynamic libraries using JNI and C++ with linux

Recently I'm learning JNI to execute C code. Of course I did basic examples that were on the web. Now Im trying to load a C library that makes dynamic library loading (dlopen). But Im fighthing with an error. Im posting my Java code, C ++ code and the error.
My Java Class
/**
*
* #author glassfish
*/
public class MediationJniWeb {
public String library ;
static {
System.loadLibrary("-core-web");
}
/**
*
* #param library name of mediation core library [32]
* #param method name of method to be executed [128]
* #param parameters parameters of method [10240]
* [partype1,value1,...,valuen]...[partypen,value1,..,valuen]
* #return
*/
private native String execute();
public static void main(String args[]) {
//new MediationJniWeb().callToFunction(null, null, null) ;
MediationJniWeb jniWeb = new MediationJniWeb();
jniWeb.library = "libtest.so" ;
System.out.println(jniWeb.execute());
}
}
I generate .class file with
javac MediationJniWeb
and I generate .h File with
javah -jni MediationJniWeb
my MediationJniWeb.h file is
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class MediationJniWeb */
#ifndef _Included_MediationJniWeb
#define _Included_MediationJniWeb
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: MediationJniWeb
* Method: execute
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_MediationJniWeb_execute
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
and my MediationJniWEb.cpp file
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
#include <dlfcn.h>
#include <iostream>
#include "MediationJniWeb.h"
using namespace std ;
typedef void (*test)(string);
/*
* Class: MediationJniWeb
* Method: execute
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_MediationJniWeb_execute
(JNIEnv * env, jobject obj){
const char * str_library ;
jfieldID fid_library ;
jstring jstr_library ;
jboolean isCopy ;
jclass cls = env->GetObjectClass( obj) ;
fid_library = env->GetFieldID( cls,"library", "Ljava/lang/String;");
jstr_library = ( jstring )env->GetObjectField( obj,fid_library);
str_library = env->GetStringUTFChars( jstr_library, &isCopy) ;
void* handle = dlopen(str_library, RTLD_NOW); // open libtest.so
if ( 0 == handle ) {
cout << "failed to load 'libtest.so'. " << dlerror () <<endl;
exit(1);
}
test t = (test)dlsym(handle, "_Z8testfuncSs"); // run default method
if ( 0 == t ) {
cout << "failed to load 'testfunc()'." << endl;
exit(1);
}
t("Hello, World!");
dlclose(handle);
/*
*/
return env->NewStringUTF( str_library); // I just return library name just for fun
}
}
I compile with
g++ -shared -fpic -I//include/ -I//include/linux/ MediationJniWeb.cpp -o lib-core-web.so MediationJniWeb.cpp -ldl
this generate lib-core-web.so file. Then I copy this to $HOME/lib and I configure
LD_LIBRARY_PATH=$HOME/lib
Now I create my library libtest.so that is going to be executed by lib-core-web.so
I create file for shared libray mylib.cpp
#include <iostream>
#include <string>
using namespace std;
void testfunc(string s)
{
cout << s << endl;
}
I compile this that is going to work as a shared library with
g++ -shared -fpic -o libtest.so mylib.cpp
This command generates libtest.so file.. and also, I copy it to $HOME/lib
That's all I do to call from JNI to a C++ library to load a dynamic library.
when I execute MediationJniWeb java class I'm having this error
failed to load. libtest.so: cannot open shared object file: No such
file or directory
What do I have to do with libtest.so ?? where do I have to put it ?
I have on mind that configuring only LD_LIBRARY_PATH variable with right path, JVM should know where to find all needed libraries to be loaded.
Please help with your comments and let me know where my mistakes are.
Thanks in advance !

A simple thing I have done
instead of
jniWeb.library = "libtest.so"
library parameter to be loaded I declared
jniWeb.library = "/home/myuser/lib/libtest.so"
And it worked !

Calling Java Methods from Visual C/C++ using C++/CLI

I'm getting a "error LNK1104: cannot open file {path}\jvm.lib" when trying tocompile a VS C++/CLI (managed) project. It's very simple and my goal is to call some Java methods in pre-existing java libs - here is the code I'm using:
// This is the main DLL file.
#include "stdafx.h"
#include <jni_md.h>
#include <jni.h>
#include "JBridge.h"
#pragma once
using namespace System;
namespace JBridge
{
public ref class JniBridge
{
// TODO: Add your methods for this class here.
public:
void HelloWorldTest()
{
System::Console::WriteLine("Hello Worldl from managed C++!");
}
JNIEnv* create_vm(JavaVM ** jvm)
{
JNIEnv *env;
JavaVMInitArgs vm_args;
JavaVMOption options;
//Path to the java source code
options.optionString = "-Djava.class.path=D:\\Java Src\\TestStruct";
vm_args.version = JNI_VERSION_1_6; //JDK version. This indicates version 1.6
vm_args.nOptions = 1;
vm_args.options = &options;
vm_args.ignoreUnrecognized = 0;
int ret = JNI_CreateJavaVM(jvm, (void**)&env, &vm_args);
if(ret < 0)
printf("\nUnable to Launch JVM\n");
return env;
}
};
}
I've verified the file does exist in the path location and I've added it to the project properties for the include dir and the linker property pages.
Update
Got the jvm.lib to be linked with a bit more fiddling.
Compilation causes following errors during build:
Error 1 error LNK2028: unresolved token (0A00000A) "extern "C" long __stdcall JNI_CreateJavaVM(struct JavaVM_ * *,void * *,void *)" (?JNI_CreateJavaVM##$$J212YGJPAPAUJavaVM_##PAPAXPAX#Z) referenced in function "struct JNIEnv_ * __cdecl create_vm(struct JavaVM_ * *)" (?create_vm##$$FYAPAUJNIEnv_##PAPAUJavaVM_###Z) c:\Temp\CLRTest\JBridge\JBridge\JBridge.obj JBridge
Error 2 error LNK2019: unresolved external symbol "extern "C" long __stdcall JNI_CreateJavaVM(struct JavaVM_ * *,void * *,void *)" (?JNI_CreateJavaVM##$$J212YGJPAPAUJavaVM_##PAPAXPAX#Z) referenced in function "struct JNIEnv_ * __cdecl create_vm(struct JavaVM_ * *)" (?create_vm##$$FYAPAUJNIEnv_##PAPAUJavaVM_###Z) c:\Temp\CLRTest\JBridge\JBridge\JBridge.obj JBridge
Error 3 error LNK1120: 2 unresolved externals c:\temp\CLRTest\JBridge\Debug\JBridge.dll JBridge

Work around was to dynamically load the JVM by using LoadLibrary("path/to/jvm"); and then invoking the native functions.