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A fatal error while creating java instance from c++ using NewObject JNI

I am trying to call Java methods from c++ using JNI. According to my understanding when c++ wants to access non static java methods we need to have instance to java to access those methods.
I am getting runtime error and I am not able to understand where exactly the error is but my code is breaking.I tracked by cout and its breaking while creating the instance
Error is : V [libjvm.so+0x2c3253] methodHandle::methodHandle(Method)+0x33*
And my code is like this:
.h file
static jclass clsEventStatus;
static jmethodID constructorEventStatus;
jobject EventStatusInstance;
.cpp file
jclass EventStatusJNI::clsEventStatus;
jmethodID EventStatusJNI::constructorEventStatus;
int EventStatusJNI::initialize() {
if(clsEventStatus==0) {
clsEventStatus = StubJava::env->FindClass("metronome/EventStatus");//no error
if(clsEventStatus == 0){
std::cout<<"class Eventstatus Not found";
}
constructorEventStatus = StubJava::env->GetMethodID(clsEventStatus, "<init>", "()V");//no error
return 0;
}
return 1;
}
EventStatusJNI::EventStatusJNI(){
EventStatusInstance = StubJava::env->NewObject(clsEventStatus, constructorEventStatus); //its breaking here when call happens
if(EventStatusInstance == 0 ){std::cout<<"No EventStatusInstance found ";}
}
In .java file:
public class EventStatus {
public EventStatus(){
System.out.println("Entered Event status.java");
setStatusValue(EventStatusValue.PROCESSING);
}
}
thank you for your time!

JNI : java - C // Using Global variables

I would like to know whether JNI accepts the use of global variables declared in the .cpp (and of type created by me).
It would be for a speech recognition program. In fact, I would like to use C to declare all the settings of the decoder and Java to manage the recording thing on Android. I don't want to create a Decoder class on Java because it should be use both on Android and iOS (I would like to have 3 separate parts :
1) set up the decoder (only in C)
2) do the recording and manage the threads (only in Android-java)
3) decode the audio (in java but calling C functions that will use the settings of the decoder)
Example :
function.cpp :
struct decoder {
char *model;
};
In the function_2.ccp file :
decoder *ps;
void set_decoder(char *modelToUse){
ps->model = modelToUse;
return;
}
void process(int *buf ) {
process_raw(ps, buf); // modify buf accordingly to the parameters of ps
return;
}
char *getHyp (){
return ps->hyp;
}
void main(){
ps = set_decoder(var1);
jclass = android_class = (*env)->FindClass(env,"android/app/nameofactivity");
// find method_ID
jmethodID android_mid = (*env)->GetStaticMethodID(env, android_class, "java_method",String_signature);
// call method
jString hyp_java = (*env)->CallIntMethod(env, android_class, android_mid, int samplerate);
EDIT (add these lines) :
const char *hyp_tmp = (*env)->GetStringUTFChars(env, hyp_java, 0);
const char *hyp = hyp_tmp;
printf(hyp_java);
(*env)->ReleaseStringUTFChars(env, hyp_java, hyp_tmp);
//END of EDIT
}
In the java file (the methods process and getHyp are declared as native methods ; the read method is a method from Android):
file.java
String java_method(int samplerate){
int buf[samplerate];
recorder.read(buf);
this.process(buf);
return this.getHyp();
}
Is it possible to do that?
EDIT : In brief, I wonder whether I can declare a global variable "ps" in C and then call a java function that will call other C functions that will use the value of the declared variable "ps".

JNI Function Causing Android App to Crash

I have the following JNI function that sends an event to my Java code.
void onIncrementAchievement(unsigned char _iArgumentCount, const void *_pArguments, void *_pUserData){
JNIEnv *pJNIEnv = GetJNIEnv();
if (pJNIEnv){
if ( _pArguments && ( _iArgumentCount > 0 ) ){
const S3DX::AIVariable *pVariables = (const S3DX::AIVariable *)_pArguments ;
if(_iArgumentCount != 2)
LOGI("INCORRECT NUMBER OF PARAMETERS");
else{
if(pVariables[0].GetType() == S3DX::AIVariable::eTypeString){
// CHANGE ME!
jclass pJNIActivityClass = pJNIEnv->FindClass ( "com/nurfacegames/testgame01/TestGame01" );
if(pJNIActivityClass == NULL)
LOGI("jclass was null!?!");
else{
jmethodID pJNIMethodID = pJNIEnv->GetStaticMethodID(pJNIActivityClass, "onIncrementAchievement", "(Ljava/lang/String;Ljava/lang/Integer;)V");
if(pJNIMethodID == NULL)
LOGI("jmethodID was null!?!?");
else{
//Create a new string
jstring arg;
arg = pJNIEnv->NewStringUTF(pVariables[0].GetStringValue());
jint arg2 = pVariables[1].GetNumberValue();
//Call the method and pass the string parameter along
pJNIEnv->CallStaticVoidMethod(pJNIActivityClass, pJNIMethodID, arg, arg2);
//Free the string
pJNIEnv->DeleteLocalRef(arg);
}
}
}
}
}
}
}
When I run my Android App, it force closes without even giving a single error in logcat, and when I compile with Ant, there are no compile errors.
I hate to post such a vague question, but if someone has an idea what is wrong with my JNI code, please give me a hint. Thanks!
The areas that I think have a problem (that I have been working on) are:
if(_iArgumentCount != 2)
LOGI("INCORRECT NUMBER OF PARAMETERS");
else{
and this section:
jint arg2 = pVariables[1].GetNumberValue();
pJNIEnv->CallStaticVoidMethod(pJNIActivityClass, pJNIMethodID, arg, arg2);
Thanks!

Well, look at your method name void onIncrementAchievement, as far as I know, that isn't the right way to declare your method in native section, it should be:
Java_com_example_yourpackagename_youractivityname_yourmethod(...)
And one more thing, the arguments in your method are also wrong I guess, check out this tutorial.

Memory leak in SWIG polymorphism across C++ and Java using directors

I have a C++ program to receive binary data from network. After data is received, it will callback the data as a byte array from C++ to a Java client. I use the director feature in SWIG to easily achieve cross language polymorphism across C++ and Java for callback. Here's a link.
But I found there is no typemaps in SWIG from char* in C++ to byte[] in Java. So, I added a patch to the virous.i. Here's a link.
/*Director specific typemaps*/
%typemap(directorin, descriptor="[B") char *BYTE {
jbyteArray jb = (jenv)->NewByteArray(strlen(BYTE));
(jenv)->SetByteArrayRegion(jb, 0, strlen(BYTE), (jbyte*)BYTE);
$input = jb;
}
%typemap(directorout) char *BYTE {
$1 = 0;
if($input){
$result = (char *) jenv->GetByteArrayElements($input, 0);
if(!$1)
return $null;
jenv->ReleaseByteArrayElements($input, $result, 0);
}
}
%typemap(javadirectorin) char *BYTE "$jniinput"
%typemap(javadirectorout) char *BYTE "$javacall"
For example. I have a class in C++ called A:
class A{
public:
virtual void onDataReceived(const char* BYTE, const size_t len) {}
};
Then in Java code I have another class B to extend A:
class B extends A {
#Override
public void onDataReceived(byte[] data, long len) {
//handling the data.
}
}
I can receive the byte array in Java code, but it seems it is never garbage collected by JVM. The onDataReceived method in SWIG generated wrapper file is like this:
void SwigDirector_A::onDataReceived(char const *BYTE, size_t const len) {
JNIEnvWrapper swigjnienv(this);
JNIEnv * jenv = swigjnienv.getJNIEnv();
jobject swigjobj = (jobject) NULL;
jbyteArray jBYTE = 0;
jlong jlen;
if (!swig_override[3]) {
A::onDataReceived(BYTE,len);
return;
}
swigjobj = swig_get_self(jenv);
if (swigjobj && jenv->IsSameObject(swigjobj, NULL) == JNI_FALSE) {
{
jbyteArray jb = (jenv)->NewByteArray(strlen(BYTE));
(jenv)->SetByteArrayRegion(jb, 0, strlen(BYTE), (jbyte*)BYTE);
jBYTE = jb;
}
jlen = (jlong) len;
jenv->CallStaticVoidMethod(Swig::jclass_DataTransferJNI, Swig::director_methids[3], swigjobj, jBYTE, jlen);
if (jenv->ExceptionCheck() == JNI_TRUE) return;
} else {
SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException, "null upcall object");
}
if (swigjobj) jenv->DeleteLocalRef(swigjobj);
}
In my C++ code, I will delete the data in the receive buffer after the callback is done. But I checked from Java VisualVM that the memory used by java client process is not GC-ed after a long time. Thanks advance for any help!
PS. The data is quite large, it is around 32KB.

I got it solved by added deletion of reference to jb in Director typemaps: (jenv)->DeleteLocalRef(jb);
Here's the updated patch.

Why does my JNI code not successfully find a jthrowable's getMessage method?

I'm trying to access the message in a jthrowable while handing an exception generated when I fail to find a class. However, I am unable to access the message ID of getMessage() on the jthrowable object, and I don't know why. I've tried changing the signature of getMessage to "()Ljava/lang/String" (without the semicolon at the end, but that's necessary, right?) with no joy. I'm confused as hell about this. I even tried replacing getMessage with toString, and that didn't work. Obviously I'm doing something trivially wrong here.
Here's the code I'm using:
jthrowable java_exception;
jclass java_class;
jmethodID method;
java_exception = (*jEnv)->ExceptionOccurred(jEnv);
assert (java_exception != NULL);
java_class = (*jEnv)->GetObjectClass (jEnv, java_exception);
assert (java_class != NULL);
method = (*jEnv)->GetMethodID (jEnv, java_class, "getMessage", "()Ljava/lang/String;");
if (method == NULL) {
printf ("Seriously, how do I get here?!\n");
(*jEnv)->ExceptionDescribe (jEnv);
return;
}
The output of this code (amongst other things) looks like this:
Seriously, how do I get here?!
Exception in thread "main" java.lang.NoClassDefFoundError: com/planet/core360/docgen/Processor
javap -p -s java.lang.Throwable gives me this:
Compiled from "Throwable.java"
public class java.lang.Throwable extends java.lang.Object implements java.io.Serializable{
...
public java.lang.String getMessage();
Signature: ()Ljava/lang/String;
...

Okay, so it looks like my problem was that GetObjectClass doesn't act the way you'd expect it to on a jthrowable, or at least the results of it are not useful for the purposes of getting methods. Replacing that portion of the code with this works:
java_class = (*jEnv)->FindClass (jEnv, "java/lang/Throwable");
method = (*jEnv)->GetMethodID (jEnv, java_class, "getMessage", "()Ljava/lang/String;");
Damnably odd, that. I hope this helps someone else in the future, though.

I tried your approach, and it worked for me. A few things though: I'm using the C++ interface (though that shouldn't make a difference), and I'm using Java 6 update 10, x64 edition, on Ubuntu 8.04. Perhaps the Java version and/or platform used will make a difference.
#include <cstdio>
#include <jni.h>
int
main(int argc, char** argv)
{
if (argc != 3) {
std::fprintf(stderr, "usage: %s class message\n", argv[0]);
return 1;
}
JavaVM* jvm;
void* penv;
JavaVMInitArgs args = {JNI_VERSION_1_6};
if (jint res = JNI_CreateJavaVM(&jvm, &penv, &args)) {
std::fprintf(stderr, "Can's create JVM: %d\n", res);
return -res;
}
JNIEnv* env(static_cast<JNIEnv*>(penv));
jint vers(env->GetVersion());
std::printf("JNI version %d.%d\n", vers >> 16, vers & 0xffff);
env->ThrowNew(env->FindClass(argv[1]), argv[2]);
jthrowable exc(env->ExceptionOccurred());
std::printf("Exception: %p\n", exc);
if (exc) {
jclass exccls(env->GetObjectClass(exc));
jclass clscls(env->FindClass("java/lang/Class"));
jmethodID getName(env->GetMethodID(clscls, "getName", "()Ljava/lang/String;"));
jstring name(static_cast<jstring>(env->CallObjectMethod(exccls, getName)));
char const* utfName(env->GetStringUTFChars(name, 0));
jmethodID getMessage(env->GetMethodID(exccls, "getMessage", "()Ljava/lang/String;"));
jstring message(static_cast<jstring>(env->CallObjectMethod(exc, getMessage)));
char const* utfMessage(env->GetStringUTFChars(message, 0));
std::printf("Exception: %s: %s\n", utfName, utfMessage);
env->ReleaseStringUTFChars(message, utfMessage);
env->ReleaseStringUTFChars(name, utfName);
}
return -jvm->DestroyJavaVM();
}
I've used jnitest java/lang/InternalError 'Hello, world!' for my testing; feel free to try with different exception types!