I am having a problem with JNI, calling a method from C++ to Java.
I am trying to call a void method that takes a boolean. My java code is the following:
public void setStatus(boolean bool) {
// Do stuff...
}
public native void initialize(int defaultPort);
In my C++ code, I am making a struct to hold the env and object and pass it to a thread:
JNIEXPORT void JNICALL Java_com_device_client_HostConnection_initialize
(JNIEnv * env, jobject obj, jint port)
{
struct javaInfo* data = (struct javaInfo*) malloc(sizeof(struct javaInfo));
data->env = env;
data->javaObjHost = obj;
pthread_t pth;
pthread_create(&pth, NULL, startServer, (void *) data);
free(data);
}
In the actual function, I am trying to obtain the class and then the MethodID and then call the void method, as follows:
void *startServer(void* arg) {
struct javaInfo* data = (struct javaInfo*) arg;
JNIEnv* env = data->env;
jobject javaObjHost = data->javaObjHost;
cls = env->GetObjectClass(javaObjHost);
mid = env->GetMethodID(cls, "setStatus", "(Z)V");
if (mid == 0) {
exit(-1);
}
env->CallVoidMethod(javaObjHost, mid, true);
}
It is hard for me to debug with JNI. I have tried putting a breakpoint in Eclipse in setStatus() but it never gets called. exit() is not called as well. The programs stomps for a second or two, then continues. I am not sure what is going on.
Could anyone please help me?
Thank you very much.
You cannot pass env pointers to other threads. You need to join the thread to the JVM.
In the original thread, called GetJavaVM to obtain a JavaVM pointer:
JavaVM *vm = 0;
env->GetJavaVM(&vm);
Then in the other thread, attach the VM to that thread and get a new env pointer:
vm->AttachCurrentThread(&env, 0);
Related
I am trying to have Java call a C function in Android and some caveats that I am met with is the documentation for callbacks in general seem very unclear and most answers on SO are just talking about theory and posting broken links with no actual code. So please post code in your answer.
I am trying to create a joystick in java and have it send input to the NDK to perform actions.
if I can just have Java call a C function and pass a int to it ,
that would be good. but I think that wont work because C in running
it's own main loop.
perhaps I need to use C to call a java
function to get controller state and execute code from there.
I did manage to find some code Here but it seems the code while it does compile by itself, but doesn't appear to work when moved to modern code .
How should I implement call backs in a Java C relationship on Android? It seems that from the code example above that it is C that is calling Java functions and these need to be used like getters functions.
Here is some code that I have and I appear to be missing somethings because it is unclear to me how I should have these call backs performed. I will mark this code with function name and where is it located, if java or C++ (CPP) .
I think there are two ways that I would like this to work.
My Javafunction that I want to call
public int Cat(){
Log.e("JniHandler", "CAT WAS CALLED!!!");
return 333;
}
Structure information CPP . Not sure if it is needed.
#include <string.h>
#include <inttypes.h>
#include <pthread.h>
#include <jni.h>
#include <android/log.h>
#include <assert.h>
typedef struct tick_context {
JavaVM *javaVM;
jclass jniHelperClz;
jobject jniHelperObj;
jclass mainActivityClz;
jobject mainActivityObj;
pthread_mutex_t lock;
int done;
} TickContext;
TickContext g_ctx;
This section works. It looks that as soon as the JVM is launched, this will initialize.
JNI_OnLoad CPP
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void* reserved) {
JNIEnv* env;
memset(&g_ctx, 0, sizeof(g_ctx));
SDL_Log(" DEBUG -- JNI INIT!!!");
g_ctx.javaVM = vm;
if (vm->GetEnv((void**)&env, JNI_VERSION_1_6) != JNI_OK) {
return JNI_ERR; // JNI version not supported.
}
jclass clz = env->FindClass("org/foo/bar/mainactivity");
g_ctx.jniHelperClz = (jclass)env->NewGlobalRef(clz); // hack
jmethodID jniHelperCtor = env->GetMethodID(g_ctx.jniHelperClz,"<init>", "()V");
jobject handler = env->NewObject(g_ctx.jniHelperClz, jniHelperCtor);
g_ctx.jniHelperObj = env->NewGlobalRef(handler);
//queryRuntimeInfo(env, g_ctx.jniHelperObj); // This when getting version returns null.
g_ctx.done = 0;
g_ctx.mainActivityObj = NULL;
return JNI_VERSION_1_6;
}
queryRuntimeInfo CPP
void queryRuntimeInfo(JNIEnv *env, jobject instance) {
SDL_Log("DEBUG QUERYRUNTIME INTO");
// Find out which OS we are running on. It does not matter for this app
// just to demo how to call static functions.
// Our java JniHelper class id and instance are initialized when this
// shared lib got loaded, we just directly use them
// static function does not need instance, so we just need to feed
// class and method id to JNI
jmethodID versionFunc = env->GetStaticMethodID(g_ctx.jniHelperClz, "getBuildVersion", "()Ljava/lang/String;"); // This returns null.
if (!versionFunc) {
SDL_Log("DEBUG versionFunc INTO");
//LOGE("Failed to retrieve getBuildVersion() methodID # line %d",__LINE__);
return;
}
SDL_Log("DEBUG BUILD VERSION INTO");
jstring buildVersion = (jstring)env->CallStaticObjectMethod(g_ctx.jniHelperClz, versionFunc); // hack
const char *version = env->GetStringUTFChars(buildVersion, NULL);
if (!version) {
SDL_Log("DEBUG buildVersion INTO");
//LOGE("Unable to get version string # line %d", __LINE__);
return;
}
//LOGI("Android Version - %s", version);
SDL_Log("DEBUG ANDROID VERSION %s", version);
env->ReleaseStringUTFChars(buildVersion, version);
// we are called from JNI_OnLoad, so got to release LocalRef to avoid leaking
env->DeleteLocalRef(buildVersion);
// Query available memory size from a non-static public function
// we need use an instance of JniHelper class to call JNI
jmethodID memFunc = env->GetMethodID(g_ctx.jniHelperClz, "getRuntimeMemorySize", "()J");
if (!memFunc) {
//LOGE("Failed to retrieve getRuntimeMemorySize() methodID # line %d",__LINE__);
SDL_Log("DEBUG Failed to retrieve memory size");
return;
}
jlong result = env->CallLongMethod(instance, memFunc);
//LOGI("Runtime free memory size: %" PRId64, result);
SDL_Log("DEBUG RUN TIME FREE MEMORY SIZE");
(void)result; // silence the compiler warning
}
This function isn't ever called and I am not sure who is the caller. CPP
extern "C" JNIEXPORT void JNICALL InvokeFunction(JNIEnv *env, jobject instance) {
SDL_Log("JNI CALL START TICKET");
pthread_t threadInfo_;
pthread_attr_t threadAttr_;
pthread_attr_init(&threadAttr_);
pthread_attr_setdetachstate(&threadAttr_, PTHREAD_CREATE_DETACHED);
pthread_mutex_init(&g_ctx.lock, NULL);
jclass clz = env->GetObjectClass(instance);
g_ctx.mainActivityClz = (jclass)env->NewGlobalRef(clz); // hack
g_ctx.mainActivityObj = env->NewGlobalRef(instance);
int result = pthread_create( &threadInfo_, &threadAttr_, UpdateTicks, &g_ctx);
assert(result == 0);
pthread_attr_destroy(&threadAttr_);
(void)result;
}
updateticks CPP // This code is never actually called.
void* UpdateTicks(void* context) {
SDL_Log("DEBUG -- UPDATE TICKS IS CALLED");
TickContext *pctx = (TickContext*) context;
JavaVM *javaVM = pctx->javaVM;
JNIEnv *env;
jint res = javaVM->GetEnv((void**)&env, JNI_VERSION_1_6);
if (res != JNI_OK) {
res = javaVM->AttachCurrentThread(&env, NULL);
if (JNI_OK != res) {
//LOGE("Failed to AttachCurrentThread, ErrorCode = %d", res);
SDL_Log("FAILED TO ATTACH THREAD");
return NULL;
}
}
jmethodID statusId = env->GetMethodID(pctx->jniHelperClz, "updateStatus", "(Ljava/lang/String;)V");
//sendJavaMsg(env, pctx->jniHelperObj, statusId, "TickerThread status: initializing...");
// get mainActivity updateTimer function
jmethodID timerId = env->GetMethodID(pctx->mainActivityClz, "updateTimer", "()V");
struct timeval beginTime, curTime, usedTime, leftTime;
const struct timeval kOneSecond = {
(__kernel_time_t)1,
(__kernel_suseconds_t) 0
};
//sendJavaMsg(env, pctx->jniHelperObj, statusId, "TickerThread status: start ticking ...");
while(1) {
gettimeofday(&beginTime, NULL);
pthread_mutex_lock(&pctx->lock);
int done = pctx->done;
if (pctx->done) {
pctx->done = 0;
}
pthread_mutex_unlock(&pctx->lock);
if (done) {
break;
}
env->CallVoidMethod(pctx->mainActivityObj, timerId);
gettimeofday(&curTime, NULL);
timersub(&curTime, &beginTime, &usedTime);
timersub(&kOneSecond, &usedTime, &leftTime);
struct timespec sleepTime;
sleepTime.tv_sec = leftTime.tv_sec;
sleepTime.tv_nsec = leftTime.tv_usec * 1000;
if (sleepTime.tv_sec <= 1) {
nanosleep(&sleepTime, NULL);
} else {
//sendJavaMsg(env, pctx->jniHelperObj, statusId, "TickerThread error: processing too long!");
}
}
//sendJavaMsg(env, pctx->jniHelperObj, statusId, "TickerThread status: ticking stopped");
javaVM->DetachCurrentThread();
return context;
}
I have the following CPP code. What I want to do is when an error occurs in my native side, I will notify Java about the error. I used How can I catch SIGSEGV (segmentation fault) and get a stack trace under JNI on Android? as reference.
static JavaVM* g_JVM = NULL;
static jobject g_thejavaobject = NULL;
void InitializeNativeSide(JNIEnv *env, jclass, jobject object)
{
env->GetJavaVM(&g_JVM);
g_thejavaobject = env->NewGlobalRef(object);
}
// this executes in another thread running in parallel with UI thread
void StartExecuting(JNIEnv *_env, jclass) {
struct sigaction sa;
memset(&sa, 0, sizeof(struct sigaction));
sigemptyset(&sa.sa_mask);
sa.sa_sigaction = SignalErrorHandler;
sa.sa_flags = SA_SIGINFO;
sigaction(SIGSEGV, &sa, NULL);
// native starts executing here. after a while, a SEGFAULT is encountered
// triggering SignalErrorHandler()
...
}
void SignalErrorHandler(int signal, siginfo_t *si, void *arg)
{
JNIEnv *env;
g_JVM->GetEnv((void**)&env, JNI_VERSION_1_6);
jclass myClass = env->FindClass("com/company/MyClass");
jmethodID myMethod = env->GetMethodID(myClass, "nativeCrashed", "()V" );
env->CallVoidMethod(g_thejavaobject, myMethod);
env->DeleteLocalRef(myClass);
}
Everything works fine but the call to myClass.nativeCrashed() does not work. What am I doing wrong?
You can't do this:
void SignalErrorHandler(int signal, siginfo_t *si, void *arg)
{
JNIEnv *env;
g_JVM->GetEnv((void**)&env, JNI_VERSION_1_6);
jclass myClass = env->FindClass("com/company/MyClass");
jmethodID myMethod = env->GetMethodID(myClass, "nativeCrashed", "()V" );
env->CallVoidMethod(g_thejavaobject, myMethod);
env->DeleteLocalRef(myClass);
}
That will not work for at least two fundamental reasons.
First, only async-signal-safe functions may be called from within a signal handler. The POSIX-specified list can be found at http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_04_03.
No Java JNI call is async-signal-safe.
Second, the Java JVM uses SIGSEGV internally - getting a SIGSEGV is not necessarily fatal:
Signals Used in Oracle Solaris, Linux, and macOS
...
SIGSEGV, SIGBUS, SIGFPE, SIGPIPE, SIGILL These signals are used in
the implementation for implicit null check, and so forth.
I am trying to call a method in my java class from within a thread in the native code but not having any success. These are the global vars:
JavaVM* javaVM = NULL;
jclass activityClass;
jobject activityObj;
Code called on initialisation of the native code:
extern "C" {
JNIEXPORT jint JNICALL
naInit(JNIEnv *pEnv, jobject pObj, jstring pFileName, jstring, defaultStorageDirectory) {
pEnv->GetJavaVM(&javaVM);
jclass cls = pEnv->GetObjectClass(pObj);
activityClass = reinterpret_cast<jclass>((jclass) pEnv->NewGlobalRef(cls));
activityObj = pEnv->NewGlobalRef(pObj);
}
}
Code used within the thread function:
void *decodeAndRender(void * args) {
JNIEnv *env;
javaVM->AttachCurrentThread(&env, NULL);
jmethodID retryStartVideoMethodID = env->GetMethodID(activityClass, "retryStartVideo", "()V");
env->CallVoidMethod(activityObj, retryStartVideoMethodID);
javaVM->DetachCurrentThread();
return 0;
}
Java code :
public void retryStartVideo() {
Log.d(TAG, "METHOD CALLED FROM CPP ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
}
Error in logcat:
JNI DETECTED ERROR IN APPLICATION: JNI CallVoidMethodV called with pending exception java.lang.NoSuchMethodError: no non-static method "Ljava/lang/Class;.retryStartVideo()V"
I have set the instances of the calling class to be a global ref and used that when calling from within the thread function but it is still failing to find the method. I can use similar code to call a static method no problem but I need to be able to call a non static one.
I'm currently developping an android app with android studio, for this project i need to use a custom library written in c/c++ .
So i in order to do that i needed to use NDK.
The library contain methods that i need to implements in order to have access to specifics fonctions in android
My question is : how can I call my jni method inside the method existing in c
which will call a java method to store session key in the android system
So for a pratical exemple since it's maybe not clear:
In a file called lib_exemple.c i have three methods
the first one is the initialisation call to the library (jni to library c) -->working
JNIEXPORT void JNICALL
Java_com_example_libExemple_Libs_ExempleLib_lib_1Exemple_1init
(JNIEnv *env, jobject instance) {
lib_Example_init('0'); // c func of the library
}
then the second one is the jni who call a java method (jni to java) -> working
JNIEXPORT jint
JNICALL Java_com_example_libExemple_Libs_ExempleLib_lib_1Exemple_1store_1session_1key
(JNIEnv * env, jobject jobject1, jbyte jbyte1, jchar jchar1, jbyte jbyte2){
jclass clazz = (*env)->FindClass(env, "com/example/libExemple/Libs/ExempleLib");
jmethodID mCurrentActivityId = (*env)->GetMethodID(env, clazz, "KeyStoreSessionKey", "(BCB)I");
jint result = (*env)->CallIntMethod(env, jobject1, mCurrentActivityId, jbyte1, jchar1, jbyte2);
return result;
}
and the third method is the one the library c have in it (library C to jni)
int lib_Exemple_store_session_key(uint8_t Session, P_KEY_ST_T pKey, uint8_t keyType) {
//i want to call jni func here , so the librairy can access the native android function
return 0;
}
then to configure the ndk in a file called ExempleLib.java i have defined
static {
System.loadLibrary("LibExemple");
}
then the prototype of the initialisation of the library
public native void libExemple_init();
the prototype of the first method in lib_exemple.c
public native int lib_Exemple_store_session_key(byte pKey, char key_length, byte keyIndex);
and the java fonction called by it
protected int KeyStoreSessionKey(byte pKey, char key_length, byte keyIndex) {
...
}
my mainActivity contain
ExempleLib LibFunc = new ExempleLib();
Log.d(TAG, "init lib" );
LibFunc.lib_Exemple_init();
My goal is that after initialising my library and call an init function , it can call the first method in the second method of lib_exemple.c (the one used in the library )
thanks
EDIT :
The solution of my problem is when i initialize the lib , i need to save jvm
so i can access the JNIenv in the library method directly
jobject Savedinstance = NULL;
static JavaVM *cachedJVM;
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *jvm, void *reserved) {
cachedJVM = jvm;
return JNI_VERSION_1_6;
}
JNIEnv *AttachJava() {
JavaVMAttachArgs args = {JNI_VERSION_1_6, 0, 0};
JNIEnv *java;
(*cachedJVM)->AttachCurrentThread(cachedJVM, &java, &args);
return java;
}
JNIEXPORT jint JNICALL
Java_com_example_vgosselin_libExemple_Libs_ExempleLib_lib_1init(JNIEnv *env,
jobject instance) {
Savedinstance = instance;
void *element = 0;
jint result;
result = lib_Exemple_init_();
return result;
}
so i can call the java method in
int lib_Exemple_store_session_key(uint8_t Session, P_KEY_ST_T pKey, uint8_t keyType) {
JNIEnv *NewEnv = AttachJava();
jclass clazz = (*NewEnv)->FindClass(NewEnv,"com/example/vgosselin/libExemple/Libs/ExempleLib");
jmethodID mCurrentActivityId = (*NewEnv)->GetMethodID(NewEnv,clazz,"KeystoreStoreKey","([BCB)I");
jint result;
jbyteArray Data = 0;
jchar Key = 0;
jbyte Type = 0;
result = (*NewEnv)->CallIntMethod(NewEnv, Savedinstance, mCurrentActivityId, Data, Key, Type);
return result;
}
and now i don't need the method in jni syntax anymore
JNIEXPORT jint JNICALL Java_com_example_libExemple_Libs_ExempleLib_lib_1Exemple_1store_1session_1key
I a Library in C that I'm leveraging for an Android application. This library has an audio stream that it occasionally flushes. When this happens it calls a write callback function of my design.
My intent is to have that C callback call a method on a specific Java Object which will handle stuff with the strem.
Currently I have code like so:
methodID compressionHandler=0;
jobject compressionHandlerClass;
int audioBufferChunkSize;
static JavaVM *gJavaVM;
JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
gJavaVM = vm;
return JNI_VERSION_1_6;
}
JNIEXPORT void JNICALL
Java_com_my_code_init(JNIEnv* env, jobject obj, /*classpath of the class we want to call against*/jstring compressedAudioHandlerPath, /*class instance we want to call against*/jobject callbackClass) {
......
// this is a global ref as per:
//http://stackoverflow.com/questions/14765776/jni-error-app-bug-accessed-stale-local-reference-0xbc00021-index-8-in-a-tabl
compressionHandlerClass = (*env)->NewGlobalRef(env,callbackClass);
// name of the class
const char *classLocation;
// convert jString to c String
classLocation = (*env)->GetStringUTFChars( env, compressedAudioHandlerPath , NULL ) ;
// tmp variable for holding the class location, relates to the above issue with garbage collection
jclass clazz = (*env)->FindClass(env, classLocation);
// the actual method that we want to call, this gets used in the writeCallback
compressionHandler = (*env)->GetMethodID(env, clazz, "handleCompressedAudio", "([B)V");
......
}
The callback method looks like so:
void writeCallback(const FLAC__StreamEncoder *encoder, const FLAC__byte buffer[], size_t bytes, unsigned samples, unsigned current_frame, void *client_data) {
JNIEnv *env;
int isAttached = 0;
if ((status = (*gJavaVM)->GetEnv(gJavaVM, (void**)&env, JNI_VERSION_1_6)) < 0) {
if ((status = (*gJavaVM)->AttachCurrentThread(gJavaVM, &env, NULL)) < 0) {
return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
}
isAttached = 1;
}
if(*env!=0 && compressionHandler!=0){
jbyteArray arr = (*env)->NewByteArray(env,bytes);
(*env)->SetByteArrayRegion(env,arr, 0, bytes, (jbyte*)buffer);
(*env)->CallVoidMethod(env,compressionHandlerClass, compressionHandler,arr);
free(arr);
free(env);
free(isAttached);
}
}
I'm getting crashes at the CallVoidMethod, that signature of which is an interface implemented by whatever object I pass in:
public interface CompressedAudioHandler {
void handleCompressedAudio(byte[] buff);
}
I suspect that I am improperly attaining/keep references to these objects, but I haven't found a great way to handle that. Any advice on how I can more correctly handle this?