Android passing large float arrays from native to java via jni. Getting error if over certain size

Question

I am wanting to pass a single large array of floats anywhere up too and beyond float[100000]. I have a setup successfully passing an array of size 212. But any larger and it crashes giving the following error message in the logcat:

"Fatal signal 11 (SIGSEGV) at 0xbe949000 (code=1)"

My code

Native function

NIEXPORT jfloatArray JNICALL  Java_carron_graphics_benchmark_NativeWrapper_getArrayNative(JNIEnv * env, jclass cls) {

    int tempSize = mParticleSystem->mSizeOfSystem*2;

    jfloat cArray[tempSize];
    jsize len = sizeof(cArray);

    jfloatArray jArray = (*env).NewFloatArray(len);

    if (jArray != NULL) {

        jint i;

        for (i = 0; i < tempSize; i++) {
            cArray[i] = mParticleSystem->mParticlePositions[i];
        }
        (*env).SetFloatArrayRegion(jArray, 0, len, cArray);
    }
    return jArray;
}

Java Pretty straight forward simply grabbing the array. If I create and pass a float array larger than 212 though I get the error as shown above.

float tempArray[] = NativeWrapper.getArrayNative();

Has anyone encountered this problem or can see how I can get around this limit? Also I apologise if this question has been answered already, I could not find this specific issue nor an answer. Any help will be appreciated :)

EDIT:

For updating a global jfloatArray to avoid the garbage collector when frequently fetching an array through jni.

static jfloatArray gArray = NULL;

JNIEXPORT jfloatArray JNICALL Java_carron_graphics_benchmark_NativeWrapper_getArrayNative(JNIEnv * env, jclass cls)  {
    int arrayLength = mParticleSystem->mSizeOfSystem*2;

    if (gArray == NULL)
    {
        // create array
        jfloatArray jArray;
        jArray = env->NewFloatArray(arrayLength);
        gArray = (jfloatArray)env->NewGlobalRef(jArray);
    }

    // Update global 
    env->SetFloatArrayRegion(gArray, 0, arrayLength, mParticleSystem->mParticlePositions);

    return gArray;
}

Answer 1

Problem with your code is that stack is limited in size. You can not put there large arrays (jfloat cArray[tempSize] variable). If you want to create large array, do that on heap, like Alex is showing you.

If mParticleSystem->mParticlePositions is float array then this code will be better:

int tempSize = mParticleSystem->mSizeOfSystem*2;
jfloatArray jArray = env->NewFloatArray(tempSize);

if (jArray != NULL)
{
    env->SetFloatArrayRegion(jArray, 0, tempSize, mParticleSystem->mParticlePositions);
}
return jArray;

If it is not float array then use following code, no need to create additional float array:

int tempSize = mParticleSystem->mSizeOfSystem*2;
jfloatArray jArray = env->NewFloatArray(tempSize);

if (jArray != NULL)
{
    if (float* ptr = env->GetFloatArrayElements(jArray, NULL))
    {
        for (int i=0; i<tempSize; i++)
        {
            ptr[i] = mParticleSystem->mParticlePositions[i];
        }
        env->ReleaseFloatArrayElements(jArray, ptr, JNI_COMMIT);
    }
}

return jArray;

EDIT

To store jArray somewhere else (for example globally) do following:

static jfloatArray gArray = NULL;

jfloatArray fun(...)
{
    jfloatArray jArray;

    if (gArray == NULL)
    {
        // create array
        jArray = env->NewFloatArray(tempSize);
        gArray = (jfloatArray)env->NewGlobalRef(jArray);
    }
    else
    {
        jArray = gArray;
    }

    // ... here fill/modify jArray
    // SetFLoatArrayRegion/GetFloatArrayElemeents/ReleaseFloatArrayElements

    return jArray;
}

When done free the memory:

void freeArray(...)
{
    env->DeleteGlobalRef(gArray);
    gArray = NULL;
}