Android 5.0 ART native DeleteGlobalReference(jobject) is failing

Question

I have an SDK/NDK based app that creates native buffers and then reads/writes data to there to communicate through JNI bridge. in 4.4 (DALVIK) it functions OK - or at least it was not throwing an exception. Once ART became mandatory, i.e. Lollipop - it now fails on app close/exit. Creating the direct buffer here:

JNIEXPORT void JNICALL Java_com_class_nativeOnDirect(JNIEnv* jenv,   jobject obj, jobject   m, jobject mv){
  GLubyte* _dData;
_dData = (GLubyte*)jenv->GetDirectBufferAddress(m);
}

Clearing the direct data:

 JNIEXPORT void JNICALL Java_com_class_nativeOnFreeNativeBuffer(JNIEnv* jenv, jobject obj, jobject m){
 jenv->DeleteGlobalRef(m);
}   

After some research into this - still not exactly clear to me as to why this happens. BTW - if the "DeleteGlobalref(jobjct) does not happen - the exception is not thrown. Afraid of a memory leak here. Thanks in advance

Answer 1

You shouldn't call DeleteGlobalRef on a local ref - only on the actual jobject pointers that you've got returned from NewGlobalRef. So in this case, as long as you aren't calling NewGlobalRef, you don't need to call DeleteGlobalRef either.

You only need to use NewGlobalRef if you store a reference to an object on the native side, for use after the JNI function call returns.

ART is a little bit stricter than dalvik when it comes to using the JNI API correctly, so the code has been incorrect all along, it just hasn't triggered any errors. See http://android-developers.blogspot.fi/2011/07/debugging-android-jni-with-checkjni.html for tips on how to enable CheckJNI for stricter checking, to be able to catch issues like these earlier.