Invalid reference during callback

Question

i have an object that is used for calling callback functions ----- static jobject o;

i have assigned the callback function to that object through a pointer, env -----

o=env->NewGlobalRef(callback);

The same pointer, env, points towards the function CallVoidMethod( ) that uses JNI to reach to the java code.

env->CallVoidMethod(o, methodId, pDeviceId, deviceStatus, statusReason, connectionProgressInfo);

However on calling this function, the system is getting crashed, and VM says that it's an invalid reference to static jobject o and then it crashes.

My code is as follows :

static jint android_net_wimax_subscribeDeviceStatusChange(JNIE nv* env, jobject clazz, jobject jdeviceId, jobject callback) {

// LOGD(" android_net_wimax_subscribeDeviceStatusChange() ->D1"); o = env->NewGlobalRef(callback); //o = callback;

// LOGD(" android_net_wimax_subscribeDeviceStatusChange() ->D2");

return (jint)::SubscribeDeviceStatusChange(deviceId, fun_IndDeviceStatusUpdate); }

void fun_IndDeviceStatusUpdate(WIMAX_API_DEVICE_ID_P pDeviceId, WIMAX_API_DEVICE_STATUS deviceStatus, WIMAX_API_STATUS_REASON statusReason, WIMAX_API_CONNECTION_PROGRESS_INFO connectionProgressInfo) {

JNIEnv *env = NULL; int nResult = -1;

// LOGD(" AttachCurrentThread() ->D1");

nResult = g_jVM->AttachCurrentThread(&env, NULL);

// LOGD(" AttachCurrentThread() ->D2-%d",nResult);

if ((nResult != 0) || (env == NULL)) { LOGD(" AttachCurrentThread() failed"); } else { // LOGD(" AttachCurrentThread() ->D3");

if(o == NULL) {

LOGD(" o is NULL ");

} else { LOGD(" o is not NULL ");

}

jclass cls = env->GetObjectClass(o);

// LOGD(" AttachCurrentThread() ->D4"); jmethodID methodId = env->GetMethodID(cls, "callback", "(Landroid/net/wimax/structs/DeviceId;III)V");

// LOGD(" AttachCurrentThread() failed->D5"); if (methodId) { env->CallVoidMethod(o, methodId, pDeviceId, deviceStatus, statusReason, connectionProgressInfo); }

if (g_jVM->DetachCurrentThread() != JNI_OK) { LOGE("%s: DetachCurrentThread() failed", FUNCTION); } }

// LOGD("JNI->CALLBACK->D3");

}

<<< D/wimax ( 1673): before CallVoidMethod() W/dalvikvm( 1673): JNI WARNING: 0x48e31dec is not a valid JNI reference W/dalvikvm( 1673): in Ldalvik/system/NativeStart;.run ()V (CallVoidMethodV) I/dalvikvm( 1673): "Thread-55" prio=5 tid=45 RUNNABLE I/dalvikvm( 1673): | group="main" sCount=0 dsCount=0 s=N obj=0x43b6c930 self=0x306370 I/dalvikvm( 1673): | sysTid=2000 nice=0 sched=0/0 cgrp=unknown handle=3194272

Kindly help me out

Answer 1

Without code to look at it's hard to say, but I would guess you're trying to use a local reference after the function it was created in has returned to the VM.

You can get some basic advice from the Android "JNI Tips" document in the Dalvik docs (see "Local vs. Global References"), and more detailed information from the official JNI documentation.

Answer 2

Hi,

Try using pastebin or the preformatted tag. In fun_IndDeviceStatusUpdate you reference deviceStatusChangeCB but I do not see where it is declared or assigned. You use o as the static global reference to the callback. Shouldn't o be where you look for the class and not deviceStatusChangeCB?

Fadden is also right that the first argument to the java callback method is an instance of class android/net/wimax/structs/DeviceId. Are you sure that WIMAX_API_DEVICE_ID_P is a jobject instance of that class? Are you sure the error message (can you post that?) is referring to o and not to the argument?

Also, are you sure it is safe to detach the JVM from the thread this method is being invoked from (e.g. is this a Java thread)?