Android JNI ReleaseByteArrayElements does not work

Issue

i have got a problem at using Android JNI. I call a java method from native C. Everything works fine, BUT after a few seconds the APP crashes, because the maximum of 512 entrys of JNI refs is full (or the memory is full).

Here is my code:

int jniBluetoothSend( TJNIAdapter *pAdapter, byte *data, int dwLength )
{
JNIEnv *pEnv;
JavaVM *pVm = NULL;
jclass cls;
jmethodID methodId;
int nRet;
jbyteArray aData;

if ( pAdapter )
{
   pVm = pAdapter->pVm;
   ( *pVm )->AttachCurrentThread( pVm, &pEnv, NULL );

   if ( pAdapter->pClasses != NULL && pAdapter->pClasses->hgs_bluetooth != NULL )
   {
      // get function
      methodId = ( *pEnv )->GetMethodID( pEnv, pAdapter->pClasses->hgs_bluetooth, "write", "([BI)I" );
      if ( methodId )
      {
         aData = ( *pEnv )->NewByteArray( pEnv, dwLength);
         ( *pEnv )->SetByteArrayRegion( pEnv, aData, 0, dwLength, data);
         // write Data to device
         nRet = ( *pEnv )->CallIntMethod( pEnv, g_hgsBthObject, methodId, aData, dwLength );

         // and delete Reference -> so GC can cleanup
         ( *pEnv )->DeleteLocalRef( pEnv, aData );
      }
   }
   //( *pVm )->DetachCurrentThread( pVm ); -> // crashes as soon as getting called
}
return nRet;

}

Everytime "ReleaseByteArrayElements()" gets called a warning shows up in Android Log from dalvik:

JNI: unpinPrimitiveArray(0x428e84a8) failed to find entry (valid=1)

So, i think, the problem is, that the created array is not getting freed. But I don't know, how to do this in the right way.

Can anyone help me with this? Thanks!

EDIT

I have done a several tests. If i add the DetachCurrentThread function to the bottom of the second if(), the APP crashes, if DetachCurrentThread is getting called.

But i have added DeleteLocalRef in an other function, and the APP does not crash anymore.

So my question is: Do i have to call DetachCurrentThread in every function i call AttachCurrentThread or is it enough if i call that once to the end of the APP?

Also updated the Code

Solution

Everytime ReleaseByteArrayElements() gets called a warning shows up in Android Log from dalvik:

JNI: unpinPrimitiveArray(0x428e84a8) failed to find entry (valid=1)

ReleaseByteArrayElements is meant to be paired with a previous call to GetByteArrayElements. From Oracle's documentation:

Release<PrimitiveType>ArrayElements Routines
void Release<PrimitiveType>ArrayElements(JNIEnv *env, ArrayType array, NativeType *elems, jint mode);

A family of functions that informs the VM that the native code no longer needs access to elems. The elems argument is a pointer derived from array using the corresponding Get<PrimitiveType>ArrayElements() function.

Since you didn't call GetByteArrayElements you also shouldn't call ReleaseByteArrayElements.

Note that SetByteArrayRegion() function is not one of the functions that pin an array, therefore it does not require a release.

Answered By - Michael