Android program that Streams MIC directly to Speaker of Phone

Question

I'm developing an Android app that streams the microphone to the phone's speaker directly. The programme and UI both hang, despite the working code. But even if the app hangs, audio transfer continues to function. What is the mistake?

 RecordBufferSize=AudioRecord.getMinBufferSize(sampleRateInHz,AudioFormat.CHANNEL_IN_MONO,AudioFormat.ENCODING_PCM_16BIT);
    TrackBufferSize= AudioTrack.getMinBufferSize(sampleRateInHz,AudioFormat.CHANNEL_OUT_MONO,AudioFormat.ENCODING_PCM_16BIT);

    am = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
    Record record = new Record();
    record.run();

}
public class Record extends Thread
{

    final short[] buffer = new short[RecordBufferSize];
    short[] readBuffer = new short[TrackBufferSize];

    public void run() {
        isRecording = true;
        android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_URGENT_AUDIO);
        AudioRecord arec = new AudioRecord(MediaRecorder.AudioSource.MIC,sampleRateInHz,AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT,RecordBufferSize);
        AudioTrack atrack = new AudioTrack(AudioManager.STREAM_MUSIC,sampleRateInHz,AudioFormat.CHANNEL_OUT_MONO, AudioFormat.ENCODING_PCM_16BIT, TrackBufferSize, AudioTrack.MODE_STREAM);
        //am.setRouting(AudioManager.MODE_NORMAL, AudioManager.ROUTE_EARPIECE, AudioManager.ROUTE_ALL);
        atrack.setPlaybackRate(sampleRateInHz);
        byte[] buffer = new byte[RecordBufferSize];
        arec.startRecording();
        atrack.play();
        while(isRecording) {
            AudioLenght=arec.read(buffer, 0, RecordBufferSize);
            atrack.write(buffer, 0, AudioLenght);
        }
        arec.stop();
        atrack.stop();
        isRecording = false;
    }
}

above is my code.