How to run multiple threads simultaneosly

Question

I am developing an Android application that opens a video stream using the class JavaCameraView, and captures frames from it. Then, my target is to realize a worker thread that saves these frames into a buffer, and another thread that takes every frame from the buffer, in order to process it with image-processing techniques. So the buffer is a resource shared between these two worker threads, that should run simultaneosly, so filling and emptying the buffer at the same time. I thought to realize the buffer as a ConcurrentLinkedQueue, and the two threads are realized implementing the Runnable interface. Then, in the Main Activity, I declare them, I istantiate them, and then I start them, but it seems that only the first becomes running, and the second never starts. I post here my code:

1)Buffer.java

public class Buffer {
private ConcurrentLinkedQueue<Mat> MyBuffer = new ConcurrentLinkedQueue<Mat>();
private static final String TAG = "MyBufferClass :: ";
private int index = 1;

public Buffer(){
    Log.d(TAG,"Buffer Created");
}

public void insertElementInTail(Mat element){
    MyBuffer.offer(element);
}

public Mat retrieveElementInHead(){
    synchronized (MyBuffer){
        if(!MyBuffer.isEmpty()){
            return MyBuffer.peek();
        }else{
            return null;
        }
    }
}

public Mat removeElementInHead(){
    synchronized (MyBuffer){
        if(!MyBuffer.isEmpty()){
            return MyBuffer.poll();
        }else{
            return null;
        }
    }
}

public int getSize(){
    return MyBuffer.size();
}
}

2)SaveInBuffer.java

public class SaveInBuffer implements Runnable {

private Handler myHandler;
private Buffer myBuffer;

public Handler myThreadHandler;
MainActivity mainActivity;
Handler mainHandler;
int what = -1;


public SaveInBuffer(Buffer myBuf, MainActivity mainActivity){
    //super("SaveInBuffer");
    this.myBuffer = myBuf;
    this.mainActivity = mainActivity;
    this.mainHandler = mainActivity.mainHandler;
}

@Override
public void run(){
    Looper.prepare();
    myThreadHandler = new Handler(){
        public void handleMessage( Message msg ){
             if(msg.what==4){
                 Mat returnedFrame = (Mat)msg.obj;
                 myBuffer.insertElementInTail(returnedFrame);
             }
        }
    };
    Looper.loop();
}

}

3)TakeFromBuffer.java

public class TakeFromBuffer implements Runnable{

public Handler consumerHandler;
private Buffer myBuffer;

public TakeFromBuffer(Buffer myBuffer){
    this.myBuffer = myBuffer;
}

@Override
public void run(){
    Looper.prepare();
    Mat consumedFrame = myBuffer.removeElementInHead();
    Looper.loop();
}
}

The buffer is created within the MainActivity, and then passed as parameter to the threads. The question is how to manage the Buffer as a shared resource, so implementing synchronization techniques, and how to start the two threads simultaneosly, because it's really important that they run at the same time.

How could I do? Any help would be very appreciated.