[SOLVED] LibGDX Server Thread

I am currently developing a MOBA like game with libGDX, but I am struggling with the Server. Currently I have got a thread for every connection and a critical region which stores the data. My problem is, that there are Threads, which are writing into the critical region and reading from it simultaneously. Can somebody help me out?

Here are my classes:
Clientthread:

package at.mobaserver;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;

import at.motm.model.GameObject;
import at.motm.model.Projectile;

import com.badlogic.gdx.math.Intersector;
import com.badlogic.gdx.math.Rectangle;

public class ClientConnection implements Runnable
{
private ObjectInputStream ois;
private ObjectOutputStream oos;
private Socket socket;
private GameServer server;
private GameObject receivedObject;
private Rectangle r;
private Projectile projectile;
private boolean found;

public ClientConnection(Socket socket, GameServer server)
{
    try
    {
        this.socket = socket;
        this.oos = new ObjectOutputStream(socket.getOutputStream());
        this.ois = new ObjectInputStream(socket.getInputStream());
        this.server = server;
        this.receivedObject = null;
        this.projectile = null;
    }
    catch (IOException e)
    {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

@Override
public void run()
{
    try
    {
        this.oos.writeLong(Thread.currentThread().getId());
        this.oos.flush();
    }
    catch (IOException e1)
    {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    while (true)
    {
        try
        {
            // Add GameObjects to list
            // this.server.getMutex().lock();
            this.oos.reset();

            // Hitdetection
            if (this.projectile != null)
            {
                projectileHitDetection();
            }

            // Write Objects to client
            this.oos.writeObject(this.server.getSendingList());
            this.oos.flush();

            // Add Objects to Severobject Arraylist
            // this.server.getMutex().lock();
            addObjectsToList();

            // Add Projectiles to Serverobject Arraylist
            readProjectiles();
            // this.server.getMutex().unlock();
            // this.server.getMutex().unlock();

        }
        catch (ClassNotFoundException e)
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        catch (IOException e)
        {
            e.printStackTrace();
            break;
        }
    }
}

private void readProjectiles() throws ClassNotFoundException, IOException
{
    synchronized (this.server.getProjectiles())
    {
        this.projectile = (Projectile) this.ois.readObject();

        if (this.projectile != null)
        {
            this.found = false;
            for (int i = 0; i < this.server.getProjectiles().size(); i++)
            {
                if (this.server.getProjectiles().get(i).getThreadID() == Thread
                        .currentThread().getId())
                {
                    this.server.getProjectiles().set(i, this.projectile);
                    this.found = true;
                    break;
                }
            }
            if (!this.found)
            {
                this.server.getProjectiles().add(this.projectile);
            }
        }
    }

}

private void addObjectsToList() throws ClassNotFoundException, IOException
{
    synchronized (this.server.getObjects())
    {
        this.receivedObject = (GameObject) this.ois.readObject();

        this.found = false;
        for (int i = 0; i < this.server.getObjects().size(); i++)
        {
            if (this.server.getObjects().get(i).getThreadID() == Thread
                    .currentThread().getId())
            {
                this.server.getObjects().set(i, this.receivedObject);
                this.found = true;

                break;
            }
        }
        if (!this.found)
        {
            this.server.addObject(this.receivedObject);
        }
    }

}

private void projectileHitDetection()
{
    synchronized (this.server.getObjects())
    {
        this.r = new Rectangle(this.projectile.getPosition().x,
                this.projectile.getPosition().y,
                this.projectile.getWidth(), this.projectile.getHeight());

        for (int i = 0; i < this.server.getObjects().size(); i++)
        {
            if (this.server.getObjects().get(0).getTeam() != this.projectile
                    .getTeam())
            {
                Rectangle r1 = new Rectangle(this.server.getObjects()
                        .get(0).getPosition().x, this.server.getObjects()
                        .get(0).getPosition().y, this.server.getObjects()
                        .get(0).getWidth(), this.server.getObjects().get(0)
                        .getHeight());
                if (Intersector.overlaps(this.r, r1))
                {
                    System.out.println("test");
                    this.server.getProjectiles().remove(this.projectile);
                    break;
                }
            }
        }
    }

}
}

Critical region: package at.mobaserver;

import java.util.ArrayList;

import at.motm.model.GameObject;
import at.motm.model.Projectile;

public class GameServer
{
private ArrayList<GameObject> objects;
private ArrayList<Projectile> projectiles;
private ArrayList<GameObject> sendList;

public GameServer()
{
    this.objects = new ArrayList<GameObject>();
    this.projectiles = new ArrayList<Projectile>();
    this.sendList = new ArrayList<GameObject>();
}

public ArrayList<GameObject> getSendingList()
{

    synchronized (this.sendList)
    {
        this.sendList.clear();
        for (GameObject o : this.objects)
        {
            if (o.isAlive())
            {
                this.sendList.add(o);
            }
        }
        this.sendList.addAll(this.projectiles);
        return this.sendList;
    }

}

public ArrayList<GameObject> getObjects()
{
    synchronized (this.objects)
    {
        return this.objects;
    }
}

public void setObjects(ArrayList<GameObject> objects)
{
    synchronized (objects)
    {
        this.objects = objects;
    }

}

public void addObject(GameObject o)
{
    synchronized (this.sendList)
    {
        this.objects.add(o);
    }

}

public ArrayList<Projectile> getProjectiles()
{
    synchronized (this.projectiles)
    {
        return this.projectiles;
    }
}

public void setProjectiles(ArrayList<Projectile> projectiles)
{
    synchronized (this.projectiles)
    {
        this.projectiles = projectiles;
    }

}

public void addProjectile(Projectile o)
{
    synchronized (this.sendList)
    {
        this.projectiles.add(o);
    }

}
}