if(outgoing_packet_handler != null) outgoing_packet_handler.stop();
    void stopThreads() {        Thread tmp;        // 1. Stop the multicast receiver thread        if(mcast_receiver != null) {            if(mcast_receiver.isAlive()) {                tmp=mcast_receiver;                mcast_receiver=null;                closeMulticastSocket();  // will cause the multicast thread to terminate                tmp.interrupt();                try {                    tmp.join(100);                }                catch(Exception e) {                }                tmp=null;            }            mcast_receiver=null;        }        // 2. Stop the unicast receiver thread        if(ucast_receiver != null) {            ucast_receiver.stop();            ucast_receiver=null;        }        // 3. Stop the in_packet_handler thread        if(incoming_packet_handler != null)            incoming_packet_handler.stop();    }