Thread in Service causes ANR

Question

I'm trying to respond to multicast DatagramPackets on my phone. This is the part of the code that keeps causing the ANR:

private void multicastLoop() {
        String res = Build.FINGERPRINT + "\n";
        final InetAddress group;
        final MulticastSocket socket;
        final DatagramPacket response;
        try {
            group = InetAddress.getByName("239.255.255.127");
            socket = new MulticastSocket(port);
            socket.setLoopbackMode(true);
            socket.setSoTimeout(1000);
            socket.joinGroup(group);
            response = new DatagramPacket(res.getBytes(), res.length(), group, port);
        } catch (IOException e) {
            e.printStackTrace();
            return;
        }

        Thread t = new Thread(new Runnable() {

            @Override
            public void run() {
                while(isRunning) {
                    try {
                        byte[] data = new byte[1024];
                        DatagramPacket dm = new DatagramPacket(data, data.length);
                        socket.receive(dm);
                        if (Arrays.equals(dm.getData(), "someone there".getBytes())) {
                            socket.send(response);
                        }
                    } catch (SocketTimeoutException e) {
                        continue;
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                try {
                    socket.leaveGroup(group);
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        });
        t.run();
    }

The method multicastLoop is called in the onCreate of the Service, after setting isRunning = true; Why does this Thread cause an ANR error? The TCP-Server-Thread is running without problems (while (isRunning) {...})

Answer 1

You need to call t.start(); instead of t.run();

t.run() will just execute the Runnable on the current thread (the UI) which causes the ANR.