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Java: Multithreading with two different input sources and reacting

First question here on StackOverflow, so please excuse me if I ask this incorrectly.
Basically, I'm writing a Multicast Client that indefinitely listens to a multicast address until the user types "quit" into the console. I've found that setting SO_TIMEOUT for the MulticastSocket, checking if "quit" has been typed, and then returning to the receive method call doesn't really work since a packet could be sent right after the timeout and the check of the console blocks. So I believe the best option is to simply have 2 threads going where one listens on the socket and blocks until it receives something, and the other thread listens to the console until told to quit. The only issue I have is that I'm unsure of how to go about having the console listening thread tell the socket thread to close the socket and terminate. System.end() would work but I fear that I'd leave a socket open, etc.
TLDR; Is there a way for the main method of a class to start a thread, and then respond a specific way once that thread ends? I need to listen to the console on one thread and a MulticastSocket on another, or just in the main of the client class.
Thanks everyone.

I would call Socket.close() to close the socket. This will produce an IOException in that thread. so before doing this I would set a flag like closed = true; and have the other thread check this before printing the error i.e. don't print an IOException if you have been closed. Something like this.
public class SocketListener implements Runnable, Closeable {
final MulticastSocket socket;
final Consumer<DatagramPacket> packetConsumer;
volatile boolean closed;
public SocketListener(MulticastSocket socket, Consumer<DatagramPacket> packetConsumer) {
this.socket = socket;
this.packetConsumer = packetConsumer;
}
#Override
public void run() {
DatagramPacket packet = new DatagramPacket(new byte[1024], 1024);
try {
while(!closed) {
socket.receive(packet);
packetConsumer.accept(packet);
}
} catch (IOException e) {
if (!closed)
e.printStackTrace();
}
}
#Override
public void close() throws IOException {
closed = true;
socket.close();
}
}
for example, in your main thread you can do
MulticastSocket socket = ...
Consumer<DatagramPacket> packetConsumer = ...
try (SocketListener listener = new SocketListener(socket, packetConsumer)) {
boolean finished = false;
do {
// read from the console
if (some condition)
finished = true;
} while(!finished);
} // calls close() for you.

Java Multiple threads for just 2 computers, how to do it in main

I'm trying to get at least two computers to connect to my server, how would i start a second thread?
public static void main(String[] args) throws InterruptedException {
// Create the server which waits for a client to request a connection.
while(true){
FileSharedServer server = new FileSharedServer();
Thread thread = new Thread(server);
thread.start();
}
}
this refuses my connection

You need to wait on serverSocket.accept() method on incoming connections in your server, and after receiving one start a thread to serve it, but the server socket stay the same, you just do waiting for next connection in a loop.
while (true) {
Socket connection = serverSocket.accept();
new Therad() {
public void run() {
serveConnection(connection);
}
}.start();
}

Java SocketException. Why is it closed?

I'm trying to get a threaded chatserver working. But my socket is closing and I have no clue why it is.
In the server class I create a new ClientHandler
addHandler(new ClientHandler(this, incoming));
addHandler starts the thread and adds the new ClientHandler to an ArrayList in server.
incoming is the client socket.
public ClientHandler(Server serverArg, Socket sockArg) {
server = serverArg;
client = sockArg;
System.out.println(client.isClosed());
}
There is nothing called between
public void run() {
try {
System.out.println(client.isClosed());
in = new Scanner(client.getInputStream());
out = new PrintWriter(client.getOutputStream(), true);
announce();
System.out.println("Waiting for input");
boolean done = false;
while(!done && in.hasNextLine()) {
System.out.println("There is input!");
server.broadcast(clientName + ": " + in.nextLine());
}
} catch (Exception e) {
System.out.println(e.toString());
}
}
When I run this code. This is the output:
false
true
java.net.SocketException: Socket is closed
Why is it closing immediately after creating this class / before starting it?

The connection is being closed by your code between when you add the handler and when the run() method is called. I suggest you add a breakpoint to the close method in the JDK and see where it is called. Or have a look at the code after you add the handler.

You can use a networking sniffer like wireshark or tcpdump.
To find out that if the connection broke due to the server side.
I guess that maybe the client side close the connection.

Socket.close() have no effect during Socket.connect()

Using the default socket implementation on Windows, I was not able to find any effective method to stop Socket.connect(). This answer suggests Thread.interrupt() will not work, but Socket.close() will. However, in my trial, the latter didn't work either.
My goal is to terminate the application quickly and cleanly (i.e. clean up work needs to be done after the socket termination). I do not want to use the timeout in Socket.connect() because the process can be killed before a reasonable timeout has expired.
import java.net.InetSocketAddress;
import java.net.Socket;
public class ComTest {
static Socket s;
static Thread t;
public static void main(String[] args) throws Exception {
s = new Socket();
InetSocketAddress addr = new InetSocketAddress("10.1.1.1", 11);
p(addr);
t = Thread.currentThread();
(new Thread() {
#Override
public void run() {
try {
sleep(4000);
p("Closing...");
s.close();
p("Closed");
t.interrupt();
p("Interrupted");
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
s.connect(addr);
}
static void p(Object o) {
System.out.println(o);
}
}
Output:
/10.1.1.1:11
Closing...
Closed
Interrupted
(A few seconds later)
Exception in thread "main" java.net.SocketException: Socket operation on nonsocket: connect

You fork the thread and then the main thread is trying to make the connection to the remote server. The socket is not yet connected so I suspect s.close() does nothing on a socket that is not connected. It's hard to see what the INET socket implementation does here. t.interrupt(); won't work because the connect(...) is not interruptible.
You could use the NIO SocketChannel.connect(...) which looks to be interruptible. Maybe something like:
SocketChannel sc = SocketChannel.open();
// this can be interrupted
boolean connected = sc.connect(t.address);
Not sure if that would help though.

Java.nio.channels.ServerSocketChannel - accept() memory leak

I got thread for server in my Android app and need to handle it properly when user decide to close it. I choose non-blocking ServerSocketChannel which accept() clients.
And got this
public class SocketServer extends Thread
{
private static final String LOG_TAG = "SocketServer";
private boolean isRunning = false;
private ServerSocketChannel listener = null;
public void _stop()
{
this.isRunning = false;
}
public void _start()
{
this.isRunning = true;
this.start();
}
private void free()
{
try
{
listener.close();
}
catch (IOException e)
{
//Error handle
}
listener = null;
}
public SocketServer(int port)
{
super();
try
{
listener = ServerSocketChannel.open();
listener.configureBlocking(false);
listener.socket().bind(new InetSocketAddress(port));
}
catch (IOException e)
{
//Error handle
}
}
public void run()
{
SocketChannel client = null;
while(isRunning)
{
try
{
client = listener.accept();//GC going mad
}
if(client != null)
Log.i(LOG_TAG, "ACCEPTED CLIENT");
catch (IOException e)
{
//Error handle
}
}
free();
}
All i'm doing is accepting new client - getting null because of no incoming connections and do it again until server is stopped.
ServerClient client is null at start and assigned to null by accept() if no connections available.
But Java's garbage collector thinks what client is somehow init by accept() or accept() somehow allocate some memory, which GC cleans after every while loop.
If comment accept() line (e.g do nothing) where will be no GC at all, so problem exactly in accept().
This quite not right in my opinion.
P.S. If there is some way to break blocking ServerSocket accept()/Socket read() state and exit properly, please tell me.
P.S. 2 Is it safe to write/ read to SocketChannel socket() as to Socket, will it block thread?

Many operations in Java create temporary objects internally to do their work.
You are much better off using a blocking SocketServer. This way the objects it creates is only on a per-accepted-Socket basis rather than a per-attempt basis.
I suggest you implement blocking NIO with a thread (or two) per connection first. If then you discover you have a performance issue with the number of threads you have, try using a Selector with non-blocking NIO.