ObjectInputStream consumes too much memory

Question

I have a Socket that sends a list of Objects every few seconds to a client through ObjectOutputStream. On the server side, after every writeObject(myList) i execute flush then reset . Using VisualVM to check for memory usage, on the server there's no memory leaks, but on the client it seems that the previously read Lists are kept in memory. I tried to execute reset on the ObjectInputStream on the client side but looks like ObjectInputStream does not support this method (it throws a java.io.IOException: mark/reset not supported ).

This is my server socket:

public class ConsultaBombas {

    public static void inicializarServidorSocket() {
        try {
            ServerSocket serverSocket = new ServerSocket(5963);
            Thread thread = new Thread(() -> {
                while (!serverSocket.isClosed()) {
                    try {
                        final Socket socket = serverSocket.accept();
                        new ThreadComunicacao(socket).start();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
            thread.setName("Consulta bombas (Inicializador)");
            thread.start();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    static class ThreadComunicacao extends Thread {
        private Socket socket;

        public ThreadComunicacao(Socket socket) {
            this.socket = socket;
            setName("Consulta bombas (Comunicação) com início: " + new SimpleDateFormat("dd/MM/yyyy HH:mm:ss").format(new Date()));
        }

        @Override
        public void run() {
            try {
                ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
                while (!socket.isClosed()) {
                    List<Bomba> bombas = new DaoBomba().findAll();
                    out.writeObject(bombas);
                    out.flush();
                    out.reset();
                    Thread.sleep(1000);
                }
            } catch (SocketException e) {
                if (e.getLocalizedMessage() != null && e.getLocalizedMessage().equalsIgnoreCase("Connection reset by peer: socket write error")) {
                    System.out.println("Cliente desconectou...");
                } else {
                    e.printStackTrace();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

}

An this is the client (started with start() method):

public class ConsultaBombasClient {

    private Socket socket;
    private Thread threadConsulta;

    public ConsultaBombasClient(BombasListener bombasListener, String maquinaDestino) {
        threadConsulta = new Thread(() -> {
            try {
                Thread.currentThread().setName("Consulta Bombas");
                System.out.println("Endereço bagual: "+maquinaDestino);
                socket = new Socket(maquinaDestino, 5963);
                ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
                Object leitura;
                while ((leitura = in.readObject()) != null) {
                    List<Bomba> bombas = (List<Bomba>) leitura;
                    bombasListener.run(bombas);
                }
            } catch (Exception e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        });
        threadConsulta.setDaemon(true);
    }

    public void start() {
        threadConsulta.start();
    }

    public interface BombasListener {
        void run(List<Bomba> bombas);
    }

}

What am i doing wrong?

Answer 1

garbage collection is not immediate, do you have any real memory troubles? Have you tried running the client with low -Xmx value, did you receive the OutOfMemoryError ? – user3707125

You're right, after some time when the memory gets close to the maximum heap size, it clears the objects from memory. I wasn't seeing this because i have a lot of RAM in my pc but with Xmx50m i could see this working as you said. – Mateus Viccari

Answer 2

Clearly bombasListener.run() , whatever it may be, is not releasing the supplied list.

NB ObjectInputStream.readObject() does not return null at end of stream. It is therefore incorrect to use this test as a termination condition for a read loop.