Multithreading with sockets JAVA

Question

I have a problem with multithreading. I don't know why, but threads run in sequence. There is a client-server application. I need to run several parallel threads for message exchange. The whole classes are too big, so I will show main parts.

Code of Client(This code runs every time when I push the button):

  public ArrayList<Action> call() {
        Thread myThready = new Thread(new Runnable()
        {
            public void run()
            {
                BufferedReader in;
                PrintWriter out;
                try{
                    Socket fromserver = new Socket(ip, PortID);
                    in = new BufferedReader(new InputStreamReader(fromserver.getInputStream()));
                    out = new PrintWriter(fromserver.getOutputStream(),true);

                    writeLog(query, ID, 0);
                    out.println(query+"ID"+ID);
                    String fserver = in.readLine();
                    writeLog(fserver, ID, 1);
                    out.println("exit");
                    out.close();
                    in.close();
                    fromserver.close();
                }
                catch (IOException io){
                    return;
                }
            }
        });
        myThready.start();
}

Code of Server:

public void run(){
    flag=true;
    System.out.println("Welcome to Server side!");

    createLog();
    ExecutorService service = Executors.newCachedThreadPool();
    ServerSocket servers = null;
    int n=4600;
    try{
    servers = new ServerSocket(n);
    } catch( Exception e){

    }
    Socket fromclient = null;

    while(true){
        try {
            System.out.print("Waiting for a client...");
            fromclient = servers.accept();
            System.out.println("Client connected.");
            Callable<ArrayList<Action>> callable = new HandleThread(fromclient);
            Future<ArrayList<Action>> future = service.submit(callable);

            list.addAll(future.get());
        } catch (Exception e) {
            System.out.println("Can't accept.");
            System.exit(-1);
        }
    }
}

This code does "accept()" and then creates new thread for some calculations.

Code of HandleThread:

public ArrayList<Action> call() {
    BufferedReader in = null;
    PrintWriter out= null;
    try {
        in  = new BufferedReader(new
                InputStreamReader(fromclient.getInputStream()));
        out = new PrintWriter(fromclient.getOutputStream(),true);
        String         input,output;

        System.out.println("Wait for messages.");

        while ((input = in.readLine()) != null) {
            //close filewriter thread if input==exit
            if(input.equalsIgnoreCase("exit")){
                break;
            }
            System.out.println(input);
            String[] arr = input.split("ID");
            System.out.println("+"+arr[0]);
            ID = Integer.parseInt(arr[1]);
            writeLog(arr[0], ID, 0);
            process(arr[0], ID);
            out.println(arr[0]);
            writeLog(arr[0], ID, 1);
        }
        out.close();
        in.close();
        fromclient.close();

    } catch(IOException e){
        return null;
    }
    return list;
}

I don't know why this doesn't work. I have logs and I see that one thread runs only after another one. Not at the same time! Please, help me!

Answer 1

Future#get() is a blocking call.

list.addAll(future.get());

The calling thread will wait until the task is done. As such, your server thread which calls accept() waits for each task to finish before it gets to the next one.