serverSocket.accept（）缓慢或无响应

Question

We created a server client relation between java (eclipse on windows/server) and android app (android studio/client). The communication seems fine, but sometimes the connecting is horrably slow, up to the point where the app and and server don't respond anymore. Yet, no real error is given and there is no pattern to when the connection goes well or when it is slow.

We looked for answers here at stack, but we could only find answers regarding the output and input streams. However, once the connection (serverSocket.accept()) is made, the program runs fine and the streams are created super fast. Thus we think the problem lies with the server side creation of sockets. The program only has to handle a maximum of 30 clients, and the only communication exists of strings (so no enormous data transfers).

Note: when one connection acceptation is slow, the next upcomming requests from clients have to wait. When it's their turn they are again randomely fast or slowly accepted by the server. All connections are made on port 8080.

The code of our server and client are given below, does anybody know why the connection is (at some random times) so slow?

SERVER:

    public void run() {
        keepGoing = true;
    try {
        serverSocket = new ServerSocket(port);

        while (keepGoing) {
            display("Server waiting for Clients on port " + port + ".");

            Socket socket = serverSocket.accept(); //<---our problem
            if (!keepGoing)     break;
            ClientThread t = new ClientThread(socket, this); //<---program doesnt reach this code when it is slow. One client thread exists for each connection.
    }catch (IOException e) {
        String msg = sdf.format(new Date())
                + " Exception on new ServerSocket: " + e + "\n";
        display(msg);
        }
    }

CLIENT THREAD CODE: (not reached if slow)

    public ClientThread(Socket socket, Server s) {
        this.server = s;
        this.socket = socket;        
    System.out.println("Thread trying to create Object Input/Output Streams");
    try {
        // make streams
        sOutput = new ObjectOutputStream(socket.getOutputStream());
        sInput = new ObjectInputStream(socket.getInputStream());

        // read user account info
        String input = (String) sInput.readObject();
        String[] accountInfo = input.split(";");
        username = accountInfo[0];
        password = accountInfo[1];
    } "catch all problems"
    }

CLIENT (android)

    Thread connect = new Thread(new Runnable() {
    @Override
        public void run()
        {
            try
            {
                socket = new Socket(ip.getText().toString(), portNr);
                sOutput = new ObjectOutputStream(socket.getOutputStream());
                sInput = new ObjectInputStream(socket.getInputStream());
            }

            catch (UnknownHostException e ){
                e.printStackTrace();
            } catch(IOException e ){
                e.printStackTrace();
            }

            "sending account information"
        }
    });
    connect.start();
    try {
        connect.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

Thanks so much!

Answer 1

You should extract your main server loop (while(keepGoing)...) into a run method and make the server implement the Runnabel interface. Then create a new Thread and start it.

Example:

public class Server implements Runnable{
    private Thread thread;
    public Server(){
        thread = new Thread(this);
        thread.start(); //I would create start() and stop() methods but for simplicity I just use thread.start()
    }

    @Override
    public void run(){
        //while....
    }
}

I hope you get what I want to say, otherwise just comment and I will upgrade my example ;)

Answer 2

You should make the streams in the ClientThread in the run() method, before you start looping. Not in the constructor. Otherwise you are doing I/O in the accept thread, which slows it down.

I have no idea why you're creating a thread in the client only to join it immediately.

Answer 3

Turns out we had a router issue. When connecting all tablets and computer to a local hotspot it ran super smooth! Tanks everyone for the help :D

Answer 4

EDIT: Try a BufferedStreamReader mentioned here: Java socket performance bottleneck: where?

Instead of:

sOutput = new ObjectOutputStream(socket.getOutputStream());

Use:

sOutput = new ObjectOutputStream(new BufferedOutputStream(socket.getOutputStream()));

and flush it with:

sOutput.flush();

Same goes for the InputStream, use BufferedInputStream.