Threads,Sockets and Streams

Question

In my program I want to send some information to another computer with sockets. The first socket send some text throw the server and when the second socket receive this information it send a answer to the first socket. The problem is that another thread receive the answer and the only thing which I get is deadlock. This is the server side:

else if(msgArray[0].compareTo("game_request") == 0){
                if(userMap.containsKey(msgArray[1])){
                    Socket socketPlayerTwo = userMap.get(msgArray[1]);
                    otherPlayer = msgArray[1];
                    sendResult(socketPlayerTwo, "game_offer?"+username);
                    Boolean willPlay =Boolean.valueOf(recieveRequest(socketPlayerTwo).split("?")[1]);
                    if(willPlay)
                        playingUser.put(username,msgArray[1]);
                    sendResult(socket, "game_accept?"+willPlay);

                }
            }

This is the client side:

private void showGameRequest(String usernameOther) {
        try{
            int status = GameWindow.getInstance().showNotification("Game Offer","The user " + usernameOther + " offers you a game!\nDo you agree?",SWT.ICON_QUESTION|SWT.YES|SWT.NO);
            if (status == SWT.YES){
                otherPlayer = usernameOther;
                sendRequest("send_message_to_user?user="+usernameOther+"&value=true");
                GameWindow.getInstance().getDisplay().asyncExec(new Runnable() {

                    @Override
                    public void run() {
                        GameWindow.getInstance().startNewGame();

                    }
                });
            }
            else
                sendRequest("send_message_to_user?user="+usernameOther+"&value=false");
            }
        catch (IOException exc){

        }
    }

Answer 1

Could you show us more of your code?

sendResult(socketPlayerTwo, "game_offer?"+username);
recieveRequest(socketPlayerTwo);
sendRequest("send_message_to_user?user="+usernameOther+"&value=true");

for starters. Judging by the little i'm seeing you have a problem with the order in which you're using them. As far as i can tell you have a inputSteram.readObject() method that has blocked somewhere waiting for a message from the other side.

Answer 2

Here is the sendRequest method:

private void sendResult(Socket socket,String request) throws IOException{
    DataOutputStream writer = new DataOutputStream(socket.getOutputStream());
    writer.writeUTF(request);
    writer.flush();
}

The client socket is created in the class Server

while (true) {
        try {
            Socket socket = serverSocket.accept();
            new GameThread(socket,databaseManager);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

and it is put in hashmap when the user pass the login level:

if(msgArray[0].compareTo("user_info") == 0){
                Integer flagUser = -1;
                String[] userInfo = {msgArray[1].substring(msgArray[1].indexOf("=") + 1, msgArray[1].indexOf("&")),msgArray[1].substring(msgArray[1].lastIndexOf("=")+ 1, msgArray[1].indexOf(";"))};
                Boolean status = databaseManager.checkUser(userInfo[0], userInfo[1]);
                if(status){
                    if(!userMap.containsKey(userInfo[0])){
                        userMap.put(userInfo[0], socket);
                        username = userInfo[0];
                        flagUser = 0;
                    }
                    else
                        flagUser = 1;
                }
                sendResult(socket, "user_info_status?"+flagUser.toString()+"");
            }

I thing I know what is the reason of the deadlock but I can't solve it. When the first user send the information to the other user he wait for response. Of course the other user send a response but this response is handle from other thread. So the deadlock is from a read method which block the thread. How can I send information from one socket to another without deadlock?

public GameThread(Socket socket, DatabaseManager databaseManager) {
    this.socket = socket;
    this.databaseManager = databaseManager;
    parser = new RequestParser(); 
    authorizationControl = new AuthorizationControl(databaseManager);
    communication = new SocketCommunication(socket);
    start();
}