How to read inputs from multiple clients at one time?

Question

I am creating a server class for a little Instant Messaging app. Everything is working when I try to have the server connect to a single client, but I am attempting to expand it be connect to multiple clients. I have tested and it is able to connect to multiple clients, but the problem lies with the fact that I cannot read inputs from all of them at the same time.

Do I need to open a new thread for each client to constantly be checking for inputs? I feel like this is extremely inefficient.

This is the code that checks for inputs from the clients, which are stored in an Arraylist at the moment. I believe that it is similar to a scanner, where it does not continue the code until there is an input.

private void chat() throws IOException{
    String message = " You are now connected! ";
    sendMessage(message);
    ableToType(true);
    do{
        try{
                //right now it is only checking the first (0) client 
                message = (String) inputs.get(0).readObject(); // this is the line that checks for inputs
            showMessage("\n" + message, new java.awt.Color(20, 124, 34));
        }catch(ClassNotFoundException classNotFoundException){
            showMessage("\nUnreadable Message Sent by Client");
        }
    }while(!message.contains("END"));

}

When you have this simple example working you could also check out the java.nio package for how to handle many connections with one or just a few threads. — Just another Java programmer, Oct 08 '16 at 19:51

GhostCat · Accepted Answer · 2016-10-08T19:31:01.623

The simple solution is: you dedicate one complete thread on your server ... per client.

But as you already figured: that is rather inefficient - as most of your threads will be idling most of the time. And even in 2016; threads are still "expensive"; meaning that you don't want to waste them.

Thus you could be looking into solutions that use pooling. Meaning: your server has a pool of n threads, that together work on m clients (where m could be much bigger than n). One starting point could be this tutorial.

But: if you are doing this for "learning purposes"; then I suggest: go with the "one thread per client" approach first. You see, it will be a challenging task to get that kind of implementation to work correctly (multi-threading quickly translates to multi-probleming). Solve that puzzle first; and only then go to the next level by using pools!

You see: in a "learning" setup with one server and a handful of clients, it really doesn't matter if you have 5 threads or 10 on your local machine. Pooling becomes interesting when we talk about values of m way beyond 100, 500, .. and given how your current code looks like; I assume all of that is "playing around" anyway. So start playing softball before going hardball.

And thanks to the anonymous downvoter. Any comments on how should improve my question in your opinion? — GhostCat, Oct 08 '16 at 19:29
Thanks for the quick response. I think that I will just open a new thread for each client and limit the number of clients because I don't really need to have more than a few clients connected. That tutorial looks very helpful, and I will use it in the future if I need to expand this further. — Slushy_G, Oct 08 '16 at 19:36

How to read inputs from multiple clients at one time?

1 Answers1