Question

My SocketServer first listens for at least 4 Socket connections before creating a WorkerThread where all four connections are served. And in the same thread, all 4 sockets will be opened to perform communication with connected clients.

Now, consider a situation where server has already accepted two socket connections, but listening to remaining 2 clients, before it can proceed with creating thread.

And while that listening phase, the connected clients are shown “Waiting…” message (since server has not yet opened the sockets to send any response back to clients, and socket.readObject() is blocking at client-end), till the server gets all 4 clients to work with. And in the meantime, one of the “already-connected” client kills that “Waiting…” thing, and closes the client app. In such a case, my WorkerThread will fire an exception due to dead socket supplied, when it attempts to open it.

How can I know if a socket is pointing to nothing (since client is lost) without having to open the socket? (since if I open it from main thread, I’ll not be able to open it again from WorkerThread, where it is actually supposed to be used).

If I get to know if Socket is dead, I can get server back to listening and attempt to get 4 connections, before it proceeds creating a thread.

I know my SocketServer will be stuck at accept() so even if its possible to check what I asked above, I’ll have to create another thread that monitors liveliness of already “accepted” socket connections.

Update

I mean by not opening the socket is something like below.

Socket s = ss.accept();
/* I'll not be doing as below, since once I close InputStream and OutputStream in main Thread, I can't open in WorkerThread.
But I still want to know if Socket s is connected to client, before I start WorkerThread.


ObjectInputStream in = new ObjectInputStream(s.getInputStream());
ObjectOutputStream out = new ObjectOutputStream(s.getOutputStream());
String msg = in.readObject().toString();
System.out.println("Client Says:");
out.writeObject("success");
in.close();
out.close();

*/
new WorkerThread(s).start();

And note that my server is accepting 4 such connections, and when 4 sockets are accept()ed, it passes all 4 in WorkerThread‘s constructor, and gets back to accept() another 4 clients.

Answer 1

I think you just need to handle your acceptions better. You should handle the IOException correctly whenever you try to read or write to the socket.

One option is to have the accepting code send a “still waiting” message to the client and get an acknowledge every so often while you are waiting for the other connections. The socket and associated streams have already been created by the accept() so you can do this, call flush() on the OutputStream, and then hand off to the handler.

As long as you don’t call close() on the streams, you should be able to re-use them without a problem. You just can’t have two different threads using the streams at the same time.