SSLServerSocket accepts SSLSocket client in thread, is there a maximum?

Question

I have a SSLServerSocket in Java, when a client is connected, I create a thread for its communication:

    System.setProperty("javax.net.ssl.keyStore", "keystore");
    System.setProperty("javax.net.ssl.keyStorePassword", "password");

    SSLServerSocket server = (SSLServerSocket)null;

    if(ipSocket == null){
        ipSocket = new HashMap<String,java.net.Socket>();
    }

    try {

        SSLServerSocketFactory sslserversocketfactory = (SSLServerSocketFactory) SSLServerSocketFactory.getDefault();
        server = (SSLServerSocket) sslserversocketfactory.createServerSocket(4380);
        log.info("Server started");

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

    while(true){

        try {
            SSLSocket client = (SSLSocket) server.accept();
            log.info("new client");

        } catch (Exception e){
            e.printStackTrace();
        }
    }

The problem is when the code sometimes rejects connections. It happens when the code is running for a while, so I think the problem is the clients lost the connection and reconect, but the previous thread is still alive, and there is a maximun SSLServerSockets.

Could this happen? What number is the maximum?

How can I kill the threads when a disconnection happens?

Answer 1

Based on your code and my understanding of networking (both from the lower level and from the API level) you may be incorrectly using the API.

At a high level, you want to do this a little differently

public static void main(String[] args) {
    System.setProperty("javax.net.ssl.keyStore", "keystore");
    System.setProperty("javax.net.ssl.keyStorePassword", "password");
    SSLServerSocket server = (SSLServerSocket)null;
    if(ipSocket == null){
        ipSocket = new HashMap<String,java.net.Socket>();
    }

    try {
        SSLServerSocketFactory sslserversocketfactory = (SSLServerSocketFactory) SSLServerSocketFactory.getDefault();
        // Creates a socket with a default backlog of 50 - meaning
        // There will be a maximum of 50 client connection attempts on this 
        // socket after-which connections will be refused. If the server is
        // overwhelmed by more than that number of requests before they can be
        // accepted, they will be refused
        // The API allows for you to speccify a backlog.
        server = (SSLServerSocket) sslserversocketfactory.createServerSocket(4380);
        log.info("Server started");
    } catch(IOException e) {
        e.printStackTrace();
    }

    while(true){
        try {
            // This will take one of the waiting connections
            SSLSocket client = (SSLSocket) server.accept();
            log.info("new client");
            // HERE is where you should create a thread to execute the
            // conversation with the client.
        } catch (Exception e){
            e.printStackTrace();
        }
    }
}

I hope that more correctly answers your question.

In regards to the comment by EJP - I have updated my explanation and cited the documentation located here:

The maximum queue length for incoming connection indications (a request to connect) is set to the backlog parameter. If a connection indication arrives when the queue is full, the connection is refused.