套接字编程 - BindException - 地址已在使用中

Question

I understand why the binding error occurs, but I have followed any solution I can find and cannot get it to work.

Stack Trace

java.net.BindException: Address already in use: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at socket.ClientWorker.run(ClientWorker.java:30)
at java.lang.Thread.run(Unknown Source)
Picked up JAVA_TOOL_OPTIONS: -Djava.vendor="Sun Microsystems Inc"

---

Server Code

@Override
public void run() {
    try {
        ServerSocket listener = new ServerSocket(port);        
        while (running) {   
            Socket socket = listener.accept();              
            new Thread(new ServerWorker(socket, airport)).start();     
        }
        listener.close();
    } catch (IOException e) {e.printStackTrace();}  
}

• Each time the server gets an incoming connection, it creates a new thread to do the work.

Server Worker

@Override
public void run() {
    try {
        // Get message
        InputStream is = socket.getInputStream();
        InputStreamReader isr = new InputStreamReader(is);
        BufferedReader br = new BufferedReader(isr);
        String number;
        number = br.readLine();

        // Add new arrival event
        String[] splitMessage = number.split(" ");
        String mode = splitMessage[2];
        int time = Integer.valueOf(splitMessage[0]);
        int airportID = Integer.valueOf(splitMessage[1]);

        if(mode.equals("STANDARD")){
            Event newEvent = new Event(EventType.ARRIVAL,time,airport); 
            airport.scheduleEvent(airportID,newEvent); 
        }

        if(mode.equals("NULL")){
            Event newEvent = new Event(EventType.NULL,time,airport); 
            airport.scheduleEvent(airportID,newEvent); 
        }

        // Close
        socket.close(); 
    } 
    catch (IOException e){e.printStackTrace();}  
}

---

Client

/*-- Send a message to a different airport --*/
public void sendMessage(int port, String message){
        new Thread(new ClientWorker(port, message)).start();
}

• The Client (airport object) calls this message when it want's to communicate with a different airport. A new thread is created to process the work.

Client Worker

@Override
public void run() {
    try {
        Socket s = new Socket("localhost", port);
        OutputStream os = s.getOutputStream();
        OutputStreamWriter osw = new OutputStreamWriter(os);
        BufferedWriter bw = new BufferedWriter(osw);
        String sendMessage = message + "\n";
        bw.write(sendMessage);
        bw.flush();
        s.close();
    } 
    catch (UnknownHostException e){e.printStackTrace(); System.exit(0);} 
    catch (IOException e){e.printStackTrace(); System.exit(0);}   
}

• The error traces back to here - 'Socket s = new Socket("localhost", port);'

---

Notes

• All work is done on the same machine.
• Hundreds of messages could be sent each second.
• All the clients are running in parallel.
• The client may have to send multiple messages in (very) quick succession.

I thought I was making a new connection per message, but I must be misunderstanding something.

Answer 1

you are using Socket socket = listener.accept(); you need to close socket after use into server code. `

Answer 2

You're probably exhausting the number of client connections you can concurrently establish; in that case abusing ServerSocket#setReuseAddress() probably isn't a good idea.

I thought I was making a new connection per message, but I must be misunderstanding something.

You are- that's the problem :) Consider some kind of connection-pooling to reuse existing connections rather than spinning up thousands at a time (if your client and server spans across hosts, even the overhead of establishing the connection could quickly become the bottleneck in a setup like this).