Java socket server gives java.net.SocketException: No buffer space available (maximum connections reached?): connect exception

Question

I have created client server application in the client side when i send multiple requests to the server some time later it gives below error.When i monitor TCPview there are lot of port connections on CLOSE_WAIT status.Has any one come across with such issue.Please find the bellow error log

 java.net.SocketException: No buffer space available (maximum connections reached?): connect
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
    at java.net.Socket.connect(Socket.java:529)
    at java.net.Socket.connect(Socket.java:478)
    at java.net.Socket.<init>(Socket.java:375)
    at java.net.Socket.<init>(Socket.java:189)
    at com.lk.cc.socketserver.Main.isHostRunning(Main.java:90)
    at com.lk.cc.socketserver.Main.main(Main.java:43)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
    Exception in thread "main" java.lang.NullPointerException
        at com.lk.cc.socketserver.Main.isHostRunning(Main.java:102)
        at com.lk.cc.socketserver.Main.main(Main.java:43)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)

Server Host class

public class ServerHost extends Thread {

  private ServerSocket serverSocket;

      public ServerHost(int port) throws IOException {
        serverSocket = new ServerSocket(port);

      }

      public void run() throws IOException{
        while (true) {
          Socket server = null;
          DataInputStream in = null;
          DataOutputStream out = null;
          try {
            System.out.println("Host 1 Established .. ");
            System.out.println("Waiting for client on port " +
                               serverSocket.getLocalPort() + "...");
            server = serverSocket.accept();
            System.out.println("Just connected to "
                               + server.getRemoteSocketAddress());
            in =
                new DataInputStream(server.getInputStream());

            if (in.available() > 0) {
              System.out.println("Recieved client message  :" + in.readUTF());

              out =  new DataOutputStream(server.getOutputStream());

              // send recieved response from host X to client

              out.writeUTF("Response from Host 1 " + server.getLocalSocketAddress() + " \nGoodbye!");

              System.out.println("client socket isClosed()    " + server.isClosed());
            }
          } catch (SocketTimeoutException s) {
            System.out.println("Socket timed out!");
            // break;
          } catch (IOException e) {
            e.printStackTrace();
            // break;
          } finally {
            if (out != null) {
              try {
                out.flush();
              } catch (IOException e) {
                e.printStackTrace();
              }
            }
            if (out != null) {
              try {
                out.close();
              } catch (IOException e) {
                e.printStackTrace();
              }
            }
            if (in != null) {
              try {
                in.close();
              } catch (IOException e) {
                e.printStackTrace();
              }
            }

            if (server != null) {
              try {
                server.close();
              } catch (IOException e) {
                e.printStackTrace();
              }
            }
          }
        }
      }

      public static void main(String[] args) {
        int port = 7881;
        try {
          Thread t = new ServerHost(port);
          t.start();
        } catch (IOException e) {
          e.printStackTrace();
      }
   }
}

Client

    public class Main {

  private static ArrayList<HostConnections> hostList;


  public static void init() {
    hostList = new ArrayList<HostConnections>();
    hostList.add(new HostConnections("localhost", 7881));
    hostList.add(new HostConnections("localhost", 7882));
    hostList.add(new HostConnections("localhost", 7883));
    hostList.add(new HostConnections("localhost", 7884));
  }

  public static void main(String[] args) {
    // write your code here
    boolean hostStatus=true;
    init();
    while (hostStatus) {
      System.out.println("Used " + hostList.get(0));
      HostConnections nextHost = hostList.get(0);
      //Collections.rotate(hostList, -1);
      System.out.println(hostList);

      hostStatus = isHostRunning(nextHost);
      System.out.println(hostStatus);
    }
  }


  private static boolean isHostRunning(HostConnections availableHost) {
    boolean isAlive = false;
    Socket client=null;
    try {
        client = new Socket(availableHost.getHostIpAddress(), availableHost.getHostPort());
      //client.getInputStream().close();

     // client.getOutputStream().close();
      isAlive = true;

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

    }finally {
      try {
        //client.getOutputStream().flush();
        client.close();
        client.isClosed();
        System.out.println(client.isClosed());
      } catch (IOException e) {
        e.printStackTrace();
      }
    }

    return isAlive;
  }
}

My requirement is to check all the connections in the list are available everytime. Thanks

Answer 1

You're leaking sockets somewhere. CLOSE_WAIT means that TCP has received a close from the peer and is waiting for the local application to close the socket.

You should also try a sleep in that testing loop. You're burnng sockets like there is no tomorrow.

In fact I question the entire purpose. The only reliable way to know whether any resource is available is to try to use it and handle the errors as they arise in the normal course of execution. Anything else is tantamount to fortune-telling.

NB:

1. flush() before close() is redundant.
2. Calling isClosed() and available() is usually a waste of time, and this is no exception.
3. Are you aware that this code only tests one host?