Java RMI timeouts (crashes)

I'm doing a server/client program in Java using RMI. When server crashes it's not a problem, clients get a RemoteException and disconnects.

However I have problems when clients crashes. My server uses a Timer to ping all client objects every now and then, when it gets no connection to a client it will catch a RemoteException.

Then, it's supposed to remove the client object from the server (just by removing it from a list), but it's impossible because when I try to do anything with the proxy client object it will throw another RemoteException. How can I solve this problem?

List<User> users;
Map<User, IClient> clients;

    class PingClients extends TimerTask {
          public void run() {
              for (IClient client : clients.values())
                try {
                    client.ping();
                } catch (RemoteException e) {
                    //removeClient(client); GENERATES REMOTEEXCEPTION
                }
          }

     }

     public boolean removeClient(IClient c) throws RemoteException{
          User u = c.getUser();
          users.remove(u);
          clients.remove(u);

          for (IClient cli开发者_运维技巧ent : clients.values())
              client.updateUsers(users);
      }

You get a RemoteException because when you try to remove the client (which is disconnected), you first call the getUser() method on the client, which obviously throws a RemoteException.

You should change your code to something like this :

  class PingClients extends TimerTask {
      public void run() {
          for (Iterator<Map.Entry<User, IClient>> it = clients.entrySet().iterator(); it.hasNext(); )
            Entry<User, IClient> entry = it.next();
            try {
                IClient client = entry.getValue();
                client.ping();
            } 
            catch (RemoteException e) {
                it.remove();
            }
      }
  }

Make sure that only one thread has access to the map at a time.

First line, you should use ConcurrentMap instead of a Map. This will avoid you a lot of troubles due to concurrent access to your map.

If IClient c is your remote object, calling getUser() on it will obviously throw an exception if the client is unavailable..