Jawad Kakar

You have to cast Naming.lookup to the interface which extends Remote.
i.e
public interface RemoteServer extends java.rmi.Remote, DataInterface{ }
and the lookup part looks like
instance = (RemoteServer) Naming.lookup("//"+hostName+":"+portNumber+"/"+"RemoteServer");
Jawad

For locking the database do we have to provide an admin gui?
Thank you
Jawad

You are right, thank you
Jawad

I changed LockManager from a singleton to a regular class, it is very easy to create multiple instance of LockManager, which is not a very good thing to do for this assignment.
synchronized public static LockManager getLockManagerInstance(){ return new LockManager(); }
Jawad

Try not to post the same msg in different forum.
Jawad

Although not important, so far I have 29 classes and 3070 lines of code.
Jawad
[ December 27, 2002: Message edited by: Jawad Kakar ]

Eugene,
Thanks for your reply
Which one is better, passing a RemotedataServer for clientId or passing an Object. As far as reusability is concern passing Object is a better idea, am I correct or there is some other reason for it too.
public synchronized void unlock(RemotedataServer owner, int recordNum){ ... } public synchronized void unlock(Object owner, int recordNum){ ... }
Thank you
Jawad
[ December 27, 2002: Message edited by: Jawad Kakar ]

Peter,
The situation that you have mentioned never happened in my test, but I see the problem in code clearly, thank you very much for the help and I have changed the unlock method to
public synchronized void unlock(RemotedataServer owner, int recordNum){ Integer recordKey = new Integer(recordNum); // returns the value to which lockedRecordes map maps recordKey key. RemotedataServer rs = (RemotedataServer)lockedRecordes.get(recordKey); if(rs == owner){ lockedRecordes.remove(recordKey); System.out.println("Client: "+ owner.hashCode() +" Released The Lock On Record "+ recordKey.toString()+" Size of lockManager is "+lockedRecordes.size()); this.notifyAll(); } }
Thank you
Jawad

Peter,
Thank you for your reply,
public synchronized void unlock(RemotedataServer owner, int recordNum){ Integer recordKey = new Integer(recordNum); [B] if(lockedRecordes.containsKey(recordKey) && lockedRecordes.containsValue(owner))[/B]{ lockedRecordes.remove(recordKey); System.out.println("Client: "+ owner.hashCode() +" Released The Lock On Record "+ recordKey.toString()+" Size of lockManager is "+lockedRecordes.size()); this.notifyAll(); } }
Moreover I test lock/unlock creating 500 threads in batch of 10 using the following test program and it seems to me if client 5 locks record 10, then only client 5 unlocks record 10 before any other client try to lock records 10.
I guess I am missing something could you please tell me how to change unlock to fix it.
Test program
public void LockingAndUnlockingTest(final int recNum){ Thread th = new Thread(){ public void run(){ try{ // returns a distinct remote connection for each client. DataClient dc = suncertify.client.ConnectionFactory.getRemoteConnection(StartupDialog.getController()); //lock dc.lock(recNum);// calls the lock() from LockManager ie lock(recNum){lockManagerInstance.lock(recNum)} // unlock dc.unlock(recNum);// calls the unlock() form LockManger ie lock(recNum){lockManagerInstance.unlock(recNum)} } catch(Exception e){ System.out.println(e.getMessage()); e.printStackTrace(); } } }; th.start(); }
Thank you
Jawad
[ December 26, 2002: Message edited by: Jawad Kakar ]

have a look at my getRemoteConnection() method, that is how I do it and it works fine for me.
I am still not done with the assignment, I might change it in future if I find a better reason to do so.
Jawad

Yes

This is a default constructor which is for getting different client id.
Jawad

Constructor which binds the remote object to the registry is called only once( when I start the server from command line) which is the following constructor
public RemotedataServer(String dbFilePath, String hostName, String port) throws RemoteException{...} public static void main(String [] agrc) throws RemoteException{ new RemotedataServer(agrc[0], agrc[1], agrc[2]); }
To bind the remote object to the registry.
The second constructor which no parameter the one you are talking about is called inside getConnection() method.
Therefor remote object is bind to the registry only once.
Jawad

Sri,
Thank you for your reply, you are right that was a mistake and I fixed it.
Thank you
Jawad

It is better to synchronized on the method, easier to read and debug, then to synchroized on block.
Jawad