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RMI

RMI. Varun Saini. Ying Chen. What is RMI?. RMI is the action of invoking a method of a remote interface on a remote object. It is used to develop applications that communicate between virtual machines RMI is a means of doing distributed computing

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RMI

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  1. RMI Varun Saini Ying Chen

  2. What is RMI? • RMI is the action of invoking a method of a remote interface on a remote object. • It is used to develop applications that communicate between virtual machines • RMI is a means of doing distributed computing • RMI hides the underlying mechanism of transporting method arguments and return values across the network.

  3. Example • Server returns sum of two numbers • Client calls the add() method of the server and passes two numbers • We will need four files • AddServerIntf.java • AddServerImpl.java • AddServer.java • AddClient.java Java Complete Reference-Schildt Naughton

  4. Remote Interface • a remote interface is an interface that declares a set of methods that may be invoked from a remote Java virtual machine. • Must extend java.rmi.Remote • The interface java.rmi.Remote is a marker interface that defines no methods • public interface Remote {} • All methods must throw RemoteException

  5. AddServerIntf.java import java.rmi.*; public interface AddServerIntf extends Remote { double add (double d1, double d2) throws RemoteException; }

  6. RMI Registry • Simple Name Repository • Server binds a name with an object implementation • Client can query the registry for checking the availability of a server object

  7. AddServerImpl.java import java.rmi.*; import java.rmi.server.*; public class AddServerImpl extends UnicastRemoteObject implements AddServerIntf { public AddServerImpl() throws RemoteException{} public double add (double d1, double d2) throws RemoteException {return d1+d2;} }

  8. Parameter Passing • Passing by Copy • Local objects and exceptions are passed by copy. • Use JAVA object serialization • Passing by Reference • Remote Object Passed by reference

  9. AddServer.java import java.rmi.*; public class AddServer { public static void main(String[] args) { try{ AddServerImpl addServerImpl=new AddServerImpl(); Naming.rebind("AddServer",addServerImpl); } catch(Exception e){System.out.println(e);} } }

  10. AddClient.java import java.rmi.*; public class AddClient { public static void main(String[] args) { try{ String addServerURL = "rmi://"+args[0]+"/AddServer"; AddServerIntf addServerIntf= (AddServerIntf)Naming.lookup(addServerURL); double d1=Double.valueOf(args[1]).doubleValue(); double d2=Double.valueOf(args[2]).doubleValue(); System.out.println("Sum= "+addServerIntf.add(d1,d2)); } catch(Exception e){System.out.println(e);} } }

  11. Stubs and Skeletons • Stub • resides on client • Provides interface of the server • Skeleton • Resides on server • Generate stubs and skeletons • rmic AddServerImpl

  12. RMI Sequence of Actions • The RMI Server creates an instance of the 'Server Object' which extends UnicastRemoteObject • The constructor for UnicastRemoteObject "exports" the Server Object. A TCP socket which is bound to an arbitrary port number is created and a thread is also created that listens for connections on that socket. • The server registers the server object with the registry.

  13. RMI Sequence of Actions • A client obtains the stub by calling the registry, which hands it the stub directly. • When the client issues a remote method invocation to the server, the stub class • opens a socket to the server on the port specified in the stub itself, and • Sends the RMI header information as described in the RMI spec.

  14. RMI Sequence of Actions • The stub class marshalls the arguments • On the server side, when a client connects to the server socket, a new thread is forked to deal with the incoming call. • The server calls the "dispatch" method of the skeleton class, which calls the appropriate method on the object and pushes the result back down the wire

  15. RMI Performance • RMI vs. Local call(200Mhz, NT, JDK no JIT) • Call time (no configuration available) • setup time: RMI 40% slower than CORBA • binding: RMI 200-1500ms slower than CORBA • CORBA vs. RMI • 1000 calls, one argument, JDK1.1.1 Pengwu97

  16. Resources • java.sun.com • http://gsraj.tripod.com/java/rmi_internals.html • http://www-csag.ucsd.edu/individual/achien/cs491-f97/reading.html[pengwu97] • Java Complete Reference-Schildt Naughton

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