RMI

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RMI
Varun Saini
Ying Chen
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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.

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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
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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

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AddServerIntf.java

• import java.rmi.
• public interface AddServerIntf extends Remote
• double add (double d1, double d2)
• throws RemoteException

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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

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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 d1d2

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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

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AddServer.java

• import java.rmi.
• public class AddServer
• public static void main(String args)
• try
• AddServerImpl addServerImplnew
  AddServerImpl()
• Naming.rebind("AddServer",addServerImpl)
• catch(Exception e)System.out.printl
  n(e)

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AddClient.java

• import java.rmi.
• public class AddClient
• public static void main(String args)
• try
• String addServerURL "rmi//"args0"/A
  ddServer"
• AddServerIntf addServerIntf
• (AddServerIntf)Naming.lookup(addServerU
  RL)
• double d1Double.valueOf(args1).doubleValue(
  )
• double d2Double.valueOf(args2).doubleValue(
  )
• System.out.println("Sum "addServerIntf.add(d
  1,d2))
• catch(Exception e)System.out.println(e)
  

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Stubs and Skeletons

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

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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.

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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.

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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

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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
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Resources

• java.sun.com
• http//gsraj.tripod.com/java/rmi_internals.html
• http//www-csag.ucsd.edu/individual/achien/cs491-f
  97/reading.htmlpengwu97
• Java Complete Reference-Schildt Naughton