Organizational%20Communications%20and%20Distributed%20Object%20Technologies

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Organizational Communications and Distributed
Object Technologies

• Lecture 11 CORBA

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CORBA

• Chapter 20 Coulouris text

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Todays Topics

• CORBA History and goals
• CORBA RMI
• CORBA services
• The Distributed Whiteboard Revisited

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CORBA History and Goals

• Object Management Group Formed in 1989
• Goals
• -- OOP on distributed systems
• -- heterogeneous hardware
• -- heterogeneous OS
• -- different programming
• languages

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History and Goals

• OMG Introduced the Object Request Broker (ORB)
• The role of the ORB is to help a client find an
  object, activate the object if necessary, and
  call a method on the object.
• Common Object Request Broker Architecture (CORBA)
  agreed to by a group of companies in 1991
• CORBA 2.0 specification released in 1996

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History and Goals

• CORBA 2.0 specification defined standards for
  different implementations of CORBA to communicate
  with one another
• These standards are called the General Inter-ORB
  protocol (GIOP) and may run over various
  transports
• GIOP over TCP/IP is called the Internet Inter-ORB
  Protocol

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CORBA RMI

• Main components
• -- An Interface Definition language (IDL) that
  promotes
• the use of different programming languages,
  stubs are
• generated in the clients language and
  skeletons are
• generated in the servers language
• -- An architecture
• -- GIOP defines an external data
  representation
• (CDR) as well as message formats and
  message
• types
• -- Message types include request and reply as
  
• well as location requests, errors, and
  request
• cancellations

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CORBA Services

• A set of generic services that can be used
• for distributed application
• -- Naming Service (location by name)
• -- Trading Service (location by attribute -
• directory service)
• -- Event Service
• -- Security Service (authentication, ACLs,
  auditing, non-
• repudiation)
• -- Transaction Service (begin, commit,
  rollback a
• series of RMI calls )
• -- Persistent Object Service (POS)

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The Distributed Whiteboard Example in CORBA
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IDL interfaces Shape and ShapeList
struct Rectangle // no class in IDL 1 long
width long height long x long y
struct GraphicalObject 2 string type
Rectangle enclosing boolean isFilled
interface Shape 3 long getVersion()
GraphicalObject getAllState() // returns
state of the GraphicalObject
typedef sequence ltShape, 100gt All
// All is a 100 element
array 4 interface ShapeList 5 exception
FullException 6 Shape newShape(in
GraphicalObject g) raises (FullException) 7 All
allShapes() // returns sequence of remote
object references 8 long getVersion()
// parameters
are in, out, or both

// parameters may be primitive, struct or array
and
// are passed
by value
//
parameters whose type is an IDL interface

// is passed by remote
reference
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idltojava

• Run idltojava on the above interface
• The command idlj is found in
• j2sdk1.4.2\bin
• The Java 2 Platform, Standard Edition, v1.4,
  provides an Object Request Broker (ORB) runtime
  component
• The JDK documentation states that its Java ORB
  has not been tested with ORBs written in other
  languages
• JDK 1.4 provides an Orb class with a pluggable
  architecture

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From the JDK Doc
OMG specifies a mapping from IDL to several
different programming languages, including Java,
C, C, Lisp, Python, Smalltalk, COBOL, and Ada.
When mapped, each statement in OMG IDL is
translated to a corresponding statement in the
programming language of choice.
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Java interface ShapeList generated by idltojava
from CORBA interface ShapeList
public interface ShapeList extends
org.omg.CORBA.Object Shape newShape(GraphicalOb
ject g) throws ShapeListPackage.FullException Sh
ape allShapes() int getVersion()
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ShapeListServant class from CORBA interface
ShapeList
import org.omg.CORBA. class ShapeListServant
extends _ShapeListImplBase ORB
theOrb private Shape theList private int
version private static int n0 public
ShapeListServant(ORB orb) theOrb orb
// initialize the other instance
variables public Shape newShape(GraphicalObjec
t g) throws ShapeListPackage.FullException
1 version Shape s new
ShapeServant( g, version) if(n gt100)
throw new ShapeListPackage.FullException()
theListn s 2 theOrb.connect(s)
return s public
Shape allShapes() ... public int
getVersion() ...
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Java class ShapeListServer
import org.omg.CosNaming. import
org.omg.CosNaming.NamingContextPackage. import
org.omg.CORBA. public class ShapeListServer
public static void main(String args)
try ORB orb ORB.init(args, null) 1

ShapeListServant shapeRef new
ShapeListServant(orb) 2 orb.connect(shape
Ref) 3
org.omg.CORBA.Object objRef
orb.resolve_initial_references("NameService")
4 NamingContext ncRef
NamingContextHelper.narrow(objRef) NameCompone
nt nc new NameComponent("ShapeList",
"") 5 NameComponent path
nc 6 ncRef.rebind(path, shapeRef)
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java.lang.Object sync new
java.lang.Object() synchronized (sync)
sync.wait() catch (Exception e) ...
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Java client program for CORBA interfaces Shape
and ShapeList
import org.omg.CosNaming. import
org.omg.CosNaming.NamingContextPackage. import
org.omg.CORBA. public class ShapeListClient pu
blic static void main(String args)
try ORB orb ORB.init(args, null)
1 org.omg.CORBA.Object objRef
orb.resolve_initial_references("NameService")
NamingContext ncRef NamingContextHelper.nar
row(objRef) NameComponent nc new
NameComponent("ShapeList", "") NameComponent
path nc ShapeList shapeListRef
ShapeListHelper.narrow(ncRef.resolve(path))
2 Shape sList shapeListRef.allShapes() 3
GraphicalObject g sList0.getAllState() 4
catch(org.omg.CORBA.SystemException e) ...

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The main components of the CORBA architecture
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Naming graph in CORBA Naming Service
initial naming context
initial naming context
initial naming context
XX
B
ShapeList
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