Ch2: CORBA: The Intergalactic Object Bus

1
Ch2 CORBA The Intergalactic Object Bus

• SNU-OOPSLA-Lab
• Prof. H.J. Kim

2
Contents

• What exactly is a CORBA 2.0 ORB?
• the anatomy of a CORBA 2.0 ORB
• CORBA method invocations Static Versus Dynamic
• whats an object adapter?
• CORBA 2.0 initialization
• CORBA 2.0 The Intergalactic ORB
• CORBA 2.0 the inter-ORB architecture
• CORBA 2.0 ORB-to -ORB Bridging
• Federated ORBs

3
What exactly is a CORBA 2.0 ORB?

• CORBA 2.0 ORB
• middleware that establishes the client/server
  relationships between objects
• a client object can transparently invoke a method
  on a server object
• provides multivendor ORB interoperabiliy

4
The Client/Server Request Using the ORB
5
The Anatomy of a CORBA 2.0 ORB

• CORBA provides both static and dynamic interfaces
• What CORBA does on the client side
• The client IDL stubs
• provide the static interfaces to object services
• Dynamic Invocation Interface(DII)
• The interface repository API
• a run time database that contains
  machine-readable versions of the IDL-defined
  interfaces
• dynamic metadata repository for ORBs
• The ORB interface

6
The Anatomy of a CORBA 2.0 ORB(Contd)

• What CORBA elements do on the server side
• server IDL stubs
• provide static interfaces to each service
  exported by the server
• dynamic skeleton Interface
• object Adapter
• Implementation repository
• ORB interface
• a few APIs to local services that may be of
  interest to an application

7
The Structure of a CORBA 2.0 ORB
8
CORBA Method Invocations Static Versus Dynamic

• Advantages of static stub interface over dynamic
  method invocation
• it is easier to program
• it provides more robust type checking
• it performs well
• it is self-documenting
• you can tell whats going on by reading the code

9
CORBAs Static and Dynamic Method Invocations
10
Language-Independent Object References
11
CORBA static method invocations from IDL to
interface stubs

• The steps you go through to create your server
  classes
• define your object classes using Interface
  Definition Language(IDL)
• the IDL is the means by which objects tell their
  potential clients what operations are available
  and how they should be invoked
• the IDL defines
• object type, attribute, the method they export,
  method parameter
• subset of ANSI C additional contracts to
  support distribution
• purely a declarative language
• uses the C syntax for constant, type, and
  operation definitions, and does not include any
  control structures or variables

12
CORBA static method invocations from IDL to
interface stubs(Contd)

• The steps you go through to create your server
  classes(Contd)
• Run the IDL file through a language precompiler
• processes the IDL files and produces language
  skeletons for the implementation server classes
• Add the implementation code to the skeletons
• you must supply the code that implements the
  methods in the skeletons

13
CORBA static method invocations from IDL to
interface stubs(Contd)

• The steps you go through to create your server
  classes(Contd)
• Compile the code
• generating at least four types of output files
• imports files describe the objects to an
  interface repository
• client stubs
• server stubs
• the code that implements the server classes
• Build the class definitions to the interface
  repository
• Register the runtime objects with the
  implementation repository
• Instantiate the objects on the server

14
(No Transcript)
15
CORBA Dynamic Method Invocations A Step-By-Step
Guide

• CORBAs dynamic invocation API
• allow a client program to dynamically build and
  invoke requests on objects
• client specifies
• the object to be invoked
• the method to be performed
• the set of parameters through a call or sequence
  of calls

16
CORBA Dynamic Method Invocations A Step-By-Step
Guide(Contd)

• The dynamic method invocation steps
• obtain the method description from the interface
  repository
• locate and describe
• create the argument list
• create the request
• invoke the request
• invoke()
• send() and get-response()
• send()

17
The CORBA Dynamic Invocation Interface
18
The Server Side of CORBA

• An object implementation need from an ORB on the
  server side
• registers the applications classes
• instantiates new objects
• gives them unique IDs
• advertise their existence
• invoke their method
• manages concurrent requests for their services
• transaction management
• load balancing
• fine-grained security

19
Whats an Object Adapter?

• Object Adapter
• the primary mechanism for an object
  implementation to access ORB services
• services provided by the Object Adapter
• registers server classes with the implementation
  repository
• instantiates new objects at run time
• generates and manages object references
• broadcasts the presence of the object servers
• handling incoming client calls
• routes the up-call to the appropriate method

20
The Structure of a Typical Object Adapter
21
BOA and Other Object Adapters

• Object Adapter
• defines how an object is activated
• BOA(Basic Object Adapter)
• functions to be provided in a BOA implementation
• an implementation repository
• mechanisms for
• generating and interpreting object references
• activating and deactivating object
  implementations
• invoking methods
• passing them their parameters

22
BOA and Other Object Adapters(Contd)

• BOA(Basic Object Adapter)
• functions to be provided in a BOA
  implementation(Contd)
• a mechanism for authenticating the client making
  the call
• activation and deactivation of implementation
  objects
• method invocations through stubs
• four activation policy that specify the rules a
  given implementation follows for activating
  objects
• shared server
• unshared server
• server-per-method
• persistent server

23
BOA Shared Server

• A shared server activation policy
• multiple objects may reside in the same program

24
The BOA Shared Server Activation Policy
25
BOA Unshared Server

• An unshared server activation policy
• each object resides in a different server process

26
The BOA Unshared Server Activation Policy
27
BOA Server-per-Method

• A server-per-method activation policy
• the server runs only for the duration of the
  particular method
• several server processes for the same object may
  be concurrently active

28
The BOA Server-per-Method Activation Policy
29
BOA Persistent Server

• A persistent server activation policy
• servers are activated by means outside BOA
• BOA treats all subsequent requests as shared
  server calls

30
The BOA Persistent Server Activation Policy
31
CORBA 2.0 Initialization-Or How Does a Component
Find Its ORB?

• How does a component first discover its ORB?
• CORBA 1.1
• left this as an exercise for the ORB vendors
• non-portable solution
• CORBA 2.0
• defining a set of initialization APIs
• allows components to discover their ORB, BOA,
  interface repository and a set of well known
  object services

32
CORBA 2.0 Initialization-Or How Does a Component
Find Its ORB?(Contd)

• CORBA 2.0 initialize scenario
• obtain an object reference for your ORB
• obtain a pointer to your object adapter
• discover what initial services are available
• obtain object references for the services you want

33
CORBA 2.0 Initialization-Or How Does a Component
Find Its ORB?(Contd)
34
CORBA 2.0 The Intergalactic ORB

• CORBA 1.1
• has some level of portability
• but have not interoperability
• CORBA 2.0
• IIOP(Internet Inter-ORB Protocol)
• for interoperability
• basically TCP/IP with some CORBA defined message
  exchanges

35
CORBA 2.0 The Inter-ORB Architecture

• Elements of the CORBA 2.0 inter-ORB architecture
• GIOP(General Inter-ORB Protocol)
• specifies a set of message formats and common
  data representations for communications between
  ORBs
• defines seven message format that cover all the
  ORB request/reply semantics
• uses CDR(Common Data Representation)
• maps data types defined in OMG IDL into a flat
  networked message representation
• takes care of inter-platform issues such as byte
  ordering and memory alignments

36
CORBA 2.0 The Inter-ORB Architecture(Contd)

• Elements of the CORBA 2.0 inter-ORB
  architecture(Contd)
• IIOP(Internet Inter-ORB Protocol)
• specifies how GIOP messages are exchanged over a
  TCP/IP network
• makes it possible to use the Internet itself as
  backbone ORB through which other ORBs can bridge

37
CORBA 2.0 The Inter-ORB Architecture(Contd)

• Elements of the CORBA 2.0 inter-ORB
  architecture(Contd)
• ESIOP(Environment-Specific Inter-ORB Protocols)
• are used for out of the box interoperation over
  specific networks
• CORBA 2.0 specifies DCE as the first of many
  optional ESIOP
• DCE/ESIOP supports IORs using a DCE tagged
  profile
• supports Kerberos security, cell and global
  directories, distribute time, and authenticated
  RPC
• transmit large amounts of data efficiently
• supports multiple underlying transport protocols
• can use both connection and ORB connectionless
  protocols
• OMG IDL and CDR types are mapped directly into
  DCEs native Network Data Representation(NDR)

38
(No Transcript)
39
CORBA 2.0 ORB-to-ORB Bridging

• DSI(Dynamic Skeleton Interface)
• is used to receive all outgoing requests
• DII(Dynamic Invocation Interface)
• is used to invoke the request on a destination
  ORB objects
• This late binding technology
• is well suited to non-CORBA object buses such as
  Microsofts OLE/COM

40
Generic ORB-to-ORB Bridging Using CORBA 2.0s
Dynamic Facilities
41
Federated ORBs

• You can use inter-ORB bridges and IIOPs to create
  flexible topologies via federations of ORBs

42
An Intergalactic Federation of Multivendor ORBs