Corba

Distributed Object Based Systems with CORBA
Slides adapted from
Coulouris (Distributed Systems: Concepts and Design) Tanenbaum (Distributed Systems: Principles and Paradigms)
Dawit Mengistu Kamilla Klonowska (2011)

Introduction
? Distributed objects form?an?important paradigm:
? An?object?means virtually anything (file,?remote procedure, or?any resource). ? Contemporary?software?development is?based on?object orientation.
? In?this?section we will see how the?priciples of distributed systems?are?applied in?distributed object‐ based systems:
? Communication ? Naming ? Synchronization Replication Fault tolerance Security...
? We will look?at?a?specific DOBS?example:?CORBA

Introduction?(cont’d)
? The?Object?Management?Group?(OMG)?was?formed?in 1989.?Its?aims?were:?
– to?make?better?use?of?distributed?systems – to?use?object‐oriented?programming – to?allow?objects?in?different?programming?languages?to communicate?with?one?another
? The?object?request?broker?(ORB)?enables?clients?to?invoke methods?in?a?remote?object ? CORBA?is?a?specification?of?an?architecture?supporting this.?
– CORBA?1?in?1990?and?CORBA?2?in?1996.
?

Generic?Architecture

CORBA?Architecture
? Remote‐object:?object?implementation?resides?in server’s?address?space?
Client Server Java Object C++ Object Skeleton Stub IIOP Object Adapter
ORB
ORB

Stub
? Provides interface?between client?object and?ORB ? Marshalling:?client?invocation ? Unmarshalling:?server?response
Client Server Java Object C++ Object Skeleton Stub ORB IIOP Object Adapter ORB

Skeleton
? Provides iterface between server?object and?ORB ? Unmarshaling:?client?invocation ? Marshaling:?server?response
Client Server Java Object C++ Object Skeleton Stub ORB IIOP Object Adapter ORB

Skeletons and?Stubs...
? Skeletons?are?generated?by?the?idl compiler?in?the server language.?There?are?idl compilers?for?java,?C, C++?and?many?more ? It?is?also?responsible?for?unmarshalling (UNPACKING) the?arguments?for?a?remote?request,?passing?them?to implementation,?and?marshalling?any?results?in?a?reply ? Stub/proxy?are?generated?by?the?idl compiler?in?the client language.?There?are?idl compilers?for?java,?C, C++?and?many?more. ? In?CORBA,?clients?and?servers?need?not?be?written?in the?same?language.

(Portable)?Object?Adapter?(POA)
? ? ? ? Register class?implementations Creates and?destroys?objects Handles method invocation Handles client?authentication and?access control
Client Server Java Object C++ Object Skeleton Stub ORB IIOP Object Adapter ORB

Object?Request Broker?(ORB)
? Communication?infrastructure?sending messages?between objects ? Communication?type:
– GIOP?(General?Inter‐ORB?Protocol) – IIOP?(Internet?Inter‐ORB?Protocol) (GIOP?on?TCP/IP)
Client Server Java Object C++ Object Skeleton Stub ORB IIOP Object Adapter ORB

CORBA?Object
Server CORBA Object Interoperable Object Reference Interface IDL C++/Java Implementation Servant

Interface?Definition?Language?(IDL)
? Describes?interface ? Language?independent ? Client?and?server?platform?independent
Server CORBA Object Interface IDL C++/Java Implementation Servant Interoperable Object Reference

Overall?CORBA?Architecture
Client C++ Object Interface Interface repository repository
Implementation repository Interface repository
Server Java Object
IDL
the the interface interface repository repository provides provides information information about about registered registered IDL IDL interfaces interfaces to to clients clients and and servers servers that that require require it. it.
Skeleton
Stub
ORB
Object Adapter Implementation Implementation repository repository IIOP on demand ? ?activates activates registered registered servers servers on demand and and locates locates running running servers servers ? ?uses uses the the object object adapter adapter name name to to register register and and activate activate servers servers
ORB

CORBA?Services
? CORBA?includes?specifications?for?services?that?may?be?required?by distributed?objects
– The?service?themselves?are?provided?and?accessed?as?CORBA?remote objects – An?index?to?documentation?on?all?of?the?services?can?be?found?at OMG’s web?site?at?https://www.360docs.net/doc/5d7283214.html,
Examples
? Naming: Keeps?track?of?association?between?object?names and?their?reference.?Allows?ORB?to?locate?referenced?objects ? Life?Cycle: Handles?the?creation,?copying,?moving,?and deletion?objects

Service?Examples?(cont’d)
? Event?and?Notification:?Facilitates?asynchronous communications?through?events ? Concurrency: Manages?locks?so?objects?can?share resources ? Query: Locates?objects?by?specified?search?criteria
? Trader: A?“yellow?pages” for?objects.?Lets?you?find?them by?the?services?they?provide ? Security ? Event?service?and?notification ? Persistent?object?(POS)
?…

Object?Invocation?Models
? Invocation?models?supported?in?CORBA
Request type Synchronous Failure semantics At-most-once Description Caller blocks until a response is returned or an exception is raised Caller continues immediately without waiting for any response from the server Caller continues immediately and can later block until response is delivered
One-way
Best effort delivery
Deferred synchronous
At-most-once

CORBA?IDL?Language
? Different?with?C++?in?several?additional?commonly?used keywords
– interface – module – any – attribute – in,?out,?inout – readonly – oneway – raises – exception – context

IDL?Structure
? Modules
– Similar?to?package?in?Java – Define?the?naming?scope
? Interfaces
– Inheritance?
? interface B: A{ };
– Multiple?inheritance?allowed
? interface Z: B, C { };
? Structs ? Typedefs

CORBA?IDL
struct Rectangle{ 1 long width; long height; long x; long y; }; interface Shape { 3 long getVersion() ; GraphicalObject getAllState() ; }; struct GraphicalObject { 2 string type; Rectangle enclosing; boolean isFilled; };
// returns state of the GraphicalObject
typedef sequence All; 4 interface ShapeList { 5 exception FullException{ }; 6 Shape newShape(in GraphicalObject g) raises FullException); All allShapes(); // returns sequence of remote object references 8 long getVersion() ; };
7

IDL?Module?Whiteboard
module Whiteboard { struct Rectangle{ ...} ; struct GraphicalObject { ...}; interface Shape { ...}; typedef sequence All; interface ShapeList { ...}; };