CORBA OverviewCORBA Overview

Distributed Systems &Middleware ICS243fApril 21, 2023

Arvind S. Krishna

Info & Comp Science Dept

University of California, Irvine

{krishnaa}@uci.edu

Brief History - OMG

OMG Formation• OMG created in 1989 with aim of promoting

object technology in Distributed Systems• OMG realizes its goals through creating standards

which allow interoperability and portability of distributed object oriented applications

• Do not produce software define standards• OMA – Object Management Architecture

• Consists of four components divided into two parts: • System oriented components Object Request

Brokers and Object Services and

• Application oriented components Application Objects and Common Facilities

• Object Request Broker is the one which constitutes the foundation of OMA and manages all communication between its components

CORBA

CORBA – Common Object Request Broker ArchitectureMotivation

• To allow objects to interact in• Heterogeneous distributed environment • independent of the platforms on which these objects reside• techniques used to implement them (languages)

CORBA – Common Object Request Broker ArchitectureMotivation

• To allow objects to interact in• Heterogeneous distributed environment • independent of the platforms on which these objects reside• techniques used to implement them (languages)

CORBA – ArchitectureObject Request Broker (ORB)

• ORB encompasses • all communication infrastructure necessary to

identify and locate objects, • handle connection management • Marshalling & de-marshalling data and • deliver data.

• The ORB is not required to be a single component; it is simply defined by its interfaces.

• The ORB Core is the most crucial part of the Object Request Broker;

• Minimum run-time layer required in every peer

CORBA – ArchitectureObject Request Broker (ORB)

• ORB encompasses • all communication infrastructure necessary to

identify and locate objects, • handle connection management • Marshalling & de-marshalling data and • deliver data.

• The ORB is not required to be a single component; it is simply defined by its interfaces.

• The ORB Core is the most crucial part of the Object Request Broker;

• Minimum run-time layer required in every peer

Overview of CORBA Components

Standard CORBA ComponentsObject This is a CORBA programming entity that consists of an identity, an interface, and an implementation, which is known as a Servant.

Servant This is an implementation programming language entity that defines the operations that support a CORBA IDL interface. Servants can be written in a variety of languages, including C, C++, Java, Smalltalk, and Ada.

Standard CORBA ComponentsObject This is a CORBA programming entity that consists of an identity, an interface, and an implementation, which is known as a Servant.

Servant This is an implementation programming language entity that defines the operations that support a CORBA IDL interface. Servants can be written in a variety of languages, including C, C++, Java, Smalltalk, and Ada.

Client This is the program entity that invokes an operation on an object implementation. Accessing the services of a remote object should be transparent to the caller. Ideally, it should be as simple as calling a method on an object, i.e., obj->op(args)

Client This is the program entity that invokes an operation on an object implementation. Accessing the services of a remote object should be transparent to the caller. Ideally, it should be as simple as calling a method on an object, i.e., obj->op(args)

Component Overview – (contd)

ORB Interface An ORB is a logical entity that may be implemented in various ways (such as one or more processes or a set of libraries). • To decouple applications from implementation details, the CORBA specification defines • an abstract interface for an ORB. • This interface provides various helper functions such as converting object references to • strings and vice versa

CORBA IDL stubs and skeletons CORBA IDL stubs and skeletons serve as the ``glue'' between the client and server applications • The transformation between CORBA IDL definitions to languages automated IDL compiler • The compiler allows for compiler optimization and automation of repetitive tasks

Object Adapter This assists the ORB with delivering requests to the object and with activating the object. • More importantly, an object adapter associates object implementations with the ORB. • Object adapters can be specialized to provide support for certain object implementation styles • The QoS requirements for a POA specified using policies passed to it at creation time• OMG provides seven standard policies and policy values • Lifespan policy with policy values PERSISTENT and TRANSPERANT

ORB Interface An ORB is a logical entity that may be implemented in various ways (such as one or more processes or a set of libraries). • To decouple applications from implementation details, the CORBA specification defines • an abstract interface for an ORB. • This interface provides various helper functions such as converting object references to • strings and vice versa

CORBA IDL stubs and skeletons CORBA IDL stubs and skeletons serve as the ``glue'' between the client and server applications • The transformation between CORBA IDL definitions to languages automated IDL compiler • The compiler allows for compiler optimization and automation of repetitive tasks

Object Adapter This assists the ORB with delivering requests to the object and with activating the object. • More importantly, an object adapter associates object implementations with the ORB. • Object adapters can be specialized to provide support for certain object implementation styles • The QoS requirements for a POA specified using policies passed to it at creation time• OMG provides seven standard policies and policy values • Lifespan policy with policy values PERSISTENT and TRANSPERANT

Interface Definition LanguageIDL - motivation

• CORBA language independent • OMG does not provide implementations

• Left to ORB implementer• OMG defines architecture of the system in

terms of “interfaces” and the operations on these interfaces

IDL – in Motion• IDL is a language that has been

developed for distribution of architecture• Each ORB implementer writes an IDL

compiler to generate programming language code

IDL – Mapping• OMG also defines a mapping from the IDL to

the programming language• IDL is a declarative language – cannot

define data members • Example, interfaces are mapped to the Java

classes or to abstract classes in C++• Arguments must also specify the direction

e.g. in means only input cannot hold output, inout holds both input and output

IDL - motivation• CORBA language independent • OMG does not provide implementations

• Left to ORB implementer• OMG defines architecture of the system in

terms of “interfaces” and the operations on these interfaces

IDL – in Motion• IDL is a language that has been

developed for distribution of architecture• Each ORB implementer writes an IDL

compiler to generate programming language code

IDL – Mapping• OMG also defines a mapping from the IDL to

the programming language• IDL is a declarative language – cannot

define data members • Example, interfaces are mapped to the Java

classes or to abstract classes in C++• Arguments must also specify the direction

e.g. in means only input cannot hold output, inout holds both input and output

interface Drone { void turn (in float degrees); void speed (in short mph); void reset_odometer (); short odometer (); // …};

interface Drone { void turn (in float degrees); void speed (in short mph); void reset_odometer (); short odometer (); // …};

CORBA Communication Model

CORBA Communication • Heterogeneous languages, platforms and also

operating systems• Big endian (Sparc)Little endian architectures

(Intel)

Problem• Traditionally programmers have had to handle

these• Offloaded to middleware

Protocol definition• General Internet Inter-ORB protocol

• Standard marshalling and demarshalling parameters

• Client marshals a request i.e. wraps a request in a given format includes padding etc

• GIOP maps to various protocols TCP/IP mapping of the protocol is IIOP same as that used by java RMI

• Standardized exchange enabling two different ORB implementations to inter operate

• Supports standardized uni-cast communication reliable one-way, two-way communication

CORBA Communication • Heterogeneous languages, platforms and also

operating systems• Big endian (Sparc)Little endian architectures

(Intel)

Problem• Traditionally programmers have had to handle

these• Offloaded to middleware

Protocol definition• General Internet Inter-ORB protocol

• Standard marshalling and demarshalling parameters

• Client marshals a request i.e. wraps a request in a given format includes padding etc

• GIOP maps to various protocols TCP/IP mapping of the protocol is IIOP same as that used by java RMI

• Standardized exchange enabling two different ORB implementations to inter operate

• Supports standardized uni-cast communication reliable one-way, two-way communication

Three broad mechanisms of communication

– synchronous– deferred synchronous– asynchronous

Three broad mechanisms of communication

– synchronous– deferred synchronous– asynchronous

Object References

Inter-operability• Many ORBs how can these ORBs talk to each other?• OMG standardizes the generation of Object references• An object reference is an ORB-specific entity that can contain a

• Repository ID, which identifies its interface type• Transport address information, e.g., a server’s TCP/IP host/port address(es)• An object key that identifies which object in the server the request is destined for

• An object reference similar to a C++ “pointer” that’s been enhanced to identify objects in remote address spaces

• Object references can be passed among processes on separate hosts• The underlying CORBA ORB will correctly convert object references into a form that can be transmitted over

the network

• The ORB provides the receiver with a pointer to a proxy in its own address space• This proxy refers to the remote object implementation

• Object references are a powerful feature of CORBA e.g., they support peer-to-peer interactions and distributed callbacks

Inter-operability• Many ORBs how can these ORBs talk to each other?• OMG standardizes the generation of Object references• An object reference is an ORB-specific entity that can contain a

• Repository ID, which identifies its interface type• Transport address information, e.g., a server’s TCP/IP host/port address(es)• An object key that identifies which object in the server the request is destined for

• An object reference similar to a C++ “pointer” that’s been enhanced to identify objects in remote address spaces

• Object references can be passed among processes on separate hosts• The underlying CORBA ORB will correctly convert object references into a form that can be transmitted over

the network

• The ORB provides the receiver with a pointer to a proxy in its own address space• This proxy refers to the remote object implementation

• Object references are a powerful feature of CORBA e.g., they support peer-to-peer interactions and distributed callbacks

StandardizedFormat

StandardizedFormat

ORB-specificFormat

ORB-specificFormat

Real-Time CORBA Overview

• RT CORBA adds QoS control to regular CORBA improve the application predictability, e.g.,• Bounding priority inversions & • Managing resources end-to-end

• Policies & mechanisms for resource configuration/control in RT-CORBA include:1.Processor Resources

• Thread pools• Priority models• Portable priorities

2.Communication Resources• Protocol policies• Explicit binding

3.Memory Resources• Request buffering

• These capabilities address some important real-time application development challenges

ClientOBJREF

Object(Servant)

in argsoperation()

out args + return

IDLSTUBS

IDLSKEL

Object Adapter

ORB CORE GIOP

Protocol Properties

End-to-End PriorityPropagation

ThreadPools

StandardSynchronizersExplicit

Binding

Portable Priorities

SchedulingService

Real-time CORBA leverages the CORBA Messaging QoS Policy framework

Motivation for ZEN Real-time ORB

Integrate best aspects of several key technologies

• Java: Simple, less error-prone, large user-base

• Real-time Java: Real-time support

• CORBA: Standards-based distributed applications

• Real-time CORBA: CORBA with Real-time QoS capabilities

ZEN project goals

• Make development of distributed, real-time, & embedded (DRE) systems easier, faster, & more portable

• Provide open-source Real-time CORBA ORB written in Real-time Java to enhance international middleware R&D efforts

Overview - ZEN R&D Plan

Phase I Apply Optimization patterns and principles

• ORB-Core Optimizations• Micro ORB Architecture Virtual

Component Pattern • Connection Management Acceptor-

Connector pattern, Reactor (java’s nio package)

• Collocation and Buffer Management Strategies

• POA Optimizations • Request Demultiplexing Active

Demultiplexing & Perfect Hashing• Object Key Processing Strategies

Asynchronous completion token pattern• Servant lookup Reverse lookup map• Concurrency Strategies

Half-Sync/Half-Async

Phase I Apply Optimization patterns and principles

• ORB-Core Optimizations• Micro ORB Architecture Virtual

Component Pattern • Connection Management Acceptor-

Connector pattern, Reactor (java’s nio package)

• Collocation and Buffer Management Strategies

• POA Optimizations • Request Demultiplexing Active

Demultiplexing & Perfect Hashing• Object Key Processing Strategies

Asynchronous completion token pattern• Servant lookup Reverse lookup map• Concurrency Strategies

Half-Sync/Half-Async

Phase II Enhance Predictability by applying RTSJ features

• Associate Scoped Memory with Key ORB Components

– I/O Layer : Acceptor-Connector, Transports– ORB Layer: CDR Streams, Message Parsers– POA Layer: Thread-Pools and Upcall

Objects

• Using NoHeapRealtimeThreads – Ultimately use NHRT Threads for

request/response processing– Reduce priority inversions from Garbage

Collector

Phase II Enhance Predictability by applying RTSJ features

• Associate Scoped Memory with Key ORB Components

– I/O Layer : Acceptor-Connector, Transports– ORB Layer: CDR Streams, Message Parsers– POA Layer: Thread-Pools and Upcall

Objects

• Using NoHeapRealtimeThreads – Ultimately use NHRT Threads for

request/response processing– Reduce priority inversions from Garbage

Collector

Phase III Build a Real-Time CORBA ORB that runs atop a mature RTSJ Layer

Phase III Build a Real-Time CORBA ORB that runs atop a mature RTSJ Layer

References•ZEN open-source download & web page:

•http://www.zen.uci.edu

•Real-time Java (JSR-1):•http://java.sun.com/aboutJava/communityprocess/jsr/ jsr_001_real_time.html

•Dynamic scheduling RFP:•http://www.omg.org/techprocess/meetings/schedule/ Dynamic_Scheduling_RFP.html

•Distributed Real-time Java (JSR-50):•http://java.sun.com/aboutJava/communityprocess/jsr/ jsr_050_drt.html

•AspectJ web page:•http://www.aspectJ.org

•JRate •http://tao.doc.wustl.edu/~corsaro/jRate/