CORBA - A Detailed Tutorial

Introduction

CORBA (Common Object Request Broker Architecture) is a middleware technology that enables seamless communication and interoperability between distributed software components, regardless of the programming languages and platforms they are implemented on. CORBA provides a platform-independent and language-independent solution for building distributed applications and systems.

How CORBA Works

The key steps involved in using CORBA are as follows:

Interface Definition Language (IDL): Developers define the interfaces of CORBA objects using the Interface Definition Language (IDL). IDL allows developers to specify the methods and data that the objects support.
IDL Compiler: The IDL compiler takes the IDL definitions and generates language-specific stubs and skeletons for the CORBA objects. Stub code resides on the client-side, while skeleton code resides on the server-side.
Object Request Broker (ORB): The ORB is responsible for handling communication between clients and server objects. It marshals and unmarshals method calls and data, routes requests to the appropriate server objects, and manages object references.
Client-Side: Clients use the stubs generated by the IDL compiler to communicate with the server objects. The stubs encapsulate the communication details, making it appear as if the objects are local.
Server-Side: Servers use the skeletons generated by the IDL compiler to handle incoming method calls from clients. The skeletons perform the necessary processing and return results to the ORB for delivery to the clients.

Example of CORBA Code

Here's a simple example of a CORBA server and client implemented in C++:

CORBA IDL Definition


        interface MyObject {
            string getMessage();
        };

CORBA Server Implementation


        #include 
        #include 

        class MyObjectImpl : public POA_MyObject {
        public:
            string getMessage() {
                return "Hello, CORBA!";
            }
        };

        int main(int argc, char* argv[]) {
            try {
                CORBA::ORB_var orb = CORBA::ORB_init(argc, argv);
                PortableServer::POA_var poa = PortableServer::POA::_narrow(orb->resolve_initial_references("RootPOA"));
                PortableServer::POAManager_var pman = poa->the_POAManager();
                MyObjectImpl* myObj = new MyObjectImpl();
                poa->activate_object(myObj);
                MyObject_var objref = myObj->_this();
                cout << orb->object_to_string(objref) << endl;
                pman->activate();
                orb->run();
                orb->destroy();
            } catch (CORBA::Exception& e) {
                cerr << "Exception: " << e << endl;
            }
            return 0;
        }

CORBA Client Implementation


        #include 
        #include 

        int main(int argc, char* argv[]) {
            try {
                CORBA::ORB_var orb = CORBA::ORB_init(argc, argv);
                CORBA::Object_var obj = orb->string_to_object("IOR:010000002b00000049444c3a4d794f626a6563743a312e30000000000100000000000000f6000102000000000e3139322e3136382e3132332e31323400000c2b0000004f41442f5254533a312e30000000000000010000000000000018000000010000000000000001000000010000005c2b000000000000");
                MyObject_var myObj = MyObject::_narrow(obj);
                if (CORBA::is_nil(myObj)) {
                    cerr << "Object reference is nil" << endl;
                    return 1;
                }
                string message = myObj->getMessage();
                cout << "Message from server: " << message << endl;
                orb->destroy();
            } catch (CORBA::Exception& e) {
                cerr << "Exception: " << e << endl;
            }
            return 0;
        }

Mistakes to Avoid

Not properly defining the IDL interfaces, which can lead to communication errors between client and server.
Incorrectly handling exceptions, which may cause unexpected behavior in the distributed system.
Overlooking security concerns and not implementing proper authentication and authorization mechanisms.

FAQs about CORBA

Q: What is CORBA?
A: CORBA (Common Object Request Broker Architecture) is a middleware technology that enables communication and interoperability between distributed software components.
Q: What is the purpose of IDL in CORBA?
A: IDL (Interface Definition Language) is used to define the interfaces of CORBA objects, allowing developers to specify the methods and data they support.
Q: How does the CORBA ORB work?
A: The CORBA ORB (Object Request Broker) handles communication between clients and server objects, marshaling and unmarshaling method calls and data.
Q: Can CORBA objects be written in different programming languages?
A: Yes, CORBA allows for interoperability between objects written in different programming languages and running on different platforms.
Q: What are some benefits of using CORBA?
A: CORBA provides platform and language independence, simplifies distributed system development, and allows for seamless integration of heterogeneous systems.

Summary

CORBA is a powerful middleware technology that facilitates interoperability and communication between distributed software components. By defining interfaces using IDL and using the ORB for communication, developers can build robust and scalable distributed systems. Despite its advantages, developers must be cautious and avoid common mistakes to ensure the success of their CORBA-based applications.