Chapter 20 corba fm
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Soft computing Lab Mannual, Distributed systems
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- Dynamic invocation interface
| Interface repository ◊ The role of the interface repository is to provide information about registered IDL interfaces to clients and servers that require it. For an interface of a given type it can supply the names of the methods and for each method, the names and types of the arguments and exceptions. Thus, the interface repository adds a facility for reflection to CORBA. Suppose that a client program receives a remote reference to anew CORBA object. Also suppose that the client has no proxy for it then it can ask the interface repository about the methods of the object and the types of parameter each of them requires. When an IDL compiler processes an interface, it assigns a type identifier to each IDL type it encounters. For each interface registered with it, the interface repository provides a mapping between the type identifier of that interface and the interface itself. Thus, the type identifier of an interface is sometimes called the repository ID because it maybe used as a key to IDL interfaces registered in the interface repository. Every CORBA remote object reference includes a slot that contains the type identifier of its interface, enabling clients that hold it to enquire of its type with the interface repository. Those applications that use static (ordinary) invocation with client proxies and IDL skeletons do not require an interface repository. Not all ORBs provide an interface repository. Dynamic invocation interface ◊ As suggested in Section 5.5, in some applications, it maybe necessary to construct a client program without knowing all the proxy classes it will need in the future. For example, an object browser might need to display information about all the CORBA objects available in the various servers in a distributed system. It is not feasible that such a program should have to include proxies for all of Implementation repository entry: object adapter name pathname of object implementation hostname and port number of server SECTION 20.2 CORBA RMI 839 these objects, particularly as new objects maybe added to the system as time passes. CORBA does not allow classes for proxies to be downloaded at run time as in Java RMI. The dynamic invocation interface is CORBA’s alternative. The dynamic invocation interface allows clients to make dynamic invocations on remote CORBA objects. It is used when it is not practical to employ proxies. The client can obtain from the interface repository the necessary information about the methods available fora given CORBA object. The client may use this information to construct an invocation with suitable arguments and send it to the server. Download 234.39 Kb. Share with your friends:
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