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  1. OMG Issue

CORBA34 — Interface Introspection

  • Key: CORBA34-25
  • Legacy Issue Number: 6391
  • Status: closed  
  • Source: Zuehlke Engineering ( Frank Pilhofer)
  • Summary:

    Inspired by a recent paper by Doug Schmidt and Steve Vinoski
    and the resulting newsgroup discussion on comp.object.corba,
    I have a feature request to introduce a better reflection
    mechanism into CORBA.

    At the moment, there is the CORBA::Object::get_interface()
    operation to access a matching InterfaceDef entry in an
    Interface Repository. Since an Interface Repository is
    seldomly deployed, using this operation is pretty much
    futile and will either return a nil reference or throw
    an exception.

    Therefore, I propose to add a new get_interface_def()
    operation to the Object interface that returns a FullInter-
    faceDef structure, as defined by the Interface Repository.
    This structure contains all that a dynamic client (such as
    the ones proposed by Schmidt&Vinoski, or software like
    CorbaScript or Combat) needs to know about an interface.

    A new _interface_def pseudo-operation then needs to be added
    to GIOP. This could probably be done without a version change,
    as no marshalling changes or new messages are involved, it's
    just another operation.

    On the server side, the IDL compiler would generate a suitable
    implementation as part of the skeleton. This implementation
    could just contain a binary representation of the FullInterface-
    Description structure (just like a "precompiled" TypeCode) that
    is dumped to the GIOP stream. (So that you don't need the
    Interface Repository IDL around.)

    Proposed resolution:

    In chapter 4.3, "Object Reference Operations," add the following
    operation to the Object interface:

    module CORBA {
    interface Object

    { // PIDL ... other operations ... FullInterfaceDescription get_interface_def (); }

    ;
    };

    Add the following explanation to 4.3.1, "Determining the Object
    Interface"

    4.3.1.2 get_interface_def

    FullInterfaceDescription get_interface_def ();

    The get_interface_def operation returns a data structure
    describing the most derived type of the object addressed by
    the reference. The FullInterfaceDescription structure includes
    descriptions of all the operations and attributes in the
    transitive closure of the inheritance graph of the interface
    being described. See the Interface Repository chapter for the
    contents of the data structure. Note that if an Interface
    Repository is not available, object references contained in
    this structure may be nil or inaccessible.

    In chapter 15.4.2, "Request Message", update the text that
    reads

    In the case of CORBA::Object operations that are defined in
    the CORBA Core (Section 4.2, "Object Reference Operations,"
    on page 4-12) and that correspond to GIOP request messages,
    the operation names are _interface, _is_a, _non_existent,
    _domain_managers and _component.

    to read

    In the case of CORBA::Object operations that are defined in
    the CORBA Core (Section 4.2, "Object Reference Operations,"
    on page 4-12) and that correspond to GIOP request messages,
    the operation names are _interface, _is_a, _non_existent,
    _domain_managers, _component or _interface_def.

    In the C++ language mapping, section 1.37.1, "Mapping of
    PortableServer::Servant", add the following operation to
    class ServantBase:

    namespace PortableServer { // C++
    class ServantBase

    { ... other operations ... virtual CORBA::FullInterfaceDescription_ptr _get_interface_def (); }

    ;
    }

    Update the paragraph that reads,

    ServantBase provides default implementations of the
    _get_interface, _is_a and _non_existent object reference
    operations [...]

    to read

    ServantBase provides default implementations of the
    _get_interface, _is_a, _non_existent and _get_interface_def
    object reference operations [...]

    Add a new paragraph,

    For static skeletons, the default implementation of the
    _get_interface_def function returns information about the
    interface associated with the skeleton class. For dynamic
    skeletons, the default implementation uses the
    _get_interface function to determine its return value.

    Other language mappings might need similar updates.

    By the way, since FullInterfaceDescription is only used as
    a return value, only a pointer to FullInterfaceDescription
    is needed. Therefore, you don't need the full Interface
    Repository interface descriptions but only a pointer to an
    incomplete type.

    On the client side, you only need to pull in the Interface
    Repository IDL if you are actually calling _get_interface_def.

    On the server side, the skeleton can do some ORB-dependent
    magic to push a precompiled binary data structure into the
    result.

  • Reported: CORBA 3.0.2 — Mon, 27 Oct 2003 05:00 GMT
  • Disposition: Deferred — CORBA 3.4
  • Disposition Summary:

    Deferred

    This proposal was generated automatically by request of the Task Force Chair Adam Mitz.

  • Updated: Mon, 30 Mar 2020 19:47 GMT