TAO Interoperable Naming Service

The CORBA Interoperable Naming Service (INS) service allows the ORB to be configured administratively to return object references from CORBA::ORB::resolve_initial_references for non-locality constrained objects. The service also introduces the iioploc and iiopname IOR formats, which can be used to bootstrap services not available at ORB installation time.

This document presents an overview of TAO's INS implementation and addresses common questions.

How does resolve_initial_references work ?

The following is the order that resolve_initial_references locates a service:

  1. ORBInitRef
  2. ORBDefaultInitRef
  3. ORB Default Settings
  4. Multicast to Service

TAO uses the ACE_Hash_Map_Manager to keep track of the ObjectID:IOR mappings specified on the command-line. The IOR could be in IOR, iiop, or iioploc format. If the ORB fails to resolve the IOR using the command-line parameters or the default settings, it uses UDP multicast to resolve the service.

The Naming Service process acts as an IIOP Agent to respond with the IOR for the given service name. If the service being resolved is the Naming Service or the Trading Service, TAO checks the appropriate environment variables prior to using multicast to obtain the appropriate port number or IOR.

The following diagram illustrates the order in which these various components interact.

ORB Parameters Used for Configuration

o -ORBInitRef : The ORB initial reference argument allows specification of an arbitrary object reference for an initial service. The format is :

-ORBInitRef [ObjectID]=[ObjectURL]

Examples of use are:

-ORBInitRef NameService=IOR:0002342344AB345 ...
-ORBInitRef MyServiceID=iioploc://tango.cs.wustl.edu:87777/myService

This mechanism allows an ORB to be configured with new initial service Object IDs that were not defined when the ORB was installed. The ObjectURL can be any of the URL schemes supported by CORBA::ORB::string_to_object.

o -ORBDefaultInitRef : The ORB default initial reference argument assists in resolution of initial references not explicitly specified with -ORBInitRef. -ORBDefaultInitRef requires a URL that, after appending a slash '/' and a stringified object key, forms a new URL to identify an initial object reference.

For example:

-ORBDefaultInitRef iioploc://tango.cs.wustl.edu:89899,merengue.cs.wustl.edu:99990

A call to resolve_initial_references ("NameService") with this argument results in a new multiple profile URL equivalent to the following:

iioploc://tango.cs.wustl.edu:89899/NameService
iioploc://merengue.cs.wustl.edu:99990/NameService

The URL is passed to CORBA::ORB::string_to_object to obtain the initial reference for the service.

iioploc:// IOR format

The CORBA::ORB::string_to_object now understands the iioploc:// format IORs. These are user-friendly multiple end-point IORs. For example -

iioploc:1.0//tango.cs.wustl.edu:99999/SimpleKey, merengue.cs.wustl.edu:99990/SimpleKey

Each of the end-points is converted into an IIOP Profile. These profiles are used to construct the Multiple Profile Object. This object is then used to construct the Object Reference.

The object references constructed using this format have a 'SimpleKey' in the Object Key field of the IOR. The server side ORB intercepts the incoming IIOP request, recognizes the Simple Key and looks up a table to get the complete IOR. It then raises a LOCATION_FORWARD or an OBJECT_NOT_EXIST exception to forward/fail the request depending on if a mapping for the given simple key exists.

All default TAO Object keys are preceded by a special sequence of octets ^t^a^o/0. This is taken care of by the POA when it generates the Object key for the IOR. The sequence is useful for the ORB to distinguish a simple key from the usual TAO object key.

Last modified Tue Apr 20 14:47:21 CDT 1999