The OMNI Naming Service
Tristan Richardson
AT&T Laboratories Cambridge
13 July 2000
1 Introduction
The OMNI Naming Service (omniNames) is an omniORB implementation of the OMG's COS Naming Service Specification. It offers a way for a client to turn a human-readable name into an object reference, on which the client can subsequently invoke operations in the normal way. See the OMG specification for full details of the functionality provided by the Naming Service.
The Naming Service stores a set of bindings of names to objects. These bindings can be arranged as an arbitrary directed graph, although they are often arranged in a tree hierarchy. Each node in the graph is a naming context. There is a ``root'' context at which name lookups usually start. This is the object returned by the call to CORBA::ORB::resolve_initial_references("NameService").
2 Log file
The Naming Service is often part of the bootstrapping process of other CORBA programs. For this reason, if an instance of omniNames crashes (or the machine on which it runs is rebooted), it is important that certain aspects of its operation persist upon restarting. Firstly the root context of the Naming Service should always be accessible through the same object reference. This helps the ORB to implement the resolve_initial_references call by allowing the object reference to be stored in a configuration file, for example. Secondly, the naming graph with all its bindings should persist between invocations.
To achieve this, omniNames generates a log file, to which it writes out an entry every time a change is made to the naming graph. The directory in which this log file is written can be specified with the OMNINAMES_LOGDIR environment variable. When omniNames is restarted it uses the log file so that it can regenerate the naming graph.
Periodically the log file is checkpointed, removing unnecessary entries from the log file. The idle time between checkpoints can be set with the OMNINAMES_ITBC environment variable. It defaults to 15 minutes.
3 Starting omniNames and setting omniORB.cfg
When starting omniNames for the first time, you can either let it start with the default TCP port of 2809, or you can specify the port number on which it should listen. This is written to the log file so that on subsequent invocations it will listen on the same port number and thus can be accessible through the same object reference. When omniNames starts up successfully it writes the stringified object reference for its root context on standard error.
At startup, omniORB tries to read the configuration file omniORB.cfg to obtain the object reference to the root context of the Naming Service. This object reference is returned by resolve_initial_references("NameService"). There are a number of methods of specifying the root naming context in omniORB.cfg---see the omniORB manual for details.
This document was translated from LATEX by HEVEA.