Bionic Buffalo Tech Note #103: Introduction to Pegasus Client Support
Moreover, the client never gets object references, and there is no protocol for invoking methods
directly by the client on a Pegasus ServiceGateway.
The other class with some similarity between the two architectures is the DSM::Stream object, which
has the Pegasus stream object. The similarity is largely superficial. The DSM-CC concept of service
objects, such as
DSM::Stream
, is radically different from the Pegasus concept of service objects. In
DSM-CC, clients share use of single objects, while in Pegasus, there is an object for each client using a
given service. For example, if a DSM-CC video server were to host the movie Casablanca, there
would be a single Casablanca
DSM::Stream
object to be shared among all clients. A Pegasus video
server, on the other hand, would instantiate a separate Casablanca stream object for each client
viewing that movie.
A DSM-CC client gains access to service objects (such as streams and files) by first establishing a
session, in a process which returns an object reference to a
DSM::ServiceGateway
object. The
DSM::ServiceGateway
object has directory operations, allowing the client to perform operations
that browse the server's contents. When it finds an object the viewer likes, such as a Casablanca stream
object, the client system merely issues a method invocation (remote procedure call) on the object's
interface. For example, the client might invoke
DSM::Stream::play
(mapped to C as
Page 5 of 11
DSM-CC Client
Session and
Resource
Manager
ServiceGateway
Module::
ServiceGateway
SessionModule::
Session
client application
attach
Session
Attach
Client
Server
SRM
User-Network
protocol
class interactions
in Pegasus systems
during session
establishment
SessionModule::
SessionGateway
Session
Attach
«instantiate»
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