distributed objects and middleware. sockets and ports source: g. coulouris et al., distributed...
TRANSCRIPT
Distributed Objects and Middleware
Sockets and Ports
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Crossing Hosts/Platforms
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Provisions of Middleware Higher-level abstractions (RPC, RMI, …) Location transparency Independent of communication protocols Independent of hardware/operating systems Use of several programming languages
The Middleware layer
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
* The operating system includes basic network protocols.
Distributed Objects
The object-based programming model is extended
to allow objects in different processes to interact
with one another. Client/Server Object References Interfaces Remote Method Invocation Exceptions
A CORBA IDL Example
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Local and Remote Method Invocations
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
A Remote Object and Its Interface
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Client Proxy (Stub) and Server Skeleton (Stub)
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
The RMI Software
Proxy: the local representative of the remote object.
Dispatcher: relays a request to the appropriate skeleton method.
Skeleton: unmarshals the request and invokes the corresponding method in the remote object.
Java Remote Interface Examples
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Java Server Example
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Java Server Example (cont’d)
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Java Client Example
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
CORBA
Defined by OMG to hide the intricacies of network programming.
An ORB (Object Request Broker) receives invocations from a client and deliver them to a target object.
The main communication protocol is GIOP (General Inter-ORB Protocol), known as IIOP when implemented over the Internet.
The CORBA Architecture
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
CORBA Object Interfaces
Each object has an interface defined in IDL. An interface defines the operations that can be
called by the clients. An interface can be implemented in one language
and called from by another. The CORBA IDL includes features such as
inheritance of interfaces, exceptions, and compound data types.
CORBA Programming with Java
Define the interfaces using IDL and compile them into Java interfaces.
Implement the interfaces with Java classes. Write a server main function that creates instances
of these classes and then inform the underlying CORBA implementation.
Register the server. Write a client main function to connect to the
server and to use server’s objects.
CORBA IDL Interfaces: Shape and ShapeList
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Java Interface Generated from the CORBA Interface ShapeList
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Java Implementation of Shapelist
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Java Implementation of ShapeList (cont’d)
Source: G. Coulouris et al., Distributed Systems: Concepts and Design
Java Implementation of a ShapeList Client
Source: G. Coulouris et al., Distributed Systems: Concepts and Design