Distributed computing

SUCCESSORS TO CORBA Microsoft Products

• COM: allow objects to call one another in a centralized setting: classes + objects of those classes. Can create objects and then invoke them.
• DCOM: COM + Object Request Broker.
• ActiveX: DCOM for the Web.

SUCCESSORS TO CORBA Java RMI

• Remote Method invocation (RMI): Define a service interface in Java.
• Register the server in RMI repository, i.e., an object request broker.
• Client may access Server through repository.
• Notion of distributed garbage collection

SUCCESSORS TO CORBA Enterprise Java Beans

• Beans are again objects but can be customized at runtime.
• Support distributed transaction notion (later) as well as backups.
• So transaction notion for persistent storage is another concern it is nice to separate.

REDUCING BUREAUCRACY: automatic registration

• SUN also developed an abstraction known as JINI.
• New device finds a lookup service (like an ORB), uploads its interface, and then everyone can access.
• No need to register.
• Requires a trusted environment.

COOPERATING DISTRIBUTED SYSTEMS: LINDA

• Linda supports a shared data structure called a tuple space.
• Linda tuples, like database system records, consists of strings and integers. We will see that in the matrix example below.

• TUPLE SPACE

• PROCESSES

LINDA OPERATIONS

• The operations are out (add a tuple to the space); in (read and remove a tuple from the space); and read (read but don’t remove a tuple from the tuple space).
• A pattern-matching mechanism is used so that tuples can be extracted selectively by specifying values or data types of some fields.
• in (“dennis”, ?x, ?y, ….)
• gets tuple whose first field contains “dennis,” assigns values in second and third fields of the tuple to x and y, respectively.