INF 123 SW ARCH, DIST SYS & INTEROP

LECTURE 9

Prof. Crista Lopes

Objectives

Understanding of Distributed Objects architectures

Acquaintance with a well-known RMI framework Java RMI

Web Services isa Distributed System

“Collection of interacting components hosted on different computers that are connected through a computer network”

Component1

Component n

Hardware

Network OS

Host 3

Component1

Component n

Hardware

Network OS

Host 2

Component1

Component n

Hardware

Network OS

Host 1

…

Network

Remote Procedure Calls (RPC)

r = foo(a, b)

define foo(a, b) …end

caller

callee

program

host

Local Procedure Calls

r = foo(a, b)

define foo(a, b) …end

caller

callee

program

host 1

host 2program

Remote Procedure Calls

Remote Procedure Calls (RPC)

r = foo(a, b)

define foo(a, b) …end

caller

callee

program

host

Local Procedure Calls

r = foo(a, b)

define foo(a, b) …end

caller

callee

program

host 1

host 2program

Remote Procedure Calls

Stub

Skeleton

RPC

Procedure Interface Definition (in IDL)

Procedure Definition Program (in PL)

Procedure Call Program (in PL)

Stub(in PL)

Skeleton(in PL)

generates

Network OS Network OS

RPC Stubs

Marshal arguments (i.e. “serialize”) Issue request to remote server, wait for

response Unmarshal return value (i.e.

“deserialize”)

RPC Skeletons

Unmarshal arguments Call local procedure Marshal return value Send back response to client

Distributed Objects model

Obj1

Host A

Obj2

Host A

Obj4

Host A

Obj5

Host A

Obj3

Obj6

Distributed Objects model

Obj1Obj2

Obj4

Obj5

Obj3

Obj6

“Transparent distribution”

Distributed Objects – Properties Very tightly coupled with PL

Compiler generates stubs and skeletons Distribution seen only in terms of

peripheral components: Security Registry Additional program arguments

Location (host) doesn’t matter [much] Remote object references do

Rest of this lecture

Java RMI tutorial athttp://java.sun.com/docs/books/tutorial/rmi/overview.html