	CS 696 Emerging Technologies: Java Distributed Computing Spring Semester, 1999 Jini Intro
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Contents of Doc 15, Jini Intro

References

Jini Architecture Specification 1.0 January 25, 1999
Jini Device Architecture Specification 1.0 January 25, 1999
Jini Distributed Leasing Specification 1.0 January 25, 1999

These documents are available at: http://www.sun.com/jini/specs/index.html

New Webster’s Dictionary, 1981


Doc 15, Jini Intro Slide # 2

Jini

Jinn (jinni, genie)

One of a class of spirits lower than the angels, capable of appearing in human and animal forms, and exercising influence over mankind for good and evil
New Webster’s Dictionary, 1981

A Jini system (djinn) is a distributed system based on the idea of federating groups of users and the resources required by those users.

A Jini system consists of the following parts:

Infrastructure components

Provides an infrastructure for federating services in a distributed system

A programming model

Supports and encourages the production of reliable distributed services

Services

Offer functionality to any other member of the federation

The end goals Jini include the following:

Enabling users to share services and resources over a network
Providing users easy access to resources anywhere on the network while allowing the network location of the user to change
Simplifying the task of building, maintaining, and altering a network of devices, software, and users


Doc 15, Jini Intro Slide # 3

Jini System Requirements
Network

Reasonable speed
Bandwidth requirements vary among devices
Reasonable latency

Jini is Java-based

Any language that produces Java byte codes can be used

Devices

Some memory and processing power to run Java or
Connected to a device (proxy) that contains the memory and processing power


Doc 15, Jini Intro Slide # 4

Jini System Overview

Terms Services

A service is an entity that can be used by a person, program or another service
A service can be: a computation, storage, communication channel to another user a software filter a hardware device another user

Lookup Service

Is used to find services in a djinn ( a Jini system)

Leasing

A lease provides access to a service for a fixed time period
If a lease is not renewed at the end of the lease period, then the user and provider of the service can free all resources connected the lease

Transactions

Provides protocol for a two-phase commit process for managing state changes between objects in a Jini system

Events

Distributed events
Distributed version of listeners or Observer-Observable


Doc 15, Jini Intro Slide # 5

Component Overview

	Infrastructure	Programming Model	Services
Base Java	Java VM RMI Java Security	Java APIs JavaBeans	JNDI Enterprise Beans JTS JMS
Java + Jini	Discorvery/Join Distributed Security Lookup	Leasing Transactions Events	Transaction Manager JavaSpaces Lookup service ...

Discovery

Service provider looks for a lookup service to register itself

Join

Service provider is registered in the lookup service
Service provider registers: A remote reference to itself Descriptive attributes about the service

Lookup

Client requests a service by Java type and/or by attributes
Client receives remote reference to the service

Jini 1.0 Service Application Names

Service	Application Name
Lookup	reggie
Transaction	mahalo
JavaSpaces	outrigger


Doc 15, Jini Intro Slide # 6

Basic Device Architecture Examples

(Note: Images are taken from Jini Distributed Leasing Specification.)

Devices with Resident Java Virtual Machines

Devices Using Specialized Virtual Machines

A Jini device does not need to support the entire JVM. One should be able to configure Personal Java or Embedded Java to support Jini. Sun’s documentation is not clear on this point.

Clustering Devices (physical option)


Doc 15, Jini Intro Slide # 7

Clustering Devices (network option)

Jini Software Services over the Internet Inter-Operability Protocol

IIOP (Internet Inter-Operability Protocol) is a Corba standard for communication between Corba orbs

Sun has RMI-IIOP which implements a subset of RMI over IIOP

The Sun documentation states:

appears that the Jini Lookup service interfaces are in conformance with the ®RMI over IIOP subset

For more information about RMI-IIOP see: http://developer.java.sun.com/developer/earlyAccess/rmi-iiop/index.html

For more information about the issues of doing RMI over IIOP see:
Java Language to IDL Mapping at ftp://ftp.omg.org/pub/docs/orbos/98-07-19.pdf and Object by Value at ftp://ftp.omg.org/pub/docs/orbos/98-01-18.pdf.

For more information about Corba see http://www.omg.org/corba/beginners.html


Doc 15, Jini Intro Slide # 8

Distributed Leasing

Distributed systems must deal with:

Failure of part of the system
Accumulation of outdated and unwanted information

Jini’s Distributed leasing:

provides a simple way of indicating time-based resource allocation or reservation
provides a uniform way of renewing and canceling leases

A lease is

"a time period during which the grantor of the lease insures (to the best of the grantor’s abilities) that the holder of the lease will have access to some resource."

Lease duration

Can be solely determined by lease grantor
Negotiated between grantor and holder of the lease

Lease holder can:

Request a renewal of the lease
Cancel a lease

When a lease is cancelled the grantor of the lease can clean up any resources allocated to support the lease and "obliges the grantor of the lease to not take any action involving the leaseholder that was part of the agreement that was the subject of the lease”.

A lease can expire

"Both the grantor and the holder are obliged to act as though the leased agreement is no longer in force."

Lease time is not measured in absolute time, but in duration. Clients should use the time they requested the lease as the beginning of the lease duration.


Doc 15, Jini Intro Slide # 9

Basic Lease OperationsInterface net.jini.core.lease.Lease
Static Fields

//Length of lease
static long FOREVER = Long.MAX_VALUE;
static long ANY = -1;
//Formating of serialized Lease object
static int DURATION = 1;
static int ABSOLUTE = 2;

Methods long getExpiration();

returns the expiration time (in milliseconds from the beginning of the epoch)

void cancel() throws UnknownLeaseException, RemoteException;

void renew(long duration) throws LeaseDeniedException,
UnknownLeaseException, RemoteException;

Duration is the new duration requested of the lease, it is not added to the remaining time of the lease

void setSerialFormat(int format);

Specifies how to store the lease time when serialized. Options are either duration (how long the lease will last from the time it was serialized) or absolute (in the current clock time). Use duration when sending a lease to a remote machine. Duration is the default.

int getSerialFormat();

LeaseMap createLeaseMap(long duration);
boolean canBatch(Lease lease);

Used in handling leases in batches.


Doc 15, Jini Intro Slide # 10

Lease Exceptions
LeaseDeniedException

An exception generated when a lease request or renewal is denied.

LeaseException

Generic superclass for specific lease exceptions.

LeaseMapException

An exception generated when a LeaseMap renewAll or cancelAll call generates exceptions on one or more leases in the map.

UnknownLeaseException

An exception used to indicate that a lease is not known to the grantor of the lease

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