Experimenting Mobility Policies in a Java Environment

1
Experimenting Mobility Policies in a Java
Environment

• Giuliano Armano
• DIEE Dipartimento di Ingegneria Elettrica ed
  Elettronica
• Università di Cagliari

2
Outline of the Talk

• Conceptual framework for classifying mobility
  mechanisms (and design paradigms)
• Distribution, Concurrency, Mobility in Java
• Introducing MODE (Mobile Objects in a Distributed
  Environment)
• Setting up experimental results
• Experimental results
• Conclusions and Future Work

3
Conceptual Framework

• Mobility mechanisms
• Design paradigms

4
Mobility Mechanisms

• Code and execution state management
• Data space management

5
Mobility Mechanisms

• Code and execution state management
• Strong mobility
• Migration
• Remote cloning
• Weak mobility
• Code shipping
• Code fetching

6
Mobility Mechanisms

• Data space management
• Binding removal
• Network reference
• Re-binding
• By copy
• By move

7
Design Paradigms

• Client Server (CS)
• Remote Evaluation (REV)
• Code on Demand (COD)
• Mobile Agent (MA)

8
Design Paradigms
9
Technological Framework

• Agent TCL
• Ara
• Mole
• Obliq
• Sumatra

• Java
• Java Aglets
• INFOBUS
• JINI

10
Why Java?

• Portable
• Clean
• Easy to learn
• General purpose
• Platform independent
• Web oriented

11
Java Features along

• Distribution
• Concurrency
• Mobility

12
Distribution in Java

• Client-server model
• Location awareness
• Remote Method Invocation (RMI)

13
Concurrency in Java

• Monitor-like model (passive objects)
• Light-weight processes (threads)
• wait / notify / notifyAll

14
Mobility in Java

• Code mobility ()
• Serialization mechanism
• Data mobility as a side effect of RMI
• () network-based class loading

15
Distribution in Java

• Pros
• Simple
• Standard
• Benefits from platform independence
• Unique references through RMI Registry
• Cons
• Handling parameters in a method call
• No integration with concurrency handling
• Class versioning

16
Concurrency in Java

• Pros
• Simple
• Standard
• Cons
• Semantics not completely specified in the JVM
  Specs
• Only monitor-like support (for passive objects)

17
Mobility in Java

• Pros
• Embedded into the JVM (class loading)
• WEB oriented
• Cons
• Obtainable only as a side-effect of method
  invocation
• The transitive closure of a slot reference may be
  very big

18
Experimenting Mobility Policies

• In a Java-like Environment

19
Goals

• Investigating some mechanisms to move / copy code
  and data separately
• Simplifying the syntax for representing
  context-aware computations
• Eventually, defining a framework able to support
  collaborative work

20
Conceptual Framework

• Mobility mechanisms
• Code and execution state management
• Weak mobility
• Code fetching gtCM
• Data space management
• By move gtDMM / DMV
• CM weak Code Mobility (only code fetching)
• DMM Data Mobility by Move / DMV Data Mobility
  by Visit

21
Conceptual Framework

• Supporting all design paradigms
• CS (Client Server)
• COD (Code on Demand)
• REV (Remote Evaluation)
• MA (Mobile Agent)
• Design Paradigms (focused on object creation and
  method invocation)

22
Technological Framework
Mobile Objects in a Distributed Environment
23
JMODE

• Is an extension of Java that allows the
  programmer to handle code and data mobility
  (without going into unnecessary details)
• Adds 4 keywords to Java
• on
• mobility
• move
• movable

24
JMODE Syntax An Example

• package weatherstation
• import Barometer mobility DMV
• import RainGauge
• public class WheatherStation implements
  IWheatherStation
• private movable Barometer barometer
• private RainGauge rainGauge
• public WheatherStation()
• barometer new Barometer() on crs4 //
  default CM
• rainGauge new RainGauge() on unica mobility
  DMM
• barometer.getRain(rainGauge) move rainGauge

25
MODEP Jmode Preprocessor

distribution
file
Mode source
(
extended syntax)
MODEP
.jmode
.java
MODEPATH
Java source
(
pure
java syntax)
configuration files
26
MODES

• Is the support layer that enforces distribution
  and mobility in a Java environment
• Services
• local or remote object creation
• local or remote method invocation (object meeting)

27
MODED

• Is a daemon that allows to execute MODE on all
  nodes involved in a given project.

MODE
MODE
MODE
MODE
28
MODEGUI

• Editor
• Support for collaborative work
• Run-time supervisor

29
Experiments Setting

• Object Creation
• O1 and C1 are located in the same node
• O1 and C1 are located in different nodes
• Method Invocation
• O1 and C1 are located in the same node
• O1 and C1 are located in different nodes
• O1 an object C1 the corresponding
  class

30
Experiments Setting

• Code Mobility
• actually code cloning, as currently there is
  no support for class deletion from a JVM
• Exploiting the capabilities of (network) class
  loaders
• Data Mobility
• no data cloning severe synchronization
  problems may arise
• Exploiting the common technique of data
  marshalling

31
Experimental Results

• Object Creation
• O1 and C1 are located in the same node

32
Experimental Results

• Object Creation
• O1 and C1 are located in different nodes

33
Experimental Results

• Object Creation
• O1 and C1 are located in different nodes

34
Experimental Results

• Method Invocation
• O1 and the C1 are located in the same node

35
Experimental Results

• Method Invocation
• O1 and C1 are located in different nodes

36
Conclusions

• Location awareness is possibly error-prone in
  pure Java
• Need for a suitable support for dealing with
  location-awareness (i.e., JmodeMODEPMODES)
• Naive code and data mobility are easy to perform
  in Java, exploiting class loading and enforcing
  data marshalling
• As expected, code mobility is usually more
  efficient (as typical JVM implementations keep
  information about classes that have been loaded
  so far)

37
Future Work

• Implementing monitor-based synchronization for
  passive objects in a distributed environment
• Implementing active objects and rendez-vous
  (CSP-style synchronization) in a distributed
  environment