1. Java Distributed Object System

2. Main Module of a Distributed System
Global address space
global identifier
registry/ name service ( central, distributed, replicated)
Transportation system
Global Control flow (Invocation/Control flow Protocol)
parameter passing across address space
method invocation semantic
entity activation
Failure Behavior
exception
consistency and persistency
CS491 presented by Peng Wu

3. RMI Overview
RMI provides distributed computing ability on the specific system(JVM) for the specific language(Java)
CORBA, RPC
System Heterogeneity
Language Heterogeneity
RMI based on homogeneity and strength it
Language Integration -- distributed object model
similar interface, preserve some behavior
exception
System Integration
garbage collection
mobile behavior
security
CS491 presented by Peng Wu

4. Language Integration -- Distributed Object Model
Java Object model
Object
Interface
declare a set of methods for Java object without implementation
Method Invocation
primitive type passed by value
object passed by reference
Distributed Object model
Remote object
object whose methods can be accessed from another address space
Remote interface
an interface that declares the methods of a remote object
Remote Implementation
RMI
non-remote object passed by value
remote object passed by reference
CS491 presented by Peng Wu

5. RMI Interfaces and Classes
Object
classes
Interfaces
Remote
RemoteObject
IOException
RemoteServer
RemoteException
Client stub
...
UnicastRemoteObject
...
extension
implementation
CS491 presented by Peng Wu

6. System Integration Distributed Garbage Collection Dynamic Stub loading
specialized class loader
security manager
pickling system
When marshalling remote object, marshal stream embeds URL info of the stub code
On demarshalling, marshal stream loads stub code if it’s not available locally
CS491 presented by Peng Wu

7. Remote Reference layer
System Architecture
Stub/Skeleton layer
Remote reference layer
Transport layer
Application
Client
Server
Stubs
Skeleton
RMI System
Remote Reference layer
Transport
CS491 presented by Peng Wu

8. Distributed object Across Address Space
Name Service
URL based name lookup, no location transparency
Non-persistent database
java..rmi.registry.Registry
java.rmi.LocateRegistry
java.rmi.naming
export
export
Remote
Server
Remote
Server
registry
registry
Locate Reg
Locate Reg
naming
naming
client
client
binding
binding
CS491 presented by Peng Wu

9. Distributed object Across Address Space
Pickling -- Object transmission across address space
Serialized representation of objects:
object type
object persistent state
relationships between objects within a stream
object implementation info
Pickling remote object
remote interface
remote object reference
CS491 presented by Peng Wu

10. RMI Performance Call time (no configuration available) CORBA vs. RMI
RMI vs. Local call(PPro 200Mhz, NT, JDK no JIT)
Call time (no configuration available)
setup time: RMI 40% slower than CORBA
binding: RMI ms slower than CORBA
CORBA vs. RMI
1000 calls, one argument, JDK1.1.1
CS491 presented by Peng Wu

11. CORBA and RMI Performance (1000 calls, one argument)
CS491 presented by Peng Wu

12. RMI Performance
Scalability -- ability of handling multiple connections to one remote object
HelloImpl.sayHello() JDK1.1, Win95, 133-Pentium
150 threads in 2 sec interval, 200 threads in 5 sec interval(RMI)
1000 threads(Java IDL)
Serialization
100 times, default serialization, buffered stream, primitive type, small array, small object array(10)
RMI 64500ms (object)
CORBA 3485ms (IDL struct)
different serialization schemes
Object[1000], each 3 attributes(String, Double,util.Data)
CS491 presented by Peng Wu

13. Performance of different serialization scheme (Solaris2
Performance of different serialization scheme (Solaris2.5 Ultra-1 with attributes String, Double,Data)
CS491 presented by Peng Wu

14. Summary
Pros
Integrating distribute object model seamlessly into Java object model
Homogeneity
Communication with non-Java object may work through JNI and JDBC
Cons
Make distributed computing in Java easily to approach, but not efficiently
Heterogeneity
A primitive implementation currently
CS491 presented by Peng Wu

15. JavaSpace -- a new distributed computing paradigm
JavaSpace -- A reliable distributed storage system
Goal -- facilitating cooperate distributed computing
Utilization
Distributed algorithms as flow of object
establish connections between participants(Client/Server, RPC, RMI)
build interfaces and protocols between participants
establish connections with a broker(JavaSpace)
build interfaces and protocols with the broker
Distributed persistence
CS491 presented by Peng Wu

16. Client read Identities write JavaSpace Write event Client write Event
Dispatcher
Transaction
notify
take
notify
write
JavaSpace
JavaSpace
CS491 presented by Peng Wu

17. JavaSpace model
Entry
basic unit of JavaSpace, a typed group of objects
Template
a “partial” entry used to match entries with specific properties
Operation
read
write
take
notify
CS491 presented by Peng Wu

18. A reliable distributed storage system
Store and retrieve entries -- object
Weak query ability
Handle concurrent access
Global control flow across multiple JavaSpaces
asynchronous retrieval
distributed transaction mechanism
CS491 presented by Peng Wu