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Distributed Systems
Remote Procedure Call & Remote Method Invocation
Distributed Systems ccsejc, November 2003 2
Middleware Layers
Applications
Middlewarelayers Request reply protocol
External data representation
Operating System
RMI, RPC and events
Distributed Systems ccsejc, November 2003 3
Remote Procedure Call (RPC)
Why RPC? Sockets are considered low-level RPCs offer a higher-level form of
communication
Client makes procedure call to “remote” server using ordinary procedure call mechanisms
Distributed Systems ccsejc, November 2003 4
Client and Server
Distributed Systems ccsejc, November 2003 5
Binding in RPC
Distributed Systems ccsejc, November 2003 6
Basic Concept of RPC
Distributed Systems ccsejc, November 2003 7
Steps for RPC
Distributed Systems ccsejc, November 2003 8
Issues in RPCCannot pass pointersWeakly typed languagesNot always possible to determine parameter typesCannot use global variables
Distributed Systems ccsejc, November 2003 9
Remote Method Invocation
Java’s version of RPCA thread may invoke a method on a remote objectAn object is considered “remote” if it resides in a separate Java Virtual Machine.
Distributed Systems ccsejc, November 2003 10
Remote Method Invocation
Distributed Systems ccsejc, November 2003 11
RPC versus RMI
RPC’s support procedural programming styleRMI supports object-oriented programming style
Parameters to RPCs are ordinary data structuresParameters to RMI are objects
Distributed Systems ccsejc, November 2003 12
Object Model
Object Data Methods
EncapsulationObject Reference unique identifier of object should not be reused
Distributed Systems ccsejc, November 2003 13
Object Model
Method Invocation object reference + method name
Interface types of arguments return values exceptions
Distributed Systems ccsejc, November 2003 14
Distributed Objects
Adopts client/server architectureMay be replicatedMay be migratedMay be accessed concurrently
Distributed Systems ccsejc, November 2003 15
Distributed Objects
invocation invocationremote
invocationremote
locallocal
local
invocation
invocationA B
C
D
E
F
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Remote Object and Interface
Remote Object Reference unique can be used as arguments and results
Remote Interface no constructors extend remote interface
Distributed Systems ccsejc, November 2003 17
Remote Object and Interface
interface
remote
m1m2m3
m4m5m6
Data
implementation
remote object
{ of methods
Distributed Systems ccsejc, November 2003 18
RMI Implementation
object A object Bskeleton
Requestproxy for B
Reply
CommunicationRemote Remote referenceCommunication
module modulereference module module
for B’s class& dispatcher
remoteclient server
Distributed Systems ccsejc, November 2003 19
RMI Implementation
Classes for proxies, skeleton, dispatchersInitialization Section (Server)Factory MethodsBinder
Distributed Systems ccsejc, November 2003 20
Events and Notifications
Events state change
Notification allows object to respond to state
changes
Distributed Systems ccsejc, November 2003 21
Distributed Event-Based System
Publish-Subscribe Paradigm Publish
type of events available (notification) Subscribe
registering interest
HeterogeneousAsynchronous
Distributed Systems ccsejc, November 2003 22
Dealing Room SystemDealer’s computer
Informationprovider
Dealer
Externalsource
Externalsource
Informationprovider
Dealer
Dealer
Dealer
Notification
Notification
Notification
Notification
NotificationNotification
Notification
Notification
Dealer’s computer
Dealer’s computerDealer’s computer
NotificationNotification
Distributed Systems ccsejc, November 2003 23
Distributed Event Notification
Object of InterestEventNotificationSubscriberObserver Objects (Event Monitor)Publisher
Distributed Systems ccsejc, November 2003 24
Distributed Event Notification
subscriberobserverobject of interest
Event service
object of interest
object of interest observer
subscriber
subscriber
3.
1.
2. notification
notification
notification
notification
