Transcript Chapter 5_Version2

Distributed Systems
Concepts and Design
Chapter 5
Distributed Objects and Remote
Invocation
 RMI – Remote Method Invocation
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Remote Objects
Remote Interface
RMI vs. Remote Procedure Call
Remote object event subscription
Distributed Objects and Remote
Invocation pp. 178-179
 Middleware
Applications
RMI, RPC and Events
Request/Reply Protocols
External Data Representation
Operating System
Distributed Objects and Remote
Invocation – Interfaces pp. 179-181
 Interface of a module hides its internal
operations
 Only procedures and variables defined in the
interface are ‘visible’
 Distributed programs- no direct access to
variables
 Instead variable values are passed
Distributed Objects and Remote
Invocation – Interfaces pp. 179-181
 Service Interfaces
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Server provides set of procedures
Defines the input/output arguments of
procedures
 Remote Interfaces
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Specifies the methods of objects
Defines the input/output arguments of objects
Methods can pass objects
 Interface Definition Language (IDL)
Communication between distributed
objects pp. 181-183
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The Object Model – object oriented program
consisting of interacting objects and the
objects sets of data and methods
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Object references
Interfaces
Actions
Exceptions
Garbage Collection
Distributed Objects pp. 183-184
 RMI for Distributed Objects – client/server
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Objects are managed by servers
Client requests invoke methods on those
objects
Result is returned to client
Distributed Objects p. 184
Distributed Objects pp. 184-185
 Extending objects to allow RMI
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Remote Object Reference
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An identifier for a unique remote object
Invoker specifies object as remote at invocation
Results may be passed as arguments and results
Remote Interface
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Classes of remote objects may be implemented
in any language with an IDL compiler
Interface lists all methods of a class available for
RMI
Distributed Objects p. 185
Distributed Objects p. 186
 Actions in a distributed system
 Garbage Collection
 Exceptions
Distributed Objects p. 187
Design Issues for Distributed Objects
 RMI Semantics for request/reply protocol
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Retry request message
Duplicate filtering
Retransmission of results
Distributed Objects p. 188
 Maybe Invocation Semantics
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Once or not at all invocation
 At-least-once Invocation Semantics
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Invoker receives either a result or an
exception – may be executed again
 At-most-once Invocation Semantics
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Invoker receives either a result or an
exception – never executes more than once
Transparency p 189
 Remote Interface
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Must be able to recover
 Remote Invocation
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Operation idempotent
Syntax of local and remote invocations
Figure 5.7 p 190
Communication Module p 190
 Transmits request and reply messages
 Provides specified invocation semantics
Remote Reference Module p 191
 Remote Object Table
Entry for all remote objects held by the
process
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Provides invocation semantics
 Remote Object Reference
 Servant
RMI Software p 191
 Proxy
 Dispatcher
 Skeleton
RMI Software p 192
 Dynamic Invocation – alternate to proxies
 Dynamic Skeletons
Server/Client Program p 193
 Classes for Dispatcher
 Classes for Skeleton
 Implements Servant Classes
 Factory Methods
 Server Threads
 Binder
Client /Server Program p 194-95
 Activation of Remote Objects
 De-activation of Remote Objects
 Persistent Objects
 Location of Objects
Distributed Garbage Collection p 196
JAVA Algorithm
 B.holders
 addRef(B)
 removeRef(B)
 Pairwise request-reply
 Leases
RPC- Remote Procedure Call p 197
 Service Interfaces
 Invocation Semantics
 Stub Procedure
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Client stub procedure
Server stub procedure
Figure 5.8 p 198
Sun RPC p 198 - 201
 XDR Interface Language
 Interface Definition
Client Stub Procedure
 Dispatcher
 Server Stub Procedure
Binding
Authentication
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Figure 5.10 p 202
Events and Notifications p 201-202
 Asynchronous
 Publish-Service Paradigm
 Heterogeneous Objects
Participants in Event/Notification
 Object of Interest
 Event
 Notification
 Subscriber
 Observer Objects
 Publisher
Figure 5.11 p 204
Roles for Observers p 204-206
 Forwarding
 Filtering of Notification
 Patterns of Events
 Notification Mailboxes
Jini Distributed Event Specs p 206-208
 Event Generators
 Remote Event Listeners
 Remote Events
 Third-party Agents
JAVA RMI p 208-211
 Remote Interfaces
 Parameter/Result Passing
 Downloading Classes
 RMI Registry
JAVA RMI p 210-211
 Server Program
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Main Method
Servant Class Implementations
RMI Security Manager
JAVA RMI p 212-213
 Client Program
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Binder
Lookup Operation
Callbacks
Design/Implement JAVA RMI
 Reflection
 JAVA Classes
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RemoteObject
RemoteServer
Activatable
UnicastRemoteObject
Servant class