Interprocess Communication and Middleware

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Interprocess CommunicationandMiddleware
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Sockets and Ports
Node 2
Node 1
Source G. Coulouris et al., Distributed Systems
Concepts and Design
3
Crossing Hosts/Platforms
Source G. Coulouris et al., Distributed Systems
Concepts and Design
4
Provisions of Middleware

• Higher-level abstractions (RPC, RMI, )
• Location transparency
• Independent of communication protocols
• Independent of hardware/operating systems
• Use of several programming languages

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The Middleware layer
The operating system includes common network
protocols (TCP/IP, ).
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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Request-Reply Communication
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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Request-Reply Communication Using HTTP
HTTP request message
HTTP reply message
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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Serialization (Marshalling)
Source G. Coulouris et al., Distributed Systems
Concepts and Design
9
Distributed Objects

• The object-based programming model is extended
  
• to allow objects in different processes to
  interact
• with one another.
• Client/Server
• Object References
• Interfaces
• Remote Method Invocation
• Exceptions

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A CORBA IDL Example
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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Local and Remote Method Invocations
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Concepts and Design
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A Remote Object and Its Interface
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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Client Proxy (Stub) and Server Skeleton (Stub)
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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The RMI Software

• Proxy the local representative of the remote
  object.
• Dispatcher relays a request to the appropriate
  skeleton method.
• Skeleton unmarshals the request and invokes the
  corresponding method in the remote object.

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RPC/RMI Semantics
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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Java Remote Interfaces
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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A Java Server
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Concepts and Design
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A Java Server (contd)
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Concepts and Design
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A Java Client
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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CORBA

• Defined by OMG to hide the intricacies of network
  programming.
• An ORB (Object Request Broker) receives
  invocations from a client and deliver them to a
  target object.
• The main communication protocol is GIOP (General
  Inter-ORB Protocol), known as IIOP when
  implemented over the Internet.

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The CORBA Architecture
Source G. Coulouris et al., Distributed Systems
Concepts and Design
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CORBA Object Interfaces

• Each object has an interface defined in IDL.
• An interface defines the operations that can be
  called by the clients.
• An interface can be implemented in one language
  and called from by another.
• The CORBA IDL includes features such as
  inheritance of interfaces, exceptions, and
  compound data types.

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CORBA Programming with Java

• Define the interfaces using IDL and compile them
  into Java interfaces.
• Implement the interfaces with Java classes.
• Write a server main function that creates
  instances of these classes and then inform the
  underlying CORBA implementation.
• Register the server.
• Write a client main function to connect to the
  server and to use servers objects.

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CORBA IDL Interfaces Shape and ShapeList
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Concepts and Design
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Java Interface Generated from the CORBA Interface
ShapeList
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Concepts and Design
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Java Implementation of Shapelist
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Concepts and Design
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Java Implementation of ShapeList (contd)
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Concepts and Design
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Java Implementation of a ShapeList Client
Source G. Coulouris et al., Distributed Systems
Concepts and Design