CM319 High Performance Computing Advanced Parallel and Distributed Programming

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CM319 - High Performance Computing (Advanced
Parallel and Distributed Programming)

• Distributed Programming
• Dr David Lancaster
• djl_at_ecs.soton.ac.uk
• Zepler 3237
• Parallel Programming
• Dr Jeff Reeve
• jsr_at_ecs.soton.ac.uk
• Zepler 4023

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The Course

• Course 22 Lectures
• 11, Distributed Programming
• 11, Parallel Programming
• Assessment Exam 70, Coursework 30
• Coursework One Assignment on distributed
  programming
• 3-tier system using JDBC and CORBA

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Course Structure

• Introduction to CORBA (2)
• The Assignment - JDBC (1)
• CORBA and Java IDL (4)
• Design techniques and special topics (3)
• Review (1)
• ltChange Lecturergt
• Parallel Programming methods/algorithms (3)
• Advanced MPI programming (3)
• Program Optimization (5)

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Books and other Reference Material

• Books
• R. Orfali and D. Harkey, Client/Server
  Programming with Java and Corba, 2nd Edition,
  Wiley, 1998.
• A.Vogel and K. Duddy, Java Programming with
  CORBA, 2nd Edition, Wiley, 1998.
• M. Henning and S. Vinoski, Advanced CORBA
  Programming with C, Addison-Wesley, 1999.
• Other
• Java JDK 1.2 Specification, API, Tutorials, Docs
• www.ecs.soton.ac.uk/notes/cm319
• www.omg.org/

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High Performance Computing

• Was Supercomputers for Science/Engineering
• Then came the Commodity Train
• Now...
• Beowulf Clusters
• Web related systems ISPs, Ebay...
• AOL -- Server has 40,000 CPUs, more than 4
  Tbytes of memory and supports more than a million
  users.

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High Performance Computing

• Science/Engineering
• Parallel Programming
• Tightly coupled homogeneous platforms
• MPI/OpenMP
• Web related systems
• Distributed Programming
• Heterogeneous platforms
• Object Oriented
• CORBA, RMI, DCOM

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Dealing with Heterogeneity

• Find platform independent models and abstractions
  that can be used to help solve a wide variety of
  problems
• Hide as much low-level complexity as possible
  without sacrificing performance
• Essentially provides a homogeneous development
  layer on top of the mess

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Programming heterogeneous distributed systems

• Write individual programs and communicate via
  sockets
• perennial
• Write individual programs that communicate via
  RPC
• 1980s
• Call remote objects as though they were local
• 1990s and beyond

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Objects in a local system

• Objects consist of data and methods
• Objects communicate by invoking methods on other
  objects
• Each object has an object reference (ObjRef)
• The ObjRef enables the object to be the target of
  a message
• ObjRefs are first class variables (can be
  assigned to variables, passed as args and
  returned as results of methods)

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Objects in a distributed system

• OO programs are logically partitioned along
  objects
• Objects are physically partitioned
• ObjRefss must be extended to IORs
• IORs should be first class variables

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Remote Operation Call
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Transparency

• Location Transparency
• The client neither knows nor cares where the
  server is
• achieved by local proxy for each remote object
• Programming Language Independence
• The client does care what language is used by the
  server
• Use an Interface Definition Language (IDL)
• Stub and skeleton are required to marshall and
  unmarshall args and results

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Common Object Request Broker Architecture (CORBA)

• A framework for distributed programming
• For heterogeneous platforms
• Transparent
• Object Oriented
• Supported by the OMG

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Object Management Group

• OMG formed 1989
• over 800 companies, NOT Microsoft
• Mission Add distributed object capabilities to
  existing OO languages via interface specification
  
• Check out www.omg.org
• Read 1-page What is CORBA

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CORBA

• Versions
• CORBA 1.0, 1991 - IDL spec and C binding
• CORBA 2.0, 1994 - IIOP spec, C binding
• CORBA 2.2, 1998 - POA
• CORBA 2.3, 1999 - Objects by value
• CORBA 3.0, 1999 draft

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CORBA

• Architectural Model
• Object Model how interfaces to objects are
  described
• Reference Model characterises interactions
  between such objects
• Specification defines
• ORB the message bus
• IDL interface definition language
• Language Mappings C,C,Java,COBOL,Smalltalk..
• Services naming, trading, event...

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Alternatives to CORBA?

• Java RMI
• language specific
• Stubs and skeletons generated directly from Java
  code
• Good for a complete Java solution
• DCOM
• Microsoft specific
• Good for complete MS solution
• CORBA (Specification only)
• language, h/w and vendor independent
• Best for developing distributed applications on
  different h/w, O/Ss, languages.
• But Bridges can link all 3.

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Java IDL A CORBA implementation

• Partial implementation of CORBA specification,
  bundled with JDK 1.2
• Compared with commercial implementations
• Java IDL is lightweight and minimalist
• no Interface repository, limited services,
  volatile naming service
• Commercial implementations support
• security, dynamic invocation, load-balancing,
  persistence, thread pooling, etc
• Can develop on 1 ORB and replace with another

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Some (only a few) other issues...

• Support for dynamic binding
• Garbage collection
• Object replication / migration
• Locating objects from a name

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Definitions

• CORBA Object - a virtual entity, make concrete
  with a servant
• Client - invokes a request
• Server - an application in which CORBA objects
  exist
• Object Reference - an opaque handle to identify,
  locate and address a CORBA Object
• Servant - a programming language entity that
  implements CORBA Objects