Dynamic Typing in CORBA Middleware

1
Dynamic Typing in CORBA Middleware

• Jeff Parsons
• ISIS
• Vanderbilt University
• Nashville, TN

2
Static vs. Dynamic Typing

• Static typing
• Type rules in compiler.
• New types at development time.
• No new types at run time.
• Dynamic typing
• Type rules also implicit in source code.
• Enables new types at run time.
• Dynamic CORBA contains type rules for IDL, not
  target language.

3
Static Typing

• All operation names and signatures known at
  compile time.
• Advantages
• Efficient marshaling.
• Streamlined invocation.
• Disadvantages
• Larger generated code footprint.
• Inflexible.
• Unacceptable in open-ended systems.

4
Dynamic Typing

• Discovery of operation names and parameter types
  at runtime.
• Advantages
• Smaller generated code footprint.
• Flexible open-ended.
• Disadvantages
• Larger ORB footprint.
• Slower marshaling.
• Pre- and post-invocation overhead.

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Dynamic CORBA Features
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Type Code

• union foo switch (char)
• case a long num
• case b string str
• struct bar
• stringlt12gt str_mem
• foo u_mem
• boolean b_mem
• Structural representation
• Basic TCs in ORB
• New TCs from IDL compiler or type code factory

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Any, NamedValue, NVList

• Any
• Represents generic IDL value
• Type code describes value
• Value is opaque
• Overloaded insertion extraction operators
• Basic types in ORB
• New types from IDL compiler
• NamedValue
• Represents operation argument
• Any name direction
• NVList
• Represents operation signature
• List of NamedValues

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Dynamic Invocation Interface (DII)

• Used when IDL compiler generated code is not
  available.
• A request object is created by a local call on
  the target object reference.
• Dynamic Skeleton Interface (DSI) is the
  server-side counterpart to DII.

9
Type Code Factory

• Problem Creating a TypeCode at run-time.
• Forces
• Family of related TypeCodes.
• Optional use by application.
• Necessary to Interface Repository.
• Avoid penalty to static application.
• Solution Abstract Factory pattern and separate
  library.

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The Interface Repository (IFR)

• Problem Providing run-time IDL type information.
• Forces
• Need persistent storage.
• Need OO database - query results are CORBA
  objects.
• Must preserve nested (scoped) structure.
• Solution
• View entries as meta-objects.
• Use the Memento pattern to capture their state.
• Use tree of hash tables for underlying storage.
• Create query results on demand.

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Managing the Interface Repository

• Problem Providing a systematic way to manage the
  repositorys contents.
• Forces
• Load from IDL files.
• Reuse IDL compilers parsing and error checking.
• IDL compiler is built monolithically.
• Solution Modularize the IDL compiler.
• Reusable front end.
• Pluggable back end.
• Top-level executable.

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Dynamic CORBA - Putting It All Together
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Evaluation of Dynamic CORBA Features

• Interdependency
• Explicit
• Implicit
• Hybrid Applications
• Need not use dynamic typing throughout.
• May use subset of features.
• Generality vs. Overhead
• Tradeoff
• Portability
• Widespread ORB vendor support.