September 21, 2005 Dynamic Typing in CORBA Middleware Jeff Parsons ISIS Vanderbilt University Nashville, TN

Jeff Parsons Dynamic Typing in CORBA Middleware 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.

Jeff Parsons Dynamic Typing in CORBA Middleware 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.

Jeff Parsons Dynamic Typing in CORBA Middleware 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.

Jeff Parsons Dynamic Typing in CORBA Middleware 5 Dynamic CORBA Features

Jeff Parsons Dynamic Typing in CORBA Middleware 6 Type Code union foo switch (char) { case ‘a’: long num; case ‘b’: string str; }; struct bar { string str_mem; foo u_mem; boolean b_mem; }; Structural representation Basic TCs in ORB New TCs from IDL compiler or type code factory

Jeff Parsons Dynamic Typing in CORBA Middleware 7 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

Jeff Parsons Dynamic Typing in CORBA Middleware 8 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.

Jeff Parsons Dynamic Typing in CORBA Middleware 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.

Jeff Parsons Dynamic Typing in CORBA Middleware 10 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.

Jeff Parsons Dynamic Typing in CORBA Middleware 11 Managing the Interface Repository Problem: Providing a systematic way to manage the repository’s contents. Forces: –Load from IDL files. –Reuse IDL compiler’s parsing and error checking. –IDL compiler is built monolithically. Solution: Modularize the IDL compiler. –Reusable front end. –Pluggable back end. –Top-level executable.

Jeff Parsons Dynamic Typing in CORBA Middleware 12 Dynamic CORBA - Putting It All Together

Jeff Parsons Dynamic Typing in CORBA Middleware 13 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.