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

September 21, 2005

Dynamic Typing in CORBA Middleware

Jeff ParsonsISIS

Vanderbilt UniversityNashville, 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.

type TYPE

TYPE type

compiler

type rules

TYPE

compiler

type rules

type

TYPE

type

TYPE

type rules

type TYPE

TYPE type

type TYPE

type

.

.

.

Static Typing Dynamic Typing

DevelopmentTime

CompileTime

RunTime

type rules

type

TYPE

type


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.

IDL File#2

IDLCompiler

StaticSkeleton

IDL File#1

StaticSkeleton

IDL File#2

IDLCompiler

StaticInvocation

IDL File#1

IDLCompiler

StaticInvocation


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.

DynamicInvocation

IDL File#1

IDL File#2

IDL File#3

IFRLoader

InterfaceRepository


5

Dynamic CORBA Features

TYPE CODEANYNAMEDVALUE / NVLIST

DII

InterfaceRepository

IDLCompiler

Client OBJREF

Object(Servant)

in argsoperation()out args +

return

DIIIDL

STUBSORB

INTERFACE

IDLSKEL DSI

Object Adapter

ORB CORE GIOP/IIOP/ESIOPS

ImplementationRepository

TYPECODE FACTORYDYNAMIC ANY

DSI

INTERFACE REPOSITORYIFR LOADER

123

4

5

67

89


6

Type Codeunion foo switch (char) { case ‘a’: long num; case ‘b’: string str;};

struct bar { string<12> str_mem; foo u_mem; boolean b_mem;};

• Structural representation

• Basic TCs in ORB• New TCs from IDL

compiler or type code factory

kind(parameters)

member namekind

idnamemember count

(parameters)bound

member namekind(parameters)

nameid

discrim. kinddefault indexmember countmember labelmember name

kind(parameters)

member labelmember name

kind(parameters)bound

member namekind(parameters)

tk_struct

"str_mem"tk_string

"IDL:bar:1.0""bar"3

12"u_mem"

tk_union

"foo""IDL:foo:1.0"

tk_char-12'a'"num"

tk_long

'b'"str"

tk_string

0"b_mem"

tk_boolean

Legend With Values

Type Code for struct 'bar'


7

Any, NamedValue, NVListTypeCode

Value

Any

• 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

Name

NamedValue

Direction

TypeCode

Value

Any

.

.

.

NVList

Name

NamedValue

Direction

TypeCode

Value

Any

Name

NamedValue

Direction

TypeCode

Value

Any

Name

NamedValue

Direction

TypeCode

Value

Any


8

Dynamic Invocation Interface (DII)

Request Object

Object Reference

String

NVList

NamedValue

Flag

Exception List

Target Object

Operation Name

Arguments

Return Value

Oneway?

User-definedExceptions

• 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 FactoryInterface

Repository

StaticApplication

DynamicApplication

ORB

TypeCodeFactorycreate_xx_tc( )

.

.

.

ORBcreate_xx_tc( )

.

.

.

InterfaceRepository

StaticApplication

DynamicApplication

• 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.


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.


11

Managing the Interface RepositoryIDL Compiler Executable

IDL CompilerExecutable

FELibrary

IDL BELibrary

IDL BELibrary

FELibrary

IDL CompilerExecutable

IFR LoaderExecutable

IFRLoaderLibrary

• 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.


12

result

response

invoke

Any

lookup_idget_operationsget_arg_typevalue

create_operation

create_interfaceIDLFile

Dynamic CORBA - Putting It All Together

Target

IFRLoader

InterfaceDefOperationDefcreate_type

Type CodeType Code

Factory

Interface Repository

Dynamic AnyDII RequestClientDynamic

AnyFactory


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.

TypeCode

Any

Dynamic Any

DII / DSI

NamedValue

NVList

TypeCodeFactory

IFR

Dependency Graph

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

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