CS551 - Lecture 15 1 CS551 Object Oriented Middleware (IV) Dynamic Requests (Chap. 6 of EDO) Yugi...

CS551 - Lecture 151

CS551 Object Oriented Middleware (IV) Dynamic Requests (Chap. 6 of EDO)

Yugi Lee

STB #555(816) 235-5932

[email protected]

www.cstp.umkc.edu/~yugi

2CS551 - Lecture 15

OutlineOutline

• Dynamic Invocation– The CORBA Dynamic Invocation Interface– COM IDispatch Interfaces

• Reflection– The CORBA Interface Repository– The COM Type Library

• Designing Generic Applications– Using CORBA– Using COM

• Dynamic Invocation– The CORBA Dynamic Invocation Interface– COM IDispatch Interfaces

• Reflection– The CORBA Interface Repository– The COM Type Library

• Designing Generic Applications– Using CORBA– Using COM

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Why Dynamic Request?Why Dynamic Request?

• Sometimes clients need to be built before their server interfaces are defined

• They need to defer request definition until they are executed

• Examples:– Object browser– Generic bridges– Scripting language interpreter

• Sometimes clients need to be built before their server interfaces are defined

• They need to defer request definition until they are executed

• Examples:– Object browser– Generic bridges– Scripting language interpreter

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Motivating Example: Object BrowserMotivating Example: Object Browser

Use run-time type information to find out about object typesattribute names

Use dynamic invocation interfaces to obtain attribute values

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Motivating Example: Generic BridgeMotivating Example: Generic Bridge

Client

ORB CoreORB Core

Obj. Imp.

DSI DII

• Generic and request-level bridge• Generic and request-level bridge

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Motivating Example: ScriptingMotivating Example: Scripting

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CommonalitiesCommonalities

• Discovery of type information at run-time

• Use of type information to build client objects that can cope with any type of server objects

• Definition of object requests at run-time

• Requires two primitives from middleware:– Dynamic invocation interfaces– Reflection mechanisms

• Discovery of type information at run-time

• Use of type information to build client objects that can cope with any type of server objects

• Definition of object requests at run-time

• Requires two primitives from middleware:– Dynamic invocation interfaces– Reflection mechanisms

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Dynamic Requests: PrinciplesDynamic Requests: Principles

• Any object request has to identify

– server object

– operation name

– actual parameters

– data structure for operation result

• In Dynamic Requests:

– server object identified by object reference

– operation name identified by string

– actual parameters as list of name/value pairs

– operation result determined by an address

• Any object request has to identify

– server object

– operation name

– actual parameters

– data structure for operation result

• In Dynamic Requests:

– server object identified by object reference

– operation name identified by string

– actual parameters as list of name/value pairs

– operation result determined by an address

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DynamicInvocation DynamicInvocation

ClientStubsClientStubs

ORBInterface ORBInterface

Implementation SkeletonsImplementation Skeletons

ClientClient Object ImplementationObject Implementation

ORB CoreORB Core

ObjectAdapter ObjectAdapter

Dynamic Requests in CORBA Dynamic Requests in CORBA

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Dynamic Requests in CORBADynamic Requests in CORBA

• Dynamic invocation interface (DII) supports dynamic creation of requests (objects).

• Request objects have attributes for – operation name,

– parameters and

– results.

• Request objects have operations to – change operation parameters,

– issue the request and

– obtain the request results.

• Dynamic invocation interface (DII) supports dynamic creation of requests (objects).

• Request objects have attributes for – operation name,

– parameters and

– results.

• Request objects have operations to – change operation parameters,

– issue the request and

– obtain the request results.


Dynamic Request in CORBADynamic Request in CORBA

:Client:Client

rrr:Requestr:Request

:Server:Server

Op()Op()

rr=create_request(…,”Op”,…)=create_request(…,”Op”,…)

addadd_arg()_arg()

invoke()invoke()

delete()delete()


Dynamic Requests in COMDynamic Requests in COM

• COM often used with interpreted scripting languages (e.g. VBScript)

• Interpreters of these languages need to make dynamic requests.

• Dynamic Requests in COM are defined in the IDispatch interface

• Any COM server that implements IDispatch can be requested dynamically

• COM often used with interpreted scripting languages (e.g. VBScript)

• Interpreters of these languages need to make dynamic requests.

• Dynamic Requests in COM are defined in the IDispatch interface

• Any COM server that implements IDispatch can be requested dynamically


Dynamic Request in COMDynamic Request in COM

:Client:Client :Server:Server

QueryInterface(IID_IDispatch)QueryInterface(IID_IDispatch)

GetIDsOfNames(“Op”)GetIDsOfNames(“Op”)

Invoke()Invoke()

Op()Op()

GetIDsOfNames(“Op”)GetIDsOfNames(“Op”)

:ITypeInfo:ITypeInfo

Invoke()Invoke()


Dual InterfacesDual Interfaces

• Are accessible both via stubs and via dynamic invocation

• Example: Interface Player: [object,dual,uuid(75DA6450-DD0E-00d1-8B59-0089C73915CB]interface DIPlayer: IDispatch { [id(1),propget] HRESULT Name([out] BSTR val); [id(2),propget] HRESULT Number([out] short val); [id(3)] HRESULT book([in] Date val)};

• Interfaces have to be defined as dual!

• Are accessible both via stubs and via dynamic invocation

• Example: Interface Player: [object,dual,uuid(75DA6450-DD0E-00d1-8B59-0089C73915CB]interface DIPlayer: IDispatch { [id(1),propget] HRESULT Name([out] BSTR val); [id(2),propget] HRESULT Number([out] short val); [id(3)] HRESULT book([in] Date val)};

• Interfaces have to be defined as dual!


Transparency of Dynamic InvocationTransparency of Dynamic Invocation

• In both COM and CORBA:

– Client programs have to be written differently Use of dynamic invocation interfaces is not transparent to client programmers

• In COM:

– Interfaces of server objects have to be designed as dual Use of dynamic invocation not transparent in server design

• In CORBA:

– Server objects are unaware of dynamic invocation Use of DII is transparent

• In both COM and CORBA:

– Client programs have to be written differently Use of dynamic invocation interfaces is not transparent to client programmers

• In COM:

– Interfaces of server objects have to be designed as dual Use of dynamic invocation not transparent in server design

• In CORBA:

– Server objects are unaware of dynamic invocation Use of DII is transparent


Reflection PrinciplesReflection Principles

• How do clients discover attributes & operations that servers have?– capture type information during interface compilation– store type information persistently – provide an interface for clients to obtain type

information during run-time

• Reflection interfaces provided by– CORBA Interface Repository– COM Type Library

• How do clients discover attributes & operations that servers have?– capture type information during interface compilation– store type information persistently – provide an interface for clients to obtain type

information during run-time

• Reflection interfaces provided by– CORBA Interface Repository– COM Type Library


CORBA Interface RepositoryCORBA Interface Repository

• Makes type information of interfaces available at run-time.

• Achieves type-safe dynamic invocations.• Supports construction of interface browser• Used by CORBA implementations themselves• Persistent storage of IDL interfaces in abstract

syntax trees (ASTs)

• Makes type information of interfaces available at run-time.

• Achieves type-safe dynamic invocations.• Supports construction of interface browser• Used by CORBA implementations themselves• Persistent storage of IDL interfaces in abstract

syntax trees (ASTs)


• Interface repository persistently stores ASTs of IDL modules, interfaces, types, operations etc.

• Interface repository persistently stores ASTs of IDL modules, interfaces, types, operations etc.

module SoccerMgmt {

};

module SoccerMgmt {

};

ModuleDefModuleDef

SoccerMgmtSoccerMgmt

InterfaceDefInterfaceDef

PlayerPlayer

InterfaceDefInterfaceDef

TeamTeam

TypedefDefTypedefDef

PlayerListPlayerList

ExceptionDefExceptionDef

InvalidNumberInvalidNumber

AttributeDefAttributeDef

membersmembers

interface Player; interface Player; interface Team {

};

interface Team {

};

typedef sequence<Player> PlayerList; typedef sequence<Player> PlayerList; exception Invalid {}; exception Invalid {}; attribute ATMList ATMs; attribute ATMList ATMs;

OperationDefOperationDef

addadd void add(in short number, in Player p); raises(InvalidNumber)

void add(in short number, in Player p); raises(InvalidNumber)

Abstract Syntax Trees (ASTs)Abstract Syntax Trees (ASTs)


ContainerContainer

AST Node TypesAST Node Types

IRObjectIRObject

ContainedContained

OperationDefOperationDef

ExceptionDefExceptionDef

TypedefDefTypedefDef AttributeDefAttributeDef

ConstantDefConstantDef

ModuleDefModuleDefInterfaceDefInterfaceDef RepositoryRepository


COM Type LibraryCOM Type Library

• COM’s provision of run-time type information

• Raw information generated by MIDL compiler

• Stored in tokenized form (.TLB files)

• Main interfaces:

• COM’s provision of run-time type information

• Raw information generated by MIDL compiler

• Stored in tokenized form (.TLB files)

• Main interfaces:

ITypeLibITypeLib ITypeInfoITypeInfo11 00..*..*


ITypeLibITypeLib

• Provides operations to browse through all interfaces contained in the type library– GetTypeInfoCount (returns number of TypeInfo

objects in the library)– GetTypeInfo (can be used to obtain type info at a

particular index number)

• Locate ITypeInfo objects using the GUIDs

• Provides operations to browse through all interfaces contained in the type library– GetTypeInfoCount (returns number of TypeInfo

objects in the library)– GetTypeInfo (can be used to obtain type info at a

particular index number)

• Locate ITypeInfo objects using the GUIDs


ITypeInfoITypeInfo

interface ITypeInfo : IUnknown {

HRESULT GetFuncDesc( UINT index, FUNCDESC **ppFuncDesc);

HRESULT GetIDsOfNames( OLECHAR **rgszNames,

UINT cNames, DISPID *pMemId);

HRESULT GetNames(DISPID memid, BSTR *rgBstrNames,

UINT cMaxNames, UINT *pcNames);

HRESULT GetTypeAttr(TYPEATTR **ppTypeAttr);

HRESULT GetVarDesc(UINT index, VARDESC **ppVarDesc);

HRESULT Invoke(VOID *pvInstance, DISPID memid, USHORT

wFlags, DISPPARAMS *pDispParams,

VARIANT *pVarResult,

EXCEPINFO *pExcepInfo, UINT *puArgErr);

...

};

interface ITypeInfo : IUnknown {

HRESULT GetFuncDesc( UINT index, FUNCDESC **ppFuncDesc);

HRESULT GetIDsOfNames( OLECHAR **rgszNames,

UINT cNames, DISPID *pMemId);

HRESULT GetNames(DISPID memid, BSTR *rgBstrNames,

UINT cMaxNames, UINT *pcNames);

HRESULT GetTypeAttr(TYPEATTR **ppTypeAttr);

HRESULT GetVarDesc(UINT index, VARDESC **ppVarDesc);

HRESULT Invoke(VOID *pvInstance, DISPID memid, USHORT

wFlags, DISPPARAMS *pDispParams,

VARIANT *pVarResult,

EXCEPINFO *pExcepInfo, UINT *puArgErr);

...

};


Static InvocationStatic Invocation

• Advantages:– Requests are simple to define.– Availability of operations checked by programming

language compiler.– Requests can be implemented fairly efficiently.

• Disadvantages:– Generic applications cannot be build.– Recompilation required after operation interface

modification.

• Advantages:– Requests are simple to define.– Availability of operations checked by programming

language compiler.– Requests can be implemented fairly efficiently.

• Disadvantages:– Generic applications cannot be build.– Recompilation required after operation interface

modification.


Dynamic InvocationDynamic Invocation

• Advantages:

– Components can be built without having the interfaces they use,

– Higher degree of concurrency through deferred synchronous execution.

– Components can react to changes of interfaces.

• Disadvantages:

– Less efficient,

– More complicated to use and

– Not type safe!

• Advantages:

– Components can be built without having the interfaces they use,

– Higher degree of concurrency through deferred synchronous execution.

– Components can react to changes of interfaces.

• Disadvantages:

– Less efficient,

– More complicated to use and

– Not type safe!


Key PointsKey Points

• Dynamic requests are used when static requests are not viable

• Dynamic requests supported by both CORBA and COM• Dynamic requests are unsafe• Reflection mechanisms provided by COM and CORBA

make dynamic requests safe• IDL compilers store type information persistently so that

reflection implementations can provide them

• Dynamic requests are used when static requests are not viable

• Dynamic requests supported by both CORBA and COM• Dynamic requests are unsafe• Reflection mechanisms provided by COM and CORBA

make dynamic requests safe• IDL compilers store type information persistently so that

reflection implementations can provide them

CS551 - Lecture 15 1 CS551 Object Oriented Middleware (IV) Dynamic Requests (Chap. 6 of EDO) Yugi...

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