How To Use A Com In A Microsoft Com 2.5 (Dsi) (Dsi) (For Microsoft) (Com) (Sib) (Operations) (Orchestra) (Ahem) (I

(1)

Distributed Object Systems

– 8 –

DCOM 2

Piet van Oostrum

Oct 7, 2008

GDOS-8

COM (and some Corba)

I _{Dynamic Invocation}

I _{Containment/Aggregation/Delegation} I _Automation

I _Monikers

Piet van Oostrum GDOS-8 1

GDOS-8

Dynamic Invocation in COM

I _{Can Dynamic invocation in COM be done as in Corba?}

I Use Request object instead of stub I marshalling/protocol remains the same

I _NO!_{In case of inproc object there is no stub/skeleton} involved

i.e. call is direct

I _{Dynamic invocation through the IDispatch interface} I _Server_{must implement}_{the IDispatch interface}

I _{Is used for dynamic programming languages (Visual Basic,} scripting languages, . . . )

I _{Wizards can help you implement IDispatch}

I _{IDispatch interface often uses special parameter types:} VARIANT,BSTRING,SAFEARRAY

I _{These are just complicated struct/unions to represent Visual} Basic datatypes.

Piet van Oostrum GDOS-8 2

GDOS-8

Dynamic Invocation

I _{The server object must implement this special IDispatch} interface (compare Corba’s DSI)

I _{Every method that the server offers through IDispatch gets a} number (index) called DISPID

I In Corba you use methodname, in COMnumber

I _{The server will usually switch on the DISPID}

I _GetTypeInfo_{can be called to get info about the types of the} methods (if available – usually from a type library)

I _{Type Library}_{= file containing compiled IDL (AST)}

Piet van Oostrum GDOS-8 3

GDOS-8

Client side

I _{The client can then use this IDispatch interface}

I So the client must be able to call at least one static interface I _{The client must do}_{QueryInterface}_{to get the IDispatch}

interface

I methodGetIDsofNamesis used to couple names of methods

and DISPIDs

I It has an array of names as in parameter and an array of

DISPIDs as out parameter

I _The_Invoke_{method is used to make the call} I The client calls theInvokemethod

I A specialVARIANTtype is used for the parameters I VARIANTcontains type info for the marshaller

I Visual Basic types can be used and some special structs

(BSTRING,SAFEARRAY,DATE,DECIMAL)

Piet van Oostrum GDOS-8 4

GDOS-8

Interfaces

I _{Multiple Interfaces}

I If multiple dispinterfaces are defined by the object, one has to

be designated asdefault.

I This is what Visual Basic uses.

I TheQueryInterfaceforIDispatchwill give the default

interface

I The others can be obtained by explicitQueryInterface

I _{Dual Interface}

I _{A dual interface is an interface that can be called both}

statically and dynamically

I It inherits from IDispatch and adds also the static methods I This may be important for high performance applications

(2)

GDOS-8

IDL notation dispinterface

[uuid(3CFDB282-CCC5-11D0-BA0B-00A0C90DF8BC)] dispinterface IStat {

properties: methods:

[id(1)] void init();

[id(2)] void addItem(double item); [id(3)] double getAvg();

[id(4)] long getNum(); };

Piet van Oostrum GDOS-8 6

GDOS-8

IDL notation dual interface

[object,

uuid(3CFDB282-CCC5-11D0-BA0B-00A0C90DF8BC), dual

]

interface IStat: IDispatch [id(1)] HRESULT init();

[id(2)] HRESULT addItem([in] double item); [id(3)] HRESULT getAvg([out] double avg); [id(4)] HRESULT getNum([out] long num); };

Piet van Oostrum GDOS-8 7

GDOS-8

Implementation inheritance in COM

I _{Microsoft literature about COM discourages inheritance} I _{Fragile Base Class problem:}

I _{Mostly for compiled languages}

I Subclass is dependent of base class (superclass) I Later changes to base class may damage subclass if not

recompiled

I The size of objects (i.e. structs or classes) I _{The offsets to "visible" (public or protected) data} I The offsets to the virtual functions in the vtable

I _{Instead of inheritance use Containment/Delegation or} Aggregation

I _{Please note:} _{In .NET one of the strong points is the} possibility to inherit even across programming languages. But there are strong checks at load time.

Piet van Oostrum GDOS-8 9

GDOS-8

Containment or Delegation

Interface A IUnknown Interface B IUnknown

Outer Object Inner Object

I _{Outer Object implements A methods and B methods (because} interface A extends B)

I _{Outer object’s implementation of B methods just calls Inner} object’s B methods

void m(int x) { b.m(x); }

I _{Inner Object is not aware of the special relationship} I _{Inner Object can be considered as a helper object}

Piet van Oostrum GDOS-8 10

GDOS-8

Aggregation

Interface A IUnknown Interface B IUnknown Inner Object Outer Object

I _{Outer object puts inner object’s method pointer in its own} method table

I _{Problem: normally Inner object would return its own} IUnknown pointer if QueryInterface is done on interface B I _{Solution: When Outer object creates Inner object, it passes its}

own IUnknown pointer as ‘Controlling Unknown’ CoCreateInstance(CLSID_CStat, pOuter, ...

(3)

GDOS-8

Inheritance and Delegation in Corba

I _{Delegation can be used when a programming language does} not support multiple inheritance

n() A B m() n() C m() p()

Piet van Oostrum GDOS-8 12

GDOS-8

Delegation

class A { void m(); } class B { void n(); } class C { private A a; private B b; C(A a, B b) { this.a = a; this.b = b; } m() { a.m(); } n() { b.n(); } p() { ... } }

Piet van Oostrum GDOS-8 13

GDOS-8

Inheritance problem

I _{The problem with this solution is that C cannot be used where} an A or B is required.

I _{A solution is to use interfaces and implementation classes}

interface A { ... } interface B { ... }

class A_impl implements A { ... } class B_impl implements B { ... } class C implements A, B

{

private A_impl a; // or private A a; private B_impl b; // or private B b; ... etc ...

}

or even interfaceCand classC_impl

Piet van Oostrum GDOS-8 14

GDOS-8

Corba Servant (Inheritance Model)

I _Interface_MyInterface

I _{Abstract Interface}_{MyInterfaceOperations} (generated by IDL compiler)

I _Skeleton_{MyInterfacePOA}

implementsMyInterfaceOperations I _{Servant extends Skeleton class}

Skeleton Operations

implement.Servant

I _{Problem if you want Servant to extend other class}

Piet van Oostrum GDOS-8 15

GDOS-8

Corba Delegation Model (Tie)

I _{Servant class doesn’t have to extend skeleton} I _{Only implement}_{MyInterfaceOperations} I _{Servant can inherit from another class}

I _{IDL compiler generates Tie class that inherits from skeleton} I _{Tie class delegates to implementation class}

I _{Tie+implementation = “actual servant”}

Skeleton Operations

Servant

implement. Tie

Delegation

Piet van Oostrum GDOS-8 16

GDOS-8

Tie class

(generated by IDL compiler)

public class HelloPOATie extends HelloPOA {

public HelloPOATie(HelloOperations delegate) { this._impl = delegate;

} ...

public String sayHello () {

return _impl.sayHello(); // delegation } // sayHello

(4)

GDOS-8

Corba Delegation Model (Tie)

class HelloImpl extends SomeOtherClass implements HelloOperations ... method implementations as usual // Server class: create a servant.

HelloImpl helloImpl = new HelloImpl(); // create a tie, with servant being the delegate.

HelloPOATie tie = new HelloPOATie(helloImpl); // obtain the objectRef for the tie

// this step also implicitly activates the object Hello href = tie._this(orb);

Piet van Oostrum GDOS-8 18

GDOS-8

COM

Piet van Oostrum GDOS-8 19

GDOS-8

(OLE) Automation

I _{Automation (formerly known as OLE Automation) is a way to}

scripta program from another program

I _{E.g. Microsoft Word: Open a document, insert some text and} save it.

I _{Usually done from scripting languages, e.g. Visual Basic,} Python, Ruby.

I _{Application must make its operations available as} (Automation) COM interfaces (IDispatch). I _{Collection of interfaces known as OLE.}

I _{For use in web browsers a stripped down collection is ActiveX.}

Piet van Oostrum GDOS-8 20

GDOS-8

Visual Basic and COM

I _{Visual Basic (up to version 6)}

I Developed as COM programming language I Seamless integration with COM

Dim statvar as Stat.Stat Dim statvar as Object

Set statvar = CreateObject("Stat") Set statvar = New Stat.Stat Dim statvar as New Stat.Stat statvar.init

statvar.AddItem 3.14 Set result = statvar.GetAvg

I _{When declared as Object uses runtime resolution}

I When declared as specific class uses compile time resolution I Type info comes from Type Library (loaded at compile time or

runtime).

Piet van Oostrum GDOS-8 21

GDOS-8

Automation with Visual Basic

Dim Word As Object Dim Doc As Object Dim Spot As Object

Set Word = CreateObject("Word.Application") Word.Visible = True

Set Doc = Word.Documents.Add() Set Spot = Doc.Range(0, 0)

Spot.InsertBefore "Hello From Visual Basic" Doc.SaveAs "test.doc"

Doc.Close Word.Quit

Piet van Oostrum GDOS-8 22

GDOS-8

Early/Late Binding

I _{VB looks up the type info from the type library}

I _{The Windows registry contains mapping from Program Id} ("Word.Application") to Class Id

I _{The registry contains the location of the type library} I _{Variables declared as}_Object_{(Dim Word As Object) must}

be resolved at runtime I _{This is called}_{Late Binding}_.

I _{VB can also do the lookup at compile time:} _{Early Binding}_:

I Register the type library at compile time I Use:Dim Word As New Word.Application

(5)

GDOS-8

Automation with Python

Can be used with ActiveState Python, or Standard Python + win32allextensions

from win32com.client import Dispatch word = Dispatch("Word.Application") word.Visible = True

doc = word.Documents.Add() spot = doc.Range(0, 0)

spot.InsertBefore("Hello from Python") doc.SaveAs("test.doc")

doc.Close() word.Quit()

Piet van Oostrum GDOS-8 24

GDOS-8

Python/COM observations

I _{Python is very simple to use for Automation}

I _{Python looks up the type library and makes all decisions at} runtime

I _{You can even do it interactively}

I _{This makes development and try-out very easy} I _{You can also run the}_makepy_script

I _{This generates additional Python files containing the methods} of the interface (like stubs)

I _{At runtime these are used if available} I _{This is comparable to Early Binding (faster)}

Piet van Oostrum GDOS-8 25

GDOS-8

Java and (D)COM

I _{Originally with Microsoft Java Virtual Machine (now defunct)} I _{Visual J++ 6.0 or MS Java SDK}

I _{Almost transparent}

I _{Java virtual machine does all the administration} I _{Build Interface pointers, refcounts etc.}

I _{Special language extension is used (in specially formatted} comments)

I _Jactivex_{program generates interface and class files from} TLB (Type Library)

I _{Wrapper classes: CCW (Com callable wrapper) to call Java} from COM, JCW (Java callable wrapper) to call COM from Java

I _{J-Integra and EZ JCom are commercial implementations of}

the COM protocol in Java (any Java).

Piet van Oostrum GDOS-8 26

GDOS-8

J-Integra example

import excel.*; ...

Application app = new Application(); app.setVisible(true);

Workbooks workbooks = app.getWorkbooks(); Workbook workbook = workbooks.add(null); Sheets worksheets = workbook.getWorksheets();

Worksheet sheet = new Worksheet(worksheets.add(null, null, null, null)); Range range = sheet.getRange("A1:C3", null); Object[][] newValue = {

{"abcd", new Boolean(false), new Double(98.0/12)}, {new Date(), new Integer(5454), new Float(22.0/7)}, {new Boolean(true), "xyzt", new Date() } };

range.setValue(newValue); // Update the spreadsheet

Piet van Oostrum GDOS-8 27

GDOS-8

Python – OpenOffice.org automation

Python as a separate process: Script programmer explicitely

writes application startup code. Startup code must connect to Ooo. Code executes slow, as every call to OOo is going through the inter process bridge.

Python process must be started separately.

OOo listens on an inter process resource (socket or named pipe). This must be switched on seperately either on command line or with the OOo configuration. OOo Process Python Process PyUNO Runtime Python Code

Piet van Oostrum GDOS-8 28

GDOS-8

Python – OpenOffice.org automation

Python embedded in OpenOffice.org process:

OOo Process

PyUNO Runtime

Python UNO

component

Script must be written as a PyUNO component (adding a coding overhead)

(6)

GDOS-8

Py-UNO example

import uno

# get the uno component context from the PyUNO runtime localContext = uno.getComponentContext()

# create the UnoUrlResolver

resolver = localContext.ServiceManager \ .createInstanceWithContext(

"com.sun.star.bridge.UnoUrlResolver", localContext )

# connect to the running office

ctx = resolver.resolve( "uno:socket,host=localhost,\ port=2002;urp;StarOffice.\ ComponentContext" ) smgr = ctx.ServiceManager

Piet van Oostrum GDOS-8 30

GDOS-8

Py-UNO example

# get the central desktop object

desktop = smgr.createInstanceWithContext(

"com.sun.star.frame.Desktop",ctx) # access the current writer document

model = desktop.getCurrentComponent() # access the document’s text property text = model.Text

# create a cursor

cursor = text.createTextCursor() # insert the text into the document

text.insertString( cursor, "Hello World", 0 )

Piet van Oostrum GDOS-8 31

GDOS-8

Mac OS X Applescript

tell application "Microsoft Word" set newDoc to make new document

insert text "Hello from Applescript" at end of text object of active document save as newDoc file name "test.doc"

end tell

Piet van Oostrum GDOS-8 32

GDOS-8

COM

Piet van Oostrum GDOS-8 33

GDOS-8

COM Monikers

I _Monikers_{are (persistent) ‘names’ for persistent objects} I _{If you want to revive a persistent object (e.g. Excel}

worksheet):

I Create an object of that class (CoCreateInstance) I Force the object to load its persistent data (IPersist...) I There can be many parameters to specify where the data

comes from, e.g file name, which part of an object

I E.g. linked worksheet in Word document: filename and range

of the worksheet

I _{How does Word know what parameters to give and what they} mean (especially if it is an unknown class)?

I _{The object needs to have this information itself} I _{Monikers are used to encapsulate this data}

I Word doesn’t have to know all the interfaces of all possible

linked objects

Piet van Oostrum GDOS-8 34

GDOS-8

Moniker Implementation

I _{Client only deals with the}_IMoniker_interface

I _{E.g. in Object linking the moniker is stored in the structured} document

I _Interface_IMoniker:

I BindToObjectbinds the moniker to an object

I _{BindToStorage}_{binds the Moniker to the Storage of the object} I 13 more methods

I Also inherits fromIPersistsStream(4 methods) I _{which inherits from}_IPersist_{(1 method)}

(7)

GDOS-8

Moniker use

1 pointer method call/return 1. client calls IMoniker:: BindToObject(IID_A) A 4. Client invokes methods

2. Moniker instantiates Object Client

Server

Moniker

the object and tells it to load its persistent data interface A is

returned via 3. Pointer to

moniker

Piet van Oostrum GDOS-8 36

GDOS-8

Moniker Examples

I _{File Moniker}_{: contents is a file, persistent data is file name} I _{Item Moniker}_{: describes an item in a composite object, e.g.}

worksheet in an Excel workbook, persistent data is the item’s name and the moniker of the object in which it is contained I _{Composite Moniker}_{: groups together other monikers, e.g.} File Moniker, worksheet item and range item. Persistent date: the component monikers

I _{Java Moniker}_{: describes a Java class (now defunct):}

Dim dat As Object

Set dat = CreateObject("java:java.util.Date") Dim s As String

s = dat.toString

Piet van Oostrum GDOS-8 37

GDOS-8

Composite Moniker

IMoniker moniker

File moniker Item moniker Item moniker IMoniker IMoniker IMoniker Client Word R1C1:R5C4 Grades.xls Sheet1 Composite

Piet van Oostrum GDOS-8 38

GDOS-8

COM Structured Storage

I _{Structured Storage}_{is used for}_{compound documents} I _{These documents can contain other (sub)documents} I _{E.g. a Word document containing an Excel sheet}

I _{Each subdocument can be accessed more or less independently} I _{COM structured documents work like a filesystem within a file} I _{It has}_streams_{(file-like) and}_containers_{(directory-like)} I _Interface_IStream_{for file-like objects}

I Read,Write,Seek. . . methods

I _Interface_Istorage_{for the}_containers

I CreateStream,OpenStreamfor Streams in the Storage I CreateStorage,OpenStoragefor sub-storages I _{methods for renaming, destroying, copying and moving} I Transaction support (Commit,Revert)

I Setting the class of an object, getting information . . .

I _{Other interfaces to deal with persistence}

Piet van Oostrum GDOS-8 39

GDOS-8

Structured Storage in general

I _{Apple and IBM worked together on OpenDoc} I _{compound document architecture}

I _{document consists of parts}

I _{different parts can have different part editors} I _{part editors work in a part of the visible window} I _{parts can have different presentations}

I _{parts can have different versions} I _{Now abandoned (sources are available)}

Piet van Oostrum GDOS-8 40

GDOS-8

Example

OpenDoc document

•

Consists of document parts

- Each having its own part editor - Which editor is user configurable

(8)

GDOS-8

Different representations

OpenDoc 14 Dept. of Comp.Science, UU

Presentations

•

Part can have different presentations

•

Part info

-

Presentation data

-

Can be stored with the frame

•

View type

-

Determines the basic kind of presentation

Piet van Oostrum GDOS-8 42

GDOS-8

What is the problem?

I _{Putting parts together in a single document}

I _{Reinventing the filesystem within a file} I Better use the real filesystem I Or make mountable filesystems I _{No need to rewrite applications} I Ship a document in a zip file

I _Versioning

I _{Use existing tools, like CVS, subversion}

I Contra: not integrated with compound documents

I _{Simultaneous access}

I Is usually done with database systems

I Maybe file access should be upgraded to include transactions I _{Can be done with an additional Transactions layer}

How To Use A Com In A Microsoft Com 2.5 (Dsi) (Dsi) (For Microsoft) (Com) (Sib) (Operations) (Orchestra) (Ahem) (I

Distributed Object Systems

Piet van Oostrum GDOS-8 1

Dynamic Invocation in COM

Piet van Oostrum GDOS-8 2

Dynamic Invocation

Piet van Oostrum GDOS-8 3

Client side

Piet van Oostrum GDOS-8 4

Interfaces

IDL notation dispinterface

Piet van Oostrum GDOS-8 6

IDL notation dual interface

Piet van Oostrum GDOS-8 7

Contents

Piet van Oostrum GDOS-8 8

Implementation inheritance in COM

Piet van Oostrum GDOS-8 9

Containment or Delegation

Piet van Oostrum GDOS-8 10

Aggregation

Inheritance and Delegation in Corba

Piet van Oostrum GDOS-8 12

Delegation

Piet van Oostrum GDOS-8 13

Inheritance problem

Piet van Oostrum GDOS-8 14

Corba Servant (Inheritance Model)

Piet van Oostrum GDOS-8 15

Corba Delegation Model (Tie)

Piet van Oostrum GDOS-8 16

Tie class

Piet van Oostrum GDOS-8 18

(OLE) Automation

Piet van Oostrum GDOS-8 20

Visual Basic and COM

Piet van Oostrum GDOS-8 21

Automation with Visual Basic

Piet van Oostrum GDOS-8 22

Early/Late Binding

Automation with Python

Piet van Oostrum GDOS-8 24

Python/COM observations

Piet van Oostrum GDOS-8 25

Java and (D)COM

Piet van Oostrum GDOS-8 26

J-Integra example

Piet van Oostrum GDOS-8 27

Python – OpenOffice.org automation

Piet van Oostrum GDOS-8 28

Python – OpenOffice.org automation

Piet van Oostrum GDOS-8 30

Py-UNO example

Piet van Oostrum GDOS-8 31

Mac OS X Applescript

Piet van Oostrum GDOS-8 32

COM Monikers

Piet van Oostrum GDOS-8 34

Moniker Implementation

Piet van Oostrum GDOS-8 36

Moniker Examples

Piet van Oostrum GDOS-8 37

Composite Moniker

Piet van Oostrum GDOS-8 38

COM Structured Storage

Piet van Oostrum GDOS-8 39

Structured Storage in general

Piet van Oostrum GDOS-8 40

Example

Part info

Piet van Oostrum GDOS-8 42

What is the problem?