COM - Component Object Model
The Microsoft Way
Original slides
Jens Gustavsson
Updated / extended (2007)
Mikhail Chalabine
Binary standard
Fundamental entities: Interface, Component
One component can implement any number
of interfaces
COM technologies
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–
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COM+
Distributed COM (DCOM)
ActiveX® Controls
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A COM component
Client variable
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A COM component
Interface node
function 1
function 2
function 3
function 4
function 5
Client variable
Interface node
Client variable
Interface node
function 1
function 2
function 3
function 4
function 5
function 6
function 7
function 8
Component
Component
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Two Questions
QueryInterface
How does a client learn about which
interfaces a component implements?
How does a client compare the identity of
COM objects?
Client variable
Interface node
Client variable
Interface node
QueryInterface
function 2
function 3
function 4
function 5
QueryInterface
function 7
function 8
Component
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How to draw them
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Reference Counting
IUnknown
All interfaces contain:
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IPersistStorage
Properties
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IViewer
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ISecure
Cycles
Simple
Fast (objects removed as soon as count is 0)
Expensive (too many operations)
Tracing Garbage Collection in .NET instead
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AddRef
Release
Determine reachable objects (transitive)
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COM object reuse
Containment
No inheritance between components
Two alternative solutions:
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IUnknown
IUnknown
Containment
Aggregation
IStream
IStream
IPrint
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Containment
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Aggregation
IUnknown
IStream
IUnknown
Outer exposes inner objects' interfaces
Inner object cooperation needed
Reference counting complicated
http://msdn2.microsoft.com/en-us/library/ms686558.aspx
IPrint
IStream
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Polymorphism
Component Categories
Type of an object is the set of interfaces it
supports
A subtype is a superset of interfaces
IStream
IPrint
IStream
Logical grouping by functionality
A set of interfaces identified by GUID (CATID)
Windows system register stores info about
COM system
Interfaces as contracts (is a mess)
Predefined categories
Custom categories allowed
IViewer
IPrint
http://edndoc.esri.com/arcobjects/9.0/ExtendingArcObjects/Ch02/ComponentCategories.htm
ISecure
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Interface versions
How to create a COM object
Published interfaces must never change
The GUID represents a specific version
Interface ID not enough
Procedural library for requesting objects
based on COM class
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CoCreateInstance(Class id, Interface id)
System registry
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COM Servers
Persistence
Contains a set of COM classes
A Factory for each class
Kinds of COM servers:
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In-process (dll)
Local (exe)
Remote
CoCreateInstance does not initialize object
Structured storage
Monikers
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Refer to objects by logical access path
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DCOM - Distributed COM
OLE
Stubs and proxies (skeletons)
Datatype conversion by using NDR (Network
Data Representation)
Object Linking and Embedding
Based on COM
Application centered paradigm vs.
Document centered paradigm
Concepts:
Master
–
–
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Document servers
Document containers
In place editing
Embed / link
Document
Referenced
Document
Reference
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Controls
.NET
VBX
OCX (OLE Control)
ActiveX
Architecture similar to Java
Source
code
Compiler
Byte code
Class
library
Virtual
Machine
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.NET
CTS - Common Type System
Architecture similar to Java
Source
code
Compiler
MSIL
System.Object - root of type hierarchy
Single inheritance
Multiple interface implementation
Access control
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–
Class
library
Location: class, assembly, universe
Related by class inheritance or not
CLR
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C#
Assemblies
Exemplary .NET language
Similar to Java
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–
–
–
–
–
–
–
No inner classes, delegates instead
Properties
Struct
No checked exceptions
Metadata
Enum
Goto
Operator overloading
Deployment format
A set of files in a directory hierarchy
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Must contain manifest (assembly metadata)
Can be tagged with culture label
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module files
resource files
Satellite assemblies
Private / Shared
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Strong names
GAC - Global Assembly Cache
Unique identification of Assemblies
Unique names (no one else has the same):
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Assembly DB in Windows XP
Assembly retrieval controlled by policies:
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publisher token
assembly name
version (major, minor, build, patch)
culture
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Publisher policy
Application policy
Machine policy
Installer-GAC cooperation
Digitally signed based on whole assembly
Strong ID on assembly. Contents addressed
relatively
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Version management
COM interoperation
The Common Type System anchors all
names in the names of the containing
assembly
Between managed and unmanaged code
COM callable wrappers
Runtime callable wrappers
http://msdn2.microsoft.com/en-us/library/ms973872.aspx
http://msdn2.microsoft.com/en-us/netframework/aa497266.aspx
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Windows Form Components
Enterprise services
Similar to JavaBeans
System.ComponentModel.IComponent
Properties, events and delegates support
connection-oriented programming
Metadata to attach design time information
and behavior
Container
Services
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–
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–
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Object pooling
Jut-in-time activation
Queued Invocation
Transactions
Resource management
Access control
[ES.Transaction(ES.TransactionOption.Required)]
[ES.JustInTimeActivation(true)]
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The Microsoft Way
Original slides
Jens Gustavsson
Updated / extended (2007)
Mikhail Chalabine
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