Understanding DCOM

312 Pages·1998·1.19 MB·English

by  William Rubin

Preface
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Copyright 1999 by Prentice Hall PTR
Prentice-Hall, Inc.
A Simon & Schuster Company
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CONTENTS
Preface xiii
ONE The Basics of COM 1
Classes and Objects 1
How COM Is Different 3
COM can Run Across Processes 3
COM Methods Can Be Called Across a Network 4
COM Objects Must Be Unique Throughout the World 5
COM is Language Indpendent 5
COM Vocabulary 5
The Interface 7
Interfaces Isolate the Client From the Server 8
Imagine a Component 10
What's in a Name? 10
The Source of All Interfaces - IUnknown 10
A Typical COM Object 11
How to Be Unique - the GUID 12
A COM Server 14
Interactions Between Client and Server 15
Summary 16
TWO Understanding the Simplest COM
Client 19
Four Steps to Client Connectivity 20
Initializing the COM Subsystem: 21
Query COM for a Specific Interface 22
Execute a Method on the Interface. 24
Release the Interface 24
Summary 25
vi
Contents
THREE Understanding a Simple COM Server 27
Where's the Code? 28
Building a DLL-Based (In-Process) COM Server 29
Creating the Server Using the ATL Wizard 30
Adding a COM Object 33
Adding a Method to the Server 36
Running the Client and the Server 40
Summary 41
FOUR Creating your own COM Clients and
Servers 43
Server Side 43
Client Side 45
FIVE Understanding ATL-Generated Code 55
The Main C++ Module 56
Object Maps 58
Export File 58
The COM Object - "CBeepObj" 60
Object Inheritance 61
The Class Definition 62
The Method 63
Server Registration 64
Registry Scripts 65
Summary 66
vii
Contents
SIX Understanding the Client and Server 67
Principles of COM 67
COM is About Interfaces 68
COM is Language-Independent 68
COM is Built Around the Concept of Transparency 69
Interfaces are Contracts Between the Client and Server 69
Software Changes. Interfaces Don't 70
Activation 71
More About Interfaces 73
VTABLES - Virtual Function Tables 75
The Class Factory 77
Singleton Classes 79
Understanding QueryInterface 81
Reference Counting with AddRef and Release 82
Method Calls 85
COM Identifiers: CLSID AND IID 87
CLSCTX -- Server Context 88
Inheritance 88
Summary 89
SEVEN An Introduction to MIDL 91
Origins of the MIDL Compiler 91
Precisely Defining Interfaces with the IDL Language 92
MIDL Generated Headers 94
Automatically Generated Proxy/Stub Modules 94
Automatic Creation of Type Libraries 95
The IDL Language 95
Interfaces and Methods in IDL 97
The Component Class in IDL 100
Type Libraries in IDL 102
MIDL Post-Processing 103
Summary 105
viii
Contents
EIGHT Defining and Using Interfaces 107
Base Types 108
Attributes 109
Double Parameters 112
Boolean Parameters 113
Working with Strings 113
Arrays 119
Structures and Enumerations 121
Summary 123
NINE OLE Automation and
Dual Interfaces 125
IDL Definitions 126
The IDispatch Interface 127
Using Invoke 133
Using Type Libraries for Early Binding 136
Dual Interfaces 137
There is no Proxy/Stub DLL for Dispatch
Interfaces 140
Properties 140
Adding Properties with the Class Wizard 142
Methods 144
The ISupportErrorInfo Interface 144
Summary 149
TEN COM Threading Models 151
Synchronization and Marshaling 151
Threading Models 153
Apartment, Free, and Single Threads 155
ix
Contents
The ATL Wizard and Threading Models 156
Apartment Threads 158
Single Threads 159
Free Threaded Servers 160
Both 161
Marshaling Between Threads 162
Using Apartment Threads 163
Free Threading Model 164
Testing the Different Models 165
Summary 166
ELEVEN The COM Registry 167
The COM Registry Structure 168
Registration of CLSIDs 171
Registration of ProgIDs 172
Registration of AppIDs 174
Self-Registration in ATL Servers 174
The RGS File 175
Automatic Registration of Remote Servers 177
In-Process Servers 178
Using the Registry API 178
Summary 178
TWELVE Callback Interfaces 181
Client and Server Confusion 183
Custom Callback Interfaces 183
A Callback Example 185
Create the Server 185
Add a COM Object to the Server 186
Adding the ICallBack Interface to IDL 187
x
Contents
Modify the Header 187
Adding the Advise Method to the Server 188
Adding the UnAdvise Method 189
Calling the Client from the Server 189
The Client Application 191
Create the Client Dialog Application 191
Adding the Callback COM Object 192
Linking to the Server Headers 194
COM Maps 194
Implementing the Callback Method 195
Adding the Object Map 195
Connecting to the Server 196
Cleaning Up 199
Adding the OnButton Code 199
A Chronology of Events 201
A Multi-Threaded Server 203
Starting the Worker Thread 205
Marshaling the Interface Between Threads 206
Starting the Worker Thread: Part 2 207
A Simple Worker Thread Class 208
Implementing the Worker Thread 209
All Good Threads Eventually Die 211
Summary 211
THIRTEEN Connection Points 213
Modifying the Callback Server 215
Adding Connection Points to the Client Program 220
Add the Callback Object to the Client 221
Modifying the CpClient Application 221
Registering With the Server’s Connection Point
Interface 222
Adding the Now and Later Buttons 226
Using the Connection Point - the Server Side 226
Adding the Later2 Method 228
Summary 228
xi
Contents
FOURTEEN Distributed COM 229
An Overview of Remote Connections 229
Converting a Client for Remote Access 231
Adding Security 234
Security Concepts 234
Access Permissions 235
Launch Permissions 236
Authentication 237
Impersonation 237
Identity 238
Custom Security 239
CoInitializeSecurity 239
Disconnection 242
Using the Registry for Remote Connections 243
Installing the Server on a Remote Computer 244
FIFTEEN ATL and Compiler Support 245
C++ SDK Programming 245
MFC COM 246
ATL - The Choice for Servers 246
Basic Templates 247
A Simple Template Example 248
Template Classes 250
Native Compiler Directives 253
The #IMPORT Directive 253
Namespace Declarations 254
Smart Interface Pointers 255
Smart Pointer Classes 256
Watch Out for Destructors 257
Smart Pointer Error Handling 258
How the IMPORT Directive Works 260
Raw and Wrapper Methods 260
Summary 261
xii
Contents
SIXTEEN Other Topics 263
Errors 263
Information Code 265
Facility Code 265
Customer Code Flag and Reserved bits 266
Severity Code 266
Looking Up HRESULTS 266
SCODES 267
Displaying Error Messages 267
Using FormatMessage 268
Aggregation and Containment 269
Building a COM Object with MFC 271
Adding Code for the Nested Classes 273
Accessing the Nested Class 275
APPENDIX COM Error Handling 277
Sources of Information 278
Common Error Messages 279
DCOM Errors 285
Get It Working Locally 285
Be Sure You Can Connect 286
Try Using a TCP/IP Address 287
Use TRACERT 287
Windows 95/98 Systems Will Not Launch Servers 288
Security is Tough 288
Using the OLE/COM Object Viewer 289
Index 291