How MTS Components Work

Component development using the COM specification is a major influence on the

way applications are designed nowadays. However, a significant percentage of

component development today is ‘stateful’ in nature (defined a little

later). Unfortunately, when these stateful components are used in an enterprise

environment under Object Request Brokers (ORBs) like Microsoft Transaction

Server (MTS), they’re unable to scale these components well, because of this

statefulness. Thus, one of the major challenges in writing components for MTS is

to ensure that they’re stateless in nature.

This article will help you understand the concepts of stateful and stateless

components, and will explain why MTS components should be stateless. We’ll

also take you through the working of stateful and stateless components using an

example.

What is statefulness?

A stateful component, by definition, is a component which maintains its state

in between calls to properties and methods. The term ‘state’ refers to the

current set of values of the various internal data members of the component. For

example, the text box control in VB is a stateful component. When you set the

‘text’ property of the control to some value, say ‘nauheed’, and then

change the font property; the change in font is reflected across, and the font

of the current contents of the ‘text’ property take on the font you just

changed to. In this example, the component–the textbox control–knew where

the change in the font should be applied–to the contents of the text property

of the component.

Likewise, let’s say you use the Winsock control and set the RemoteHost

property to ‘www.pcquest.com’, the

RemotePort property to 80, and then call the Connect method to connect to the

remote system, followed by a ‘SendData’ to transmit some information. The

Connect method will attempt to connect to www.pcquest.com

on port 80. That is, the Connect method knows which system it has to connect to

and on which port. This information or state was maintained by the component in

between setting the properties to their respective values and the call to the

Connect method. Assuming that a connection was made successfully, the SendData

method transmits information to the remote system across the TCP connection

established by the Connect method. So, the details or the state regarding the

established connection was maintained by the component for the call to SendData,

which used the connection to transmit information. So, Winsock is a stateful

component.

What is statelessness?

A stateless component, as the name implies, is a component that doesn’t

maintain its state in between calls to its properties and methods. Continuing

with our example of the Winsock control, had it been stateless, then all the

details (state information), like which system and port to connect to, and what

data to be sent, would have to be packed as parameters of a single SendData

method of the component. A stateless SendData method would look something like

this:

Function SendData(byval RHost as string, byval RPort as integer, byval data

as string) as boolean

Here, the SendData method itself makes a connection to the remote system (in

contrast to the Connect method in the stateful example) and sends the data.

Statelessness implies that a different state can be maintained during each

call to a method of a stateless component. So, while the first call to stateless

SendData can send data to www.pcquest. com on port 80, the second call can send

data to say, www.123.com on port 2000. Hence, if you have to change the state in

the stateful SendData example, you’ll need to change the values of the

properties of the component, before calling SendData again.

Typical layout of the Windows 95/98/Me registry

<+> My Computer

-<+> HKEY_CLASSES_ROOT (HKCR): Software settings, DDE,

OLE, drag-n-drop, Win31 backward compatibility, shortcut settings and

subkeys for every defined file association, also found at HKEY_LOCAL_MACHINE SOFTWARE\Classes.

-<+> HKEY_CURRENT_USER (HKCU): Currently logged on user

configuration settings, also found at HKEY_USERS.

Subkeys:

-<+> AppEvents: Assigned system and applications sound

events settings.

-<+> Control Panel: Control Panel settings, similar to

those defined in System.ini, Win.ini, and Control.ini in Windows/WfWG 3.xx.

-<+> Identitites: Created and used by MS Outlook Express

4/5 and its Address Book.

-<+> InstallLocationsMRU (Most Recently Used):

Installation and Startup folders paths.

-<+> Keyboard: Current keyboard layout.

-<+> Network: Network connection settings.

-<+> RemoteAccess: Current logon location settings, if

using Dial-Up Networking (DUN).

*-<+> Software: Software configuration settings for the

currently logged on user, sorted by vendor or developer.

-<+> HKEY_LOCAL_MACHINE (HKLM): User independent hardware

and software machine specific information: bus type, device drivers,

keyboard layout etc. Subkeys:

-<+> Config: System and software configuration.

-<+> Drivers: Used by the Device Manager to keep track of

active loaded drivers for hardware peripherals like plug-n-play devices, PC

cards, PCMCIA etc.

-<+> Enum: Hardware devices’ information and settings.

-<+> Hardware: Serial communication port(s)’

information and settings.

-<+> Network: Information and settings about network(s)

the user is currently logged on to.

-<+> Security: Network security information and settings.

-<+> SOFTWARE: Software-specific information and settings

sorted by developer or vendor.

*-<+> System: System startup, device driver, and

operating system information and settings.

-<+> HKEY_USERS (HKU): Information about desktop and user

specific settings for each user who logs on to the same Windows 9x/Me

system. Each user has a separate subkey here. If there is only one user, the

only subkey is ".Default".

-<+> HKEY_CURRENT_CONFIG (HKCC): Information about the

current hardware profile used by the local computer at startup, pointing to

HKEY_LOCAL_ MACHINE\SYSTEM\CurrentControlSet\Hardware Profiles\Current.  

*-<+> HKEY_DYN_DATA (HKDD): Virtual key (exists only in

memory) created every time Windows 9x/Me initializes; dynamic configuration

data about installed plug-n-play devices. Changes constantly when hardware

devices are added, swapped or removed on-the-fly.

-<+> Config Manager: Hardware problem codes and status.

*-<+> PerfStats: System and network performance

statistics.

Registry editors

To modify the registry, you need to use a Registry Editor,

which would be one of the following:

• Regedit.exe (Windows 95/98/Me/NT/2000): located in
  
  %WinBootDir%,

• Regedt32.exe (Windows NT/2000): located in %System
  
  Root%\System32\Config, or

• a third-party Registry editing tool like Registrar Lite
  
  (freeware).

The Windows 95/98/NT/2000/Me Registry Editor is a tool used

to display, search, modify, create, delete, save, import, and export the

registry’s (sub)keys and values (see table).

You can use either RegEdit’s or RegEdt32’s interface in

protected mode Windows environment from within the Windows GUI. Alternatively,

you can use REGEDIT’s DOS based (Windows 95/98/ME) command line parameters in

real mode MS-DOS from outside Windows.

To learn how to use the regedit.exe available DOS mode

switches, run the following from native MS-DOS:

RegEdit.exe versus RegEdt32.exe comparison

Creating a shortcut to the registry editor

To create a RegEdit shortcut, right-click on an empty raised

Taskbar spot. Select Properties, click Start Menu>Programs, and click the ‘Add...’

button. Browse to your main Windows folder, double-click on regedit.exe, and

click the Next button. Double-click Start Menu>Programs> Accessories>

System Tools, click the Next button, and type Registry Editor in the ‘Select

name for the shortcut’ box. Click the Finish button.

If you are not familiar with ‘messing around’ with your

Registry, don’t attempt to make any changes. However, if you are familiar

enough with your system registry’s "innards" and would like to tweak

it for maximum performance, but don’t like to modify your registry directly,

an alternative is to use one of the free Windows 9x/NT/2000/Me

system-cum-registry tweakers. Some of these are:

• Xteq X-Setup: tweaks more than 700 system or registry
  
  settings

• Microsoft TweakUI 1.33: More information on this is
  
  available at http://home.aol.com/AXCEL216/98-3.htm#TWK98

• DirectControl: tweaks DirectX, video, audio, and 3D
  
  settings

• CacheMan: tweaks disk and file cache settings.

Words of caution

When editing the registry, backup all your hard drives to a

safe location before making any system changes (for details on how to do this,

go to http://home.aol.com/axcel216/newtip12.htm#

regbak). Remember that when you

add, delete or modify a registry (sub)key or value using RegEdit, all changes

take place instantly, and you aren’t prompted for confirmation upon saving

changes to before closing the registry editor. Take extreme caution when

modifying your system settings, because faulty registry changes may result in

computer crashes, lockups, or permanent data loss, and may cause you to

reinstall the entire operating system. And, always have your most recent system

backup ready.

Reprinted with permission from http://home.aol.com/AXCEL216/reg.htm