Visual Basic 6'0 WebClasses Support issues and best practices J'D' Meier Developer Support Engineer

1
Visual Basic 6.0 WebClassesSupport issues and
best practices J.D. MeierDeveloper Support
EngineerASP Product LiaisonMicrosoft Corporation
2
Todays Topics

• In a nutshell
• What about Active Server Pages (ASP)?
• What problems do WebClasses solve?
• Security issues
• Threading issues
• State management

3
More Topics

• Deployment
• Scalability
• Performance tuning
• Resources

4
In a Nutshell

• COM components running under ASP/IIS
• Bound to the ASP TypeLib
• A framework for leveraging existing Microsoft
  Visual Basic (VB) knowledge in an Internet
  environment

5
What About ASP?

• 10 threads per processor
• Threading issues
• Security context
• InProc vs. object oriented programming (OOP)
  (isolated process)

6
What Problems Do WebClasses Solve?

• Leverage existing VB knowledge
• Add an event model to an otherwise synchronous
  environment
• Increase performance
• Win32 application programming interface (API) is
  accessible

7
Security Primer (1)

• Authentication methods
• Windows NT Challenge/Response (Windows NT LAN
  Manager NTLM)
• Great for your intranet!
• Not supported by Netscape Navigator
• Access limited to local machine and
  non-authenticated protocols (sockets)
• Basic authentication
• Supported by Netscape Navigator
• Access not limited to local machine
• Account information transferred in clear-text
  (Base64 encoded) across the wire
• Allow Anonymous

8
Security Primer (2)

• Application settings determine your thread's
  security context
• In processSYSTEM impersonates authenticated
  account
• Out of processIWAM_ltmachinegt impersonates
  authenticated account

9
Security Issues

• Access Denied (local and remote resources)
• Works during design, fails in production
• Desktop issues

10
Troubleshooting Security (1)

• Who am I?
• Set authentication method to Basic
• Use GetUserName() API
• Windows NT? Registry Monitor (RegMon)
• Windows NT File Monitor (FileMon)
• Enable auditing

11
Troubleshooting Security (2)

• GetUserName() API
• Private Declare Function GetUserName Lib
  "advapi32.dll _
• Alias "GetUserNameA" (ByVal lpBuffer As String, _
• nSize As Long) As Long
• Public Function WhoAmI() As String
• Dim strBuff As String
• Dim lngConst As Long
• Dim lngRet As Long
• Dim strName As String
• lngConst CLng(199)
• strBuff Space(200)
• lngRet GetUserNameA(strBuff, lngConst)
• WhoAmI Trim(Left(strBuff, lngConst))
• End Function

12
Troubleshooting Security (3)

• Windows NT? RegMon and FileMon
• Available for free at http//www.sysinternals.com
• Enable Auditing
• Log all resource accesses to the Event Log

13
Threading Primer

• ASP has 10 threads per processor allocated by
  default
• MTS manages threads
• Page-scoped STA objects perform best
• Do not store STA objects in Session object

14
Threading COMplications (1)

• VB objects
• Support STA
• Calls are serialized
• Do not store in Session object
• Avoid global data

15
Threading COMplications (2)

• Running under IIS means multiple client threads
• Debug mode can be misleading
• Single-thread executing during debug
• Different security context during run-time

16
Threading Issues

• Apartment model objects in Session contribute to
  the following problems
• Application doesn't perform past N users
• Application seems to hang
• Users corrupt each other's data
• Removing objects from Session solves the majority
  of the above problems

17
Troubleshooting Threading Issues

• Turn off ASP server-side debugging
• IDE is not a good test
• PerfMon
• ASP Requests Executing
• ASP Requests Queued
• GetCurrentThreadId() API

18
GetCurrentThreadId() API

• Private Declare Function GetCurrentThreadId _
• Lib "kernel32" () As Long
• Public Function GetThreadId() As Long
• GetThreadId GetCurrentThreadId()
• End Function

19
State Management

• Implications of a statefull WebClass
• The WebClass is stored in Session
• Limits scalability
• The best way to reduce performance
• Locks the Session to a specific thread

20
Safer State Management

• Database
• Cookies
• URLData

21
Deployment

• Package and Deployment Wizard has problems
• Read the Readme
• Virtual directory needs to exist
• Target server needs Posting Acceptor correctly
  installed
• Multiple versions of the Posting Acceptor

22
Deployment in the Real World

• Create a standard setup
• Manual method
• Create a dependency list
• Manually register each file
• Key files
• VB 6 run-time
• WebClass run-time
• Your project.dll
• Other project dependencies

23
Scalability Issues

• Paradigm shift from desktop to server
• Acquire resources late and release them early
• Pool db connections (ODBC connection pooling with
  ADO)
• Avoid storing objects in Session
• IIS must ensure that the same thread services
  each request associated with the session
• Defeats the purpose of having a thread pool
• Design stateless WebClasses

24
Performance Tuning (1)

• Project properties
• Unattended Execution
• Retain in Memory
• Set TagPrefix property to empty string
• Specify string name in URLFor methods, not the
  object reference
• Minimize the use of templates

25
Performance Tuning (2)

• Response.Write is faster than a template
• Lost the flexibility of templates
• Avoid run-time parsing of templates by setting
  TagPrefix and URLData to null
• Move business logic out of WebClasses and into
  MTS objects

26
General Troubleshooting

• Network Monitor
• Trace HTTP Traffic
• WebCat
• Stress test for performance
• PerfMon
• Watch ASP and IIS counters

27
Resources

• Microsoft Visual Basic? docs
• Choose Index and type WebClasses
• Knowledge Base
• kbWebClasses
• VB 6 Readme
• MSDN? feature
• http//msdn.microsoft.com/vbasic

28
(No Transcript)