Overview of ADO.NET Whidbey

1
Scalable Development, Inc. Building systems today
that perform tomorrow.
Designing BuildingWindows Serviceswith VB.NET

• Wallace B. McClure
• Scalable Development, Inc.

2
.NET Experiences

• PDC 2000 Build (July 2000).
• Visual Studio 1.0 Beta 1 (November 2000).
• Book began (January 2001).
• Visual Studio 1.0 Beta 2 (June 2001).
• First Production ASP.NET App (July 2001).
• Production Windows Service (November 2001). Runs
  today.
• 4 Production Applications by shipment.
• Multiple running applications.

3
.NET Resources

• ASP.NET www.asp.net
• AspAdvice www.aspadvice.com
• Windows Forms www.windowsforms.net
• Architecture msdn.microsoft.com/architecture
• .NET News www.dotnetwire.com

4
What are Windows Services?

• Applications (Database, Web Server, ).
• Good for long running / complicated operations.
• Run all the time.
• No User Interface.
• Run within their own security context.
• Limited access to local resources.
• Limited access to remote resources.
• Debugging.
• Non-interactive.

5
Design Guidelines

• Consistency.
• No popup messages.
• Information/Errors need to be written to
  somewhere.
• EventLog.
• Database.
• Be careful blocking.

6
Types of .NET Applications

• ASP.NET.
• Web Services.
• WinForms.
• Components.
• Windows Services.
• Others.

7
.NET Support for Services

• System.ServiceProcess namespace.
• Inherit from the ServiceBase Class.
• Installation.
• ServiceController Class Allows communication from
  authorized user (WinForms, ASP.NET, or other) to
  a Service (thru SCM).

8
Languages Support

• C (Managed Unmanaged).
• Visual Basic.
• C.
• Other .NET Languages.

9
Parts of a .NET Windows Service

• Service Control Manager (SCM).
• System.ServiceProcess.ServiceBase class
• Events.
• Installation.
• Process Installation.
• Service Installation.

10
Events in ServiceBase

• OnStart().
• OnStop().
• OnPause().
• OnContinue().
• OnShutdown().
• OnPowerEvent().
• OnCustomCommand().

11
OnStart() Event

• Called when the Service is issued the start
  command.
• VB SyntaxProtected Overridable Sub OnStart
• ( _ByVal args() as String )
• Hard to Debug By Default.

12
Debugging the OnStart() Event

• Create a dummy service that is a part of your
  process.
• Start the dummy service to start the process.
• Attach to running process.
• Place breakpoint.
• Start real service.

13
OnStop() Event

• Called when the Service is issued the stop
  command.
• Protected Overridable Sub OnStop().

14
OnPause() Event

• Called when the Service is issued the pause
  command.
• Protected Overrideable Sub OnPause().

15
OnContinue() Event

• Called when the Service is issued the continue
  command.
• Protected Overrideable Sub OnContinue().

16
OnShutdown() Event

• Called when the System sends the shutdown command
  to all Applications specifying that a system
  shutdown is inprogress.
• Similar to the OnStop() event.
• Protected Overrideable Sub OnShutdown().

17
OnPowerEvent() Event

• Called when the computers power status has
  changed. Typically, this applies to a laptop
  computer when it goes into a suspended state.
• Not the same as a system shutdown.
• Protected Overrideable Function OnPowerEvent(
  ByVal powerStatus as PowerBroadcastStatus ) as
  Boolean
• Boolean return value is a response to a
  QuerySuspend broadcast.
• True Application is in a state where a suspend
  is ok. False suspend is not ok.
• PowerBroadcastStatus is an enumertion with 9
  values.

18
OnCustomCommand() Event

• Executed when a custom command is passed from the
  SCM to the service.
• Protected Overridable Sub OnCustomCommand( ByVal
  command as Integer )
• Command values between 128 255.

19
Security Context

• Service runs within a defined security context
  (UserId/PassWord).
• What you do not necessarilyhave access to
• Desktop.
• Remote Resources.
• Mapped Drives.
• What you do have access to
• Local FileSystem.
• Network Protocols (TCP/IP, ).
• Database (ODBC, OleDb, MP).

20
Custom Commands /ServiceController

• Use the ServiceController class.
• ExecuteCommand( ByVal command as Integer )
  method.
• Start, Stop, Pause, Continue.
• MachineName, ServiceName, Status properties.

21
Installation

• Each executable must have a process installer.
• Each service within a process must have a service
  installer.
• Command line utility (installutil.exe)

22
App.Config

• XML Format.
• Excellent for read only information.

23
Great, Now What canYou do with a Service?

• Listen for events to occur.
• Network requests.
• Timer countdown.
• Messages arriving in a message queue.
• File system changes.
• Other.

24
Example

• Timer.
• When the Timer counts down to zero, an event
  fires and our application performs an operation.
• No continual polling occurs, no blocking, and no
  extra processing occurs on the system.

25
Whats Not to Like?

• Requires the .NET Framework.
• If a framework exception occurs when the
  framework stops, the Windows Service stops.and
  there is nothing within the framework to restart
  that Windows Service.
• Problem is rare, but possible. (ODP.NET
  9.2.0.2.100.0 users, problem has been resolved)

26
Monitoring a Windows Service

• Need something that wont stop.
• Can do it with .NET and a Console application.
• Drop back to COM/API.
• Use WMI Scheduled Tasks.
• Use ServiceController class.
• Run every few days/hours/minutes to monitor the
  status of your Service.

27
Things to look at / Last Thoughts

• Event Processing vs. Blocking.
• EventLog.
• Multiple Threads of Execution.
• Weak References.
• Performance Monitor Integration.
• Nothing wrong with Interop.

28
Questions?
Scalable Development, Inc. Building systems today
that perform tomorrow.

• Scalable Development, Inc.
• Consulting Development Services.
• http//www.scalabledevelopment.com
• 865-693-3004.
• wallym_at_scalabledevelopment.com

END